Digital technology for growing alkali halide crystals in an argon atmosphere based on the Bridgman method

A process for the purification and growth of alkali halide crystals (AHCs) has been demonstrated using the KCl:Li crystal as a representative example. The experiments were performed on an experimental crystal growth setup manufactured by Across International (USA). The procedure comprised the following sequential stages: (i) establishment of a deep static vacuum ( 10^-3 Pa or 10^-6 Torr) within a quartz reactor containing a quartz ampoule with a raw material; (ii) introduction of high-purity argon at room temperature to a pressure of 0.3–0.5 bar, calculated to reach 1.1–1.3 bar at the melt temperature of the material (770–800°C), in order to suppress the evaporation of aggressive halogen vapors. Crystal growth was conducted in strict accordance with the protocol of the Eurotherm system and the MCGS (Monitor and Control Generated System) human–machine interface (HMI) platform. Owing to this integrated control architecture, a controlled slow-cooling regime of the “superheated” crystal at a rate of 20–30 °C/h was implemented, a capability not previously attainable in comparable crystal growth systems. The newly developed integrated crystal growth system differs fundamentally from conventional designs and does not require: (i) quartz-sealing laboratory facilities for ampoule sealing, since the raw material within the quartz ampoule is maintained under vacuum inside the quartz reactor; (ii) additional water cooling of the installation, as the crystallization center is formed close to the thermal block and ends of the quartz tube are positioned outside the high-temperature zone. In a test regime, X-ray luminescence (XRL) spectra of freshly grown KCl:Li crystals were recorded as a function of lithium ion concentration. The anticipated enhancement of the luminescence light yield was observed, attributed to the recombination assembly of electron–hole pairs within the field of lithium ions. The result constitutes an important parameter for the development of the scientific basis of scintillation detectors.