新型闪烁晶体Gd2Si2O7:Ce的结晶行为、制备及性能研究

Cerium doped gadolinium pyrosilicate (Gd2Si2O7:Ce,GPS:Ce) crystal has been a novel and promising scintillation crystal in recent years. GPS:Ce scintillator exhibits the desired qualities such as high light output, high density, fast decay time outstanding high temperature scintillation performance and non-hygroscopic, which would be widely used for nuclear medical imaging, security inspection and well logging. However, the GPS material melts incongruently, leading to the difficulty of crystal growth and the systematic research on the relationship between defects and scintillation performance is insufficient. Through slow cooling floating zone and quenching method, combined with first-principle thermodynamics calculation, this project intends to carry out the crystallization behavior research, reveal impact factors of component doping on Gd2O3-SiO2 phase diagram structure and mechanism of crystallization behavior, and to guide the component design; stabilize crystallization process through optimizing the craft of crystal growth and after treatment to obtain high performance GPS:Ce scintillation crystal under the premise of ensuring the scintillation properties; reveal the kinds of defects, formation reason and its impact mechanism on scintillation performance. Implement of this project could contribute to clarify the inner relationship between constitution and phase diagram structure, reveal the impact mechanism of defects on scintillation performance, develop the design theory of inorganic scintillation crystal, and promote the application development and growth theory of GPS:Ce crystal directly.

铈掺杂焦硅酸钆(Gd2Si2O7:Ce,GPS:Ce)晶体是近年发现的一种新型高性能闪烁晶体。它具有光输出高、衰减快、高温闪烁性能优异、不潮解等优点，可望在核医学成像、安全检查及油井勘测等领域获得广泛应用。但该晶体非一致熔融，造成制备困难，而且其缺陷和闪烁性能之间的关系缺乏系统的研究。本项目拟通过缓冷浮区法、淬冷法，结合第一性原理热力学计算，研究GPS:Ce体系结晶行为，揭示组分掺杂对Gd2O3-SiO2相图结构的影响和内在原因，进而指导组分设计；在确保闪烁性能的前提下，通过组分调整稳定GPS:Ce结晶过程，通过生长和后处理工艺优化，制备出高性能GPS:Ce晶体；进而揭示缺陷种类、形成原因及其对闪烁性能的影响机理。项目的开展有助于阐明该体系组分掺杂与相图结构和结晶行为与的内在关系，揭示缺陷对闪烁性能的影响机理，丰富和发展无机闪烁晶体的结构设计理论，直接推动GPS:Ce的晶体生长及开发应用。

本项目围绕一种高性能闪烁晶体铈掺杂焦硅酸钆(Gd2Si2O7:Ce,GPS:Ce)晶体制备和闪烁性能的研究展开，针对焦硅酸钆的非一致熔融特性，研究了Gd2Si2O7-Ce2Si2O7、Gd2Si2O7-Y2Si2O7、Gd2Si2O7-Lu2Si2O7和Gd2Si2O7-La2Si2O7体系，对比固相烧结和获得晶体的物相，考察体系的相关系和结晶行为。通过研究获得多晶或单晶材料的光学和闪烁性能，包括透过谱，荧光激发发射谱，X射线激发发射谱，多道能谱等，研究系统中的Gd→Ce能量传递过程，优化体系的闪烁性能。.通过固相烧结方法获得了Gd2Si2O7-Ce2Si2O7体系多晶样品，通过光学浮区法和提拉法获得体系单晶样品。确定固相烧结合成GPS样品的路径为Gd2O3+SiO2→ GSAP(apatite)→GPS(orthorhombic)，合成条件为1600 ℃烧结8 h。GPS–CPS体系呈现3种不同的结构：正交–三斜–单斜。Ce掺杂量为8.00%以下为正交结构；8.00%~10.00%为正交和三斜两相共存区，不适合晶体的生长。分别通过浮区法和提拉法获得了GPS:Ce不同铈掺杂浓度单晶样品，其结构都为正交结构，表明在结晶和降温过程中，未发生相变或包晶反应。Gd→Ce能量传递会导致闪烁发光的慢分量。通过固相烧结方法获得了Ce掺杂的Gd2Si2O7-Y2Si2O7体系多晶样品，通过光学浮区法获得单晶样品。确定闪烁性能最优的组分为(Gd0.5Y0.5)2Si2O7:Ce。在Y/Y+Gd为0~0.7范围内，体系为连续固溶体，且晶体制备过程中，并未发生相变或包晶反应。系列样品发光过程中的慢分量来自Gd→Ce的非辐射能量传递。随着Y含量的增加，313nm处的Gd3+的6P7/2→8S7/2的跃迁发光显现，并逐渐增加。通过光学浮区法系统制备了Ce掺杂Gd2Si2O7-Lu2Si2O7混晶体系，表明在Lu/Lu+Gd为0~0.5浓度范围，体系可以形成固溶体，并且在晶体生长过程中，并未发现相变或包晶反应。系列晶体的基本光学和闪烁性能进行了表征，体系的发光峰位位于370nm，在样品的荧光和闪烁过程中存在Gd→Ce的声子辅助的非辐射能量传递过程，导致样品的3500ns的慢分量出现，且含量较高，需通过提高Ce浓度来加以改善，其Lu/Gd混晶比例对能量传递和闪烁性能的影响有待进一步研究。