High-performance narrow-band green-emitting phosphor enabled by substituting Na with Rb

Exploring green phosphors with satisfactory peak position (525-535 nm) and full width at half-maximum (FWHM) to replace the commercial narrow-band green beta-SiAlON:Eu2+ phosphor (lambda(em) = 540 nm, FWHM = 54 nm) is crucial for realizing wide-gamut full-color liquid crystal display (LCD) devices. Here, taking the UCr4C4-type tetragonal phase RbNa3(Li3SiO4)(4):3%Eu2+ (RN3(LSO)(4):Eu2+) blue phosphor as starting model, we substitute Na+ with Rb+ to synthesize a series of Rb1+xNa2.97-x(Li3SiO4)(4):3%Eu2+ (0.1 <= x <= 2.5) (R1+xN2.97-x(LSO)(4):Eu2+) phosphors that exhibit tunable emission from blue to green. We demonstrate that Rb+-substitution triggers tetragonal-to-monoclinic phase transition, making Eu2+ ions enter two new, cuboid-like Rb and Na sites and resultant green emission. With optimized content of Rb+, Rb3Na(Li3SiO4)(4):3%Eu2+ (R3N(LSO)(4):Eu2+) green phosphor not only shows appropriate peak position (similar to 526 nm) and FWHM (similar to 43 nm) compared to beta-SiAlON:Eu2+ phosphor, but also high internal quantum efficiency (IQE) of 90.2% and superior thermal stability (integrated emission intensity at 150 degrees C is 105.7% of room-temperature performance). Using the green R3N(LSO)(4):Eu2+ phosphor, white light-emitting diode prototype shows a wide-color-gamut (111.2% National Television System Committee, NTSC). This work demonstrates that as-prepared green R3N(LSO)(4):Eu2+ phosphor has a potential application in LCD backlight display, and may stimulate more researches on exploring high-performance narrow-band UCr4C4-type phosphors.