Photoluminescence up-conversion induced by intersubband absorption in asymmetric coupled quantum wells

We report a new mechanism of photoluminescence up-conversion in undoped GaAs-AlGaAs asymmetric coupled quantum wells. Under band-to-band excitation, resonant excitation of the ${\mathit{E}}_1$→${\mathit{E}}_2$ intersubband transition is shown to result in a finite nonthermal occupation of the ${\mathit{E}}_2$ subband, giving rise to an ${\mathit{E}}_2$→${\mathit{HH}}_1$ photoluminescence. The induced luminescence closely follows the polarization selection rules and the spectral dependence of the intersubband absorption. We show that this up-conversion scheme can be used to estimate the intersubband scattering time, which is found to be 2.5±0.7 ps.