I1 line shape as a temperature probe: The thermal relaxation of highly excited CdS

We demonstrate that analysis of the line shape of the acoustic-phonon wings of the I1 bound-exciton emission in CdS can provide a means to determine crystal temperature T and use this result to investigate the thermal relaxation of CdS following photoexcitation by an intense N2-laser pulse. We find T∼15 °K for ∼1-kW incident power and T varies as the fourth root of the absorbed energy in accord with the Debye theory of specific heat. In addition the crystal-temperature rise is found to persist for long times (∼1-100 μsec). From the variation of the crystal temperature with time, we deduce a constant value of heat flow from the sample to the liquid-helium bath (∼4 W/cm2).