The Exciton and Excitonic Molecule in Cuprous Halides

Abstract

The exciton in cuprous halides has a large binding energy and this makes it possible to realize the high-density exciton state in wide temperature regions. The CuCl crystal is the first case where the excitonic molecule (EM) has been found to be created through exciton-exciton collisions. The EM is annihilated radiatively leaving an exciton behind. It can also be created directly through two-photon excitation with giant oscillator strength. Raman scattering to the exciton states occurs simultaneously with the generation of a real EM. In the case of resonant excitation the Raman scattering and luminescence processes coexist. The redistribution of EMs, after being created with a definite wave vector by the two-photon excitation, has been clarified through the line-shape analysis of the luminescence bands in the backward and forward scattering configurations. A technique called stepwise two-photon excitation is found to be effective for the creation of EMs of large wave vector and for the determination of the spatial dispersions of the exciton and EM.