Relaxation properties of rare-earth ions in sulfide glasses: Experiment and theory

Both radiative and nonradiative relaxation rates for a series of rare-earth ions doped 20Ge-5Ga-10Sb-65S (GeGaSbS) sulfide (chalcogenide) glasses have been determined. Temperature-dependent lifetimes were carried out for various excited levels of the sample. Radiative decay rates were derived by using the Judd-Ofelt approach. Nonradiative decay rates are evaluated by comparing the inversion of measured lifetimes with the calculated radiative decay rates. We have found that the multiphonon relaxation rates should be a predominant decay mechanism among the excited states if the energy gap to the next lower level is smaller than 2500 cm(-1), and the decay mechanism can be determined using the semiempirical energy-gap law. For an energy gap larger than 2500 cm(-1), additional nonradiative decay processes become dominant over the multiphonon decay. Additional nonradiative decay processes have been quantitatively identified with the diffusion-limited relaxation calculations.