Emission-tunable Sr8.5-mMg2+m(PO4)7:Eu2+/Mn2+ phosphors for multifunctional applications

A series of Sr8.5-mMg2+m(PO4)(7):Eu2+,Mn2+ (m = 0 and +/- 0.5) phosphors were prepared by solid-state reaction. The phase purity, luminescence properties and thermal stability were investigated systematically. Under 365 nm excitation, the Sr8.5-mMg2+m(PO4)(7):Eu2+ exhibits a wide emission band covering from 425 to 850 nm with three main peaks centered at 412, 515 and 625 nm, which are attributed to the 4f(6)5 d(1)-> 4f(7) transitions of Eu2+ in different crystallographic sites. The emission color can be tuned by changing the concentrations of Mg2+, Eu2+ and Mn2+. To obtain white-emitting light, the Eu2+-Mn2+ co-doped samples were designed, in which an energy transfer from Eu2+ to Mn2+ was found. On the other hand, the fluorescence intensity ratio (FIR) technique was utilized in the Eu2+-single-doped sample for optical temperature-sensing. The high absolute and relative sensitivities were achieved. The above investigations indicate that the developed phosphors could show multifunctional applications in white LEDs and optical thermometers.