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 Na 5 K 3 (Li 3 SiO 4 ) 8 :Eu 2+ (N 5 K 3 :Eu 2+ ) phosphor (λ em = 483 nm) with full width at half maximum (FWHM) of only 18 nm is developed from some typical UCr 4 C 4 frameworks phosphors by slightly modifying crystal structure and symmetry. Through controllable regulation of the ratio of Na and K from Na 4 K 4 (Li 3 SiO 4 ) 8 :Eu 2+ (N 4 K 4 :Eu 2+ ) and Na 6 K 2 (Li 3 SiO 4 ) 8 :Eu 2+ (N 6 K 2 :Eu 2+ ) to N 5 K 3 :Eu 2+ , the lattice sites forming shoulder peaks are further squeezed to generate the narrowest cyan emission. Moreover, the N 5 K 3 :Eu 2+ 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.