Research On Simultaneous Morphology And Upconversion Fluorescence Of NaYF₄:Yb,Er Crystals Through Alkali Ions Doping

NaYF₄, as the best host material for UC lanthanide ions among these materials, hasbeen explored out with remarkable performance when doped with various lanthanideions.These materials have the advantages of high photochemical stability, sharp emissionbandwidths and long luminescence lifetime. Yb/Er co-doped NaYF₄crystals have beenreported as the most efficient near-infrared to visible upconversion materials. However, theapplications of these materials are still constrained because of their low UC intensities. Inthis paper, different metal ions including K⁺、Li⁺and Mn²⁺ions are doped into theNaYF₄:Yb,Er crystals, and the effects of metal ions on the crystal structure and theupconversion fluorescence emission are systematically investigated. The main contents andresults are as follows:1. The NaYF₄:Yb,Er crystals doped with K⁺ions are synthesized by a facile solvothermalmethod, meanwhile the doping effects on the crystal structure and the upconversionfluorescence emission are investigated in detail. With the dosage of K⁺ions intoNaYF₄:Yb,Er crystals, the crystal structure will not be changed even if K⁺reaches0.85.Furthermore, it is an exciting experimental result that the upconversion emissionintensities of KxNa1-xYF₄:Yb,Er crystals doped with K⁺ions are significantly enhanced.Visible green and red upconversion emissions in K0.7Na0.3YF₄:Yb,Er crystals areseparately enhanced by up to8and7times. Moreover, the lifetime for the dominategreen emitting of K⁺-doped NaYF₄:Yb/Er crystal is longer than that of NaYF₄:Yb/Ercrystal.2. The Li_xNa_1-xYF₄:Yb,Er crystals with different morphologies are synthesized by a facilesolvothermal method, meanwhile the doping effects on the crystal structure and theupconversion fluorescence emission are investigated in detail. When a little dosage ofLi⁺ions is doped, the phase of Li_xNa_1-xYF₄:Yb,Er crystals may keep the hexagonalphase. With increasing in the dosage of Li⁺ions, the crystal phase of Li_xNa_1-xYF₄:Yb,Ercrystals changes gradually from hexagonal β-phase to tetragonal phase. The upconversion emission intensities of Li_xNa_1-xYF₄:Yb,Er crystals are reduced when Li⁺ions are doped into the crystal lattice.3. The NaYF₄:Yb,Er crystals doped with Mn²⁺ions are synthesized by a facilesolvothermal method, meanwhile the doping effects on the crystal structure and theupconversion fluorescence emission are investigated in detail. When a little dosage ofMn²⁺ions is doped, the phase of NaYF₄:Yb,Er crystals may keep the hexagonal phase.With increasing in the dosage of Mn²⁺ions, the crystal structure of samples changesgradually from NaYF₄to NaMn3F10. The doping of Mn²⁺making the upconversionfluorescence color of NaYF₄:Yb,Er crystals convert from green to red, and greencompletely change to red when the doping concentration reaches30%.