Journal of Physics Condensed Matter 21, May 17, 2009
The scintillation yield, scintillation decay, and x-ray excited emission of pure LaCl3 was studie... more The scintillation yield, scintillation decay, and x-ray excited emission of pure LaCl3 was studied as a function of temperature between 80 and 600 K. Two broad band emissions centered around 325 nm and 400 nm were identified and correlated to emissions from two localized exciton states named STE1 and STE2, respectively. Different temperature dependences were observed for the short and long wavelength band intensity. From 80 to 150 K, the 400 nm band intensity increases at the expense of the 325 nm band intensity. Above 150 K almost all emission is in the 400 nm band. From 150 to 600 K, the intensity of this band decreases and its lifetime shortens. These results are analyzed and interpreted with a model that comprises the creation of STE1 and STE2 self-trapped excitons, thermally activated quenching of STE1 and STE2 emission, and thermally activated transfer of excitation energy from STE1 to STE2.
We report on the first measurement of the decay times of NaI(Tl) as a function of the deposited e... more We report on the first measurement of the decay times of NaI(Tl) as a function of the deposited electron energy. It has been suggested that the decay curve depends on the ionization density, which is correlated with the electron energy deposit in the scintillator. The ionization creates excitation states, which can decay radiatively and non-radiatively through a number of competing
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2014
ABSTRACT We present new results obtained from single crystals of Ba binary halides of BaCl2, BaBr... more ABSTRACT We present new results obtained from single crystals of Ba binary halides of BaCl2, BaBr2 and BaI2 activated with Eu2+. While these compounds were known as scintillator materials, due to improvements in the crystal growth process and availability of higher purity compounds, we obtained crystals with better performances than what have been reported before. The luminosities of BaCl2:5%Eu2+, BaBr2:5%Eu2+ and BaI2:5%Eu2+ are about 90%, 70% and 60%, respectively, of their theoretical limit.
ABSTRACT The structure and scintillation properties of BaBrCl:xEu2+(x=0–0.12) and Eu2+ activated ... more ABSTRACT The structure and scintillation properties of BaBrCl:xEu2+(x=0–0.12) and Eu2+ activated solid solutions in the BaCl2–BaBr2 system are reported. Samples were synthesized in the form of 1–5 mm crystals by melting the reactants in sealed quartz tubes followed by slow cooling. The solid solutions form an orthorhombic PbCl2-type crystal structure with an ordered arrangement of the anions. Upon optical and X-ray excitation, the samples show an intense emission centered between 407 and 412 nm. The samples exhibit a fast decay characteristic of Eu2+, with the primary decay component between 550 and 700 ns, depending on the Eu concentration. The luminosity for the solid solutions is estimated to be similar to the binary halide end members.
ABSTRACT Finding new inorganic scintillator crystals with better performance for demanding applic... more ABSTRACT Finding new inorganic scintillator crystals with better performance for demanding applications, such as high-energy physics, medical imaging, and radiation detection, has been a long-standing challenge. Thanks to an intensive interdisciplinary effort between theoreticians, experimentalists and crystal growers, current scintillator performances are reaching the intrinsic limits imposed by the crystal. However, demand continues for more efficient scintillators with higher light output, better energy resolution and lower cost of production. This article discusses the basic concepts of scintillation in inorganic materials, focusing on how physics can provide pathways to assist in scintillator discovery.
Additional to a correct color and a high efficiency, phosphors for plasma display panels must mai... more Additional to a correct color and a high efficiency, phosphors for plasma display panels must maintain their light output for thousands of hours. Often the degradation is the restricting factor in using phosphors. In this article, the mechanism of luminance decrease in blue-emitting BaMgAl10O17:Eu2+ phosphor during the operation of the PDPs has been studied. It is shown experimentally that the aging process is mainly due to the vacuum-ultraviolet excitation (VUV). It is demonstrated that the degradation mechanism can be accelerated by using a 193 nm laser excitation. Based on excitation, reflectance, thermoluminescence spectra, and aging or annealing processes by laser excitation, the main causes of the degradation are demonstrated. The aging process can be separated in two different processes according to the temperature: a first one, at low temperature, corresponding to the autoionization of luminescent centers (Eu2+-->Eu3+) and a second one, at high temperature, linked to the formation of traps in the phosphor. These traps induce a perturbation of the energy migration in the phosphor. In addition, the relevant parameters of trap formation are highlighted: density of the VUV excitation, temperature, and atmosphere/pressure surrounding the phosphor. A model of BaMgAl10O17:Eu2+ phosphor degradation mechanism is proposed.
Nuclear Instruments & Methods in Physics Research Section A-accelerators Spectrometers Detectors and Associated Equipment, 2011
We report the structure and scintillation of Eu 2+-activated solid solutions in the BaBr 2-BaI 2 ... more We report the structure and scintillation of Eu 2+-activated solid solutions in the BaBr 2-BaI 2 system. Samples were synthesized in the form of ˜1 mm size crystals by melting the reactants in a sealed quartz tube followed by slow cooling. The solid solutions form an orthorhombic PbCl 2-type crystal structure with an ordered arrangement of the anions. Upon optical and X-ray excitation, the Eu 2+-activated samples show an intense emission centered between 410 and 423 nm. The samples exhibit a fast decay characteristic of Eu 2+, with the primary decay time between 315 and 600 ns for ˜75% of the total emitted light. Light yields for the compositions are compared to a newly discovered scintillator, BaBrI:Eu 2+, measured under identical conditions.
Nuclear Instruments & Methods in Physics Research Section A-accelerators Spectrometers Detectors and Associated Equipment, 2011
We report the structure and scintillation of Eu2+-activated solid solutions in the BaBr2–BaI2 sys... more We report the structure and scintillation of Eu2+-activated solid solutions in the BaBr2–BaI2 system. Samples were synthesized in the form of ∼1mm size crystals by melting the reactants in a sealed quartz tube followed by slow cooling. The solid solutions form an orthorhombic PbCl2-type crystal structure with an ordered arrangement of the anions. Upon optical and X-ray excitation, the Eu2+-activated
Journal of Physics Condensed Matter 21, May 17, 2009
The scintillation yield, scintillation decay, and x-ray excited emission of pure LaCl3 was studie... more The scintillation yield, scintillation decay, and x-ray excited emission of pure LaCl3 was studied as a function of temperature between 80 and 600 K. Two broad band emissions centered around 325 nm and 400 nm were identified and correlated to emissions from two localized exciton states named STE1 and STE2, respectively. Different temperature dependences were observed for the short and long wavelength band intensity. From 80 to 150 K, the 400 nm band intensity increases at the expense of the 325 nm band intensity. Above 150 K almost all emission is in the 400 nm band. From 150 to 600 K, the intensity of this band decreases and its lifetime shortens. These results are analyzed and interpreted with a model that comprises the creation of STE1 and STE2 self-trapped excitons, thermally activated quenching of STE1 and STE2 emission, and thermally activated transfer of excitation energy from STE1 to STE2.
We report on the first measurement of the decay times of NaI(Tl) as a function of the deposited e... more We report on the first measurement of the decay times of NaI(Tl) as a function of the deposited electron energy. It has been suggested that the decay curve depends on the ionization density, which is correlated with the electron energy deposit in the scintillator. The ionization creates excitation states, which can decay radiatively and non-radiatively through a number of competing
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2014
ABSTRACT We present new results obtained from single crystals of Ba binary halides of BaCl2, BaBr... more ABSTRACT We present new results obtained from single crystals of Ba binary halides of BaCl2, BaBr2 and BaI2 activated with Eu2+. While these compounds were known as scintillator materials, due to improvements in the crystal growth process and availability of higher purity compounds, we obtained crystals with better performances than what have been reported before. The luminosities of BaCl2:5%Eu2+, BaBr2:5%Eu2+ and BaI2:5%Eu2+ are about 90%, 70% and 60%, respectively, of their theoretical limit.
ABSTRACT The structure and scintillation properties of BaBrCl:xEu2+(x=0–0.12) and Eu2+ activated ... more ABSTRACT The structure and scintillation properties of BaBrCl:xEu2+(x=0–0.12) and Eu2+ activated solid solutions in the BaCl2–BaBr2 system are reported. Samples were synthesized in the form of 1–5 mm crystals by melting the reactants in sealed quartz tubes followed by slow cooling. The solid solutions form an orthorhombic PbCl2-type crystal structure with an ordered arrangement of the anions. Upon optical and X-ray excitation, the samples show an intense emission centered between 407 and 412 nm. The samples exhibit a fast decay characteristic of Eu2+, with the primary decay component between 550 and 700 ns, depending on the Eu concentration. The luminosity for the solid solutions is estimated to be similar to the binary halide end members.
ABSTRACT Finding new inorganic scintillator crystals with better performance for demanding applic... more ABSTRACT Finding new inorganic scintillator crystals with better performance for demanding applications, such as high-energy physics, medical imaging, and radiation detection, has been a long-standing challenge. Thanks to an intensive interdisciplinary effort between theoreticians, experimentalists and crystal growers, current scintillator performances are reaching the intrinsic limits imposed by the crystal. However, demand continues for more efficient scintillators with higher light output, better energy resolution and lower cost of production. This article discusses the basic concepts of scintillation in inorganic materials, focusing on how physics can provide pathways to assist in scintillator discovery.
Additional to a correct color and a high efficiency, phosphors for plasma display panels must mai... more Additional to a correct color and a high efficiency, phosphors for plasma display panels must maintain their light output for thousands of hours. Often the degradation is the restricting factor in using phosphors. In this article, the mechanism of luminance decrease in blue-emitting BaMgAl10O17:Eu2+ phosphor during the operation of the PDPs has been studied. It is shown experimentally that the aging process is mainly due to the vacuum-ultraviolet excitation (VUV). It is demonstrated that the degradation mechanism can be accelerated by using a 193 nm laser excitation. Based on excitation, reflectance, thermoluminescence spectra, and aging or annealing processes by laser excitation, the main causes of the degradation are demonstrated. The aging process can be separated in two different processes according to the temperature: a first one, at low temperature, corresponding to the autoionization of luminescent centers (Eu2+-->Eu3+) and a second one, at high temperature, linked to the formation of traps in the phosphor. These traps induce a perturbation of the energy migration in the phosphor. In addition, the relevant parameters of trap formation are highlighted: density of the VUV excitation, temperature, and atmosphere/pressure surrounding the phosphor. A model of BaMgAl10O17:Eu2+ phosphor degradation mechanism is proposed.
Nuclear Instruments & Methods in Physics Research Section A-accelerators Spectrometers Detectors and Associated Equipment, 2011
We report the structure and scintillation of Eu 2+-activated solid solutions in the BaBr 2-BaI 2 ... more We report the structure and scintillation of Eu 2+-activated solid solutions in the BaBr 2-BaI 2 system. Samples were synthesized in the form of ˜1 mm size crystals by melting the reactants in a sealed quartz tube followed by slow cooling. The solid solutions form an orthorhombic PbCl 2-type crystal structure with an ordered arrangement of the anions. Upon optical and X-ray excitation, the Eu 2+-activated samples show an intense emission centered between 410 and 423 nm. The samples exhibit a fast decay characteristic of Eu 2+, with the primary decay time between 315 and 600 ns for ˜75% of the total emitted light. Light yields for the compositions are compared to a newly discovered scintillator, BaBrI:Eu 2+, measured under identical conditions.
Nuclear Instruments & Methods in Physics Research Section A-accelerators Spectrometers Detectors and Associated Equipment, 2011
We report the structure and scintillation of Eu2+-activated solid solutions in the BaBr2–BaI2 sys... more We report the structure and scintillation of Eu2+-activated solid solutions in the BaBr2–BaI2 system. Samples were synthesized in the form of ∼1mm size crystals by melting the reactants in a sealed quartz tube followed by slow cooling. The solid solutions form an orthorhombic PbCl2-type crystal structure with an ordered arrangement of the anions. Upon optical and X-ray excitation, the Eu2+-activated
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Papers by gregory bizarri