Ga²⁺ hole centers and photostimulated luminescence in the x-ray storage phosphor RbBr:Ga⁺

It was previously shown that RbBr doped with Ga⁺ is an efficient x-ray storage phosphor with a figure of merit comparable to that of the commercially used BaFBr:Eu²⁺. The paramagnetic hole centers generated upon x-irradiation involved in the storage and read-out process were investigated by measuring the magnetic circular dichroism of the optical absorption (MCDA), the MCDA-detected electron paramagnetic resonance (MCDA-EPR) and the photostimulated luminescence (PSL). Two different Ga²⁺ hole centers with a hyperfine interaction with Ga of A = 8.2 GHz and A = 6.0 GHz, respectively, were found. No superhyperfine interaction was resolved. Therefore, the structural difference between the two Ga²⁺ centers could not be established from EPR. The PSL effect is correlated only to one of the two Ga²⁺ centers, namely that with A = 8.2 GHz. The generation mechanism of the two hole centers is investigated. It is proposed that the PSL-active Ga²⁺ center is an isolated Ga²⁺ on a Rb⁺ site, whereas the other center is a Ga²⁺-cation vacancy complex.