Influence of tungsten on the emission features of Nd3+, Sm3+ and Eu3+ ions in ZnF2–WO3–TeO2 glasses

The glasses of the composition (45−x)ZnF2–xWO3–49TeO2:1.0Nd2O3/Sm2O3/Eu2O3 with x varying from 5 to 20 mol% were synthesized. Optical absorption, fluorescence spectra (in the spectral range 400–2300 nm) and also fluorescence decay were studied at ambient temperature. The Judd–Ofelt theory analysis was applied to characterize the absorption and luminescence spectra of Ln3+ ions in these glasses. Following the luminescence spectra, various radiative properties like transition probability A, branching ratio β and the radiative life time τ for 4F3/2 → 4I11/2, 4G5/2 → 6H7/2, 5D0 → 7F2 emission levels respectively for Nd3+, Sm3+ and Eu3+ doped glasses of these glasses have been evaluated. The variations observed in these parameters were discussed following of varying co-ordinations (tetrahedral and octahedral positions) and the valence states of tungsten ions in the glass network. A significant enhancement in the intensities of 4F3/2 → 4I11/2 (Nd3+), 4G5/2 → 6H7/2 (Sm3+) and 5D0 → 7F2 (Eu3+) emission lines has been observed with increase of WO3 content; this is attributed to the increase in the concentration W5+ ions in the glass network that acts as modifiers. The quantitative analysis of these results (with the aid of the data on ESR, IR and Raman spectral studies) has indicated that the glasses mixed with around 15 mol% of WO3 have the optimum concentration for yielding the highest quantum efficiency with low phonon losses for the above-mentioned principal transitions.

Research highlights▶ The optical absorption and photoluminescence spectra of Nd3+, Sm3+, Eu3+ ions in ZnF2–TeO2 glasses mixed with different content of WO3 have been reported. The radiative transition probabilities and branching ratios evaluated for various luminescent transitions observed in the luminescence spectra are found to be the highest for the transitions 4F3/2 → 4I11/2 (Nd3+), 4G5/2 → 6H7/2 (Sm3+) and 5D0 → 7F2 (Eu3+). The comparison of branching ratios (βr values) of these transitions and the luminescence efficiencies showed the largest value for glass mixed with 15 mol% of WO3.