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 480-520nm). The lead-free all-inorganic cesium copper halide phosphor beta-Cs3Cu2Cl5 shows an interesting cyan-green emission. Herein, a novel synthesis method based on low-temperature evaporation recrystallization is demonstrated. beta-Cs3Cu2Cl5 shows an intense and broad emission band centered at 526nm, a full width at half maximum (FWHM) of 112nm, 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 beta-Cs3Cu2Cl5, BaMgAl10O17:Eu2+ (blue), and (Sr,Ca)AlSiN3:Eu2+ (red) phosphor mixtures by a 365nm UV LED chip, which exhibits a CRI of 96 (R9=83 and R12=93) and a correlated color temperature (CCT) of 4203K. It demonstrates that the cyan-green-emitting beta-Cs3Cu2Cl5 phosphor would be potentially applied in full-spectrum wLEDs for high-quality general lighting.

Automated summary

Phosphor-converted white-light-emitting diodes (pc-wLED) are widely used for general lighting due to their energy-saving, high-efficient, long-lifetime, and environmentally friendly properties. However, achieving full-spectrum wLEDs with super-high color rendering index (CRI) is still a challenge because of the cyan cavity. The lead-free all-inorganic cesium copper halide phosphor beta-Cs3Cu2Cl5 shows a cyan-green emission, and a novel synthesis method based on low-temperature evaporation recrystallization is demonstrated, resulting in a high PLQY of 97.3%. Super-high color rendering wLEDs are created by pumping the phosphor mixtures, showing a CRI of 96 and a CCT of 4203K.