A nonlinear optical effect is shown to occur in gallium and indium selenides at photon energies of the order of 1.5 eV. It corresponds to transitions from a lower-energy valence band to the uppermost one when a nonequilibrium degenerate hole gas is created in the latter by a laser pulse. This inter-valence-band transition is allowed by crystal symmetry. Its oscillator strength is estimated through the f-sum rule and turns out to be about two orders of magnitude higher than that of the fundamental transition. The intensity of this effect is stronger when the pump pulse photon energy is close to that of the inter-valence-band transition; a condition that can be fulfilled only in indium selenide. The transient behavior of the sample transmittance is shown to be controlled by the balance between absorption and stimulated emission, which depends on the hole quasi-Fermi level and the gap renormalization due to Coulomb interaction in the electron-hole gas generated by the pump.

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The intensity of a He-Ne laser ͑633 nm, 5 mW͒ transmitted by different GaSe samples is observed to change in correlation with a Nd-yttrium-aluminum-garnet laser pulse ͑532 nm, 7.8 ns, 3 mJ͒ which excites them. Such time response has been attributed to a nonlinear optical effect, i.e., a decrease in the refractive index due to the exciton screening by the photogenerated carriers. A calculation of the absorption coefficient and refractive index at different carrier concentrations has led to a reconstruction of transmittance transients which fully agree with the experimental data at different incident intensities and temperatures.

Photoluminescence of strained Si1-x-yGexCy alloy layer and Si1-x-yGexCy /Si1-xGex structures selectively grown by RT-CVD is investigated. Spectroscopic PL at low temperature (14K) and integrated PL at room temperature were performed. We report the effect of C atoms on SiGe photoluminescence spectra features, especially intensity ratio between the no-phonon (NP) and transverse-optical (TO) transitions. Using dedicated Si1-x-yGexCy /Si1-xGex structures, influence on SiGe PL spectra of C atoms supposed in non-substitutional positions is reported.