Upconversion luminescence in Tm 3+/Yb 3+co-doped lead tungstate tellurite glasses

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This work reports the upconversion luminescence properties of Tm 3+/Yb 3+ ions in lead tungstate tellurite (LTT) glasses. Judd–Oflet intensity parameters have been obtained from the absorption band intensities of Tm 3+ singly-doped and Tm 3+/Yb 3+ co-doped LTT glasses. The spontaneous emission probabilities, radiative lifetimes and branching ratios for 1G 4 and 3H 4 emission levels of Tm 3+ have been determined. Upconversion luminescence has been observed by exciting the samples at 980 nm (Yb 3+: 2F 7/2→ 2F 5/2) at room temperature. Four upconversion emission bands corresponding to the 1G 4→ 3H 6 (477 nm), 1G 4→ 3F 4 (651 nm), 1G 4→ 3H 5 (702 nm) and 3H 4→ 3H 6 (810 nm) transitions have been identified. The relative variation in the intensities of upconversion bands, the different channels responsible for upconversion spectra and the effect of Yb 3+ ions concentration on the upconversion luminescence of Tm 3+ ions have also been discussed.