X-ray excited optical luminescence studies on the system BaXY (X,Y=F, Cl, Br, I)

The present paper reports the experimental observations on the x-ray excited optical luminescence (XEOL) along with the afterglow and colour center features found for the barium salts, represented by the formula,BaXY, whereX andY are the halides. The system thus consists of four dihalides (BaF₂,. . . ,BaI₂) and six mixed halides (BaFCl,. . . ,BaBrI). To start with, it was found that on two of the binary halides of barium, BaClI and BaBrI, no literature exists, and so these were prepared for the first time and their crystal structures were determined. An x-ray generator of 3-kW rating was next coupled to a spectrometer via a high throughput fiberoptic sensor for recording the luminescence spectra under x-irradiation. Also presented in this paper are the observations on the BaXY compounds in which about 0.1 mole% of Eu²⁺ was doped, in order to study the efficiency between the prompt luminescence and the photostimulated luminescence in these compounds. The crystal structure varies from fluorite (BaF₂), to matlockite (BaFX) and finally to orthorhombic (BaCl₂,. . .,BaBrI) for these compounds. Hence searching for systematics and empirical relations in the observed XEOL behaviour of these compounds is still a challenging problem.