Flux growth of Cs_1-xRb_xBF₃ (B = Ca, Sr) crystals by the micro-pulling-down method

The possibility of growing Cs_1-xRb_xBF₃ (B = Ca, Sr) crystals by micro-pulling-down was investigated due to their potential for application in ultrafast scintillation detectors. A LiF flux was applied to lower the melting point and therefore suppress evaporation of CsF from the melt. Suitable growth conditions were obtained through careful choice of the hot zone elements. A crucible with minimal nozzle length improved mass transport and an afterheater with four windows provided a steep temperature gradient. Inclusion and crack-free crystals of Cs_1-xRb_xCaF₃ (x = 0, 0.1, 0.25, 0.5, 0.75, 0.9, and 1) and CsCa_1-xSr_xF₃ (x = 0, 0.1, and 0.25) were grown under optimized conditions. Despite the hygroscopic nature of the heavy alkali metal fluorides, all the grown crystals are non-hygroscopic which significantly improves their application potential. Growth of CsCa_1-xSr_xF₃ crystals with higher Sr concentration was complicated by the low solubility of SrF₂ in the LiF-CsF melt and the hygroscopic nature of the CsSrF₃. The formation of solid solution in the Cs_1-xRb_xCaF₃ and CsCa_1-xSr_xF₃ systems was investigated through the dependence of lattice parameters on nominal composition.