Photoluminescence tuning of Ca8-xSrxMgGd(PO4)7:Eu2+,yMn2+ phosphors for applications in white LEDs with excellent color rendering index

Abstract

Two series of novel phosphors of green-yellow emitting Ca8-xSrxMgGd(PO4)7:Eu2+ and yellow-orange emitting Sr8MgGd(PO4)7:Eu2+,yMn2+ were successfully synthesized by a solid-state reaction. The crystal structures, photoluminescence (PL), PL excitation (PLE) spectra and decay times were investigated in detail. Upon excitation at 350 nm, the Ca4Sr4MgGd(PO4)7:Eu2+ phosphor showed strong green emission centered at 513 nm, and the Sr8MgGd(PO4)7:Eu2+ phosphor showed strong yellow emission centered at 513 nm and 593 nm, and Sr8MgGd(PO4)7:Eu2+,Mn2+ showed strong orange emission centered at 510 nm and 616 nm. In addition, a standard warm white-light emitting single-phased phosphor of Sr8MgGd(PO4)7:Eu2+,Mn2+ with chromaticity coordinates (x, y), correlated color temperature (CCT) and Commission Internationale de l'Eclairage (CIE) coordinates of (0.4497, 0.3929), 2705 K, and 89.7 was realized via energy transfer between Eu2+ and Mn2+. The energy transfer was demonstrated to be a resonant type dipole-quadrupole mechanism. Moreover, the obtained LED device exhibits an excellent color-rendering index (Ra = 97) at a correlated color temperature of 5651 K with the CIE coordinates (0.3290, 0.3410).