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

Abstract

Both radiative and nonradiative relaxation rates for a series of rare-earth ions doped $20\mathrm{Ge}\text{\ensuremath{-}}5\mathrm{Ga}\text{\ensuremath{-}}10\mathrm{Sb}\text{\ensuremath{-}}65\mathrm{S}$ $(\mathrm{GeGaSbS})$ 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 $2500\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}$, and the decay mechanism can be determined using the semiempirical ``energy-gap law.'' For an energy gap larger than $2500\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}$, additional nonradiative decay processes become dominant over the multiphonon decay. Additional nonradiative decay processes have been quantitatively identified with the diffusion-limited relaxation calculations.