Design of K2SrCa(PO4)2-x(BO3)x:Eu2+ phosphors with full-visible spectrum by crystal structure modification

Abstract

In recent years, much attention has been paid to the development of rare-earth-activated borophosphate phosphors for white light-emitting diodes (LEDs). Herein, Eu2+ single-doped K2SrCa(PO4)2-x (BO3)x white phosphors with full-visible-spectrum continuous emission in the range of 400 nm–720 nm were developed by the modification of the local structure in the crystal. The structural variation resulted from the substitution of (PO4)3- ions by (BO3)3- in host lattice were investigated in detail by X-ray powder diffraction and Fourier transform infrared spectroscopy. Furthermore, the phase structure of sample was also confirmed by the Rietveld method, indicating its Rhombohedral structure with the R-3c space group and the occupation of K and Ca sites by Eu2+ ions, then combined luminescence lifetime decay, revealing insights of site-selective occupation of Eu2+ in the borophosphate white light phosphors. The emission spectra of K2SrCa(PO4)1.4(BO3)0.6:0.05Eu2+ phosphor exhibited full-visible-spectrum continuous emission centered at 455 and 595 nm by adjusting the concentration of the (BO3)3- groups under near ultraviolet excitation at 365 nm. Especially, the WLEDs obtained from the broad-spectrum phosphors showed ultra-high color quality of color rendering index (CRI) values (Ra = 95, R9 = 66, and R13 = 95) and excellent fidelity/gamut index values (Rf = 94 and Rg = 98), which was almost similar to sunlight streaming. The investigation results indicated that the device by using as-prepared K2SrCa(PO4)1.4(BO3)0.6:0.05Eu2+ phosphor could be a potential candidate for full-spectrum lighting.