High-Entropy Rare-Earth Halide Double Perovskites Convert Compositional Disorder Into Ion-Transport-Stabilized...

The high-entropy halide-perovskite field has expanded rapidly, yet two central chemical questions remain insufficiently understood: how compositional disorder in complex ionic lattices can be converted into predictable, component-differentiated photophysical behavior with tailorable functionality, and what atomistic origin underlies the enhanced environmental robustness. Here we address these questions using entropy-engineered rare-earth halide double-perovskite single crystals, Cs₂Na(Sb, RE)Cl₆ (RE³⁺ = Sc³⁺, Er³⁺, Yb³⁺, and Tm³⁺), as a composition-tunable platform. Near-equiatomic B(III)-site alloying yields a single-phase high-entropy solid solution (ΔS_config ≈ 1.6R), where cations assume complementary, component-specific photophysical functions. The ns²-configured Sb³⁺ centers provide broadband absorption and sensitization, whereas RE³⁺ define orthogonal NIR emissive manifolds. By integrating chemically distinct optical centers within one lattice, compositional disorder is converted from a mere entropy-stabilization motif into a tailorable emissive architecture, producing multipeak NIR emission across ∼850-1600 nm for self-referenced ratiometric sensing. Accelerated aging verifies relatively improved phase and emission stability, while combined DFT and MD analyses provide, a mechanistic, simulation-supported rationalization of high-entropy stabilization in halide double perovskites: configurational entropy thermodynamically disfavors decomposition, whereas suppressed RE³⁺/Cl^- self-diffusion kinetically retards ion-migration-assisted reconstruction and degradation. Together, these results translate role-differentiated emission into stable broadband NIR LEDs, validating entropy engineering for durable perovskite photonics.