Luminescent properties of NaGdF4: Ln3+ (Ln3+ = Ce3+, Tb3+) phosphors

Ln3+ (Ln3+ = Ce3+, Tb3+) single doped and/or co-doped NaGdF4 phosphors have been synthesized through a solid state reaction method under a weak reducing N2/H2 (95/5) atmosphere. The phosphors were characterized by X-ray diffraction (XRD) patterns, room temperature photoluminescence (PL) excitation and emission spectra, and luminescent dynamics decay curves. XRD analysis indicated that the phosphors were in the hexagonal phase and crystallized well. Under Ce3+ 4f-5d 252 nm excitation, the Ce3+ single doped phosphor emitted near ultraviolet light peaking at 398 nm. Under host Gd3+ 275 nm sensitization and direct Tb3+ 4f-4f 380 nm excitation, the Tb3+ single doped NaGdF4 phosphor gave blue and/or green light. Under sensitizer Ce3+ 4f-5d 252 nm and host Gd3+ 4f-4f 275 nm sensitization and direct Tb3+ 4f-4f 380 nm excitation, the Ce3+/Tb3+ co-doped NaGdF4 phosphors had blue and/or green light. With fixed Ce3+ concentrations in the Ce3+/Tb3+ co-doped phosphors, the blue light of Tb3+ became weaker and the green light of Tb3+ became stronger with the increase of Tb3+ concentrations, which was caused by the cross relaxation process 5D3 --> 5D4:7F6 --> F0. The experimental results suggested that the Ce3+/Tb3+ co-doped and Tb3+ single doped NaGdF4 phosphors might be used as blue and/or green light emitting materials.