Spontaneous and Stimulated Luminescence in CdS and ZnS Excited by Multiphoton Optical Pumping

Spontaneous and stimulated emission at 85 °K in CdS and ZnS single crystals is reported. The exciting source was a ruby laser and its second harmonic. The two-photon spectrum of CdS shows stimulation effects in the phonon-assisted excitonic lines at a pumping level of about ${10}^{26}$ (photons/${\mathrm{cm}}^2$)/sec. The same effect is observed in cubic ZnS with the second-harmonic light. A three-photon excited spontaneous luminescence is also obtained in this last sample. The results are in good agreement with the theoretical predictions of multiphoton-absorption theory.