Photostimulated Luminescence (PSL) and Color Centers in BaFX : Eu2 + ( X = Cl , Br , I ) Phosphors

Single crystals of phosphors have been prepared. Optical absorption spectra and stimulation spectra measured with polarized light are in good agreement with each other. The experimental ESR spectra of the F − ‐rich and X − ‐rich undoped powder phosphors which have been x‐rayed coincide with the calculated spectra of F(X − ) and F(F − ) centers, respectively. In addition, the decrease of the ESR signal intensity with light exposure is substantially in agreement with the stimulation spectra for each case. It is concluded that the PSL of phosphors is caused by the liberation of electrons trapped at F centers created by the x‐ray exposure.