Sb3+-Activated 0D Cs3LuCl6: A Cyan–Green Phosphor with Near-Unity Quantum Yield for Ultrahigh-CRI Full-Spectrum White LEDs

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.