Color-Tunable and White Luminescence Properties via Energy Transfer in Single-Phase KNaCa2(PO4)2:A (A = Ce3+, Eu2+, Tb3+, Mn2+, Sm3+) Phosphors

A series of single-phase phosphors based on KNaCa2(PO4)(2) (KNCP):A (A = Ce3+, Eu2+, Tb3+, Mn2+, Sm3+) have been prepared via the Pechini-type sol-gel method. Photoluminescence (PL) and cathodoluminescence (CL) properties of Ce3+-, Eu2+-, Tb3+-, Mn2+-, and Sm3+-activated KNCP phosphors were investigated. For the A singly doped KNCP samples, they exhibit the characteristic emissions of the A activator. Na+ ions exhibit the best charge compensation result among Li+, Na+, and K+ ions for Ce3+-, Tb3+-, and Sm3+-doped KNCP samples. The energy transfers from Ce3+ to Tb3+ and Mn2+ ions as well as Eu2+ to Tb3+ and Mn2+ have been validated. The emission colors of KNCP:Ce3+/Eu2+, Tb3+/Mn2+, Na+ samples can be adjusted by energy transfer process and changing the Tb3+/Mn2+ concentration. More importantly, white light emission in KNCP:Eu2+, Mn2+ system has been obtained. The KNCP:Tb3+, Na+ sample shows tunable luminescence from blue to cyan and then to green with the change of Tb3+ concentration due to the cross-relaxation from D-5(3) to D-5(4). A white emission can also be realized in the single-phase KNCP host by reasonably adjusting the doping concentrations of Tb3+ and Sm3+ (reddish-orange emission) under low-voltage electron beam excitation. Additionally, the temperature-dependent PL properties of as-prepared phosphors reveal that the KNCP host has good thermal stability. Therefore, the KNCP:A (A = Ce3+, Eu2+, Tb3+, Mn2+, Sm3+) phosphors could be regarded as good candidates for UV W-LEDs and FEDs.