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

Time-dependent photoluminescence of yellow band in GaN has been investigated under various excitation conditions using a Q-switched Nd : YAG laser as an excitation source. An anti-Stokes photoluminescence of the yellow band that dominates the photoluminescence (PL) spectra has been observed under the below band-gap excitation. The intensity of the anti-Stokes PL shows a non-linear dependence on the excitation intensity. Our results suggest that the energy up-conversion is via a two-step two-photon absorption process.