Laser-induced absorption and photoluminescence techniques were used to investigate band states and deep levels in these crystals. It was found that inter-band 2-photon and 2-step absorption processes occurred, and furnished information concerning the main parameters of the deep levels. It was noted that doping and heat treatment affected the degree of contamination with native defects.

Characterization of Intrinsic and Impurity Deep Levels in ZnSe and ZnO Crystals by Nonlinear Spectroscopy. Gavryushin, V., Raciukaitis, G., Juodzbalis, D., Kazlauskas, A., Kubertavicius, V.: Journal of Crystal Growth, 1994, 138[1-4], 924-33