Exciton relaxation dynamics in quantum dots with strong confinement

We report on the investigation of exciton relaxation, as traced by time-resolved photoluminescence, in nanoscale InP islands embedded in an ${\mathrm{In}}_{0.48}$ ${\mathrm{Ga}}_{0.52}$P matrix. Excitons are generated in excited, high-energy states. Depending on excitation energy, up to three LO-phonon replicas into lower-energy exciton states are observed. The rise of all phonon replicas, which we attribute to the LO-phonon emission time, is faster than 10 ps, our time resolution. Their $\frac{1}{e}$ decay times, which we attribute to acoustical-phonon scattering times, vary between 20 and 50 ps with decreasing energy of the excited exciton states. The exciton ground state is populated by acoustical phonon emission in several tens of picoseconds.