Charge Transfer and Charge Trapping Processes in Ca- or Al-Co-doped Lu 2 SiO 5 and Lu 2 Si 2 O 7 Scintillators Activated by Pr 3+ or Ce 3+ Ions.

Lutetium oxyorthosilicate Lu 2 SiO 5 (LSO) and pyrosilicate Lu 2 Si 2 O 7 (LPS) activated by Ce 3+ or Pr 3+ are known to be effective and fast scintillation materials for the detection of X-rays and γ-rays. Their performances can be further improved by co-doping with aliovalent ions. Herein, we investigate the Ce 3+ (Pr 3+ ) → Ce 4+ (Pr 4+ ) conversion and the formation of lattice defects stimulated by co-doping with Ca 2+ and Al 3+ in LSO and LPS powders prepared by the solid-state reaction process. The materials were studied by electron paramagnetic resonance (EPR), radioluminescence spectroscopy, and thermally stimulated luminescence (TSL), and scintillation decays were measured. EPR measurements of both LSO:Ce and LPS:Ce showed effective Ce 3+ → Ce 4+ conversions stimulated by Ca 2+ co-doping, while the effect of Al 3+ co-doping was less effective. In Pr-doped LSO and LPS, a similar Pr 3+ → Pr 4+ conversion was not detected by EPR, suggesting that the charge compensation of Al 3+ and Ca 2+ ions is realized via other impurities and/or lattice defects. X-ray irradiation of LPS creates hole centers attributed to a hole trapped in an oxygen ion in the neighborhood of Al 3+ and Ca 2+ . These hole centers contribute to an intense TSL glow peak at 450-470 K. In contrast to LPS, only weak TSL peaks are detected in LSO and no hole centers are visible via EPR. The scintillation decay curves of both LSO and LPS show a bi-exponential decay with fast and slow component decay times of 10-13 ns and 30-36 ns, respectively. The decay time of the fast component shows a small (6-8%) decrease due to co-doping.