Structural analysis and luminescence studies of Ce3+: Dy3+ co-doped calcium zinc gadolinium borate glasses using EXAFS. (June 2020) - Rajaramakrishna, R.
Abstract: Ce 3+: Dy 3+ - codoped calcium zinc gadolinium borate glasses were synthesized by traditional melt quenching technique. These glasses after synthesizing they were characterized through density, molar volume, refractive index, FTIR, absorption spectra, photoluminescence properties, structural studies using XANES/EXAFS and life time profile analysis. XANES spectra of Gd L III -edge and Dy L III -edge for 20CaCO3 - 20 ZnO - 10Gd2 O3 - 49.5B2 O3 - 0.5Dy2 O3 (C2) and 20CaCO3 - 20 ZnO - 10Gd2 O3 – 49B2 O3 - 0.5Dy2 O3 - 0.5CeF3 (D) glass showed absorption edge at 7249.8 eV and 7795.7 eV respectively confirming the presence of Gd 3+ and Dy 3+ ions. Ce- L III edge for D glass shows peaks at ~ 5728 eV confirming the presence of Ce 3+ . The Judd-Ofelt (JO) theory investigations have been applied for Dy 3+ ions to calculate the Judd-Ofelt (JO) intensity parameters and found that the trend follows Ω2 > Ω4 > Ω6 . The ionic nature of RE 3+ -O were evaluated by using bonding parameter (δ) value for C2 and D glass and found to be −0.0076 and −0.0102. Radiative properties were subsequently estimated using JO parameters and investigated radiative transition probabilities (AR ), stimulated emission cross section (σR ) and branching ratio (βR ). The photoluminescence and radio luminescence spectra exhibit two prominent emission peaks at 484 (blue) and 575 nm (yellow) that corresponds to the 4 F9/2 → 6 H15/2 and 4 F9/2 → 6 H13/2 transitions respectively. The chromaticity coordinates were evaluated and found that these coordinates positioned in the white region with (x, y) = (0.348 0.382) and (0.325, 0.353) values for C2 and D glasses. The fluorescence decay from the 4 F9/2 level was measure by monitoring the intense 4 F9/2 to 6 H9/2 transition. The decay time is found to be bi-exponential when monitored at λexi = 387 nm. The results obtained in present work demonstrate that the present glasses could be potential candidate for use in white light solid state lighting applications. Highlights: Photo-luminescence properties of Dy 3+ /Ce 3+ doped 20CaCO3 –20ZnO-10Gd2 O3 –49B2 O3 glasses were investigated. Transfer characteristics of Gd 3+ .→ Dy 3+ and back transfer characteristics of Dy 3+ → Ce 3+ ions were analyzed. Radioluminescence spectra were analyzed and found to be similar to that of photoluminescence. XANES analysis were employed to understand the oxidation state of rare-earth ions embedded in the glasses. EXAFS well fitted with the standard model to understand their coordination number.