The initial cooling of hot carriers and the subsequent exciton formati
on in GaSe are studied by time-resolved photoluminescence (PL) using f
emtosecond up-conversion techniques. From the time-resolved PL spectra
of this layered III-VI semiconductor two different energy relaxation
channels are derived. After an initial subpicosecond cooling due to Fr
ohlich-type interaction of carriers with longitudinal optical E'(2(2))
phonons a slower regime follows. which is dominated by deformation po
tential interaction with the nonpolar optical A(1)'(1(2)) phonons. The
coupling constant for nonpolar optical phonon scattering is derived.
The subsequent formation of excitons is studied at different carrier d
ensities and detection energies. A cross section for the free-exciton
formation is determined based on a rate equation model.