I1line 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 $I_1$ 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 ${\mathrm{N}}_2$-laser pulse. We find $T\sim 15$ °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 ${\mathrm{W}/\mathrm{c}\mathrm{m}}^2$).