Sb 3+ ‐Activated 0D Cs 3 LuCl 6 : A Cyan–Green Phosphor with Near‐Unity Quantum Yield for Ultrahigh‐CRI Full‐Spectrum White LEDs

Abstract Overcoming the long‐standing “cyan gap” remains a critical challenge in the development of full‐spectrum white light‐emitting diodes (wLEDs). In this work, a 0D cyan–green‐emitting phosphor, Cs 3 LuCl 6 : Sb 3+ , synthesized via a facile HCl‐assisted solid‐state method is presented. Under 365 nm excitation, Cs 3 LuCl 6 : Sb 3+ exhibits a broad emission band centered at 525 nm with a full width at half maximum (FWHM) of ≈105 nm and an exceptional photoluminescence quantum yield (PLQY) of 99%. Hybrid density functional theory calculations reveal that Sb 3+ incorporation narrows the bandgap from 5.96 to 3.75 eV and induces strong hybridization among Sb 5s, Cl 3p, and Lu 5d orbitals, promoting the formation and radiative recombination of self‐trapped excitons. Temperature‐dependent photoluminescence measurements confirm robust thermal stability, with 82% of the emission intensity retained at 398 K and an activation energy of 0.3488 eV. When integrated with BaMgAl 10 O 17 :Eu 2+ (blue) and K 2 SiF 6 :Mn 4+ (red) on a 365 nm UV LED chip, the fabricated wLEDs achieve a high color rendering index (CRI) of 94 and a correlated color temperature (CCT) of 5565 K. These results establish Cs 3 LuCl 6 : Sb 3+ as a highly promising cyan–green phosphor for full‐spectrum wLEDs.