EXCITONIC ORIGIN OF FEMTOSECOND NONLINEARITY NEAR THE BANDGAP OF A COMMERCIAL CDSSE SEMICONDUCTOR-DOPED GLASS

To determine the origin of the nonlinearity near the bandgap of II-VI commercial semiconductor-doped glasses (SDG) with no apparent excitoni c features, we studied the temperature dependence of the dephasing tim e near the bandgap using degenerate four-wave mixing (FWM). The deduce d coupling constant with LO phonons was comparable, or nearly equal, t o the exciton-LO phonon coupling constants in other II-VI semiconducto rs and quantum wells. We contend that the nonlinearity observed in FWM is due to excitons, whose features in absorption are overshadowed by the inhomogeneity in the crystal sizes.