Radiative and non-radiative relaxation of rare-earth ions in Ga 2S 3–GeS 2–La 2S 3 glasses

Abstract

Spectroscopic properties of Nd 3+ and Ho 3+ in a Ga 2S 3–GeS 2–La 2S 3 glass system were investigated on the basis of the Judd–Ofelt analyses for 60GaS 3/2 · 10GeS 2 · 27LaS 3/2 · 3LnS 3/2 glasses (Ln=Nd or Ho) and emission lifetime measurements for 60GaS 3/2 · 10GeS 2 · 29.7LaS 3/2 · 0.3LnS 3/2 glasses (Ln=Nd or Ho). The obtained Judd–Ofelt Ω 2 parameter for Nd 3+ was larger than those of other glass systems such as oxides and fluorides. For Ho 3+, on the other hand, the Ω 2 parameter was so small that it could not be determined with enough accuracy. Non-radiative transition rates for 4G 5/2 and 2K 13/2 levels of Nd 3+ and 5F 5 and 5S 2 levels of Ho 3+ were obtained by the difference between the inverse of the measured emission lifetimes and the calculated radiative transition rates of these levels. The non-radiative transition rate of the 5S 2 of Ho 3+ was about one order larger than predicted from the so called `energy-gap law'. We assumed that the energy transfer from the 5S 2 of Ho 3+ to an electronic state of the host glass occurs. Multiphonon relaxation rates were comparable with those of a ZnCl 2-based glass.