Crystallographic Engineering to Develop Ultra-Narrow-Band Cyan-Emitting UCr4C4-Type Phosphor for Healthy LED Lighting and Display

Abstract

Narrow-band cyan-emitting materials for white light-emitting diode (wLED) application have shown great potential in increasing the maximum accessible display gamut and improving the color rendering of full-spectrum healthy lighting. However, the discovery of novel narrow-band cyan emitters with excellent luminescence performances remains challenging. Here, an ultra-narrow-band cyan-emitting Na₅K₃(Li₃SiO₄)₈:Eu²⁺ (N₅K₃:Eu²⁺) phosphor (λ_em = 483 nm) with full width at half maximum (FWHM) of only 18 nm is developed from some typical UCr₄C₄ frameworks phosphors by slightly modifying crystal structure and symmetry. Through controllable regulation of the ratio of Na and K from Na₄K₄(Li₃SiO₄)₈:Eu²⁺ (N₄K₄:Eu²⁺) and Na₆K₂(Li₃SiO₄)₈:Eu²⁺ (N₆K₂:Eu²⁺) to N₅K₃:Eu²⁺, the lattice sites forming shoulder peaks are further squeezed to generate the narrowest cyan emission. Moreover, the N₅K₃:Eu²⁺ exhibits low photoluminescence thermal quenching (90%@150 °C) and high internal quantum efficiency (IQE) of 50%. The color rendering index of wLED for full-spectrum health lighting is enhanced from 92 to 94. Using this short-wavelength cyan emission instead of a part of the emission from a blue chip can effectively prevent “blue hazard”. This work provides basic principles for the design of ultra-narrow-band phosphors, thus achieving their applications in the fields of healthy lighting and eye-friendly display.