Improvement of thermal stability and luminescence in Ca6Ce2Na2(PO4)6F2:Mn2+/Tb3+via the substitution of Ca with Sr/Ba for structural modification

A series of Ca6-x-ySrxBayCe2Na2(PO4)(6)F-2 (CMCNPF, M = Sr2+/Ba2+), CMCNPF:0.1Mn(2+) and CMCNPF:0.1Tb(3+) phosphors were synthesized by a high temperature solid-state method. In order to improve the luminescence properties of the phosphors, Sr2+ and Ba2+, which are in the same main group as Ca2+, are used to partially substitute Ca2+ in the host. The excited state electrons of Ce3+ and Mn2+ are located in the outermost layer of the ions and are easily influenced by the external crystal field. Therefore, when substituted for cations, the emission peaks of Ce3+ and Mn2+ tend to shift, while that of Tb3+ remains unchanged. For the peak shift of Ce3+, this may be considered from the two aspects of nephelauxetic effect and crystal field splitting. However, the low-temperature spectra and lifetimes of the two emission peaks show that the shift of the Ce3+ emission peak is only influenced by the Ca-1 lattice. In addition, the blueshift of the luminescence center Mn2+ is influenced by the average bond length of the polyhedron and the symmetry of the polyhedron. Regulating the composition of the cations can improve the symmetry of the polyhedron occupied by the luminescence center, increase the rigidity of the crystal structure, and improve the thermal stability of the luminescence center to a certain extent.

Automated summary

A series of phosphors with different compositions were synthesized in this study to investigate the influence of partially substituting Ca2+ with Sr2+ and Ba2+. The shift of emission peaks of Ce3+, Mn2+, and Tb3+ were explained, with the significant impact of the Ca-1 lattice on the shift of the Ce3+ emission peak being discovered.