Exciton Interaction in CdSe

The emission spectrum of CdSe platelets has been observed at 2 K under laser excitation from 0.1 to 10 MW/cm 2 . By light pulses from a frequency‐doubled Nd:YAG laser (531 nm) hot electrons are created in CdSe, which thermalize into the exciton bands within 10 −13 s and decay radiatively within 10 −9 s. The spectra, obtained by this excitation, show a considerable increase of the temperature of the crystals. By resonant excitation, i.e. direct excitation of the valence band electrons into the exciton bands by a tunable laser, this temperature increase could be avoided. A Bose condensation of the excitons, as expected by Gross et al., was not observed. Instead, results have been obtained which seem to indicate the formation of exciton molecules and the condensation of the excitons into drops with an electron‐hole pair density of about 2 × 10 17 cm −3 .