Lanthanum-stabilized europium-doped cubic barium chloride: An efficient x-ray phosphor

Abstract

We report the photoluminescence and x-ray luminescence of lanthanum-stabilized cubic barium chloride with europium (Eu2+) doping, of general composition Ba1−x−yEuyLaxCl2+x. X-ray diffraction patterns confirm that the material adopts a cubic fluorite structure for x=0.125 and 0<y<0.1. The photoluminescence shows an intense band comprising two components with maxima at 420 and 394 nm. The 394 nm band is assigned to Eu2+ substituting for Ba2+ giving a site of cubic symmetry, based on the excitation spectra which show a T2g band and Eg band similar to those in cubic SrCl2:Eu. The 420 nm band has a very different lifetime and excitation spectrum and is assigned to Eu2+ ions which have an associated chlorine interstitial ion. The two bands are also found in the x-ray luminescence spectra. For both bands, and an additional minor emission at 520 nm found only at low temperatures and for high Eu concentrations, there is a common excitation in the UV from 150 to 200 nm which we attribute to excitons associated with the high concentration of chlorine interstitials. ESR measurements support a two-site model for the interpretation of the optical spectra. A measurement of the x-ray luminescence intensity compared to a standard commercial Gd2O2S:Tb phosphor sheet shows approximately equal brightness.