Synthesis and luminescence enhancement of Eu³⁺/Sm³⁺ co-doped Ca₉Bi(VO₄)₇ phosphor for white-light-emitting diodes

A series of Ca₉Bi(VO₄)₇:Eu³⁺ and Ca₉Bi(VO₄)₇:Eu³⁺, Sm³⁺ red-emitting phosphors were prepared via a citric acid-assisted sol combustion method. X-Ray diffraction profiles illustrated that all the samples were well matched to the rhombohedral crystal structure of pure Ca₉Bi(VO₄)₇ phase with the R3c space group. The excitation spectra showed two effective excitation peaks, which are located near-ultraviolet light (393 nm) and blue light (464 nm) respectively. It can be concluded from the emission spectrum that the strongest emission peak was located at 618 nm at the excitation of 464 nm, which is due to the ⁵D₀→⁷F₂ transition of Eu³⁺. The Eu³⁺/Sm³⁺ co-doped Ca₉Bi(VO₄)₇ sample exhibited stronger emission intensity at 618 nm owing to the energy transfer between Sm³⁺ and Eu³⁺. By analyzing the energy level diagram, the energy transfer process between is Sm³⁺ and Eu³⁺ explained. Moreover, the chromaticity coordinates of Ca₉Bi(VO₄)₇:0.07Eu³⁺, 0.08Sm³⁺ was located near the standard red light region, and it also exhibited higher color purity than the blue-light-excited commercial SrS:Eu²⁺. Under the excitation of blue light, the excellent luminescence properties of Ca₉Bi(VO₄)₇:Eu³⁺, Sm³⁺ makes it a potential red phosphor which can be used in white-light-emitting diodes.