Light from porous silicon by multiphoton vibronic excitation

We study the emission of photons from porous Si after high-level vibrational excitation in the Si-O absorption band using a pulsed ${\mathrm{CO}}_2$ laser. Narrow resonances in the efficiency of light generation are discovered at 1030 and 1084 ${\mathrm{cm}}^{\mathrm{-}1}$. Time-resolved experiments on the luminescence and the ir-induced changes in optical transparency show that the two excitation modes are characterized by different temporal responses. Additionally, their spectral distributions differ substantially. For excitation at 1030 ${\mathrm{cm}}^{\mathrm{-}1}$ the familiar photoluminescence band of porous Si appears. We suggest microscopic processes responsible for the light emissions.