Bound-exciton cathodoluminescence in ZnSe crystals and two-phonon resonance

A study has been made of the cathodoluminescence of ZnSe crystals annealed in vacuum ZnSe(Vac)], in vacuum and, subsequently, in antimony melt (ZnSe(Vac)(Sb)], or in a zinc melt with subsequent annealing in antimony ZnSe(Zn)(Sb)]. The emission of all samples contained the I ₁ ^s,d -nLO series. The LO-phonon replicas of the emission line I ₁ ^s observed in ZnSe(Vac) samples are accompanied by single-plasmon satellites. The plasmon energy determining the replica separation is ?ω_p?10 meV. The emission lines of ZnSe(Zn)(Sb) samples have the smallest half-width. We report the first observation of anomalous broadening of the zero-phonon line I ₁ ^s in ZnSe(Vac) samples caused by a high zinc vacancy content. A theory on the shape of the emission spectrum under two-phonon resonance is developed including bound-exciton interaction with mixed plasmon-phonon vibrational modes. It is shown that the splitting of the I ₁ ^d line at T?2 K may originate from resonance exciton-phonon interaction between exciton-impurity complexes.