We use time-resolved photoluminescence spectroscopy to measure the thermal relaxation of hot excitons in ZnSe-based diluted magnetic semiconductors at low temperatures (${\mathrm{T}}_{\mathrm{lat}}$<10nK). Unlike other direct-gap semiconductors, the strong Fröhlich interaction in ZnSe semiconductors means that a spectral line associated with recombination of excitons accompanied by the emission of 1 or 2 optic phonons is easily visible in the photoluminescence spectra. The emission of the optic phonon relaxes the momentum selection rules so that any exciton in the band is allowed to recombine. Thus, the 1-LO and 2-LO phonon replica lines give a direct measure of the electronic temperature of the excitons within their bands. We find that the excitons relax within 300 ps to the lattice temperature, and that this relaxation can be accurately described by the emission of acoustic phonons through deformation-potential scattering theory.

• Received 23 August 1996

DOI:https://doi.org/10.1103/PhysRevB.55.5062