Crystal Growth and Optimization of Cs₂LiLaBr₆Scintillator via the Cs₂LaBr₅-LiBr Phase Diagram Construction

Gamma/neutron dual detection has occupied significant territory in the field of homeland security and nuclear energy development. Cs2LiLaBr6 (CLLB) has shown both neutron/gamma dual-mode detection capability and excellent scintillation properties. Herein, we explored the Cs2LaBr5-LiBr phase diagram through powder X-ray diffraction (XRD) and differential scanning calorimetry (DSC) tests of synthesized polycrystalline materials. The Cs2LaBr5-rich side of the phase diagram is similar to a binary peritectic phase diagram, where the peritectic line (447 °C) extends to a LiBr content of 61%. The LiBr-rich side of the phase diagram resembles a binary eutectic phase diagram, where the eutectic point (395 °C) is located at 80% LiBr concentration. Guided by the phase diagram, CLLB ingots were designed to grow from the LiBr-rich side with different concentrations of LiBr. The scintillator properties of CLLB crystals were found to be deteriorated by the increasing defects with elevated LiBr contents. A concentration of LiBr around 55% was a preference for the growth of high-quality CLLB. A better understanding of the Cs2LaBr5-LiBr phase diagram benefits the growth of CLLB crystals and provides considerations for other halide double perovskites.