Anti-Stokes photoluminescence of yellow band in GaN: evidence of two-photon excitation process

Time-dependent photoluminescence of yellow band in GaN has been investigate d under various excitation conditions using a Q-switched Nd : YAG laser as an excitation source. An anti-Stokes photoluminescence of the yellow band t hat dominates the photoluminescence (PL) spectra has been observed under th e below band-gap excitation. The intensity of the anti-Stokes PL shows a no n-linear dependence on the excitation intensity. Our results suggest that t he energy up-conversion is via a two-step two-photon absorption process. (C ) 1999 Elsevier Science B.V. All rights reserved.