Fig. 1. (Color online) Illustration of a configuration coordinate model. (a) Energy levels before and after taking into account the lattice relaxation. (b) Transition energies in relaxed configuration coordinates.

Fig. 2. (Color online) Photoluminescence spectrum of the isolated nitrogen bound exciton in GaP:N (4.2 K, [N] = 10¹⁶ cm^-3, A line at 2.317 eV)^[6].

Fig. 3. (Color online) Resonant Raman spectra of ZnTe measured by a 532 nm laser at room temperature for one high quality single crystal sample and a thin-film sample grown on a Si (211) substrate. Strong PL background of the single crystal sample has been removed.