X-RAY EXCITED OPTICAL LUMINESCENCE, PHOTOLUMINESCENCE, PHOTOSTIMULATED LUMINESCENCE AND X-RAY PHOTOEMISSION SPECTROSCOPY STUDIES ON BAFBR-EU

The results of x-ray excited optical luminescence (XEOL), photolumines cence (PL), photostimulated luminescence (PSL) and x-ray photoemission spectroscopy (XPS) studies on the x-ray storage phosphor BaFBr:Eu are presented in this paper. Analyses of XEOL, PL and PSL spectra reveal features corresponding to the transitions from 4f(6) 5d(1) to 4f(7) co nfigurations in different site symmetries of Eu2+. Increasing x-ray do se is seen to lead to a red shift in the maximum of the PL excitation spectrum for the 391 nm emission. The XEOL and XPS spectra do not show any signature of Eu3+ in the samples studied by us, directly raising doubts about the model of Takahashi et al in which Eu2+ is expected to ionize to Eu3+ upon x-ray irradiation and remain stable until photost imulation. XEOL and PSL experiments with simultaneous x-ray irradiatio n and He-Ne laser excitation as well as those with sequential x-ray ir radiation and laser stimulation bring out the competition between the F centre population and depopulation rates. A time scale similar to 1- 2 s, possibly related to the process of production of the electron/hol e traps themselves, during x-ray irradiation, is observed. Relaxation of these traps upon photostimulation is also seen.