Optical-luminescence yield spectra produced by x-ray excitation

Abstract

A general formula for the optical-luminescence yield spectra arising from the core excitation is derived, making use of a simple phenomenological model. In this model, it is assumed that various excitations from core electron levels give rise to an identical luminescence in the individual yields. A smaller yield of the inner-core electron excitation than that of the outer-core electron excitation results in a variety of anomalous yield spectra such as those with a negative jump, a positive jump with an inverted oscillation part, and an overtone oscillation. Effective thickness is introduced to explain the optical-luminescence yield spectrum of an opaque powdered specimen. It is pointed out, within the framework of the present model, that for a certain physical condition of the specimens, the yield spectra are deformed and its oscillatory part lacks the precise structural information. The theory is examined by applying it to the yield spectra observed in ${\mathrm{CaF}}_{2}$, where the original spectra taken from the differently prepared forms---the powdered layers in different thicknesses, a pressed pellet, and a single crystal---at 30 and 90 K are presented. A switching of the edge jump is observed in the single crystal and the pressed pellet with increasing temperature. Experimental results are consistently explained by the proposed model and the observed yield spectra are well reproduced from the absorption spectrum.