Site-selective occupation, optical spectrum regulation and photoluminescence property investigation of Eu 2+ -activated blue light-excited yellow-orange emitting phosphors.

We report yellow-orange emitting phosphors Sr 9- x Ca x Mg 1.5 (PO 4 ) 7 :0.05Eu 2+ (SC x MPO:Eu 2+ , x = 0.5-2.5) and Sr 9- y Ba y Mg 1.5 (PO 4 ) 7 :0.05Eu 2+ (SB y MPO:Eu 2+ , y = 0.5-3.0) with broad emission bands (450-800 nm). All these phosphors can be excited efficiently by blue light and n-UV light. Their crystal structure, photoluminescence spectra, fluorescence decay curves and thermal stability were investigated in detail. As doping concentrations of Ca 2+ or Ba 2+ increase, Eu 2+ emitting centers will selectively occupy different Sr 2+ sites, thus leading to the regulation of optical spectra of SC x MPO:Eu 2+ and SB y MPO:Eu 2+ . Accordingly, the emission colors of SC x MPO:Eu 2+ and SB y MPO:Eu 2+ samples can gradually turn from yellow to orange when excited using 460 nm blue light. And the emission colors of a given sample can also be varied under different excitations because there are three kinds of emitting centers in SC x MPO:Eu 2+ and SB y MPO:Eu 2+ . In addition, introducing Ca 2+ and Ba 2+ can enhance the thermal stability of the phosphors obviously, and overall, the thermal stability of SB y MPO:Eu 2+ is better than that of SC x MPO:Eu 2+ . We chose SB 2.5 MPO: z Eu 2+ as an example to further investigate its photoluminescence properties, and found that the optimal doping concentration of Eu 2+ is 0.08, and dipole-quadrupole interaction is dominated in the concentration quenching mechanism. Furthermore, high-quality warm white light can be obtained by two ways: (a) 470 nm blue LED chip + SC 1.5 MPO:Eu 2+ [CCT = 3639 K, R a = 82.21] and (b) 470 nm blue LED chip + SB 2.5 MPO:Eu 2+ and YAG:Ce 3+ [CCT = 4284 K, R a = 86.69]. The excellent performances indicate that SC x MPO:Eu 2+ and SB y MPO:Eu 2+ are attractive candidates for warm WLEDs.