Configuration Interaction in Alkali Halide Phosphors

Abstract

It is shown that excited state wave functions of free activator ions do not provide a completely adequate basis for a quantitative theory of the luminescence of alkali halides activated by heavy metals. It is proposed that better zero-order wave functions may be obtained by allowing interaction between different types of states of excitation, and as a practical example of an electronic configuration which can interact with excited activator configurations, the electron transfer states of the Seitz model are discussed in detail. These states have generally been ruled out because of the absence of a halogen-like doublet in the phosphor absorption spectra, but a closer analysis shows that the doublet character of the activator atom is of equal importance. Neither of the doublets is expected to appear explicitly in the spectra. A numerical estimate of the coupling between an excited activator 6s6p state and a typical electron transfer state indicates the possibility of strong interaction between these configurations. It is concluded that the Seitz model is capable of explaining recent experiments on excitation bands, polarization effects, and lattice structure dependence of absorption spectra, provided that more emphasis is placed on electron-transfer states or other excited states of the host crystalmore » which can interact with excited activator configurations. (auth)« less