We report a detailed investigation of phonon-assisted anti-Stokes photoluminescence (ASPL) of light-hole (LH) excitons under heavy-hole (HH) exciton resonant excitation within a single shallow $\mathrm{GaAs}/{\mathrm{Al}}_{0.03}{\mathrm{Ga}}_{0.97}\mathrm{As}$ quantum well (QW). The ASPL results from transitions between excitonic states within the same system, made possible by the design of a high-quality QW with a HH-LH excitonic splitting of only 4 meV. Maximum ASPL was observed at 25 K and a clearly detectable signal was still seen even at 4 K. Power- and temperature-dependent measurements confirm the phonon-assisted origin of the underlying intersubband scattering. Our findings provide direct insight into excitonic transitions between subband-resolved states in high-quality QWs, offering opportunities for optical cooling of semiconductors.

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• Excitons
• Quantum wells
• Photoluminescence