Spectroscopy of resonant excitation of exciton luminescence of GaSe–GaTe solid solutions

The luminescence excitation spectra of localized excitons in GaSe$_{0.85}$Te$_{0.15}$ solid solutions have been investigated at the temperature $T$ = 2 K. It has been shown that the excitation spectra of excitons with the localization energy $\varepsilon>$ 10 mV exhibit an additional maximum $M_{E}$ located on the low-energy side of the maximum corresponding to the free exciton absorption band with $n$ = 1. It has been found that the shift in the position of the maximum $M_{E}$ in the excitation spectrum with respect to the energy of detected photons increases as the energy of detected photons decreases, i.e., with an increase in the localization energy of excitons. Under the resonant excitation of localized excitons by a monochromatic light from the region of the exciton emission band, in the exciton luminescence spectrum on the low-energy side from the excitation line, there is also a maximum of the luminescence $(M_L)$. The energy distance between the position of the excitation line and the position of the maximum in the luminescence spectrum increases with a decrease in the frequency of the excitation light. The possible mechanisms of the formation of the described structure of the luminescence excitation and exciton luminescence spectra of GaSe$_{0.85}$Te$_{0.15}$ have been considered. It has been concluded that the maximum $M_{E}$ in the excitation spectrum and the maximum $M_L$ in the luminescence spectrum are attributed to electronic–vibrational transitions with the creation and annihilation of localized excitons, respectively.