Refractive index changes in CdSxSe1-x doped glasses through the photodeflection method. Evidence for an electronic contribution together with reversible and irreversible effects

Using the photo-deflection method in quasi c.w. regime refractive index variations of CdSx Se1 − x doped glasses have been observed consisting of two independent contributions Δn = Δnt + Δne. The photothermal term Δnt = (dn/dT) ΔT (ΔT is the temperature increase) is positive and slow in time, the electronic term Δne is negative and fast. The electronic term appears at first due to a reversible contribution (during a time scale of 1/ω, where ω is the chopper frequency) and after a time of a few tenths of seconds disappears irreversibly. It is attributed to a redistribution in space and energy levels of electrons in the semiconductor microcrystals. This redistribution is large enough when the electron relaxation is not too fast. The consequent refractive index change decreases in time and disappears under prolonged laser irradiation. A model is presented in which the presence of traps is taken into account.