Fluorescence Regulation Based On YF₃:RE³⁺ Submicron Crystals

Lanthanide doped luminescent fluoride materials with high chemical stability, high quantum yield, low toxicity, low phonon energy, long luminescence lifetime, narrow band emission have drawn enormous attention due to their wide application in various fields of modern science such as solid state lasers, solar cells, photoswitching, fluorescent labels, and phosphors. Therefore, the research of preparation of lanthanide doped luminescent fluoride materials with high luminescence efficiency and improving the quantum yield of as-prepared lanthanide doped luminescent fluoride materials have far-reaching significance. So far, the main approach to enhance the fluorescence emission intensity of the rare earth ions includes multi-ion co-doping, matrix transformation, introducing noble metal nanostructure. YF₃ is usually emphasized as a fluorescence host due to its efficient light emissions and higher yttric content in the earth's crust. In this thesis, YF₃ was chosen as matrix and a facial wet-chemical method was employed to synthesize YF₃:RE³⁺ submicrocrystals and Au@YF₃:RE³⁺ submicrostructures. The downconversion luminescence emission enhancement of Eu³⁺ ion and upconversion luminescence emission enhancement of Ho³⁺ ion were realized separately via matrix transformation and introducing noble metal nanostructures.The main work of this thesis is concluded as follows:In the first part, the YF₃:Eu³⁺ submicrocrystals were prepared by a facile co-precipitation method. The effect of fluoride source and calcination temperature on the morphology and luminescence properties of YF₃:Eu+ were investigated systematically. It was found that the sample morphology was different via using different fluoride source and the crystallinity influenced the luminescent property significantly. With increase of calcination temperature from 400? to 1000?, the luminescence intensity of the samples increased rapidly. Meanwhile, both the samples with different morphologies underwent an obvious matrix transformation from yttrium fluoride to yttrium oxide fluoride, and then to yttrium oxide after a calcination treatment. Besides, the local symmetry of the optically active Eu³⁺ ions decreased with increase of the calcination temperature at the lower calcination temperature region, and then kept almost unchanged when the temperature was over 700?.In the second part, bundle-like YF₃:RE³⁺ ?RE=Yb,Ho/Eu? submicrocrystals and Au@YF₃:RE³⁺?RE=Yb,Ho/Eu? submicrostructures were prepared by a facile wet-chemical method. The influence of Au nanoparticles on luminescence properties of YF₃:RE³⁺ submicrostructures were studied systematically. It was found that the upconversion luminescence emission was enhanced while downconversion luminescence emission was quenched via introducing Au nanoparticles. Under unsaturated excitation condition, enhanced upconversion red and green luminescence emission of Ho³⁺ were obtained and the enhancement factors were almost the same. However, the enhancement factor of green emission was larger than that of red emission under high pump power excitation condition. The upconversion emission enhancement could be attributed to the strong local electromagnetic field enhancement. The better overlap between the 5S2/5F4?5Ig emission transitions and the plasmonic absorption band of Au nanoparticles resulted in a greater intensity increase at higher power excitation. The decreased enhancement factor of the red emission could be resulted from the excitation saturation effect. After introducing Au nanoparticles into the system, the downconversion luminescence emission was quenched for the luminescence enhancement caused by the additional local field could not make up the luminescence quench arised from nonradiative energy transfer process under the excitation of 532 nm as well as the local inversion symmetry decreased.