LUMINESCENCE SPECTRUM OF GALLIUM SELENIDE UNDER STRONG OPTICAL EXCITATION CONDITIONS.

The first and second harmonic of ruby laser radiation (one- and two-photon excitation) were used in the excitation of photoluminescence spectra of GaSe at 4 and 77 degree K. The spectra were compared with the published reports, with the luminescence spectra of GaSe obtained under weak excitation conditions, as well as with the absorption spectra. It was found that the main peaks of the luminescence emitted under strong excitation conditions corresponded to a structure in the absorption and to luminescence lines emitted by weakly excited crystals, so that the peaks were attributed to bound excitons. This conclusion, confirmed by a study of the luminescence kinetics and by the dependence on the intensity of the exciting radiation, was not in agreement with the attribution of luminescence peaks to collisions between excitons and electrons. The long-wavelength line, predominating in the spectrum of the highest excitation rates, was interpreted as the luminescence of the electron-hole plasma. A characteristic property of the two-photon excitation was the absence of a free-exciton resonance line from the luminescence spectrum.