Mg共掺杂Gd3(Al,Ga)5O12:Ce晶体快发光的作用机理

Gd₃(Al,Ga)₅O₁₂:Ce (GAGG:Ce)闪烁体综合性能优异, 应用前景广阔。为加快GAGG的发光衰减速度, 本研究通过提拉法生长了Mg共掺的Gd₃(Al,Ga)₅O₁₂:Ce单晶。测试结果显示, 随着Mg²⁺掺杂浓度增加, 晶体的闪烁衰减速度加快, 光输出降低。传统解释认为, Mg²⁺通过电荷补偿作用将部分Ce³⁺转换成Ce⁴⁺, 后者的发光速度更快。本研究尝试从缺陷的形成与抑制的角度来讨论Mg改善GAGG:Ce晶体闪烁性能的作用机理。由于Ce的离子半径比Gd大, Ce离子掺入将导致发光中心Ce_Gd附近的晶格发生畸变。畸变结果为近邻的八面体格位空间变大, 反位缺陷将更容易在这些变大的八面体格位形成。最终每个发光中心Ce_Gd被四个反位缺陷Gd_Al包裹, 后者捕获载流子, 延缓从基体到发光中心的能量传递, 导致发光速度变慢。由于Mg的离子半径介于Gd和Al之间, Mg_Al将更容易在上述畸变的八面体格位形成, 这会抑制反位缺陷Gd_Al在发光中心Ce_Gd附近形成(或富集), 最终降低(甚至消除)反位缺陷对发光中心的不良影响。XEL测试结果显示, 随着Mg掺杂量增大, 与反位缺陷相关的发射峰强度变弱, 这可以证明Mg对反位缺陷有抑制作用。

Mechanism of Mg-codoping in Improving the Time Performance of Gd3(Al,Ga)5O12:Ce Scintillator

With its excellent comprehensive performance, Gd₃(Al,Ga)₅O₁₂:Ce (GAGG:Ce) scintillation crystal has broad application prospects. To accelerate the luminescence decay rate, Mg-codoped Gd₃(Al,Ga)₅O₁₂:Ce single crystals were grown by Czochralski method. The test results show that with the concentration of Mg²⁺ increasing, the scintillation decay of the crystal accelerates and the light output decreases. The conventional interpretation suggests that Mg²⁺ could convert part of Ce³⁺ into Ce⁴⁺ through charge compensation, and the Ce⁴⁺ luminesces more quickly. This study tries to discuss the mechanism of Mg-codoping in GAGG:Ce crystals from the perspective of antisite defect. Since the ionic radius of Ce is larger than Gd, the doping of Ce ions leads to a distortion of the crystal lattice near the luminescence center Ce_Gd. As a result of the distortion, the space of the adjacent octahedral sites become larger, and the antisite defects are more likely to form in these larger octahedral sites. Eventually each luminescence center Ce_Gd is surrounded by four antisite defects Gd_Al, which would capture carriers and delay the energy transfer from the matrix to the luminescence center. As the ionic radius of Mg is between Gd and Al, Mg_Al also prefers to form in those distorted octahedral sites, which inhibits the formation (or enrichment) of the antisite defect Gd_Al near the luminescence center Ce_Gd, and eventually reduces (or even eliminates) the adverse effects of the antisite defect on the luminescence center. XEL results show that with the increase of Mg concentration, the emission peak related to the antisite defect becomes weaker, which indicates that Mg could inhibit the formation of the antisite defect.