Improvement of X-ray storage properties of C12A7:Tb³⁺photo-stimulable phosphors through controlling encaged anions

Lanthanide-doped oxide photo-stimulable (PS) phosphors (C12A7:Tb³⁺) with different encaged anions (O²⁻, H⁻, OH⁻and e⁻) have been prepared by a combustion method in combination with treatment under different conditions. Electron spin resonance (ESR) and Fourier transform IR (FTIR) transmittance data confirm the existences of encaged electrons, O₂⁻(indicating the existence of encaged O^2-anions) and OH⁻anions in C12A7:Tb³⁺. PS luminescence, thermoluminescence (TL), X-ray storage properties and luminescent kinetics analysis show that the more encaged OH⁻anions appear in C12A7, the shallower the depths of the two deeper traps (E_trap1 = ∼0.72 eV and E_trap2 = ∼0.95 eV), the smaller the glow-peak intensity ratio (I_trap2/I_trap1), the shorter the X-ray storage time and the lower the quality of X-ray imaging become. Our results suggest that, among all the anions, encaged OH⁻anions in C12A7:Tb³⁺play a key role in influencing X-ray storage properties of PS phosphors. High-quality X-ray image with a resolution of ∼15 line pairs per mm (lp/mm) has been obtained by reducing encaged OH⁻anions in PS phosphors. The C12A7:Tb³⁺PS phosphor is a potential candidate material for computed radiography system and erasable/rewritable optical memory media.