Intrinsically Thermally Robust Nanocrystals for High‐Flux Photonics

High-brightness photonic platforms driven at high currents self-heat beyond 400 K; under such conditions, colloidal emitters (II-VI, III-V, I-III-VI₂, group-IV semiconductors, and both leaded and lead-free halide perovskite nanocrystals) typically lose efficiency and drift in color. Extrinsic passivation offers limited thermal gains with trade-offs such as organic-matrix degradation or oxide-shell phonon bottlenecks. Here we establish a lattice-encoded chemical strategy that imparts intrinsic thermal resilience to colloidal nanocrystals via defect-phonon-exciton coupling in a zero-dimensional Sb³⁺-doped Cs₃LnCl₆ lattice. A controlled-ramp synthesis co-modulates site occupancy and defect chemistry, creating rigid, low-phonon [BX₆]^3- octahedra that localize lattice expansion and suppress multiphonon relaxation. Ångström-scale engineered deep traps (∼0.6-1.2 eV) recycle thermally activated carriers, enabling trap-compensated anti-thermal quenching and stabilizing emission through Ln³⁺ 4f cascade coupling. Tunable from deep violet to ultra-narrow green and yellow, these nanocrystals show enhanced photoluminescence at elevated temperatures (Cs₃LnCl₆:Sb³⁺ reaches 160% intensity at ∼410 K while retaining >93% photoluminescence quantum yield). High-power devices retain >90% luminous flux after 50 h at 1.4 A (junction temperature ∼410 K) with <1% chromaticity shift. This work turns thermal robustness from extrinsic protection into intrinsic bonding, providing a molecular design framework for high-flux photonics.