Effect of CsBr addition on the emission properties of Tm3+ ion in Ge-Ga-S glass

Absorption and emission properties of Tm 3+ in (1-x) (Ge 0.25 Ga 0.10 S 0.65 )-xCsBr glass (x = 0.00–0.12) were investigated. Upon 10 mol% CsBr addition, the absorption cross sections of Tm 3+ decreased accompanied by a large increase in the lifetime of the Tm 3+ : 3 H 4 level to 1.23 ms since Tm 3+ ions were surrounded by the Br ions of [GaS 3/2 Br] − units. As the concentration of Tm 3+ increased, the 3 H 4 level lifetime decreased due to cross relaxation (Tm 3+ : 3 H 4 , 3 H 6 →Tm 3+ : 3 F 4 , 3 F 4 ). Temperature dependence of the 3 H 4 level lifetime showed that cross relaxation in Tm 3+ is a phonon-assisted energy transfer process. When Tm 3+ were surrounded by Br ions, cross relaxation among Tm 3+ was also suppressed due to a decrease in the transition probability among Tm 3+ energy levels, a decrease in phonon energy of the host glasses, as well as an increase in the number of phonons participating in the cross relaxation process. The potential of Tm 3+ -doped Ge-Ga-S-CsBr glasses for S-band fiber amplifiers is also discussed.