Books by Varnakavi Naresh
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Papers by Varnakavi Naresh
Nano Research, 2020
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The present paper reports on the results concerning structural, thermal, optical (absorption & em... more The present paper reports on the results concerning structural, thermal, optical (absorption & emission), dielectric and ac conductivity properties of host glass in the chemical composition of 50P2O5-30ZnO-20LiF (PZL), and two different transition metal ions doped glasses such as (0.5 mol%) Cr 3+ :49.5P2O5-30ZnO-20LiF and (0.5 mol%) Cu 2+ :49.5P2O5-30ZnO-20LiF glasses have successfully been prepared by a melt quenching technique. Thermal analysis has been carried out on the host (PZL) precursor chemical mix in evaluating weight loss from its TG profile and glass transition temperature (Tg) and crystalline temperature (Tc) from its DTA profile. The presence of Cr 3+ and Cu 2+ has been confirmed from their EDX profiles and absorption spectra. From the absorption spectrum of Cr 3+ : PZL glass, a couple of bands at 460 nm ( 4 A2g (F) 4 T1g (F)) and 664 nm ( 4 A2g (F) 4 T2g (F)) have been displayed where as a broad absorption band at 824 nm ( 2 B1g → 2 B2g) is observed from Cu 2+ : PZL...
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Physics and Chemistry of Glasses: European Journal of Glass Science and Technology Part B, 2015
We report the absorption and emission characteristic properties of (0·1–1·5 mol %) Er3+ doped Bi2... more We report the absorption and emission characteristic properties of (0·1–1·5 mol %) Er3+ doped Bi2O3–AlF3–TeO2–B2O3 (BiAFTB) glasses prepared via the melt quenching method. From the optical absorption spectrum, absorption and stimulated emission cross-sections have been evaluated by applying McCumber’s theory and cross-sectional gain has also been calculated for Er3+:BiAFTB glasses. On excitation in the near ultraviolet (λexci=379 nm), these prepared glass samples displayed two emission bands in visible region 2H11/2Æ4I15/2 (526 nm; green), 4S3/2Æ4I15/2 (549 nm; green). Upon pumping with a laser diode at λexci=980 nm (NIR), a broad emission spectra at 1533 nm attributed to 4H13/2Æ4I15/2 is observed in the NIR region. For concentrations exceeding 1·0 mol% quenching of the Er3+ emission is observed. The photoluminescence quenching results from the interaction between Er3+ ions (cross relaxations) and/or the effect of OH− groups on Er3+ emission. The mechanism that governs interactions between Er3+ ions has been explained in terms of their emission spectra, emission decay curves, energy level diagram and energy transfer characteristic parameters.
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Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, 2017
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Materials Today: Proceedings, 2016
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Optical Materials, 2016
Abstract Here, we present results pertaining to thermal, structural, optical and photoluminescenc... more Abstract Here, we present results pertaining to thermal, structural, optical and photoluminescence properties of Li 2 O LiF ZnF 2 B 2 O 3 P 2 O 5 : (0.1–1.5 mol.%) MnO glasses. DTA profiles revealed a change in glass transition temperature with the addition of MnO suggesting an increase in glass stability. The modifications in structural units are interpreted from FTIR and Raman spectral profiles, which confirm the formation of stable P O B bonds. The host Li 2 O LiF ZnF 2 B 2 O 3 P 2 O 5 (labelled as LZBP) glass exhibits emission in the blue region on excitation with 361 nm. The red shift in optical absorption edge and decrease in energy of band gap as a function of MnO concentration is analysed from Tauc’s plot. The nature of local symmetry around manganese ions in LZBP matrix has been understood by evaluating the crystal field strength (Dq) and Racah inter-electronic repulsion parameters ( B & C ) from absorption spectrum and electron-lattice interaction energy ( Sħω ) factor from emission spectrum. The emission spectra of (0.1–1.5 mol.%) Mn 2+ : LZPB glasses have shown broad band at 613 nm assigned to electronic transition 4 T 1g (G) → 6 A 1g (S) displaying orange-red emission upon excitation at 413 nm. Octahedral coordination of Mn 2+ ions has been estimated from the position of emission in luminescence spectra. The effect of Mn 2+ concentration on emission properties has been discussed from lifetime curves and energy level scheme.
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AIP Conference Proceedings, 2013
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AIP Conference Proceedings, 2015
Here, we report on the results related to the absorption and emission properties of (0.05-1.5 mol... more Here, we report on the results related to the absorption and emission properties of (0.05-1.5 mol%)Tm3+ doped oxy fluoro-borosilicate glasses prepared by a standard melt quenching method. Tm3+ glasses exhibited a series of emission bands in the visible region at 415 nm (1I6→3H5), 456 nm (1D2→3F4), 481 nm (1G2→3H6) and 520 nm (1D2→3H) with an UV excitation 358 nm (3H0→1D2). Upon exciting with 514.5 nm (Ar+ LD source), Tm3+ glasses have shown a broad NIR emission band at 1.80 µm (3F4→3H6). The effect of Tm2O3 concentration, on luminescence quenching in Visible and NIR regions due to energy transfer through cross-relaxation channels has been explained. Stimulated emission cross-section (σe) and effective bandwidth (Δeff) were also calculated for the NIR emission bands.
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The present paper reports on the results pertaining to the emission properties of 0.5 mol% Er3+ a... more The present paper reports on the results pertaining to the emission properties of 0.5 mol% Er3+ and together (0.5 Yb3+ /0.5 Er3+) doped PZL (P2O5-ZnO-LiF) glasses prepared by a melt quenching method. From the optical absorption data, absorption and stimulated emission cross-sections have been evaluated using McCumber’s theory and further cross-sectional gain has also been computed for Yb3+/Er3+ doped glass. On exciting the single (Er3+) and dual rare earth ions (Yb3+/Er3+) doped glass sample at λexci = 379 nm, three emission bands in the visible region 2H11/2→4I15/2 (526 nm), 4S3/2→4I15/2 (549 nm) and 4F9/2→4I15/2 (664 nm) are observed and while at λexci = 980 nm (Laser Diode) excitation a broad emission at 1530 nm attributed to 4H13/2→4I15/2 is observed in the NIR region. The enhancement in visible and NIR emission intensities with the addition of Yb3+ to Er3+ due to an energy transfer process from Yb3+ to Er3+ has been explained in terms of an energy level diagram.
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Journal of Alloys and Compounds, 2015
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Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, 2015
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ABSTRACT In the present paper, we report on the absorption and emission properties of (0.1-1.5 mo... more ABSTRACT In the present paper, we report on the absorption and emission properties of (0.1-1.5 mol %) Ho3+ doped LFBCd (Li2O-LiF-B2O3-CdO) glasses prepared via melt quenching method. On exciting these glasses at (λexci) = 452 nm, two emissions at 556 nm (5S2→5I8; Green), 655 nm (5F5→5I8; Red) have been obtained. Upon exciting these glasses with a 980 nm diode laser, NIR emissions at 1195 nm (5I6→5I8), 1951 nm (5I7→5I8) have been measured for 1 mol % Ho3+:LFBCd glass. For higher concentration beyond 1.0 mol %, emission quenching of Ho3+ glass has been noticed and which has successfully been explained in terms of an energy level diagram. From absorption cross-section data, stimulated emission cross-section has been evaluated by applying McCumber's theory and further cross-sectional gain has also been computed for the emissions at 1195 nm (̃1.20 μm) and 1951 nm (̃2.0 μm) of 1 mol % Ho3+:LFBCd glass.
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Materials Sciences and Applications, 2011
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Journal of Luminescence, 2014
Abstract The present paper brings out the results concerning the preparation and optical properti... more Abstract The present paper brings out the results concerning the preparation and optical properties of Sm 3+ and Dy 3+ each ion separately in four different concentrations (0.1, 0.5, 1.0 and 1.5 mol%) and also together doped (1 mol% Dy 3+ + x mol% Sm 3+ ): Li 2 O–LiF–B 2 O 3 –CdO (where x =0.1, 0.5, 1.0 and 1.5 mol%) glasses by a melt quenching method. Sm 3+ doped base glasses have displayed an intense orange emission at 602 nm ( 4 G 5/2 → 6 H 7/2 ) with an excitation at 403 nm and Dy 3+ doped glasses have shown two emissions located at 486 nm ( 4 F 9/2 → 6 H 15/2 ; blue ) and 577 nm ( 4 F 9/2 → 6 H 13/2 ; yellow ) with λ exci =387 nm. The co-doped (Dy 3+ +Sm 3+ ) lithium fluoro-boro cadmium glasses have been excited with an excitation at 387 nm of Dy 3+ which has resulted in with a significant reduction in Dy 3+ emission, at the same time there exists an increase in the reddish-orange emission of Sm 3+ due to an energy transfer from Dy 3+ to Sm 3+ . The non-radiative energy transfer from Dy 3+ to Sm 3+ is governed by dipole–quadrupole interactions as is explained in terms of their emission spectra, donor lifetime, energy level diagram and energy transfer characteristic factors.
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Journal of Luminescence, 2013
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Ferroelectrics Letters Section, 2011
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Ferroelectrics, 2012
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Books by Varnakavi Naresh
Papers by Varnakavi Naresh