Two-photon generation of excitonic molecules in CuCl and CuBr

Abstract

Radiative recombination of excitonic molecules in CuCl and CuBr is reviewed. The emission consists of ML and MT bands in CuCl and of ML, MT and Mf bands in CuBr. These bands correspond to the recoil of an exciton into the longitudinal, transverse and triplet states, respectively When excitonic molecules are generated indirectly by the excitation of crystals into the band-to-band region, the line shape of the bands is explained by considering that excitonic molecules are in Maxwell-Boltzmann distribution. Excitonic molecules are found to be generated directly by the giant two-photon absorption. In this case, extremely sharp emission lines appear at the high energy edges of each M band, which are attributed to the Bose condensation of excitonic molecules. The two-photon resonance Raman scattering is discussed in connection with the emission from the Bose condensed state.