Excitation Spectra of Luminescence in Cadmium Sulfide

Excitation spectra of the excitonic luminescence in CdS are presented for three types of samples: doped, pure, and surface contaminated samples. The positions and relative magnitudes of peaks appearing in some of these spectra are analyzed and quantitatively explained in terms of indirect creation of free excitons. The different behaviour of the three types of samples investigated allows a more general discussion which leads to important discriminations between direct and indirect optical absorption and between volume and surface radiative recombination.