Charge Transfer and Charge Trapping Processes in Ca- or Al-Co-doped Lu2SiO5 and Lu2Si2O7 Scintillators Activated by Pr3+ or Ce3+ Ions

Abstract

Lutetium oxyorthosilicate Lu2SiO5 (LSO) and pyrosilicate Lu2Si2O7 (LPS) activated by Ce3+ or Pr3+ 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 Ce3+(Pr3+) → Ce4+(Pr4+) conversion and the formation of lattice defects stimulated by co-doping with Ca2+ and Al3+ 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 Ce3+ → Ce4+ conversions stimulated by Ca2+ co-doping, while the effect of Al3+ co-doping was less effective. In Pr-doped LSO and LPS, a similar Pr3+ → Pr4+ conversion was not detected by EPR, suggesting that the charge compensation of Al3+ and Ca2+ 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 Al3+ and Ca2+. 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.

Photoluminescence and scintillation properties of Pr-doped (Lu, Y)2Si2O7 crystals

“…The trend is the same as Al or Ca-admixed Pr-doped LPS. 48) Additionally, some emissions due to the 4f-4f transitions of Pr 3+ were confirmed at 600-700 nm. 47) A broad emission was also confirmed at 350-500 nm although the intensity was relatively low in comparison with the emissions at 300 and 600 nm.…”

Visible to Near-Infrared Mechanoluminescence from Pr-Doped LiTaO3 for Stress-Sensing Applications

“…An interesting XPS observation that a large part of praseodymium ions are in the 4+ oxidation state in all examined samples may also be important for ML efficiency. The Pr 4+ ions may serve as electron traps and/or quenching centers . The role of Pr 4+ ions should be carefully examined, which will be done in the following research.…”