双读出量能器用硅酸铋闪烁晶体生长与性能优化研究

The dual-readout calorimeter is a new designed equipment to detect high-energy particles. The Cherenkov light and scintillation light can be detected at the same time and a comprehensive information of high-energy particles is collected. Up to now, traditional Cherenkov materials and scintillators are unable to meet the requirements of the calorimeter. Bi4Si3O12 (BSO) crystal was one of the most promising candidates due to its small cut-off wavelength and moderate decay time. However, it is difficult to grow BSO crystal and little knowledge on fluorescence mechanism of BSO crystal was reported. In this project, pure and doped BSO crystals are grown by the vertical Bridgman method and the crystallization behavior is modified by adding a small amount of GeO2 in the melt. The fluorescence mechanism will be discussed and ion dopants will be optimized by the first principle theory. By ion doping, the absorption edge and the intensity of Cherenkov light are improved, thus the scintillation light and Cherenkov light can be separated effectively. Doped BSO crystal will be developed finally to meet the requirement of the dual-readout calorimeter.

双读出量能器是一种全新设计的高能粒子探测装置，它能同时收集到激活介质发出的Cherenkov光和闪烁光并实现有效分离，从而获得高能粒子的更全面信息。现有Cherenkov辐射体和闪烁体都无法满足这种设计的要求。Bi4Si3O12（BSO）晶体因为较短的吸收边和适中的衰减时间被认为是最有潜力的候选材料。但BSO晶体生长难度大，离子掺杂对发光影响的研究很少。本项目在已有研究基础上采用坩埚下降法生长掺杂BSO晶体，通过添加少量GeO2来抑制组分偏析；探讨掺杂对BSO晶体发光机制的影响，通过理论计算优选掺杂离子；利用离子掺杂来调节晶体的吸收边，提高Cherenkov光发光效果，实现与闪烁光的有效分离；最终解决BSO晶体Cherenkov光弱、光输出较低、信号有效分离难等问题，推进BSO晶体的双读出应用。

Bi4Si3O12（BSO）晶体具有较短的吸收边、较快的衰减时间和适中的光输出，被认为是双读出量能器等应用的最佳候选材料。但BSO晶体生长难度大，离子掺杂对发光的影响研究还比较少。本项目研究了Sm、Yb、Ho、Gd、Tb、Eu、Tm、Dy、Ce等稀土掺杂BSO晶体的下降法生长，系统测试了这些晶体的发光特性和闪烁性能，发现Ce掺杂可将BSO晶体吸收边红移40nm，而Dy掺杂则可显著提高BSO晶体的光产额，最多比纯BSO晶体高出50%。研究还发现，少量Dy掺杂对BSO晶体闪烁发光起到敏化作用，超过0.1mol%的Dy掺杂会与Bi发光产生竞争，降低晶体的光输出。稀土掺杂还能有效抑制组分偏析，有利于晶体生长。此外，高浓度稀土掺杂BSO晶体还可作为荧光材料用于大功率LED照明。