Near‐Unity Cyan‐Green Emitting Lead‐Free All‐Inorganic Cesium Copper Chloride Phosphors for Full‐Spectrum White Light‐Emitting Diodes

Phosphor‐converted white‐light‐emitting diodes (pc‐wLED) have been widely used for general lighting because of their advantages of energy saving, high efficiency, long lifetime, environmentally friendly, etc. However, it is still a great challenge to obtain full‐spectrum wLEDs with super‐high color rending index (CRI) due to the cyan cavity (a gap between the blue and green emissions in the range of 480–520 nm). The lead‐free all‐inorganic cesium copper halide phosphor β‐Cs3Cu2Cl5 shows an interesting cyan‐green emission. Herein, a novel synthesis method based on low‐temperature evaporation recrystallization is demonstrated. β‐Cs3Cu2Cl5 shows an intense and broad emission band centered at 526 nm, a full width at half maximum (FWHM) of 112 nm, and a photoluminescence quantum yield (PLQY) of 97.3%. The broad‐band cyan‐green emission is assigned to the self‐trapping excitons (STEs) based on the calculation and experimental results. Super‐high color rendering wLEDs can be created by pumping the β‐Cs3Cu2Cl5, BaMgAl10O17:Eu2+ (blue), and (Sr,Ca)AlSiN3:Eu2+ (red) phosphor mixtures by a 365 nm UV LED chip, which exhibits a CRI of 96 (R9 = 83 and R12 = 93) and a correlated color temperature (CCT) of 4203 K. It demonstrates that the cyan‐green‐emitting β‐Cs3Cu2Cl5 phosphor would be potentially applied in full‐spectrum wLEDs for high‐quality general lighting. This work demonstrates a novel method to synthesize the cyan‐green‐emitting β‐Cs3Cu2Cl5 phosphor based on low‐temperature evaporation recrystallization. The phosphor exhibits a near‐unity photoluminescence quantum yield of 97.3% and high stability. Based on this, the phosphor is used to fabricate a white light‐emitting diode with a color rendering index of 96.