Preparation And Investigation Of Optical Properties Of Rare-earth Fluoride Composite Nanocrystals

Ultrasonically assisted, hydrothermal and solvent thermal were used to prepare a series of rare-earth fluorides nanocrystals. The microstructure and performance of the products were characterized using various modern analytical techniques, while their photics behaviors were evaluated. At the same time, the possible crystal growth mechanisms of the different methods were discussed. The main scopes and results of the thesis are as below.1. Synthesis of CeF₃ nanostructures via ultrasonically assisted route and characterizationA series of disk-like CeF₃ nanocrystals were successfully fabricated using an ultrasonically assisted method. The morphology and crystal structure of the products were investigated with respect to irradiation time, reaction temperature, and quantity of the PVP, based on analyses of transmission electron microscopy (TEM), field emmision scanning electron microscopy (SEM), X-ray powder diffraction (XRD). Moreover, the photoluminescence behavior of the CeF₃ nanocrystals was evaluated. The results show that the shape and size of products are strongly depended on the ultrasonic time and temperature. With the increment of the ultrasonic time, the morphology of the CeF₃ nanocrystals changes from"lantern"particles to uniform disk-like particles. The UV absorp tion peak and the band edge of the CeF₃ nanocrystals exhibit a pronounced blue shift as the size of the particles decreasing; the PL intensity of CeF₃ nanocrystals is related to the crystalline extent.2. Hydrothermal synthesis of CeF₃ and LaF₃:5%Nd³⁺ nanocrystals and characterizationCeF₃ and LaF₃:5%Nd³⁺ nanocrystals with plate-like and perforated morphologies were successfully synthesized via a facile hydrothermal route. The nanocrystals of CeF₃@silica with a strong fluorescence in aqueous solution were also prepared. The effects of fluoride sources on the morphology and microstructure of the nanocrystals were investigated by means of transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM) and powder X-ray diffraction (XRD). Results indicate that the morphology of the rare earth compound nanocrystals can be well tuned by selecting proper fluoride sources. The ultraviolet (UV) absorption peak of the CeF₃ nanocrystals is slightly blue shifted along with the decrease of size. And the photoluminescence (PL) intensity of the CeF₃ nanocrystals is closely related to size and microstructure as well. The disk-like nanocrystals have potential applications in nano-lens and biological fields. Besides, the perforated morphologies nanocrystals have potential application as hydrogen storage materials.3. Solvent thermal synthesis of CeF₃:5%Nd³⁺, LaF₃:5%Nd³⁺ and LaF₃:5%Nd³⁺@SiO₂ nanocrystals and characterizationThe disk-like CeF₃:5%Nd³⁺, hexagonal structure LaF₃:5%Nd³⁺ and silica-coated nanocrystals were synthesized from solvent thermal approach using glycol as solvent and KBF4 as fluoride sources. And the morphology and structure of the products were studied by TEM, HRTEM, XRD. The rare-earth nanocrystals with complex structure were successfully fabricated via surface modification on the core shell structure nanocrystals. The as-formed LaF₃:5%Nd³⁺@SiO₂ nanocrystals were functionalized with amino groups and grafted with glutathione. The application of the resultant amino-functionalized glutathione-grafted composite nanocrystals in biology was primarily investigated.