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

• Received 19 May 2006

DOI:https://doi.org/10.1103/PhysRevB.74.184103