A Facile-Synthesized Cyan-Emitting Copper(I) Halide Hybrid Phosphor for 410 nm-Driven pc-WLEDs

The lack of efficient cyan phosphors (470–510 nm) activated by 410 nm LED chips poses a significant challenge in realizing full-spectrum and healthy lighting. In this work, a novel cyan-emitting organic–inorganic copper(I) halide hybrid phosphor, CuI(mmt-pz) (mmt-pz = 2-methyl-3-(methylthio)pyrazine), is facilely synthesized using CuI and a pyrazine derivative. This phosphor has a relatively wide cyan emission band at around 450–650 nm, a photoluminescent quantum yield (PLQY) of 36.6% under 425 nm excitation, and an external quantum yield (EQY) of 27.8%. The study of the luminescent mechanism reveals that its luminescence involves a thermally activated delayed fluorescence (TADF) process. When applied to phosphor-converted white LEDs (pc-WLEDs), CuI(mmt-pz) effectively bridges the cyan gap, enhancing the color rendering index (CRI) from 89.0 to 93.9 and even up to 95.2. This work presents a promising cyan phosphor with great application potential in high-quality, full-spectrum lighting.