Ai. Bobrysheva et al., THE RENORMALIZATION OF THE ENERGETICAL SPECTRUM AND THE PECULIARITIESOF HIGH-DENSITY PARAEXCITON LUMINESCENCE BAND, Physica status solidi. b, Basic research, 190(2), 1995, pp. 481-486
The renormalization of the energetical spectrum of paraexcitons in the
presence of a Bose-Einstein condensate (BEG) of orthoexcitons or at l
east of their saturation is studied. Due to the conversion of a pair o
f orthoexcitons into a pair of paraexcitons an absolute instability in
the energy spectrum of paraexcitons appears. The appeared paraexciton
s can be downscattered by optical phonons Gamma(5)(-) (88 cm(-1)) into
a state above the bottom of the paraexciton band. This can be the rea
son of the observed peculiarities in the paraexciton luminescence band
. On this basis a new explanation of the appearance of an extra peak i
n the luminescence spectrum of the uniaxially stressed Cu2O crystal is
suggested. It has the same origin as the bump of the luminescence ban
d in unstrained crystals. The spectral positions of the extra peak and
of the bump differ due to the diminution of the ortho-para splitting
in uniaxially stressed crystals. The difference of their widths is due
to different densities of the condensed orthoexcitons in stressed and
unstrained crystals.