Item

Abstract

The photoluminescence spectrum of melt-grown GaSe single
crystals was investigated with a confocal Raman microscope
equipped with a HeNe laser. Three luminescence bands of
different intensity were observed, which are mainly located to
the blue of the laser line. The luminescence signals show a
quadratic dependence on excitation intensity. The effect is
interpreted as second-harmonic generation in the strongly
optically nonlinear material followed by the excitation of
electrons into the conduction band and luminescence emission
from direct-gap Wannier excitons. The relative intensities of
the three luminescence peaks exhibit a spatial variation on the
crystal surface, which was mapped with the confocal microscope.
Possible explanations of this effect are discussed. In an
external electric field the luminescence shows a strong
increase and a quadratic redshift, whose magnitude is
consistent with the Franz-Keldysh mechanism. (C) 2002 American
Institute of Physics.