Cross relaxation mechanism among Tm3+ ions in Ge30Ga2As6S62 glass

Cross relaxation among Tm3+ ions in Ge30Ga2As6S62 glass, where an ion excited to the 3H4 level transfers part of its energy to a nearby ion in the ground state 3H6 (3H4, 3H6→3F4, 3F4), was investigated in the temperature range of 20–300 K. The relative intensity ratio of the 1.48 μm emission to 1.84 μm increased with decreasing temperature. At the same time, the lifetime of the 3H4 level increased. Analysis of decay curves of the 1.48 μm emission suggested that cross relaxation was assisted by phonons of 390 cm−1 in frequency. These phonons are generated from the asymmetrical stretching vibration of GeS4 tetrahedra. Critical distance for cross relaxation decreased from 0.73 to 0.58 nm as the temperature decreased.