Nickel impurity excitons and photoinduced lattice distortion in ZnSe1?y Sy:Ni and Zn1?x CdxSe:Ni solid solutions

A heavy dependence of the zero-phonon line of the donor Ni excitons and of a series of its phonon replicas on the composition of ZnSe_1?y S_y:Ni and Zn_1?x Cd_xSe:Ni solid solutions was studied. A model of nonradiative recombination of impurity excitons with allowance made for an intermediate virtual state {d ⁸} is discussed in detail. It is shown that this state depends on the lattice distortion induced by the Ni³⁺ impurity center whose charge is positive in reference to the lattice.