Optical and Photoluminescence Properties of Erbium-Doped Chalcogenide Glasses (GeGaS:Er)

We have examined the optical and photoluminescence (PL) properties ofEr³⁺\!-doped GeGaS glasses of near-stoichiometric compositionGe₂₈Ga6.2S65.3:Er0.5. We have also used powdered samples of various mean sizesLto examine the dependence of the 1.54-μm PL emission spectrum and the PL decay time on the average sample size. Optical absorption spectra ofEr³⁺ions arising from transitions between different energy manifolds, such as⁴I15/2--⁴I13/2,⁴I15/2--⁴I11/2, etc., have been used to extractΩ₂, Ω ₄,\, and\ Ω ₆values using the Judd–Ofelt analysis and a Judd–Ofelt radiative lifetimeτ _ JO = 2.6ms for the⁴I13/2--⁴I15/2transition. The PL emission spectra and the decay time have been found to depend on the mean sample size. The spectra are broader and the decay times are longer for larger sample sizes, due to photon trapping occurring in the sample. The extrapolated decay time to zero particle size yields a decay time that matches the Judd–Ofelt radiative lifetime almost perfectly, and confirms the argument that the true PL lifetime needs to be measured in fine powders to avoid reabsorption effects. We have estimated the maximum emission cross section as15.5 × 10⁻²¹\ cm².