Abstract
Phosphor-converted white LEDs rely on combining a blue-emitting InGaN chip with yellow and red-emitting luminescent materials. The discovery of cyan-emitting (470–500 nm) phosphors is a challenge to compensate for the spectral gap and produce full-spectrum white light. Na0.5K0.5Li3SiO4:Eu2+ (NKLSO:Eu2+) phosphor was developed with impressive properties, providing cyan emission at 486 nm with a narrow full width at half maximum (FWHM) of only 20.7 nm, and good thermal stability with an integrated emission loss of only 7% at 150 °C. The ultra-narrow-band cyan emission results from the high-symmetry cation sites, leading to almost ideal cubic coordination for UCr4C4-type compounds. NKLSO:Eu2+ phosphor allows the valley between the blue and yellow emission peaks in the white LED device to be filled, and the color-rendering index can be enhanced from 86 to 95.2, suggesting great applications in full-spectrum white LEDs.
Highlights
White light-emitting diodes (LEDs) have been successfully used in solid-state lighting or backlight units for liquid crystal displays due to their high efficiency, tunable color, durability, long lifetime, energy saving, and environmental friendliness[1,2,3]
It is found that the first cation is fully occupied by K+ ions, the second site is intermixed K/Na with a ratio of 0.67/0.33, and the third site is fully occupied by Na+ ions (Fig. 1b)
The as-obtained structural parameters were stable with low R-factors (Supplementary Fig. S1a and Supplementary Table S1)
Summary
White light-emitting diodes (LEDs) have been successfully used in solid-state lighting or backlight units for liquid crystal displays due to their high efficiency, tunable color, durability, long lifetime, energy saving, and environmental friendliness[1,2,3]. After the discovery of highly efficient red-emitting phosphors, such as CaAlSiN3:Eu2+, Sr2Si5N8:Eu2+, K2SiF6: Mn4+, or SrLiAl3N4:Eu2+, the Ra values can be enhanced to ~907–11. Some solid solution phosphors with multiple emission centers have been discovered to improve the Ra values[11,12]. There is still a challenge in enhanced color rendition because of the cyan gap between blue and yellow emission in the 470–500 nm region, which is not suitable for high-quality general lighting. It is of fundamental importance to develop a novel phosphor emitting in this spectral region for filling the valley between the blue and yellow emission peaks in a white LED device. The development of narrow-band cyan-emitting phosphors excited by blue light with a small Stokes shift is necessary for improving the optical performance of pc-LEDs13
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