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Summary form only given. Temperature in direct-gap semiconductor show collective quantum mechanical effects such as the formation of electron-hole liquid and exciton condensation. In the usual band to band excitation, the initial temperature of the carriers remains high within their lifetime. However, creating electron-hole pairs via exciton Mott transition can a good system to realize such a transition, because of its large (213 meV) is Z/sub 3/ exciton binding energy. Recently we have reported on the observation of broad band emission at 100 meV below the exciton band for resonant exciton excitation in CuCl. We perform pump probe measurements in the mid-infrared region in order to understand the origin of the emission band. If high density excitons form plasma, change in reflectivity, increase below plasma frequency and decreases above plasma frequency.