White Light Emission and Energy Transfer in CaHf₄(PO₄)₆: Ce³⁺, Dy³⁺

For the first time, a series of Ce³⁺/Dy³⁺ single-doped and co-doped orthophosphate CaHf₄(PO₄)₆ (CHPO) samples were produced by solid-state reaction technique in a carbon reduction environment. The morphology, crystal structure, photoluminescence characteristics, and energy transfer between ions were investigated. The crystal structure was confirmed to be a diamond-shaped NASICON-type structure of the R3c space group. By investigating the photoluminescence emission and excitation spectra of the samples, we have verified the existence of the energy transfer from Ce³⁺ to Dy³⁺. The energy transfer efficiency was calculated and the mechanism was determined as dipole-quadrupole interaction. Temperature-dependent photoluminescence experiments confirmed the good thermal stability of the samples. By adjusting the concentration ratio of Ce³⁺ and Dy³⁺ under UV illumination, tunable emission from blue-purple to yellow-white could well be achieved. The CIE coordinate of the 4% Ce³⁺ and 4% Dy³⁺ co-doped sample is (0.291,0.308), i.e., blue-white color. It is suggesting that CHPO: Ce³⁺, Dy³⁺ could be interesting candidate materials in the applications of ultraviolet-excited WLEDs.