Spectroscopic properties and energy transfer in Er-Tm co-doped bismuth silicate glass

In this paper, we investigate the spectroscopic properties of and energy transfer processes in Er-Tm co-doped bismuth silicate glass. The Judd-Ofelt parameters of Er3+ and Tm3+ are calculated, and the similar values indicate that the local environments of these two kinds of rare earth ions are almost the same. When the samples are pumped at 980 nm, the emission intensity ratio of Tm:F-3(4) -> H-3(6) to Er:I-4(13/2) -> I-4(15/2) increases with increased Er3+ and Tm3+ contents, indicating energy transfer from Er:I-4(13/2) to Tm:F-3(4). When the samples are pumped at 800 nm, the emission intensity ratio of Er:I-4(13/2) -> I-4(15/2) to Tm:H-3(4) -> F-3(4) increases with increased Tm2O3 concentration, indicating energy transfer from Tm:H-3(4) to Er:I-4(13/2). The rate equations are given to explain the variations. The microscopic and macroscopic energy transfer parameters are calculated, and the values of energy transfer from Er:I-4(13/2) to Tm:F-3(4) are found to be higher than those of the other processes. For the Tm singly-doped glass pumped at 800 nm and Er-Tm co-doped glass pumped at 980 nm, the pumping rate needed to realize population reversion is calculated. The result shows that when the Er2O3 doping level is high, pumping the co-doped glass by a 980 nm laser is an effective way of obtaining a low-threshold similar to 2 mu m gain. (C) 2013 Elsevier B.V. All rights reserved.