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

The glasses of the composition (45(1-x))ZnF2-xWO3-49TeO(2):1.0Nd(2)O(3)/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 Ln(3+) ions in these glasses. Following the luminescence spectra, various radiative properties like transition probability A, branching ratio beta and the radiative life time tau for F-4(3/2) -> I-4(11/2), (4)G(5/2) -> H-6(7/2), D-5(0) -> F-7(2) 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 F-4(3/2) -> I-4(11/2) (Nd3+), (4)G(5/2) -> H-6(7/2) (Sm3+) and D-5(0) -> F-7(2) (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. (C) 2010 Elsevier B.V. All rights reserved.