Exciton Luminescence in Tin Dioxide Single Crystals

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The exciton spectra of SnO₂ single crystals with the low and high concentrations of the oxygen vacancies (OV) are investigated. The series of luminescence lines adjacent to the lowest free exciton states (the excitons localized by the isolated OV and OV clusters) increases superlinearly with the optical excitation level. It is shown that the luminescence spectra of SnO₂ can be described as the zero-phonon and one LO-phonon assisted anihilation of the free and localized excitons. The shape of LO-phonon replicas of the free exciton luminescence corresponds to Maxwellian distribution of the excitons which have the effective temperature significantly higher than the lattice temperature in the case of pulse excitation level 10⁶–10⁷ W/cm².