Electron traps in Ca2+- or Sr2+-doped BaFBr:Eu2+ x-ray storage phosphors

The x-ray storage phosphor BaFBr:Eu2+ may be made sensitive to stimulation further into the infrared by doping with Ca2+ or Sr2+. This enables the use of light-emitting diodes instead of gas lasers for photostimulation. It is shown by electron paramagnetic resonance (EPR), electron nuclear double resonance (ENDOR), and optically detected EPR and ENDOR that upon x irradiation F-A(Br-, Ca2+) centers are formed as photostimulable electron traps in Ca2+-doped BaFBr, in which one of the two nearest Ba2+ neighbors along the c axis is replaced by Ca2+. The F-A(Br-, Ca2+) center has tetragonal symmetry as has the F(Br-) center. The optical absorption band of those F-A(Br-,Ca2+) centers is red shifted. No F-A(Br-, Ca2+) centers have been detected upon additive coloration only. The red shift of the photostimulation spectrum is caused by formation of the F-A(Br-, Ca2+, or Sr2+) centers as electron traps. (C) 1996 American Institute of Physics.