Time-dependent excitation spectroscopy, coupled with quantum-chemical calculations, was used to demonstrate that the photoluminescence which resulted from the ultra-violet optical pumping of an etched porous surface resulted from a Si oxyhydride-like fluorophor which was bound to the surface. The early appearance of the luminescence was consistent with the formation of a surface-bound emitter which was created over a time scale (less than 10s) that was much shorter than that needed for pore formation. Laser excitation spectra, for wavelengths extending from 193 to 400nm, produced an almost identical time-dependent photoluminescence emission between 550 and 700nm. Calculated infra-red spectra were related to experimentally observed features and were consistent with the existence of a surface-based oxyhydride-like emitting fluorophor. A recent analysis which had associated the line-width, of the triplet optically detected magnetic resonance spectrum, with an inhomogeneous distribution of quantum-confined crystallites was shown to be incorrect. It was demonstrated that the correct deduction to be drawn from the arguments used in this analysis constituted clear evidence for the existence of a common radiative center that was associated with a molecule-like species which was bound to the surface of the porous framework. The present results were therefore not consistent with quantum-confinement, and indicated a surface-bound emitter to be the source of porous Si photoluminescence.

J.L.Gole, F.P.Dudel, D.Grantier, D.A.Dixon: Physical Review B, 1997, 56[4], 2137-53