Tackling Single Crystal Growth Challenges for Mixed-Elpasolite Scintillators

The rising demand for efficient radiation detectors in various applications has led to intense research on single crystal scintillators. The scintillation performance strongly depends on the as-grown crystal quality. Mixed-anion elpasolite single crystals with Ce-doping such as Cs2NaREBr3I3 (RE = La, Y) are among the most promising candidates as next generation scintillators. However, there are multiple challenges to traditional single crystal synthesis using melt freeze growth techniques due to the complicated composition, as well as impurities, and varying thermal behavior of the starting materials. To improve the as-grown single crystal quality and optimize their scintillation properties, a series of investigations on material treatment and synthesis, ampule design, and crystal growth parameters were conducted. Effective purification of the carbon- and oxygen-based impurities improved the optical transmittance of the crystal. Differential scanning calorimetry and thermal gravimetric analysis results revealed the thermal instability of the compounds upon heating above the melting temperature. Multiple cycles of heating-soaking-cooling synthesis were applied, which significantly increased the completeness of chemical reactions. Improvements of the scintillation light yield and energy resolution of Ce-doped Cs2NaLaBr3I3 and Cs2NaYBr3I3 were achieved. Our results led to a better understanding of the crystal growth of mixed-anion elpasolites, as well as the optimization of techniques to engineer metal halide crystals in the future.