  We investigate the energy relaxation of excitons during the real-space
transport in ZnSe quantum wells by using microphotoluminescence with spatial
resolution enhanced by a solid immersion lens. The spatial evolution of the
LO-phonon sideband, originating from the LO-phonon assisted recombination of
hot excitons, is measured directly. By calculating the LO-phonon assisted
recombination probability, we obtain the nonthermal energy distribution of
excitons and observe directly the energy relaxation of hot excitons during
their transport. We find the excitons remain hot during their transport on a
length scale of several micrometers. Thus, the excitonic transport on this
scale cannot be described by classical diffusion.
