Dynamics of upconversion photoluminescence in Ge–Ga–S: Er3+: application of quadrature frequency resolved spectroscopy

Abstract

Quadrature frequency resolved spectroscopy (QFRS) on green (~550 nm) upconversion photoluminescence (UCPL) of Ge–Ga–S: Er3+ glasses pumped at 975 nm revealed double-peaked spectra with long lifetime τ1 ranging from 0.2 to 2 ms and short lifetime τ2 ≈ several tens of μs. The results are analysed in terms of the transfer function derived by linearizing rate equations for a three-level model. The τ1 component is attributed to the relaxation at the intermediate level 4I11/2 of Er3+ ions and the τ2 component, to that at the upper 4S3/2 manifold. The dominance of energy transfer upconversion over excited state absorption in the UCPL manifest itself as a greater dependence of τ1 on the pump power and a lower ratio of the components of τ2 to τ1 in the QFRS spectra of a heavily Er-doped sample.