Enhancement of luminescence in Sr9MgK(PO4)7:Eu2+ phosphor by doping Ce3+ ions for white LEDs

Abstract

Sr9MgK(PO4)7:Eu2+ has been reported to be a potential orange-yellow phosphor for UV-based w-LEDs. Sr9MgK(PO4)7:Eu2+ prepared in reducing atmosphere exhibit both broadband emission of Eu2+ and line emission of Eu3+ under UV light excitation. The coexistence of Eu3+ ions in the Sr9MgK(PO4)7:Eu2+ phosphor suppresses the Eu2+ luminescence and largely limits the luminescence performance. In this study, the reduction of Eu3+ to Eu2+ is successfully facilitated via doping Ce3+ ions. The amount of Eu3+ is greatly minimized and the effective number of Eu2+ ions is obviously increased in the crystal lattice. Under the 393 nm radiation excitation, the integrated luminescent intensity of Sr9MgK(PO4)7:0.01Eu2+,0.06Ce3+ is found to be about 163% that of Sr9MgK(PO4)7:0.01Eu2+. The reduction mechanism of Eu3+ to Eu2+ is discussed based on the optical analyses and the incorporation of other optical−inert rare earth ions such as Y3+, La3+, Gd3+, and Lu3+. Therefore, Sr9MgK(PO4)7:Eu2+,Ln3+ (Ln = Ce, Y, La, Gd, Lu) phosphors may have potential application as orange-yellow-emitting phosphors for w-LEDs. The strategy proposed in this work should be also effective for various luminescent materials containing mixed valent Eu2+/Eu3+.