Spectroscopic properties of Tm3+ ions in chalcogenide Ge–As–S glass containing minute amount of Ga and CsBr

We have experimentally confirmed that the absorption and emission properties for intra-4f-configurational transitions of Tm3+ ions doped in Ge–As–S glass, one of representative chalcogenide glasses, are modified dramatically upon the introduction of minute amount of Ga and CsBr, tantamount to a low doping level. This compositional adjustment makes local chemical environments of Tm3+ being rearranged spontaneously without any further thermal treatment applied. The hypersensitive 3H6 ↔ 3F4 transition, in particular, turns out to reflect the modified chemical environments more significantly than other transitions. Redistribution of the stark levels of 3F4 manifold is mainly responsible for the significant changes in emission spectra for 3H4 → 3F4 and 3F4 → 3H6 transitions. Since the addition of small amount of the group III elements and alkali halides alters only the optical properties of rare-earth ions, while keeping thermal stability of the chalcogenide glass hosts unchanged, our compositional adjustment method would be quite useful for practical applications of rare-earth activated chalcogenide glasses.