Relations between IR induced photoconductivity and IR stimulated luminescence in ZnS

IR induced photoconductivity (INP) and IR stimulated luminescence (STL) have been simultaneously measured in self-activated ZnS crystals. The stimulation spectra of INP and STL for the λ_IR = 1.2 μm to 6.4 μm spectral range were identical including broad, structureless responses and many narrow characteristic lines. Transient characteristics of INP and STL were strongly temperature dependent and showed a large variation from sample to sample. In every case, STL began to decay while INP was still increasing during steady IR excitation. Many different features were found in the magnitudes of INP and STL as a function of temperature and in photoconductivity and luminescence decay processes after UV excitation. The photoelectronic effects observed in these IR sensitive ZnS crystals lead us to conclude the following: the same centers are responsible for INP and STL; charge transport through a band exists before recombination occurs; bound-bound transitions and bound-free transitions are possible; and a wide variety of shallow, intermediate, and deep traps are present.