Dephasing of localized excitons inCdS1−xSexmixed crystals

We performed photon-echo experiments in the alloy semiconductor ${\mathrm{CdS}}_{1\mathrm{-}\mathit{x}}$ ${\mathrm{Se}}_{\mathit{x}}$ to study the influence of the localization depth on the dephasing of localized excitons. It was found that the laser pulse width critically influences the measured values for the phase coherence time ${\mathit{T}}_2$, as well as the observed behavior of the investigated localized states. At ${\mathit{T}}_{\mathit{L}}$=1.8 K ${\mathit{T}}_2$ increases from 400±40 ps on the high-energy side of the luminescence band, close to the extended states, up to 2.2±0.7 ns on the low-energy side of this emission band for deeply localized states. These extremely large values are comparable with the lifetime of these resonantly excited states. If we raise the lattice temperature ${\mathit{T}}_{\mathit{L}}$ the scattering rate increases significantly. We find ${\mathit{T}}_2$ to be 1.5 ns at 2.208 eV and ${\mathit{T}}_{\mathit{L}}$=5 K and ${\mathit{T}}_2$=80 ps at 15 K at the same energy. At shorter wavelengths the influence of the temperature is less pronounced.