Influence of some thermally resistant transition metal oxides on emission features of Pr³⁺ ions in zinc borate glasses

This work consists of studies on the influence of thermally resistant transition metal oxides (TMO) viz., Ta₂O₅, Nb₂O₅ and ZrO₂ on orange emission and NIR emission (1.3 μm) of Pr³⁺ ions in zinc borate glasses. Glasses of the composition 40ZnO–2Ta₂O₅/2Nb₂O₅/2ZrO₂–56B₂O₃: 2Pr₂O₃ were synthesized by melt quenching technique. Optical absorption (OA), photoluminescence (PL) emission (in the wavelength region 500–2500 nm at λ_exc = 443 nm) and decay profiles of the two of the prominent transitions viz., ³P₀ → ³H₆ and ¹G₄ → ³H₅ of Pr³⁺ ions were recorded. The spectra were analysed using standard J–O calculations and various radiative parameters associated with prominent transitions were estimated. Intensity of PL bands exhibited substantial increase due to addition of Ta₂O₅, Nb₂O₅ and ZrO₂ to the host glass. Among the three studied glasses, ZrO₂ mixed glasses exhibited the highest luminescence output. All the radiative parameters including quantum efficiency are observed to be the largest for ZrO₂ mixed glasses. The results of IR spectral studies were also used for the analysis of emission spectra. The analysis indicated the degree of structural variations in the vicinity of luminescent Pr³⁺ ions is different due to addition of different transition metal oxides and such variations are found to be responsible for the changes in the PL output. Since a substantial improvement of PL emission corresponding to ¹G₄ → ³H₅ transition is observed due to the admixing of TMOs, these glasses may be considered as the favourable candidates for the applications in telecommunications. Additionally, the emission in the green spectral region (which is predicted to be feeble under normal conditions) in the PL spectrum of Pr³⁺ ions is also found to be considerably increased and it is attributed to the transfer of energy from ZnO to Pr³⁺ ions in this region.