Rare-earth halide scintillators: A DFT-TDDFT-Geant4 study of Rb 2 NdX 5 for gamma detection

Abstract In this study, we investigate the scintillation potential of the rare-earth halide series Rb 2 NdX 5 ( X = Cl , Br , I ) through a synergistic approach combining first-principles density functional theory (DFT), time-dependent DFT (TDDFT), and Geant4 Monte Carlo simulations. Structural, elastic, electronic, and optical properties were systematically analyzed to assess phase stability, mechanical robustness, and electronic band characteristics. All compounds crystallize in the orthorhombic Pnma phase, exhibiting both dynamic and mechanical stability. Halide substitution strongly influences band gaps, optical response, and scintillation relevant metrics. Notably, Rb 2 NdI 5 demonstrates a low band gap (3.06 eV), high refractive index (n = 1.80), short radiative lifetime (4.18 ns), and an exceptional theoretical light yield (131,000 photons/MeV), surpassing benchmarks such as LaBr 3 : Ce . Geant4 simulations confirm enhanced γ -ray energy absorption in the iodide variant due to its higher density and atomic number. These findings position Rb 2 NdX 5 , particularly Rb 2 NdI 5 , as promising candidates for next generation fast response scintillators in high-resolution gamma detection systems.