Exciton thermalization in quantum-well structures

We show that a unified picture, namely, thermalization within the inhomogeneously broadened exciton band, can be used to explain the excitonic photoluminescence (PL) spectra in quantum wells independently of the presence, or lack thereof, of the low-energy shift of the PL line with respect to the absorption peak (Stokes shift). The Stokes shift itself turns out to be a mere consequence of the thermal equilibrium with a quadratic dependence on the absorption linewidth and a linear dependence on the inverse of the excitonic temperature. The predictions are found to be in excellent agreement with careful measurements in GaAs/${\mathrm{Al}}_{\mathit{x}}$ ${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$As single-quantum-well structures.