Tunable emission properties of tri-doped Ca_9LiY_(2/3)(PO_4)_7:Ce~(3+),Tb~(3+),Mn~(2+) phosphors with warm white emitting based on energy transfer

Tri-doped Ca₉LiY_2/3(PO₄)₇:Ce³⁺,Tb³⁺,Mn²⁺ phosphors were prepared by a high-temperature solid state method. Under UV light excitation, Ca₉LiY_2/3(PO₄)₇:Ce³⁺ samples exhibit a broad band ranging from 320 to 500 nm. At 77 K, the emission spectra of Ca₉LiY_2/3(PO₄)₇:Ce³⁺ samples present two obvious emission peaks, indicating that Ce³⁺ ions occupy two different kinds of lattice sites (Ca(1/2) and Ca(3)). As a good sensitizer for Tb³⁺, Ce³⁺ ions in Ca₉LiY_2/3(PO₄)₇ lattice can effectively transfer part of energy to Tb³⁺, and the energy transfer mechanism is determined to be dipole-dipole interaction. Consequently, the emitting color for Ce³⁺ and Tb³⁺ co-doped Ca₉LiY_2/3(PO₄)₇ samples can be tuned from bluish violet to green. In order to further enlarge the emission gamut, Mn²⁺ ions as red emission components were added, forming tri-doped single-phase Ca₉LiY_2/3(PO₄)₇:Ce³⁺,Tb³⁺,Mn²⁺ phosphors. The Ca₉LiY_2/3(PO₄)₇:Ce³⁺,Tb³⁺,Mn²⁺ phosphors exhibit tunable emission properties through controlling the relative doping concentration of Ce³⁺, Tb³⁺ and Mn²⁺. Especially, Ca₉LiY_2/3(PO₄)₇:0.09Ce³⁺,0.12 Tb³⁺, 0.30Mn²⁺ can emit warm white light. The sample shows good thermal stability. At 150 °C, the emission intensity for Ce³⁺ (360 nm), Tb³⁺ (545 nm) and Mn²⁺ (655 nm) decreases to 63%, 69%, and 72% of its initial intensity, respectively. Moreover, the sample obtains good stability after 10 cycles between room temperature and 150 °C.