Ab initio study of alkaline earth thallium chloride perovskites ( ATlCl 3 ; A = Mg , Ca , Sr , Ba ) for advanced scintillator applications

Abstract Thallium-based scintillators remain benchmarks for radiation detection, yet new materials with enhanced stability and performance are needed. Here, we employ density functional theory (DFT) and time-dependent DFT (TDDFT) to investigate the structural, electronic, and optical properties of orthorhombic ATlCl 3 ( A = Mg , Ca , Sr , Ba ) perovskites. Formation energy analysis confirms their thermodynamic stability, with CaTlCl 3 and SrTlCl 3 dynamically stable, MgTlCl 3 slightly unstable, and BaTlCl 3 showing soft phonon modes. Elastic constants reveal systematic softening from Mg to Ba , though all satisfy Born stability criteria. Wide band gaps (4.58–5.28 eV) and high transparency support their suitability as scintillators. Predicted light yields range from 75, 763 to 87, 425 photons/MeV, with MgTlCl 3 performing best. TDDFT calculations yield ultrafast radiative lifetimes (0.65–1.16 ns), highlighting their potential for fast-timing applications. These results position ATlCl 3 perovskites as promising next generation scintillators, linking atomic scale properties to high performance radiation detection.