Nonlinear optical properties of the system CdS1-xSex

The influence of localization on the nonlinear optical properties of CdS1-xSex is investigated for 0 ≤ x ≤ 1 in the temperature range from 5 to 300 K. Results from time-integrated and time-resolved luminescence, from pump- and probebeam experiments, and from measurements using laser-induced gratings are given. From all investigations likewise free and 'localized' excitons are found in the mixed crystals at temperatures below 60 K, with a spectrally rather broad transition region. The mobility of the 'localized' excitons is non-zero but is decreased by more than a factor three with respect to free excitons. Above 60 K, the optical properties approach those of the pure compounds and are dominated by the formation of an electron-hole plasma at high excitation intensities. This process reflects a delocalization of the excited electron-hole pairs due to thermal reexcitation from 'localized' into extended states. (author)