Role of Yb 3+ and Tm 3+ ions in upconversion emission of Tb 3+ under 798 and 980 nm laser excitations in Tb 3+–Tm 3+–Yb 3+ doped tellurite glass

Abstract

Upconversion emission and energy transfer processes in singly, doubly and triply doped tellurite glasses have been studied under 798 and 980 nm laser excitations. Emissions have been observed at 482, 544, 584, 655 nm and at 477, 655, 698, 800 nm corresponding to Tb 3+: 5D 4 → 7F 6, 7F 5, 7F 4, 7F J ( J = 0, 1, 2, 3) and Tm 3+: 1G 4 → 3H 6, 1G 4 → 3F 4, 3F 3 → 3H 6, 3H 4 → 3H 6 transitions, respectively. Among Tm 3+, Yb 3+and Tb 3+ ions only Tm 3+ has a ground state absorption at 798 nm excitation due to 3H 4 ← 3H 6 transition. For 980 nm excitation only Yb 3+ can absorb the incident radiation. However, for both types of excitations, emission from all the three ions Tb, Yb and Tm has been observed. Possible mechanisms are proposed as follows: under 798 nm excitation Tm 3+ ions are excited which excite Yb 3+ ions through energy transfer. Finally “cooperative energy transfer” from a pair of Yb 3+ ions to Tm 3+ and Tb 3+ ions takes place. Under 980 nm excitation Yb 3+ ions absorb the incident energy and excite Tm 3+ and Tb 3+ ions via cooperative energy transfer. Variation of emission intensity with the ion concentrations of Yb 3+, Tm 3+ and Tb 3+ has been studied. The lifetime of the 1G 4 level has also been measured.