Modification of Ce³⁺ luminescence in Li⁺ and Mg²⁺ codoped GAGG:Ce scintillators: A comparative study using synchrotron radiation

The luminescence characteristics of Gd3Al2Ga3O12:Ce3+ garnet scintillator crystals codoped with Li+ and Mg2+ ions were investigated. The excitation and emission spectra were obtained within the energy range of 3.6-21.6 eV, at both liquid helium and room temperature conditions to examine the effects of Li+ and Mg2+ codoping on cerium valence states, gadolinium-cerium energy transfer, and defect formation. Codoping with Mg2+ was found to efficiently convert Ce3+ to Ce4+, evidenced by significant changes in the shapes of the excitation spectra profile for Ce3+ luminescence in the exciton range, while Li+ had little impact. The presence of the high concentration of Ce4+ ions hampered the Gd3+→Ce4+ energy transfer. Redshifts in Ce3+ emission peaks indicated codopant-induced perturbations to the crystal field environment. The significant changes in the location of the Ce3+ excitation bands of Ce3+ luminescence in the exciton range further suggested alterations in the elemental distributions by the creation of complex defect clusters, particularly with Mg2+ codoping. The results demonstrate that Li+ and Mg2+ uniquely impact cerium valence, energy transfer processes, and structural properties in GAGG:Ce crystals

本研究针对共掺杂锂离子（Li⁺）与镁离子（Mg²⁺）的Gd₃Al₂Ga₃O₁₂:Ce³⁺石榴石闪烁晶体的发光特性展开系统探究。实验在液氦温度与室温两种条件下，于3.6~21.6电子伏特（eV）的能量区间内采集了激发与发射光谱，以此分析Li⁺与Mg²⁺共掺杂对铈价态、钆-铈能量转移以及缺陷形成的影响。研究发现，Mg²⁺共掺杂可有效将Ce³⁺转化为Ce⁴⁺，该结论可通过激子区间内Ce³⁺发光的激发光谱轮廓发生的显著变化得以验证；而Li⁺共掺杂对此几乎无影响。高浓度Ce⁴⁺离子的存在会抑制Gd³⁺向Ce⁴⁺的能量转移过程。Ce³⁺发射峰的红移现象表明，共掺杂会对晶体场环境造成扰动。激子区间内Ce³⁺发光的激发峰位置发生显著变化，进一步表明共掺杂（尤其是Mg²⁺共掺杂）会通过形成复杂缺陷团簇改变元素分布状态。本研究结果证实，Li⁺与Mg²⁺两种掺杂剂会分别对GAGG:Ce晶体中的铈价态、能量转移过程以及结构特性产生独特影响。