Gd3(Al,Ga)5O12:Ce闪烁晶体缺陷对其发光性能的影响

新型闪烁晶体Gd₃(Al,Ga)₅O₁₂:Ce(GAGG:Ce)在制备过程中易出现包裹体及反格位缺陷等问题,严重影响晶体的性能.为了抑制这些缺陷以得到大尺寸高质量的GAGG:Ce晶体,本文以Gd₃(Al,Ga)₅O₁₂为基质、Ce3+为掺杂离子,采用提拉法生长得到了GAGG:Ce晶体,并对不同晶体部位的物相结构、微区成分、透光性质、发光及时间性能进行了测试和对比分析.结果表明,GAGG:Ce晶体的透过谱中存在340和440 nm两处Ce³⁺特征吸收带,且位于550 nm处的直线透过率为82%.晶体尾部因杂相包裹体等宏观缺陷的影响,导致其透过率下降至70%左右.微区成分分析进一步表明GAGG:Ce晶体中存在三种类型的包裹体,分别为富Gd相、富Ce相及(Al,Ga)₂O₃相.GAGG:Ce晶体的X射线激发发射谱中在550 nm附近存在Ce³⁺宽发射带,且380 nm处还存在GdAl/Ga反格位缺陷引起的发射.晶体中存在的杂相包裹体及GdAl/Ga反格位缺陷等因素导致Ce³⁺在GAGG基质的发光强度下降12.5%;GdAl/Ga反格位离子与近邻Ce的隧穿效应使得GAGG:Ce晶体的衰减时间由117.7 ns延长至121.9 ns,且慢分量比例由16%增加至17.2%.

Influence of defects on luminescence properties of Gd3(Al,Ga)5O12:Ce scintillation crystals

There are many problems during the preparation of the scintillation crystal Gd₃(Al,Ga)₅O₁₂:Ce(abbreviated as GAGG:Ce),such as inclusions and antisite-defect.In order to inhibit these defects and obtain large-size and high-quality GAGG:Ce crystal,this study uses Gd₃(Al,Ga)₅O₁₂as the matrix and Ce³⁺as the doping ions to grow the GAGG:Ce crystal by the Czochralski method.The phase structure,micro-region composition,optical and scintillation properties of GAGG:Ce are tested and compared.It is found that tipical Ce3+absorption bands are at 340 nm and 440 nm,and the linear transmittance at 550 nm is 82%.The transmittance of the crystal tail drops to about 70%due to the macroscopic defects such as inclusions.The micro-region composition analysis shows that the three types of inclusions in GAGG:Ce crystal are Gd-rich phase,Ce-rich phase,and(Al,Ga)₂O₃phase.The Ce³⁺ion emission wavelength of GAGG:Ce crystal is about 550 nm excited by the X-ray,and there is also an emission wavelength caused by the GdAl/Ga antisite-defect at 380 nm.The emission intensity of GdAl/Ga antisite-defect in the lack of(Al,Ga)component is higher than that in the excess(Al,Ga)component.The inclusions and GdAl/Ga antisite-defect make the luminous efficiency of GAGG:Ce crystal decrease by 12.5%and the corresponding light yield decreases from 58500 to 52000 photon/MeV.The tunneling effect between GdAl/Ga antisite-defect ions and neighboring Ce3+ions makes the decay time of the GAGG:Ce crystal extend from 117.7 to 121.9 ns,and the ratio of slow component increases from 16%to 17.2%.The migration of energy along the Gd3+sublattice makes the rise time of the GAGG:Ce crystal extend from 8.6 to 10.7 ns.The above conclusions further deepen the understanding of the source of inclusions and the relationship between the GdAl/Ga antisite-defect and crystal composition,and provide a theoretical basis for restraining the defects and improving the crystal properties.