Eco-friendly cryolite-type Cs₃CeI₆ halide: DFT+U insights into optoelectronic properties and defect-modulated...

Eco-friendly rare-earth halide luminescent materials have emerged as promising candidates for deep-blue light-emitting devices, yet severe intrinsic luminescence quenching induced by intrinsic point defects severely limits their photoluminescence quantum yield (PLQY). In this work, we systematically investigate the optoelectronic properties, defect behavior, and carrier recombination mechanism of cryolite-type Cs₃CeI₆via first-principles calculations. The orbital composition of the valence band and conduction band of perfect Cs₃CeI₆ is analyzed, and the intrinsic radiative limitation originating from the low Γ-point transition probability and parity-forbidden I 5p → Ce 4f transitions is clarified, which inherently results in weak deep-blue emission. We further calculate the formation energies and charge transition energy levels of typical intrinsic point defects including V_Cs and V_I. The results reveal that V_Cs defects act as detrimental deep acceptor traps within the bandgap, which can simultaneously capture photogenerated electrons and holes and may serve as a potential source of nonradiative recombination and PLQY degradation. The density of deep quenching traps can be precisely regulated by tuning precursor chemical potentials: I-rich/Cs-poor growth environments reduce the formation energy of V_Cs and promote trap aggregation, while Cs-rich conditions effectively suppress the generation of V_Cs defects. Experimentally observed PLQY enhancement after CsI passivation is consistent with the interpretation that passivation suppresses nonradiative channels associated with V_Cs defects, thereby allowing photogenerated carriers to recombine through the parity-permitted Ce 5d → Ce 4f channel and significantly boost deep-blue luminescence efficiency. This work establishes a complete atomic-scale structure-defect-luminescence correlation for Cs₃CeI₆ halides, providing fundamental theoretical guidance for optimizing precursor stoichiometry and developing efficient defect passivation strategies to fabricate high-performance, stable rare-earth halide deep-blue emitters.