Intrinsically Thermally Robust Nanocrystals for High‐Flux Photonics

ABSTRACT High‐brightness photonic platforms driven at high currents self‐heat beyond 400 K; under such conditions, colloidal emitters (II–VI, III–V, I–III–VI 2 , 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 Sb 3+ ‐doped Cs 3 LnCl 6 lattice. A controlled‐ramp synthesis co‐modulates site occupancy and defect chemistry, creating rigid, low‐phonon [BX 6 ] 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 Ln 3+ 4f cascade coupling. Tunable from deep violet to ultra‐narrow green and yellow, these nanocrystals show enhanced photoluminescence at elevated temperatures (Cs 3 LnCl 6 :Sb 3+ 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.