Synthesis and Optical Properties of Eu3+ Doped NaYF4 and KYF4 Micro/Nanocrystals.

Through a hydrothermal method, 1 mol% Eu3+ doped NaYF4 and KYF4 micro/nanocrystals have been synthesized. The materials were characterized by X-ray diffraction (XRD) patterns, field emission scanning electron microscopy (FE-SEM) images, room temperature photoluminescence (PL) excitation and emission spectra, and luminescent dynamic decay curves. The XRD analysis suggested the crystalline structures of the obtained samples. The FE-SEM images indicated the morphology and size of the obtained samples. The PL spectra illustrate the optical properties of Eu3+ in the two samples. Since it is sensitive to the local environment of the ion, the Eu3+ presents different optical properties in the NaYF4 and KYF4 materials.

Synthesis, phase evolution and optical properties of Tb(3+)-doped KF-YbF3 system materials.

KF-YbF3 system materials have been synthesized by a hydrothermal method without any surfactant or template. By controlling the reactant ratios of KF:Yb(3+), the hydrothermal temperature and the pH of the prepared solutions, the final products can evolve among the orthorhombic phase of YbF3, the cubic phase of KYb3F10 and the cubic phase of KYbF4. The X-ray diffraction (XRD) patterns of the samples prove the phase evolution of the final products. The morphologies of the samples were characterized using field emission scanning electron microscopy (FE-SEM) images and the evolution of the morphology is consistent with that of the crystalline phases. The optical properties of Tb(3+) in the samples were characterized by PL excitation and emission spectra, as well as luminescent decay curves.

Synthesis, optical properties, and energy transfer of Ce(3+)/Tb(3+) co-doped MyGdFx (M=Li, Na, K).

Through a solid-state reaction method, the Ce(3+)/Tb(3+) co-doped MyGdFx (M=Li, Na, K; x=3, 4, 6; y=0, 1, 3) system samples have been synthesized by controlling the annealing temperatures and the ratios of raw materials. The samples were characterized by X-ray diffraction (XRD) patterns, photoluminescence (PL) excitation and emission spectra as well as luminescent dynamic decay curves. The experimental results suggest that the LiF is more difficult to react with the prepared material compared that of NaF or KF under similar reaction conditions. The samples crystallized in different crystalline phases. The energy transfer from Ce(3+) to Tb(3+) or Ce(3+) to Gd(3+) to Tb(3+) has been observed in all the samples. The Ce(3+) and Tb(3+) present different optical properties for they are sensitive to the local environment. In addition, the deduced lifetime of Tb(3+)(5)D4→(7)F5 transition decreases in the same system samples with the annealing temperature increasing. The deduced lifetime of Tb(3+)(5)D4→(7)F5 also decreases with the increase of the KF concentration in the KF system samples.

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.