Dipole-Center in ZnSe Crystals

It has been found that the well-known luminescence band with a maximum near 630 nm in undoped ZnSe crystals is associated with the recombination of free electrons at localized holes and free holes at localized electrons. The result was achieved by comparing experimental values for the stationary luminescence intensity with the phosphorescence and thermally stimulated luminescence intensities, as well as values obtained for the conductivity under stationary conditions with curves registered for the relaxation current and the thermally stimulated conductivity. For the explanation of uncharacteristic spectral features of the luminescence band at about 630 nm,the existence of a complex (non localized) center has been proposed, with a possibility for both recombination mechanisms to be realized at it. We propose to call it "dipole-center". A theoretical analysis is performed for the multicenter model of crystal phosphor with a recombination dipole-center. It is shown that just the presence of the dipole-center gives rise to the appearance of a wide luminescence band with a general maximum at 630 nm. This fact allows a scintillation material of the new type to be proposed, where the dipole-center plays the role of a luminescence center that does not demand traps for a high luminescence yield.