We repon time-resolved photoluminescence spearoscopy oi highly porous silicon. Our results show that lhe luminescence i s due to localized quantumanfined cxcilons in undulating ayslalline silicon wires. The resonantly excited photoluminescence spec" exhibits sateUite suuclure due to momentumsonsewing phonons of aystalline silicon. l3i.s p r w i d s a desr signature of the crystalline-silimn elecuonic band Smcture. ?he spin s l a t s of Le localized exciton are split @ lhe elclron-hole exchange interaction. lhis splitting is manifested both in the strong dependence of the luminescence lifetime 011 temperatuq and as an energy gap m B e resonantly exated photoluminescence specuum. The aperimental splitting i in good agreement with the value calculated for a localiied m i t o n in aystalline silicon.The demonstration [ 11 of efficient visible luminescence from highly porous Si has stimulated a great deal of interest The attribution of this luminescence to quantumconfined camers in crystalline Si wires [l] has been supported by transmission electron microscopy [2] (EM) which shows the structure to consist of undulating columns of crystalline Si. Fit-principles calculations 131 for wires of the dimensions observed in EM account for both the quantum upshift of the luminescence energy and the radiative lifetimes. We report time-resolved photoluminescence (PL) spectroscopy which confirms the model of quantum confinement in crystalline S i . Our experiments show that the radiative states, even at room temperature, are localized excitons with a large exchange splitting. Our observation of momentumanserving phonon satellites

The observation of a many-body, Fermi-energy edge singularity in the low-temperature photoluminescence spectra of InGaAs-InP quantum wells is reported. Strong enhancement of the photoluminescence intensity towards the electron Fermi energy {E%) is observed, due to multiple electron-hole scattering processes to states above E%. Recombination of electrons in states up to E% is allowed by hole localization. The many-body processes are analogous to the core-hole phenomena in the soft-x-ray emission spectra of metals.

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