ELECTRON TRAPS IN CA2-DOPED OR SR2+-DOPED BAFBR-EU2+ X-RAY STORAGE PHOSPHORS()

The x-ray storage phosphor BaFBr:Eu2+ may be made sensitive to stimula tion further into the infrared by doping with Ca2+ or Sr2+. This enabl es the use of light-emitting diodes instead of gas lasers for photosti mulation. It is shown by electron paramagnetic resonance (EPR), electr on nuclear double resonance (ENDOR), and optically detected EPR and EN DOR that upon x irradiation F-A(Br-, Ca2+) centers are formed as photo stimulable 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. Th e optical absorption band of those F-A(Br-,Ca2+) centers is red shifte d. No F-A(Br-, Ca2+) centers have been detected upon additive colorati on only. The red shift of the photostimulation spectrum is caused by f ormation of the F-A(Br-, Ca2+, or Sr2+) centers as electron traps. (C) 1996 American Institute of Physics.