Probing the electron–LO-phonon interaction of a single impurity state in a semiconductor

The photoluminescence of single emission centers in the energy range of donor-acceptor pair transitions is studied in ZnSe by spatially resolved imaging spectroscopy at the diffraction limit. Addressing single impurity states, the electron--LO-phonon interaction is probed locally and a microscopic Huang-Rhys parameter between $S=0.08$ and 0.51 is found, related to a variation of the homogeneous linewidth between 1 meV and 15 meV. Based on our results the donor-acceptor pair model is reconsidered in the limit of large variation of the pair energies Δ(EA+ED)>ωLO.