This paper presents the results of Fourier transform infrared (FTIR) spectroscopy of a synthetic ... more This paper presents the results of Fourier transform infrared (FTIR) spectroscopy of a synthetic beryl, containing D2O molecules in its c-axis channels, which we synthesized under hydrothermal conditions at 600 °C and 1.5 kbar. The frequencies of absorbance bands in the range of the stretching vibrations and their overtones and combination modes for D2O and HDO molecules have been assigned for the first time. On the basis of our assignments, the absorbance bands observed for the natural beryl in the range of the OD stretching vibrations have been explained. Note! Unfortunately during publication's processing Greek letters ν and δ were unintentionally transformed into Latin letters 'n' and 'd', respectively. Also symbol 'perpendicular' was transformed to ^.
Impurity inhomogeneities and other structural defects
have been studied by means of transmission ... more Impurity inhomogeneities and other structural defects have been studied by means of transmission electron microscopy (TEM), X-ray microanalysis and electron paramagnetic resonance (EPR) in untreated and heat-treated quartz samples of three genetic types: hydrothermal, pegmatitic and magmatic. The impurities present are A1, Na and H20 , which occupy tetrahedral (A13+) or interstitial (Na +, H20 ) positions in the quartz lattice. Impurities form imperfections of various degrees of segregation: from point defects to micropores with a gas-liquid content. Their size, form, density and distribution in the lattice depend on the formation conditions of the quartz, the presence of dislocations and plane defects serving as sinks for the impurity atoms, and the heat treatment regime. Experimental data indicate that gas-liquid inclusions of dimensions up to some microns are the result of impurity segregation during postcrystallizational cooling. Crystalline quartz amorphizes upon electron irradiation. A model of structural water explaining experimentally observed features of this phenomenon is proposed whereby the water molecule, represented as a dipole, enters microregions of the silica lattice with a high impurity content and there forms a bond between 'defective' [SiO3] 2- and [A104] 5- tetrahedra. On irradiation, the Si---O donor-acceptor bonds trap nonelastically scattered electrons and are ruptured as a result. The water released by this lattice discontinuity forms microbubbles that diffuse along sinks into the larger micropores thus further increasing their volume.
The shock-metamorphosed quartz exhibits
thermal luminescence (TL) with maxima at 365 nm, 470 nm
a... more The shock-metamorphosed quartz exhibits thermal luminescence (TL) with maxima at 365 nm, 470 nm and 610-680 nm. By electron paramagnetic resonance (EPR) analysis E 1 type electron centers and hole centers have been found which originate from vacancies including those from the substitution of A13+ and/or Fe 3+, for Si 4+. The EPR and TL spectra may be interpreted mainly in terms of vacancy type defects associated with dislocations in the crystal structure of quartz.
We have studied the polarized optical absorption
and the EPR spectra of Ni-doped beryls grown by
... more We have studied the polarized optical absorption and the EPR spectra of Ni-doped beryls grown by hydrothermal, flux and gas-transport methods, and chrysoberyl grown by the Czochralski and flux methods. In beryls, three groups of bands belonging to three various Ni centres were distinguished by analysis of the absorption band intensities. The first group, bands with maximums at 21740 (E ^ c), 17240 (E || c) and 9260 (E ^ + || c), 7140 (E || + ^ c) cm1, are due to Ni3+ in octahedral Al3+ site. The second group is bands at 25640 (E ^ c), 22220 (E || c) and 13520 (E ||+^ c), 13160 (E ^+|| c) cm1 and 8930 (E ^+|| c), 7460 (E || c) cm1, which are caused by Ni2+ in octahedral Al3+ site. Weak wide bands at 17540 (E ^ c), 15500 (E || c) cm1 and 6580 (E || + ^ c), 5950 (E || c) cm1 are related to Ni2+ in tetrahedral Be2+ site. The occurrence of Ni ions in Be2+ site is proved by the EPR spectra of 1VNi+ in c-irradiated samples. According to the spectra of optical absorption of Ni-doped chrysoberyl, two types of Ni centres have been established: Ni3+ and Ni2+ ions in octahedral Al3+ sites. From the EPR spectra of the X-ray irradiated crystals BeAl2O4: Ni, it follows that 68% of Ni+ ions occupy octahedral Al3+ sites with mirror symmetry and 32% are in Al3+ sites with inversion symmetry. In the approximation of trigonal field with regard to Trees correction, the energy levels of Ni3+ and Ni2+ have been calculated in octahedral and tetrahedral coordination. There is good agreement between the obtained experimental and calculated data. The polarization dependence of the optical absorption bands is well explained in terms of the spin– orbit interaction.
We have studied the polarized optical
absorption and EPR spectra of Co-doped beryls grown
by hydr... more We have studied the polarized optical absorption and EPR spectra of Co-doped beryls grown by hydrothermal, flux, and gas-transport methods, and chrysoberyl grown by the Czochralski method. In beryls three groups of bands, belonging to three various Co centers, were distinguished by analysis of the absorption band intensities. The first group, bands with maxima at 22 220 (E ? c), 17 730 (E k c), and 9090 (E k c), 7520 (E ? c) cm)1 are due to Co2+ in octahedral site of Al3+. The second group is bands at 18 940, 18 250, 17 700 (E ? c), 18 300, 17 700, 17 000 (E k c) and 8830 (E ? c), 7350 (E k c) cm-1 and 5320 (E ? c), 3880 (E k c) cm)1, which are caused by Co2+ in tetrahedral site of Be2+. A weak wide band in flux and gas-transport beryl in the region of 12 500– 8300 cm-1 (E k, ? c) is related to Co3+ in octahedral Al3+ site. In hydrothermal beryl, bands 13 200 (E ? c), 10 900 (E k c), and 8500 (E ? c) cm)1 are caused by an uncontrolled impurity of Cu2+ ions. For Co-doped chrysoberyl one type of center of Co has been established: Co2+ in the octahedral site of Al3+. In the approximation of the trigonal field with regard to Trees’ correction, the energy levels of Co2+ have been calculated in octahedral and tetrahedral coordination. There is good agreement between the obtained experimental and calculated data. The polarization dependence of the optical absorption bands is explained well in terms of the spin-orbit interaction.
Electron paramagnetic resonance (EPR) is applied to study Al-, Sc-, In-, and Nb-doped KTiOAsO4 (K... more Electron paramagnetic resonance (EPR) is applied to study Al-, Sc-, In-, and Nb-doped KTiOAsO4 (KTA) crystals. Paramagnetic hole centers O– are observed after ionizing irradiation of KTA crystals. These centers are, as a rule, unstable at room temperature and are slowly annealed for about two weeks. Oxygen ions are bridging two cations in KTA. Near the impurity, two -orbitals of oxygen atoms participate in covalent bonding with cations, whereas the third p-orbital remains free and under the radiation effect captures the hole thus forming the paramagnetic center of Mn+–O––M(n–1)+ (here Mn+ is the lattice cation and M(n–1)+ is the impurity cation of Al, In, Sc, or Nb). In the centers investigated the specific principal direction of the g-factor g ~2 is normal to the Mn+–O––M(n–1)+ plane, and the main value of gmax falls in this plane. The direction of the O––M(n–1)+ bond is close to the selected direction of the hyperfine interaction with the impurity ion. The models of six hole centers and the found parameters of EPR spectra are discussed. Keywords: EPR, hole centers, KTiOAsO4 (KTA).
Electron paramagnetic resonance and optical absorption in the visible and infrared regions have
b... more Electron paramagnetic resonance and optical absorption in the visible and infrared regions have been used to study flux-grown KTiOAs04 crystals doped with In, Sc, and Fe. An unstable broad absorption band and paramagnetic hole centres in KTA: In or Sc after y-irradiation are observed. The analysis of EPR data leads to a model wherein the holes are trapped on bridging oxygen ions between two titanium ions. The optical absorption band at 2.7 eV is ascribed to the light-induced transfer of holes from one oxygen ion to another. Infrared absorption bands at 3584 and 3594 cm-' are observed in all crystals and possible positions of the OH group in the structure are discussed.
A natural quartz, annealed first at 800ºC and then irradiated with a 3.5 MeV electron beam, has b... more A natural quartz, annealed first at 800ºC and then irradiated with a 3.5 MeV electron beam, has been investigated by single-crystal electron paramagnetic resonance (EPR) spectroscopy at X- and W-band frequencies from 110 K to 298 K. The W-band EPR spectra allow better separation of two previously reported radiation-induced defects (D and E) and improved determinations of their spin Hamiltonian parameters. These defects have similar g tensors with the gmax axes pproximately along an O-O pair and gmin axes perpendicular to the short Si-O bonds, but different 27Al hyperfine structures. Centre E is also characterized by a 29Si hyperfine structure (A/h = ~0.4 mT). These spinHamiltonian parameters, together with results from density functional theory (DFT) calculations, suggest centre E to be a new variant of peroxy radicals in quartz, whereas a peroxy radical model for centre D remains tentative. Thermal stabilities and decay kinetics of centres D and E have been investigated by use of isochronal and isothermal annealing experiments on a neutron-irradiated quartz and six smoky quartz crystals indruses from a U deposit.
The X- and W-band single-crystal electron paramagnetic resonance spectra of an electron-irradiate... more The X- and W-band single-crystal electron paramagnetic resonance spectra of an electron-irradiated natural quartz permit quantitative analysis of a 29Si hyperfine structure (A ~12.6 MHz) and an 27Al hyperfine structure (A< 0.8 MHz) for a previously reported holelike center. The 29Si hyperfine structure arises from interaction with two equivalent Si atoms and is characterized by the direction of the unique A axis close to a Si–O bond direction. The 27Al hyperfine structure, onfirmed by pulsed electron nuclear double resonance and electron spin echo envelope modulation spectra, is characterized by the unique A axis approximately along a twofold symmetry axis. These 29Si and 27Al hyperfine data, together with published theoretical results on peroxy radicals in SiO2 as well as our own density functional theory (DFT) calculations on model peroxy centers, suggest this hole-like center to have the unpaired spin on a pair of oxygen atoms linked to two symmetrically equivalent Si atoms and a substitutional Al3+ ion across the c-axis channel, a first peroxy radical in quartz. The nuclear quadrupole matrix P also suggests that the Al3+ ion corresponds closely to the diamagnetic precursor to the [AlO4]0 center.
Single-crystal electron paramagnetic resonance (EPR) spectra of a natural citrine quartz without ... more Single-crystal electron paramagnetic resonance (EPR) spectra of a natural citrine quartz without any artificial irradiation, measured at W-band frequencies (~94 GHz) and temperatures of 77, 110 and 298 K, allow better characterization of three previously-reported Centers (#6, #7 and B) and discovery of three new defects (B', C' and G'). The W-band EPR spectra reveal that Centers #6 and #7 do not reside on twofold symmetry axes, contrary to results from a previous X-band EPR study. The W-band spectra also show that the previously reported Center B is a mixture of two defects (B and B') with similar g matrices but different-sized 27Al hyperfine structures. Center C' has similar principal g values to the previously reported Center C but is distinct from the latter by a larger 27Al hyperfine structure with splittings from 0.10 to 0.22 mT. Also, Center G' has a similar g matrix to the previously reported Center G but a different 27Al hyperfine structure with splittings from 0.41 to 0.53 mT. These spin-Hamiltonian parameters, together with observed thermal properties and microwavepower dependence, suggest that Centers #6 and #7 probably represent O2\3- type defects. Centers B and B' are probably superoxide radicals (O2 -) with the unpaired spin localized on the same pair of oxygen atoms around a missing Si atom but linked to a substitutional Al3+ ion each at different neighboring tetrahedral sites. Similarly, Centers G and G' are most likely superoxide radicals with the unpaired spin localized on another pair of oxygen atoms around a missing Si atom and linked to a substitutional Al3+ ion each at different neighboring tetrahedral sites. Center C' is probably an ozonide radical associated with a missing Si atom and linked to a substitutional Al3+ ion at the neighboring tetrahedral site. This study exemplifies the value of high-frequency EPR for discrimination of similar defect centers and determination of small local structural distortions that are often difficult to resolve in conventional X- and Q-band EPR studies.
Single-crystal W-band electron paramagnetic
resonance (EPR) spectra of an electron-irradiated qua... more Single-crystal W-band electron paramagnetic resonance (EPR) spectra of an electron-irradiated quartz, measured at room temperature, 110 and 77 K, disclose three previously reported hole centers (#1, G and an ozonide radical). The W-band EPR spectra of these three centers clearly resolve six magnetically nonequivalent sites each, whereas previous X- and Q-band EPR studies reported Centers #1 and the ozonide radical to consist of only three symmetry-related components and interpreted them to reside on twofold symmetry axes in the quartz structure. The calculated g matrices of Center #1 and the ozonide radical show that deviations from twofold symmetry axes are \10, which are probably attributable to distortion related to neighboring charge compensating ions. The W-band EPR spectra of Center G not only result in improved g matrices but also allow quantitative determination of the nuclear hyperfine (A) and quadrupole (P) matrices of its 27Al hyperfine structure that was incompletely resolved before. In particular, the g-maximum and g-minimum principal axes of Center G are approximately along two pairs of O–O edges of the SiO4 tetrahedron,
It is shown the possibility to determine the coordination of paramagnetic ions in disordered soli... more It is shown the possibility to determine the coordination of paramagnetic ions in disordered solid structures, e.g., in barium borate glasses. For this purpose the electron paramagnetic resonance (EPR) method was used to study a-and b-BaB2O4 crystals and glasses of 45BaO9 55B2O3 and 40BaO9 60B2O3 (mol%) composition activated by Ag+ and Pb2+ ions. After the samples were exposed to X-rays at 77 K, different EPR centers were observed in them. In a-and b-BaB2O4 crystals and glasses the EPR centers Ag2+, Ag0 , Pb+ , Pb3+, and hole centers of O- type were studied. The EPR parameters of these centers and their arrangement in crystal structure were determined. It is shown that Pb3+ ions in b-BaB2O4 crystals occupy Ba2+ position in an irregular polyhedron from the eight oxygen, whereas in a-BaB2O4 crystals they occupy Bf2 position in a sixfold coordination. Pb+ ions in a-BaB2O4 crystals occupy Bf1 position in a ninefold coordination from oxygen. In barium borate glasses, Pb3+ ions were studied in coordination polyhedron from six oxygen atoms and in a polyhedron from nine to ten oxygen atoms. It is assumed that the established difference in the structural position of Pb3+ ions in glasses is due to their previous incorporation in associative cation–anion complexes (AC) and ‘‘free’’ structure-forming cations (FC). Computer simulations have been performed to analyze the stability of specific associative complexes and to compare their bond lengths with experimental data.
A silver atom in synthetic beryl is investigated by the EPR and electron spin echo (ESE) spectros... more A silver atom in synthetic beryl is investigated by the EPR and electron spin echo (ESE) spectroscopy. It is established that silver ions were first introduced into the structural channels of beryl by thermodiffusion at 800C. The Ag+ ions are then converted to the Ag0 state by the X-ray irradiation of samples at room temperature. Charge changes in manganese and chromium impurities located at the aluminum positions are observed at the same conditions. Four different Ag0 centers with isotropic hyperfine interactions (HFI) with 107Ag and 109Ag nuclei and hyperfine constants less than those for the free Ag atom are revealed by the EPR method. ESE investigations enable us to confirm the positions of silver atoms that are stable up to 230 C.
Two new paramagnetic centers (NI and N2) have been observed after gamma-irradiation of a beryl si... more Two new paramagnetic centers (NI and N2) have been observed after gamma-irradiation of a beryl single crystal. The observation of zero-field splitting from the electronic spin-state quartet and the isotropic hyperfine splitting with values similar to that of the free nitrogen atom enables us to suppose that the new paramagnetic eenters are nitrogen atoms resulting from radiolysis of molecular nitrogen inside the structural channels of beryl. The following parameters of the spin Hamiltonian were determined: g = 2.0021 + 0.0003, A/h = 13.7 _ 0.1 MHz, and D/h = 44.6 _ 0.2 for N1 and 37.6 _ 0.2 MHz for N2 with unique directions of zero-field splitting D along the optical axis c. An amazing resilience of the atomic properties of nitrogen trapped within the structural cavity has been experimentaily observed. The NI paramagnetic atom is stable up to 280 C. We suggest that the structural cavity in beryl could be a shelter for qubits encoded in electron spins of hydrogen or nitrogen atoms.
The contents of the structural channels of beryl, grown hydrothermally from an ammonium-containin... more The contents of the structural channels of beryl, grown hydrothermally from an ammonium-containing solution, were investigated by IR and EPR spectroscopy. Using IR spectroscopy we found that water molecules, ammonium ions, and a small number of HCl molecules enter the structural channels of beryl in the course of mineral growth. In these beryls, the ammonium ions play the role of alkali cations. The ammonium ions are as rigidly fixed in the lattice as are water molecules; they are eliminated by calcination at high temperatures close to the decomposition temperature. On exposure to radiation at 77 K, the paramagnetic NH3 and H0 radicals are stabilized in the structural channels of beryl. In addition to the known H0 radical, other states of atomic hydrogen, interacting with medium protons, are observed as well. For one of the additional radicals, Hb, we suggest the model of atomic hydrogen stabilized at the center of a silicon-oxygen ring with two water molecules in adjacent cavities.
Infrared spectra and EPR of channel constituents in beryls synthesized hydrothermally in the pres... more Infrared spectra and EPR of channel constituents in beryls synthesized hydrothermally in the presence of NH4Cl were investigated.
Hydrothermal synthetic emeralds manufactured by Biron, Regency and Tairus have been distinguished... more Hydrothermal synthetic emeralds manufactured by Biron, Regency and Tairus have been distinguished from natural and synthetic emeralds using chemical analysis and infrared (IR) spectroscopy. Polarized IR spectra have been obtained from plates. Hydrothermal synthetic emeralds possess infrared absorption features not present in natural emeralds, and these features have been investigated. We infer that the system of five narrow bands in the 3000-2600 cm-1 region is related to the dimer formation of HCl molecules, which have been incorporated in the channels parallel to the c-axis during growth of Biron and Regency emeralds. In Regency emeralds, a double band with maximum at 3295 and shoulder near 3232 cm-1 and a broad band between 3000 and 2500 cm-1 are attributed to hydrogen- bonded NH4 + ions. In Russian hydrothermal synthetic emeralds the strong infrared spectral features related to molecular water are generally similar to those of some natural emeralds but there are also broad bands due to Ni2+ and Cu2+ ions in the near-infrared regions which enable one to distinguish Russian hydrothermal synthetic from natural emeralds. Other bands unrelated to water in hydrothermal synthetic emeralds are also discussed.
Plastically deformed differently colored diamond crystals from the Internatsionalnaya pipe (Yakut... more Plastically deformed differently colored diamond crystals from the Internatsionalnaya pipe (Yakutia) have been studied using synchrotron radiation in Laue geometry (Laue-SR method) and UV-Vis-IR absorption spectroscopy. According to the Laue-SR data, brown, smoky-gray and gray with a light purple-pink hue diamonds have suffered a high degree of deformation during the post-crystallization period. Strong asterism of Laue spots, intense continuous optical absorption throughout the visible spectrum, monotonically increasing toward shorter wavelengths, and ‘‘amber centers’’ in the IR region from 4,000 to 6,000 cm-1 are typical of these diamond crystals. Light purplish pink diamonds with gray or brown hue have experienced lesser degree of deformation. This group of diamonds has two absorption bands with maximums at 480 and 550 nm and ‘‘amber centers’’ in the IR region. A distinct polygonization is typical of the inner structure of light purplish pink diamonds. Light purplish pink diamonds have an intensive absorption band with maximum at 550 nm and are characterized by the lack of ‘‘amber centers.’’ The relationship between the deformation levels, diamond color characteristics and manifestation of the ‘‘amber centers’’ in the IR region has been traced based on the obtained results.
This paper presents the results of Fourier transform infrared (FTIR) spectroscopy of a synthetic ... more This paper presents the results of Fourier transform infrared (FTIR) spectroscopy of a synthetic beryl, containing D2O molecules in its c-axis channels, which we synthesized under hydrothermal conditions at 600 °C and 1.5 kbar. The frequencies of absorbance bands in the range of the stretching vibrations and their overtones and combination modes for D2O and HDO molecules have been assigned for the first time. On the basis of our assignments, the absorbance bands observed for the natural beryl in the range of the OD stretching vibrations have been explained. Note! Unfortunately during publication's processing Greek letters ν and δ were unintentionally transformed into Latin letters 'n' and 'd', respectively. Also symbol 'perpendicular' was transformed to ^.
Impurity inhomogeneities and other structural defects
have been studied by means of transmission ... more Impurity inhomogeneities and other structural defects have been studied by means of transmission electron microscopy (TEM), X-ray microanalysis and electron paramagnetic resonance (EPR) in untreated and heat-treated quartz samples of three genetic types: hydrothermal, pegmatitic and magmatic. The impurities present are A1, Na and H20 , which occupy tetrahedral (A13+) or interstitial (Na +, H20 ) positions in the quartz lattice. Impurities form imperfections of various degrees of segregation: from point defects to micropores with a gas-liquid content. Their size, form, density and distribution in the lattice depend on the formation conditions of the quartz, the presence of dislocations and plane defects serving as sinks for the impurity atoms, and the heat treatment regime. Experimental data indicate that gas-liquid inclusions of dimensions up to some microns are the result of impurity segregation during postcrystallizational cooling. Crystalline quartz amorphizes upon electron irradiation. A model of structural water explaining experimentally observed features of this phenomenon is proposed whereby the water molecule, represented as a dipole, enters microregions of the silica lattice with a high impurity content and there forms a bond between 'defective' [SiO3] 2- and [A104] 5- tetrahedra. On irradiation, the Si---O donor-acceptor bonds trap nonelastically scattered electrons and are ruptured as a result. The water released by this lattice discontinuity forms microbubbles that diffuse along sinks into the larger micropores thus further increasing their volume.
The shock-metamorphosed quartz exhibits
thermal luminescence (TL) with maxima at 365 nm, 470 nm
a... more The shock-metamorphosed quartz exhibits thermal luminescence (TL) with maxima at 365 nm, 470 nm and 610-680 nm. By electron paramagnetic resonance (EPR) analysis E 1 type electron centers and hole centers have been found which originate from vacancies including those from the substitution of A13+ and/or Fe 3+, for Si 4+. The EPR and TL spectra may be interpreted mainly in terms of vacancy type defects associated with dislocations in the crystal structure of quartz.
We have studied the polarized optical absorption
and the EPR spectra of Ni-doped beryls grown by
... more We have studied the polarized optical absorption and the EPR spectra of Ni-doped beryls grown by hydrothermal, flux and gas-transport methods, and chrysoberyl grown by the Czochralski and flux methods. In beryls, three groups of bands belonging to three various Ni centres were distinguished by analysis of the absorption band intensities. The first group, bands with maximums at 21740 (E ^ c), 17240 (E || c) and 9260 (E ^ + || c), 7140 (E || + ^ c) cm1, are due to Ni3+ in octahedral Al3+ site. The second group is bands at 25640 (E ^ c), 22220 (E || c) and 13520 (E ||+^ c), 13160 (E ^+|| c) cm1 and 8930 (E ^+|| c), 7460 (E || c) cm1, which are caused by Ni2+ in octahedral Al3+ site. Weak wide bands at 17540 (E ^ c), 15500 (E || c) cm1 and 6580 (E || + ^ c), 5950 (E || c) cm1 are related to Ni2+ in tetrahedral Be2+ site. The occurrence of Ni ions in Be2+ site is proved by the EPR spectra of 1VNi+ in c-irradiated samples. According to the spectra of optical absorption of Ni-doped chrysoberyl, two types of Ni centres have been established: Ni3+ and Ni2+ ions in octahedral Al3+ sites. From the EPR spectra of the X-ray irradiated crystals BeAl2O4: Ni, it follows that 68% of Ni+ ions occupy octahedral Al3+ sites with mirror symmetry and 32% are in Al3+ sites with inversion symmetry. In the approximation of trigonal field with regard to Trees correction, the energy levels of Ni3+ and Ni2+ have been calculated in octahedral and tetrahedral coordination. There is good agreement between the obtained experimental and calculated data. The polarization dependence of the optical absorption bands is well explained in terms of the spin– orbit interaction.
We have studied the polarized optical
absorption and EPR spectra of Co-doped beryls grown
by hydr... more We have studied the polarized optical absorption and EPR spectra of Co-doped beryls grown by hydrothermal, flux, and gas-transport methods, and chrysoberyl grown by the Czochralski method. In beryls three groups of bands, belonging to three various Co centers, were distinguished by analysis of the absorption band intensities. The first group, bands with maxima at 22 220 (E ? c), 17 730 (E k c), and 9090 (E k c), 7520 (E ? c) cm)1 are due to Co2+ in octahedral site of Al3+. The second group is bands at 18 940, 18 250, 17 700 (E ? c), 18 300, 17 700, 17 000 (E k c) and 8830 (E ? c), 7350 (E k c) cm-1 and 5320 (E ? c), 3880 (E k c) cm)1, which are caused by Co2+ in tetrahedral site of Be2+. A weak wide band in flux and gas-transport beryl in the region of 12 500– 8300 cm-1 (E k, ? c) is related to Co3+ in octahedral Al3+ site. In hydrothermal beryl, bands 13 200 (E ? c), 10 900 (E k c), and 8500 (E ? c) cm)1 are caused by an uncontrolled impurity of Cu2+ ions. For Co-doped chrysoberyl one type of center of Co has been established: Co2+ in the octahedral site of Al3+. In the approximation of the trigonal field with regard to Trees’ correction, the energy levels of Co2+ have been calculated in octahedral and tetrahedral coordination. There is good agreement between the obtained experimental and calculated data. The polarization dependence of the optical absorption bands is explained well in terms of the spin-orbit interaction.
Electron paramagnetic resonance (EPR) is applied to study Al-, Sc-, In-, and Nb-doped KTiOAsO4 (K... more Electron paramagnetic resonance (EPR) is applied to study Al-, Sc-, In-, and Nb-doped KTiOAsO4 (KTA) crystals. Paramagnetic hole centers O– are observed after ionizing irradiation of KTA crystals. These centers are, as a rule, unstable at room temperature and are slowly annealed for about two weeks. Oxygen ions are bridging two cations in KTA. Near the impurity, two -orbitals of oxygen atoms participate in covalent bonding with cations, whereas the third p-orbital remains free and under the radiation effect captures the hole thus forming the paramagnetic center of Mn+–O––M(n–1)+ (here Mn+ is the lattice cation and M(n–1)+ is the impurity cation of Al, In, Sc, or Nb). In the centers investigated the specific principal direction of the g-factor g ~2 is normal to the Mn+–O––M(n–1)+ plane, and the main value of gmax falls in this plane. The direction of the O––M(n–1)+ bond is close to the selected direction of the hyperfine interaction with the impurity ion. The models of six hole centers and the found parameters of EPR spectra are discussed. Keywords: EPR, hole centers, KTiOAsO4 (KTA).
Electron paramagnetic resonance and optical absorption in the visible and infrared regions have
b... more Electron paramagnetic resonance and optical absorption in the visible and infrared regions have been used to study flux-grown KTiOAs04 crystals doped with In, Sc, and Fe. An unstable broad absorption band and paramagnetic hole centres in KTA: In or Sc after y-irradiation are observed. The analysis of EPR data leads to a model wherein the holes are trapped on bridging oxygen ions between two titanium ions. The optical absorption band at 2.7 eV is ascribed to the light-induced transfer of holes from one oxygen ion to another. Infrared absorption bands at 3584 and 3594 cm-' are observed in all crystals and possible positions of the OH group in the structure are discussed.
A natural quartz, annealed first at 800ºC and then irradiated with a 3.5 MeV electron beam, has b... more A natural quartz, annealed first at 800ºC and then irradiated with a 3.5 MeV electron beam, has been investigated by single-crystal electron paramagnetic resonance (EPR) spectroscopy at X- and W-band frequencies from 110 K to 298 K. The W-band EPR spectra allow better separation of two previously reported radiation-induced defects (D and E) and improved determinations of their spin Hamiltonian parameters. These defects have similar g tensors with the gmax axes pproximately along an O-O pair and gmin axes perpendicular to the short Si-O bonds, but different 27Al hyperfine structures. Centre E is also characterized by a 29Si hyperfine structure (A/h = ~0.4 mT). These spinHamiltonian parameters, together with results from density functional theory (DFT) calculations, suggest centre E to be a new variant of peroxy radicals in quartz, whereas a peroxy radical model for centre D remains tentative. Thermal stabilities and decay kinetics of centres D and E have been investigated by use of isochronal and isothermal annealing experiments on a neutron-irradiated quartz and six smoky quartz crystals indruses from a U deposit.
The X- and W-band single-crystal electron paramagnetic resonance spectra of an electron-irradiate... more The X- and W-band single-crystal electron paramagnetic resonance spectra of an electron-irradiated natural quartz permit quantitative analysis of a 29Si hyperfine structure (A ~12.6 MHz) and an 27Al hyperfine structure (A< 0.8 MHz) for a previously reported holelike center. The 29Si hyperfine structure arises from interaction with two equivalent Si atoms and is characterized by the direction of the unique A axis close to a Si–O bond direction. The 27Al hyperfine structure, onfirmed by pulsed electron nuclear double resonance and electron spin echo envelope modulation spectra, is characterized by the unique A axis approximately along a twofold symmetry axis. These 29Si and 27Al hyperfine data, together with published theoretical results on peroxy radicals in SiO2 as well as our own density functional theory (DFT) calculations on model peroxy centers, suggest this hole-like center to have the unpaired spin on a pair of oxygen atoms linked to two symmetrically equivalent Si atoms and a substitutional Al3+ ion across the c-axis channel, a first peroxy radical in quartz. The nuclear quadrupole matrix P also suggests that the Al3+ ion corresponds closely to the diamagnetic precursor to the [AlO4]0 center.
Single-crystal electron paramagnetic resonance (EPR) spectra of a natural citrine quartz without ... more Single-crystal electron paramagnetic resonance (EPR) spectra of a natural citrine quartz without any artificial irradiation, measured at W-band frequencies (~94 GHz) and temperatures of 77, 110 and 298 K, allow better characterization of three previously-reported Centers (#6, #7 and B) and discovery of three new defects (B', C' and G'). The W-band EPR spectra reveal that Centers #6 and #7 do not reside on twofold symmetry axes, contrary to results from a previous X-band EPR study. The W-band spectra also show that the previously reported Center B is a mixture of two defects (B and B') with similar g matrices but different-sized 27Al hyperfine structures. Center C' has similar principal g values to the previously reported Center C but is distinct from the latter by a larger 27Al hyperfine structure with splittings from 0.10 to 0.22 mT. Also, Center G' has a similar g matrix to the previously reported Center G but a different 27Al hyperfine structure with splittings from 0.41 to 0.53 mT. These spin-Hamiltonian parameters, together with observed thermal properties and microwavepower dependence, suggest that Centers #6 and #7 probably represent O2\3- type defects. Centers B and B' are probably superoxide radicals (O2 -) with the unpaired spin localized on the same pair of oxygen atoms around a missing Si atom but linked to a substitutional Al3+ ion each at different neighboring tetrahedral sites. Similarly, Centers G and G' are most likely superoxide radicals with the unpaired spin localized on another pair of oxygen atoms around a missing Si atom and linked to a substitutional Al3+ ion each at different neighboring tetrahedral sites. Center C' is probably an ozonide radical associated with a missing Si atom and linked to a substitutional Al3+ ion at the neighboring tetrahedral site. This study exemplifies the value of high-frequency EPR for discrimination of similar defect centers and determination of small local structural distortions that are often difficult to resolve in conventional X- and Q-band EPR studies.
Single-crystal W-band electron paramagnetic
resonance (EPR) spectra of an electron-irradiated qua... more Single-crystal W-band electron paramagnetic resonance (EPR) spectra of an electron-irradiated quartz, measured at room temperature, 110 and 77 K, disclose three previously reported hole centers (#1, G and an ozonide radical). The W-band EPR spectra of these three centers clearly resolve six magnetically nonequivalent sites each, whereas previous X- and Q-band EPR studies reported Centers #1 and the ozonide radical to consist of only three symmetry-related components and interpreted them to reside on twofold symmetry axes in the quartz structure. The calculated g matrices of Center #1 and the ozonide radical show that deviations from twofold symmetry axes are \10, which are probably attributable to distortion related to neighboring charge compensating ions. The W-band EPR spectra of Center G not only result in improved g matrices but also allow quantitative determination of the nuclear hyperfine (A) and quadrupole (P) matrices of its 27Al hyperfine structure that was incompletely resolved before. In particular, the g-maximum and g-minimum principal axes of Center G are approximately along two pairs of O–O edges of the SiO4 tetrahedron,
It is shown the possibility to determine the coordination of paramagnetic ions in disordered soli... more It is shown the possibility to determine the coordination of paramagnetic ions in disordered solid structures, e.g., in barium borate glasses. For this purpose the electron paramagnetic resonance (EPR) method was used to study a-and b-BaB2O4 crystals and glasses of 45BaO9 55B2O3 and 40BaO9 60B2O3 (mol%) composition activated by Ag+ and Pb2+ ions. After the samples were exposed to X-rays at 77 K, different EPR centers were observed in them. In a-and b-BaB2O4 crystals and glasses the EPR centers Ag2+, Ag0 , Pb+ , Pb3+, and hole centers of O- type were studied. The EPR parameters of these centers and their arrangement in crystal structure were determined. It is shown that Pb3+ ions in b-BaB2O4 crystals occupy Ba2+ position in an irregular polyhedron from the eight oxygen, whereas in a-BaB2O4 crystals they occupy Bf2 position in a sixfold coordination. Pb+ ions in a-BaB2O4 crystals occupy Bf1 position in a ninefold coordination from oxygen. In barium borate glasses, Pb3+ ions were studied in coordination polyhedron from six oxygen atoms and in a polyhedron from nine to ten oxygen atoms. It is assumed that the established difference in the structural position of Pb3+ ions in glasses is due to their previous incorporation in associative cation–anion complexes (AC) and ‘‘free’’ structure-forming cations (FC). Computer simulations have been performed to analyze the stability of specific associative complexes and to compare their bond lengths with experimental data.
A silver atom in synthetic beryl is investigated by the EPR and electron spin echo (ESE) spectros... more A silver atom in synthetic beryl is investigated by the EPR and electron spin echo (ESE) spectroscopy. It is established that silver ions were first introduced into the structural channels of beryl by thermodiffusion at 800C. The Ag+ ions are then converted to the Ag0 state by the X-ray irradiation of samples at room temperature. Charge changes in manganese and chromium impurities located at the aluminum positions are observed at the same conditions. Four different Ag0 centers with isotropic hyperfine interactions (HFI) with 107Ag and 109Ag nuclei and hyperfine constants less than those for the free Ag atom are revealed by the EPR method. ESE investigations enable us to confirm the positions of silver atoms that are stable up to 230 C.
Two new paramagnetic centers (NI and N2) have been observed after gamma-irradiation of a beryl si... more Two new paramagnetic centers (NI and N2) have been observed after gamma-irradiation of a beryl single crystal. The observation of zero-field splitting from the electronic spin-state quartet and the isotropic hyperfine splitting with values similar to that of the free nitrogen atom enables us to suppose that the new paramagnetic eenters are nitrogen atoms resulting from radiolysis of molecular nitrogen inside the structural channels of beryl. The following parameters of the spin Hamiltonian were determined: g = 2.0021 + 0.0003, A/h = 13.7 _ 0.1 MHz, and D/h = 44.6 _ 0.2 for N1 and 37.6 _ 0.2 MHz for N2 with unique directions of zero-field splitting D along the optical axis c. An amazing resilience of the atomic properties of nitrogen trapped within the structural cavity has been experimentaily observed. The NI paramagnetic atom is stable up to 280 C. We suggest that the structural cavity in beryl could be a shelter for qubits encoded in electron spins of hydrogen or nitrogen atoms.
The contents of the structural channels of beryl, grown hydrothermally from an ammonium-containin... more The contents of the structural channels of beryl, grown hydrothermally from an ammonium-containing solution, were investigated by IR and EPR spectroscopy. Using IR spectroscopy we found that water molecules, ammonium ions, and a small number of HCl molecules enter the structural channels of beryl in the course of mineral growth. In these beryls, the ammonium ions play the role of alkali cations. The ammonium ions are as rigidly fixed in the lattice as are water molecules; they are eliminated by calcination at high temperatures close to the decomposition temperature. On exposure to radiation at 77 K, the paramagnetic NH3 and H0 radicals are stabilized in the structural channels of beryl. In addition to the known H0 radical, other states of atomic hydrogen, interacting with medium protons, are observed as well. For one of the additional radicals, Hb, we suggest the model of atomic hydrogen stabilized at the center of a silicon-oxygen ring with two water molecules in adjacent cavities.
Infrared spectra and EPR of channel constituents in beryls synthesized hydrothermally in the pres... more Infrared spectra and EPR of channel constituents in beryls synthesized hydrothermally in the presence of NH4Cl were investigated.
Hydrothermal synthetic emeralds manufactured by Biron, Regency and Tairus have been distinguished... more Hydrothermal synthetic emeralds manufactured by Biron, Regency and Tairus have been distinguished from natural and synthetic emeralds using chemical analysis and infrared (IR) spectroscopy. Polarized IR spectra have been obtained from plates. Hydrothermal synthetic emeralds possess infrared absorption features not present in natural emeralds, and these features have been investigated. We infer that the system of five narrow bands in the 3000-2600 cm-1 region is related to the dimer formation of HCl molecules, which have been incorporated in the channels parallel to the c-axis during growth of Biron and Regency emeralds. In Regency emeralds, a double band with maximum at 3295 and shoulder near 3232 cm-1 and a broad band between 3000 and 2500 cm-1 are attributed to hydrogen- bonded NH4 + ions. In Russian hydrothermal synthetic emeralds the strong infrared spectral features related to molecular water are generally similar to those of some natural emeralds but there are also broad bands due to Ni2+ and Cu2+ ions in the near-infrared regions which enable one to distinguish Russian hydrothermal synthetic from natural emeralds. Other bands unrelated to water in hydrothermal synthetic emeralds are also discussed.
Plastically deformed differently colored diamond crystals from the Internatsionalnaya pipe (Yakut... more Plastically deformed differently colored diamond crystals from the Internatsionalnaya pipe (Yakutia) have been studied using synchrotron radiation in Laue geometry (Laue-SR method) and UV-Vis-IR absorption spectroscopy. According to the Laue-SR data, brown, smoky-gray and gray with a light purple-pink hue diamonds have suffered a high degree of deformation during the post-crystallization period. Strong asterism of Laue spots, intense continuous optical absorption throughout the visible spectrum, monotonically increasing toward shorter wavelengths, and ‘‘amber centers’’ in the IR region from 4,000 to 6,000 cm-1 are typical of these diamond crystals. Light purplish pink diamonds with gray or brown hue have experienced lesser degree of deformation. This group of diamonds has two absorption bands with maximums at 480 and 550 nm and ‘‘amber centers’’ in the IR region. A distinct polygonization is typical of the inner structure of light purplish pink diamonds. Light purplish pink diamonds have an intensive absorption band with maximum at 550 nm and are characterized by the lack of ‘‘amber centers.’’ The relationship between the deformation levels, diamond color characteristics and manifestation of the ‘‘amber centers’’ in the IR region has been traced based on the obtained results.
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Papers by Rudolf Mashkovtsev
Note! Unfortunately during publication's processing Greek letters ν and δ were unintentionally transformed into Latin letters 'n' and 'd', respectively. Also symbol 'perpendicular' was transformed to ^.
have been studied by means of transmission electron
microscopy (TEM), X-ray microanalysis and electron paramagnetic resonance (EPR) in untreated and heat-treated
quartz samples of three genetic types: hydrothermal, pegmatitic
and magmatic. The impurities present are A1, Na and H20 , which occupy tetrahedral (A13+) or interstitial (Na +, H20 ) positions in the quartz lattice.
Impurities form imperfections of various degrees of segregation: from point defects to micropores with a gas-liquid
content. Their size, form, density and distribution in the
lattice depend on the formation conditions of the quartz,
the presence of dislocations and plane defects serving as
sinks for the impurity atoms, and the heat treatment regime.
Experimental data indicate that gas-liquid inclusions of dimensions up to some microns are the result of impurity
segregation during postcrystallizational cooling.
Crystalline quartz amorphizes upon electron irradiation.
A model of structural water explaining experimentally observed
features of this phenomenon is proposed whereby
the water molecule, represented as a dipole, enters microregions
of the silica lattice with a high impurity content and
there forms a bond between 'defective' [SiO3] 2- and
[A104] 5- tetrahedra. On irradiation, the Si---O donor-acceptor
bonds trap nonelastically scattered electrons and are
ruptured as a result. The water released by this lattice discontinuity forms microbubbles that diffuse along sinks into
the larger micropores thus further increasing their volume.
thermal luminescence (TL) with maxima at 365 nm, 470 nm
and 610-680 nm. By electron paramagnetic resonance (EPR)
analysis E 1 type electron centers and hole centers have been
found which originate from vacancies including those from
the substitution of A13+ and/or Fe 3+, for Si 4+. The EPR
and TL spectra may be interpreted mainly in terms of
vacancy type defects associated with dislocations in the
crystal structure of quartz.
and the EPR spectra of Ni-doped beryls grown by
hydrothermal, flux and gas-transport methods, and
chrysoberyl grown by the Czochralski and flux methods.
In beryls, three groups of bands belonging to three various
Ni centres were distinguished by analysis of the
absorption band intensities. The first group, bands
with maximums at 21740 (E ^ c), 17240 (E || c) and 9260
(E ^ + || c), 7140 (E || + ^ c) cm1, are due to Ni3+ in
octahedral Al3+ site. The second group is bands at
25640 (E ^ c), 22220 (E || c) and 13520 (E ||+^ c), 13160
(E ^+|| c) cm1 and 8930 (E ^+|| c), 7460 (E || c) cm1,
which are caused by Ni2+ in octahedral Al3+ site. Weak
wide bands at 17540 (E ^ c), 15500 (E || c) cm1 and 6580
(E || + ^ c), 5950 (E || c) cm1 are related to Ni2+ in
tetrahedral Be2+ site. The occurrence of Ni ions in Be2+
site is proved by the EPR spectra of 1VNi+ in c-irradiated
samples. According to the spectra of optical absorption of
Ni-doped chrysoberyl, two types of Ni centres have been
established: Ni3+ and Ni2+ ions in octahedral Al3+ sites.
From the EPR spectra of the X-ray irradiated crystals
BeAl2O4: Ni, it follows that 68% of Ni+ ions occupy
octahedral Al3+ sites with mirror symmetry and 32% are
in Al3+ sites with inversion symmetry. In the approximation
of trigonal field with regard to Trees correction,
the energy levels of Ni3+ and Ni2+ have been calculated
in octahedral and tetrahedral coordination. There is good
agreement between the obtained experimental and calculated
data. The polarization dependence of the optical
absorption bands is well explained in terms of the spin–
orbit interaction.
absorption and EPR spectra of Co-doped beryls grown
by hydrothermal, flux, and gas-transport methods, and
chrysoberyl grown by the Czochralski method. In
beryls three groups of bands, belonging to three various
Co centers, were distinguished by analysis of the
absorption band intensities. The first group, bands
with maxima at 22 220 (E ? c), 17 730 (E k c), and
9090 (E k c), 7520 (E ? c) cm)1 are due to Co2+ in
octahedral site of Al3+. The second group is bands at
18 940, 18 250, 17 700 (E ? c), 18 300, 17 700, 17 000
(E k c) and 8830 (E ? c), 7350 (E k c) cm-1 and 5320
(E ? c), 3880 (E k c) cm)1, which are caused by Co2+
in tetrahedral site of Be2+. A weak wide band in flux
and gas-transport beryl in the region of 12 500–
8300 cm-1 (E k, ? c) is related to Co3+ in octahedral
Al3+ site. In hydrothermal beryl, bands 13 200
(E ? c), 10 900 (E k c), and 8500 (E ? c) cm)1 are
caused by an uncontrolled impurity of Cu2+ ions. For
Co-doped chrysoberyl one type of center of Co has
been established: Co2+ in the octahedral site of Al3+.
In the approximation of the trigonal field with regard
to Trees’ correction, the energy levels of Co2+ have
been calculated in octahedral and tetrahedral coordination.
There is good agreement between the obtained
experimental and calculated data. The polarization
dependence of the optical absorption bands is
explained well in terms of the spin-orbit interaction.
crystals. Paramagnetic hole centers O– are observed after ionizing irradiation of KTA crystals. These
centers are, as a rule, unstable at room temperature and are slowly annealed for about two weeks. Oxygen
ions are bridging two cations in KTA. Near the impurity, two -orbitals of oxygen atoms participate in covalent bonding with cations, whereas the third p-orbital remains free and under the radiation effect captures the hole thus forming the paramagnetic center of Mn+–O––M(n–1)+ (here Mn+ is the lattice cation and M(n–1)+ is the impurity cation of Al, In, Sc, or Nb). In the centers investigated the specific principal direction
of the g-factor g ~2 is normal to the Mn+–O––M(n–1)+ plane, and the main value of gmax falls in this plane.
The direction of the O––M(n–1)+ bond is close to the selected direction of the hyperfine interaction with the
impurity ion. The models of six hole centers and the found parameters of EPR spectra are discussed.
Keywords: EPR, hole centers, KTiOAsO4 (KTA).
been used to study flux-grown KTiOAs04 crystals doped with In, Sc, and Fe. An unstable broad
absorption band and paramagnetic hole centres in KTA: In or Sc after y-irradiation are observed.
The analysis of EPR data leads to a model wherein the holes are trapped on bridging oxygen ions
between two titanium ions. The optical absorption band at 2.7 eV is ascribed to the light-induced
transfer of holes from one oxygen ion to another. Infrared absorption bands at 3584 and 3594 cm-'
are observed in all crystals and possible positions of the OH group in the structure are discussed.
reported radiation-induced defects (D and E) and improved determinations of their spin Hamiltonian parameters. These defects have similar g tensors with the gmax axes pproximately along an O-O pair and gmin axes perpendicular to the short Si-O bonds, but different 27Al hyperfine structures. Centre E
is also characterized by a 29Si hyperfine structure (A/h = ~0.4 mT). These spinHamiltonian parameters, together with results from density functional theory (DFT) calculations, suggest centre E to be a new variant of peroxy radicals in quartz, whereas a peroxy radical model for centre D remains tentative. Thermal stabilities and decay kinetics of centres D and E have been investigated by use of isochronal and isothermal annealing experiments on a neutron-irradiated quartz and six smoky quartz crystals indruses from a U deposit.
own density functional theory (DFT) calculations on model
peroxy centers, suggest this hole-like center to have the
unpaired spin on a pair of oxygen atoms linked to two
symmetrically equivalent Si atoms and a substitutional Al3+
ion across the c-axis channel, a first peroxy radical in quartz.
The nuclear quadrupole matrix P also suggests that the Al3+
ion corresponds closely to the diamagnetic precursor to the
[AlO4]0 center.
but different-sized 27Al hyperfine structures. Center C' has
similar principal g values to the previously reported Center
C but is distinct from the latter by a larger 27Al hyperfine
structure with splittings from 0.10 to 0.22 mT. Also, Center
G' has a similar g matrix to the previously reported Center
G but a different 27Al hyperfine structure with splittings
from 0.41 to 0.53 mT. These spin-Hamiltonian parameters,
together with observed thermal properties and microwavepower dependence, suggest that Centers #6 and #7 probably represent O2\3- type defects. Centers B and B' are
probably superoxide radicals (O2 -) with the unpaired spin
localized on the same pair of oxygen atoms around a
missing Si atom but linked to a substitutional Al3+ ion each
at different neighboring tetrahedral sites. Similarly, Centers
G and G' are most likely superoxide radicals with the
unpaired spin localized on another pair of oxygen atoms
around a missing Si atom and linked to a substitutional
Al3+ ion each at different neighboring tetrahedral sites.
Center C' is probably an ozonide radical associated with a
missing Si atom and linked to a substitutional Al3+ ion at
the neighboring tetrahedral site. This study exemplifies the
value of high-frequency EPR for discrimination of similar
defect centers and determination of small local
structural distortions that are often difficult to resolve in
conventional X- and Q-band EPR studies.
resonance (EPR) spectra of an electron-irradiated quartz,
measured at room temperature, 110 and 77 K, disclose
three previously reported hole centers (#1, G and an
ozonide radical). The W-band EPR spectra of these three
centers clearly resolve six magnetically nonequivalent sites
each, whereas previous X- and Q-band EPR studies
reported Centers #1 and the ozonide radical to consist of
only three symmetry-related components and interpreted
them to reside on twofold symmetry axes in the quartz
structure. The calculated g matrices of Center #1 and the
ozonide radical show that deviations from twofold symmetry
axes are \10, which are probably attributable to
distortion related to neighboring charge compensating ions.
The W-band EPR spectra of Center G not only result in
improved g matrices but also allow quantitative determination
of the nuclear hyperfine (A) and quadrupole (P)
matrices of its 27Al hyperfine structure that was incompletely
resolved before. In particular, the g-maximum and
g-minimum principal axes of Center G are approximately
along two pairs of O–O edges of the SiO4 tetrahedron,
were observed in them. In a-and b-BaB2O4 crystals and
glasses the EPR centers Ag2+, Ag0 , Pb+ , Pb3+, and hole
centers of O- type were studied. The EPR parameters of
these centers and their arrangement in crystal structure
were determined. It is shown that Pb3+ ions in b-BaB2O4
crystals occupy Ba2+ position in an irregular polyhedron
from the eight oxygen, whereas in a-BaB2O4 crystals they
occupy Bf2 position in a sixfold coordination. Pb+ ions in
a-BaB2O4 crystals occupy Bf1 position in a ninefold
coordination from oxygen. In barium borate glasses, Pb3+
ions were studied in coordination polyhedron from six
oxygen atoms and in a polyhedron from nine to ten oxygen
atoms. It is assumed that the established difference in the
structural position of Pb3+ ions in glasses is due to their
previous incorporation in associative cation–anion complexes
(AC) and ‘‘free’’ structure-forming cations (FC).
Computer simulations have been performed to analyze the
stability of specific associative complexes and to compare
their bond lengths with experimental data.
observed at the same conditions. Four different Ag0 centers with isotropic hyperfine interactions (HFI) with 107Ag and 109Ag nuclei and hyperfine constants less than those for the free Ag atom are revealed by the EPR method. ESE investigations enable us to confirm the positions of silver atoms that are stable up to 230 C.
were determined: g = 2.0021 + 0.0003, A/h = 13.7 _ 0.1 MHz, and D/h = 44.6 _ 0.2 for N1 and 37.6 _ 0.2 MHz for N2 with unique directions of zero-field splitting D along the optical axis c. An
amazing resilience of the atomic properties of nitrogen trapped within the structural cavity has been experimentaily observed. The NI paramagnetic atom is stable up to 280 C. We suggest that the structural cavity in beryl could be a shelter for qubits encoded in electron spins of hydrogen or nitrogen atoms.
solution, were investigated by IR and EPR spectroscopy. Using IR spectroscopy we found that water
molecules, ammonium ions, and a small number of HCl molecules enter the structural channels of beryl in
the course of mineral growth. In these beryls, the ammonium ions play the role of alkali cations. The
ammonium ions are as rigidly fixed in the lattice as are water molecules; they are eliminated by calcination
at high temperatures close to the decomposition temperature. On exposure to radiation at 77 K, the
paramagnetic NH3 and H0 radicals are stabilized in the structural channels of beryl. In addition to the
known H0 radical, other states of atomic hydrogen, interacting with medium protons, are observed as well.
For one of the additional radicals, Hb, we suggest the model of atomic hydrogen stabilized at the center of a
silicon-oxygen ring with two water molecules in adjacent cavities.
and UV-Vis-IR absorption spectroscopy. According to the Laue-SR data, brown, smoky-gray and gray with a light purple-pink hue diamonds have suffered a high degree of deformation
during the post-crystallization period. Strong asterism of Laue spots, intense continuous optical absorption throughout the visible spectrum, monotonically increasing toward shorter
wavelengths, and ‘‘amber centers’’ in the IR region from 4,000 to 6,000 cm-1 are typical of these diamond crystals. Light purplish pink diamonds with gray or brown hue have experienced lesser degree of deformation. This group of diamonds has two absorption bands with maximums at 480 and 550 nm and ‘‘amber centers’’ in the IR region. A distinct polygonization is typical of the inner structure of light purplish pink diamonds. Light purplish pink diamonds have an intensive absorption band with maximum at 550 nm and are characterized by the lack of ‘‘amber centers.’’ The relationship between the deformation levels, diamond color characteristics and manifestation of the ‘‘amber centers’’ in the IR region has been traced based on the obtained results.
Note! Unfortunately during publication's processing Greek letters ν and δ were unintentionally transformed into Latin letters 'n' and 'd', respectively. Also symbol 'perpendicular' was transformed to ^.
have been studied by means of transmission electron
microscopy (TEM), X-ray microanalysis and electron paramagnetic resonance (EPR) in untreated and heat-treated
quartz samples of three genetic types: hydrothermal, pegmatitic
and magmatic. The impurities present are A1, Na and H20 , which occupy tetrahedral (A13+) or interstitial (Na +, H20 ) positions in the quartz lattice.
Impurities form imperfections of various degrees of segregation: from point defects to micropores with a gas-liquid
content. Their size, form, density and distribution in the
lattice depend on the formation conditions of the quartz,
the presence of dislocations and plane defects serving as
sinks for the impurity atoms, and the heat treatment regime.
Experimental data indicate that gas-liquid inclusions of dimensions up to some microns are the result of impurity
segregation during postcrystallizational cooling.
Crystalline quartz amorphizes upon electron irradiation.
A model of structural water explaining experimentally observed
features of this phenomenon is proposed whereby
the water molecule, represented as a dipole, enters microregions
of the silica lattice with a high impurity content and
there forms a bond between 'defective' [SiO3] 2- and
[A104] 5- tetrahedra. On irradiation, the Si---O donor-acceptor
bonds trap nonelastically scattered electrons and are
ruptured as a result. The water released by this lattice discontinuity forms microbubbles that diffuse along sinks into
the larger micropores thus further increasing their volume.
thermal luminescence (TL) with maxima at 365 nm, 470 nm
and 610-680 nm. By electron paramagnetic resonance (EPR)
analysis E 1 type electron centers and hole centers have been
found which originate from vacancies including those from
the substitution of A13+ and/or Fe 3+, for Si 4+. The EPR
and TL spectra may be interpreted mainly in terms of
vacancy type defects associated with dislocations in the
crystal structure of quartz.
and the EPR spectra of Ni-doped beryls grown by
hydrothermal, flux and gas-transport methods, and
chrysoberyl grown by the Czochralski and flux methods.
In beryls, three groups of bands belonging to three various
Ni centres were distinguished by analysis of the
absorption band intensities. The first group, bands
with maximums at 21740 (E ^ c), 17240 (E || c) and 9260
(E ^ + || c), 7140 (E || + ^ c) cm1, are due to Ni3+ in
octahedral Al3+ site. The second group is bands at
25640 (E ^ c), 22220 (E || c) and 13520 (E ||+^ c), 13160
(E ^+|| c) cm1 and 8930 (E ^+|| c), 7460 (E || c) cm1,
which are caused by Ni2+ in octahedral Al3+ site. Weak
wide bands at 17540 (E ^ c), 15500 (E || c) cm1 and 6580
(E || + ^ c), 5950 (E || c) cm1 are related to Ni2+ in
tetrahedral Be2+ site. The occurrence of Ni ions in Be2+
site is proved by the EPR spectra of 1VNi+ in c-irradiated
samples. According to the spectra of optical absorption of
Ni-doped chrysoberyl, two types of Ni centres have been
established: Ni3+ and Ni2+ ions in octahedral Al3+ sites.
From the EPR spectra of the X-ray irradiated crystals
BeAl2O4: Ni, it follows that 68% of Ni+ ions occupy
octahedral Al3+ sites with mirror symmetry and 32% are
in Al3+ sites with inversion symmetry. In the approximation
of trigonal field with regard to Trees correction,
the energy levels of Ni3+ and Ni2+ have been calculated
in octahedral and tetrahedral coordination. There is good
agreement between the obtained experimental and calculated
data. The polarization dependence of the optical
absorption bands is well explained in terms of the spin–
orbit interaction.
absorption and EPR spectra of Co-doped beryls grown
by hydrothermal, flux, and gas-transport methods, and
chrysoberyl grown by the Czochralski method. In
beryls three groups of bands, belonging to three various
Co centers, were distinguished by analysis of the
absorption band intensities. The first group, bands
with maxima at 22 220 (E ? c), 17 730 (E k c), and
9090 (E k c), 7520 (E ? c) cm)1 are due to Co2+ in
octahedral site of Al3+. The second group is bands at
18 940, 18 250, 17 700 (E ? c), 18 300, 17 700, 17 000
(E k c) and 8830 (E ? c), 7350 (E k c) cm-1 and 5320
(E ? c), 3880 (E k c) cm)1, which are caused by Co2+
in tetrahedral site of Be2+. A weak wide band in flux
and gas-transport beryl in the region of 12 500–
8300 cm-1 (E k, ? c) is related to Co3+ in octahedral
Al3+ site. In hydrothermal beryl, bands 13 200
(E ? c), 10 900 (E k c), and 8500 (E ? c) cm)1 are
caused by an uncontrolled impurity of Cu2+ ions. For
Co-doped chrysoberyl one type of center of Co has
been established: Co2+ in the octahedral site of Al3+.
In the approximation of the trigonal field with regard
to Trees’ correction, the energy levels of Co2+ have
been calculated in octahedral and tetrahedral coordination.
There is good agreement between the obtained
experimental and calculated data. The polarization
dependence of the optical absorption bands is
explained well in terms of the spin-orbit interaction.
crystals. Paramagnetic hole centers O– are observed after ionizing irradiation of KTA crystals. These
centers are, as a rule, unstable at room temperature and are slowly annealed for about two weeks. Oxygen
ions are bridging two cations in KTA. Near the impurity, two -orbitals of oxygen atoms participate in covalent bonding with cations, whereas the third p-orbital remains free and under the radiation effect captures the hole thus forming the paramagnetic center of Mn+–O––M(n–1)+ (here Mn+ is the lattice cation and M(n–1)+ is the impurity cation of Al, In, Sc, or Nb). In the centers investigated the specific principal direction
of the g-factor g ~2 is normal to the Mn+–O––M(n–1)+ plane, and the main value of gmax falls in this plane.
The direction of the O––M(n–1)+ bond is close to the selected direction of the hyperfine interaction with the
impurity ion. The models of six hole centers and the found parameters of EPR spectra are discussed.
Keywords: EPR, hole centers, KTiOAsO4 (KTA).
been used to study flux-grown KTiOAs04 crystals doped with In, Sc, and Fe. An unstable broad
absorption band and paramagnetic hole centres in KTA: In or Sc after y-irradiation are observed.
The analysis of EPR data leads to a model wherein the holes are trapped on bridging oxygen ions
between two titanium ions. The optical absorption band at 2.7 eV is ascribed to the light-induced
transfer of holes from one oxygen ion to another. Infrared absorption bands at 3584 and 3594 cm-'
are observed in all crystals and possible positions of the OH group in the structure are discussed.
reported radiation-induced defects (D and E) and improved determinations of their spin Hamiltonian parameters. These defects have similar g tensors with the gmax axes pproximately along an O-O pair and gmin axes perpendicular to the short Si-O bonds, but different 27Al hyperfine structures. Centre E
is also characterized by a 29Si hyperfine structure (A/h = ~0.4 mT). These spinHamiltonian parameters, together with results from density functional theory (DFT) calculations, suggest centre E to be a new variant of peroxy radicals in quartz, whereas a peroxy radical model for centre D remains tentative. Thermal stabilities and decay kinetics of centres D and E have been investigated by use of isochronal and isothermal annealing experiments on a neutron-irradiated quartz and six smoky quartz crystals indruses from a U deposit.
own density functional theory (DFT) calculations on model
peroxy centers, suggest this hole-like center to have the
unpaired spin on a pair of oxygen atoms linked to two
symmetrically equivalent Si atoms and a substitutional Al3+
ion across the c-axis channel, a first peroxy radical in quartz.
The nuclear quadrupole matrix P also suggests that the Al3+
ion corresponds closely to the diamagnetic precursor to the
[AlO4]0 center.
but different-sized 27Al hyperfine structures. Center C' has
similar principal g values to the previously reported Center
C but is distinct from the latter by a larger 27Al hyperfine
structure with splittings from 0.10 to 0.22 mT. Also, Center
G' has a similar g matrix to the previously reported Center
G but a different 27Al hyperfine structure with splittings
from 0.41 to 0.53 mT. These spin-Hamiltonian parameters,
together with observed thermal properties and microwavepower dependence, suggest that Centers #6 and #7 probably represent O2\3- type defects. Centers B and B' are
probably superoxide radicals (O2 -) with the unpaired spin
localized on the same pair of oxygen atoms around a
missing Si atom but linked to a substitutional Al3+ ion each
at different neighboring tetrahedral sites. Similarly, Centers
G and G' are most likely superoxide radicals with the
unpaired spin localized on another pair of oxygen atoms
around a missing Si atom and linked to a substitutional
Al3+ ion each at different neighboring tetrahedral sites.
Center C' is probably an ozonide radical associated with a
missing Si atom and linked to a substitutional Al3+ ion at
the neighboring tetrahedral site. This study exemplifies the
value of high-frequency EPR for discrimination of similar
defect centers and determination of small local
structural distortions that are often difficult to resolve in
conventional X- and Q-band EPR studies.
resonance (EPR) spectra of an electron-irradiated quartz,
measured at room temperature, 110 and 77 K, disclose
three previously reported hole centers (#1, G and an
ozonide radical). The W-band EPR spectra of these three
centers clearly resolve six magnetically nonequivalent sites
each, whereas previous X- and Q-band EPR studies
reported Centers #1 and the ozonide radical to consist of
only three symmetry-related components and interpreted
them to reside on twofold symmetry axes in the quartz
structure. The calculated g matrices of Center #1 and the
ozonide radical show that deviations from twofold symmetry
axes are \10, which are probably attributable to
distortion related to neighboring charge compensating ions.
The W-band EPR spectra of Center G not only result in
improved g matrices but also allow quantitative determination
of the nuclear hyperfine (A) and quadrupole (P)
matrices of its 27Al hyperfine structure that was incompletely
resolved before. In particular, the g-maximum and
g-minimum principal axes of Center G are approximately
along two pairs of O–O edges of the SiO4 tetrahedron,
were observed in them. In a-and b-BaB2O4 crystals and
glasses the EPR centers Ag2+, Ag0 , Pb+ , Pb3+, and hole
centers of O- type were studied. The EPR parameters of
these centers and their arrangement in crystal structure
were determined. It is shown that Pb3+ ions in b-BaB2O4
crystals occupy Ba2+ position in an irregular polyhedron
from the eight oxygen, whereas in a-BaB2O4 crystals they
occupy Bf2 position in a sixfold coordination. Pb+ ions in
a-BaB2O4 crystals occupy Bf1 position in a ninefold
coordination from oxygen. In barium borate glasses, Pb3+
ions were studied in coordination polyhedron from six
oxygen atoms and in a polyhedron from nine to ten oxygen
atoms. It is assumed that the established difference in the
structural position of Pb3+ ions in glasses is due to their
previous incorporation in associative cation–anion complexes
(AC) and ‘‘free’’ structure-forming cations (FC).
Computer simulations have been performed to analyze the
stability of specific associative complexes and to compare
their bond lengths with experimental data.
observed at the same conditions. Four different Ag0 centers with isotropic hyperfine interactions (HFI) with 107Ag and 109Ag nuclei and hyperfine constants less than those for the free Ag atom are revealed by the EPR method. ESE investigations enable us to confirm the positions of silver atoms that are stable up to 230 C.
were determined: g = 2.0021 + 0.0003, A/h = 13.7 _ 0.1 MHz, and D/h = 44.6 _ 0.2 for N1 and 37.6 _ 0.2 MHz for N2 with unique directions of zero-field splitting D along the optical axis c. An
amazing resilience of the atomic properties of nitrogen trapped within the structural cavity has been experimentaily observed. The NI paramagnetic atom is stable up to 280 C. We suggest that the structural cavity in beryl could be a shelter for qubits encoded in electron spins of hydrogen or nitrogen atoms.
solution, were investigated by IR and EPR spectroscopy. Using IR spectroscopy we found that water
molecules, ammonium ions, and a small number of HCl molecules enter the structural channels of beryl in
the course of mineral growth. In these beryls, the ammonium ions play the role of alkali cations. The
ammonium ions are as rigidly fixed in the lattice as are water molecules; they are eliminated by calcination
at high temperatures close to the decomposition temperature. On exposure to radiation at 77 K, the
paramagnetic NH3 and H0 radicals are stabilized in the structural channels of beryl. In addition to the
known H0 radical, other states of atomic hydrogen, interacting with medium protons, are observed as well.
For one of the additional radicals, Hb, we suggest the model of atomic hydrogen stabilized at the center of a
silicon-oxygen ring with two water molecules in adjacent cavities.
and UV-Vis-IR absorption spectroscopy. According to the Laue-SR data, brown, smoky-gray and gray with a light purple-pink hue diamonds have suffered a high degree of deformation
during the post-crystallization period. Strong asterism of Laue spots, intense continuous optical absorption throughout the visible spectrum, monotonically increasing toward shorter
wavelengths, and ‘‘amber centers’’ in the IR region from 4,000 to 6,000 cm-1 are typical of these diamond crystals. Light purplish pink diamonds with gray or brown hue have experienced lesser degree of deformation. This group of diamonds has two absorption bands with maximums at 480 and 550 nm and ‘‘amber centers’’ in the IR region. A distinct polygonization is typical of the inner structure of light purplish pink diamonds. Light purplish pink diamonds have an intensive absorption band with maximum at 550 nm and are characterized by the lack of ‘‘amber centers.’’ The relationship between the deformation levels, diamond color characteristics and manifestation of the ‘‘amber centers’’ in the IR region has been traced based on the obtained results.