Double 2s-1s resonance in LO-phonon-assisted secondary emission of quantum-well structures

We report on the observation of the doubly resonant secondary emission involving 2s- and 1s-exciton states. The resonance conditions have been realized in CdTe/${\mathrm{Cd}}_{1\mathrm{-}\mathit{x}}$${\mathrm{Mn}}_{\mathit{x}}$Te quantum-well structures by magnetic-field tuning of the 2s-1s energy spacing to the LO-phonon energy. Theoretical analysis shows the doubly resonant process to be indirect, with hot 1s excitons acting as intermediate states. It is concluded that the resonance width of 2.6 meV gives the 2s-exciton homogeneous linewidth governed by elastic scattering into the hot 1s-exciton states.