From blue to cyan emission: Ce³⁺ and Tb³⁺ co-doped silicon phosphate phosphors with high thermal stability

A series of Ca15(PO4)2(SiO4)6:xCe3+,yTb3+ phosphors have been prepared by a high-temperature solid-state reaction. Under the excitation of near-UV with 371 nm wavelength, Ca15(PO4)2(SiO4)6:xCe3+ phosphors exhibit strong blue emission with a broad peak at 432 nm. Based on the photoluminescence of Ca15(PO4)2(SiO4)6:xCe3+ phosphors, the coordination environment around Ce3+ ions and the concentration quenching mechanism are inferred. With the doping of Tb3+ ions into Ca15(PO4)2(SiO4)6:1.33%Ce3+, the luminescence color from blue to cyan can be well tuned. By measuring the luminescence intensity and lifetime of the as-prepared phosphors, it can be judged that there exists an energy transfer from Ce3+ to Tb3+. To achieve white light, the optimal Ca15(PO4)2(SiO4)6:1.33%Ce3+, 9%Tb3+ phosphors are mixed with commercial SrAlSiN3:Eu2+ powders and finally warm white light emission could be obtained. The results show that Ca15(PO4)2(SiO4)6:xCe3+,yTb3+ phosphors have potential applications in warm white light-emitting diodes.