Transient behavior of the second-order optical process in CdₓZn₁₋ₓTe: Transformation from luminescence into Raman scattering

We report on the transient behavior of the second-order optical process in the picosecond time region in mixed semiconducting crystals. Time-integrated spectra under resonant excitation below the band gap exhibit ``Raman-like'' lines associated with localized excitons. However, time-resolved spectroscopy enabled us to resolve these Raman-like lines into resonant luminescence and Raman scattering lines. We have found the transformation of luminescence into Raman scattering as a function of incident frequencies without changing the spectral shape. Furthermore, the intensity ratio between Raman scattering and luminescence was determined for a wide range of the off-resonance frequency. The result is unambiguously explained by the theory by taking into account the finiteness of the correlation time of the reservoir. This gives the first experimental evidence for the non-motional-narrowing effect in the second-order optical process.