Multiphonon energy gap law in rare-earth doped chalcogenide glass

The parameters for multiphonon relaxation of rare earth (RE) ions in the sulfide glass Ge25As8.33Ga1.67S65 have been re-evaluated using the temperature dependence of the fluorescence lifetime to separate out true multiphonon decay from other non-radiative processes. It is found that for energy gaps to the next lowest level greater than 2500 cm−1, other non-radiative processes become dominant over multiphonon decay. The most likely process for this additional non-radiative decay is energy transfer to vibrational impurities such as OH and SH. The newly derived parameters lead to an electron–phonon coupling parameter ϵ=0.058, which is more in line with other glass types than the previously accepted value of ϵ=0.36. These new multiphonon relaxation parameters and the existence of additional non-radiative decay mechanisms has implications for the modeling of chalcogenide-based active devices.