Exploring the Impacts of Zone Refining on the Purification and Optical Band Gap of CsPbBr3 Crystals for Radiation Detection

Multiple cesium lead bromide (CsPbBr3) crystal ingots were produced through synthesis, purification, and zone refining under consistent experimental conditions. The crystals, measuring 15 mm $\times 25$ mm $\times 235$ mm with a mass of 200 g, exhibited a gradient from a transparent, pure tip to a darker, impurity-rich heel. Phase analysis of the synthesized powders and the bulk crystals after zone refining confirmed a pure orthorhombic CsPbBr3 structure. Comparative materials characterization using Scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (SEM/EDX) revealed a reduction in predominant carbon (C) impurity from 11% to 12% in the heels to below 5% in the tips by weight, along with trace amounts of iron (Fe) and silicon (Si). Optical band gap measurements on the ingots with varying crystal quality and impurity content identified a stable average band gap of 2.30 eV via UV-Vis reflectance spectroscopy, closely aligning with theoretical values. The results suggest that band gap energies remain unaffected by variations in carbon impurity levels or crystal quality, underscoring the robustness of CsPbBr3 crystals under the studied conditions. This study demonstrates the potential of the optimized zone refining technique in producing high-purity CsPbBr3 crystals for radiation detection applications.