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Time‐resolved spectroscopic study of the photoluminescence response to femtosecond pulse excitation and free carrier absorption at different wavelengths, thermally stimulated luminescence measurements and investigation of differential absorption are applied to amend the available data on excitation transfer in GAGG:Ce scintillators, and an electronic energy‐level diagram in this single crystal is suggested to explain the influence of codoping with divalent Mg on luminescence kinetics and light yield. The conclusions are generalized by comparison of the influence of aliovalent doping in garnets (GAGG:Ce) and oxyorthosilicates (LSO:Ce and YSO:Ce). In both cases, the codoping facilitates the energy transfer to radiative Ce3+ centers, while the light yield is increased in the LYSO:Ce system but reduced in GAGG:Ce. [ABSTRACT FROM AUTHOR]

GGAG:Ce crystals with various Ca concentrations were grown by the Czochralski technique. The introduction of Ca2+ ions into a trivalent site results in a change in the Ce valence state as well as an additional F+ luminescence center. The changes of Ce valence state could be affected by various annealing atmospheres and were investigated via measuring the Ce3+ absorbance and observing the color change of the sample. Photoluminescence spectra and photoluminescence decay were used to reveal the occurrence of F+ center related to the oxygen vacancies during the annealing. A redox mechanism and a charge compensation process are proposed to explain the change in Ce state charge and F+ center during the annealing. [ABSTRACT FROM AUTHOR]

Commercially available Lu2SiO5:Ce (LSO:Ce) scintillators for the nuclear medical imaging applications, such as positron electron tomography (PET), normally have a light yield of 30 000–32 000 photons/MeV and a scintillation decay time of 43–45 ns. We demonstrate a simultaneous improvement of light yield and decay time of LSO:Ce single crystal scintillators with lithium codoping. Li codoping significantly enhances the light yield of LSO:Ce from 32 500 to 39 000 photons/MeV, shortens the scintillation decay time from 45.4 to 42.1 ns, and reduces the room temperature afterglow by around one order of magnitude. The physical insights on the role of Li codopants in scintillation mechanism are provided by studying cerium oxidation state, luminescence properties of cerium activator centers, defect structure, and preferential occupation of lithium ions. The improved light yield and afterglow are explained in terms of the dissociation of spatially correlated oxygen vacancies (VO) and Ce centers or the suppression of VO formation, allowing a more efficient electron migration to Ce centers. We attribute the decay time shortening upon Li+ codoping to the reduction of slow Ce2 emissions via a non‐radiative energy transfer from six‐coordinated Ce2 to seven‐coordinated Ce1 centers. This letter reports a simultaneous improvement of light yield, decay time, and afterglow of Lu2SiO5:Ce3+ scintillation detectors by Li+ codoping. Analysis reveals the non‐conversion of stable Ce3+ to Ce4+ upon Li codoping, and the critical role of Li site occupancy on the suppression of oxygen vacancies. This strategy is also expected to be extended to other oxide scintillators. [ABSTRACT FROM AUTHOR]