Controllable Synthesis, Paramagnetic And Photoluminescence Properties Of Upconversion Nanocrystals

Interests in rare earth ion doped fluoride nanocrystals (NCs) have been increasingdue to their unique upconversion (UC) properties and potential applications in thefields of three-dimensional three-dimensional displays, solar cells, biological labels,laser security and photocatalyst.Especially for the application in biological labels,compared with traditional semiconductor quantum dot excitated by UV, rare earthfluoride NCs have the advantage of low toxicity, penetration ability, photochemicalstability, ect. In addition, due to intrinsic paramagnetism of rare earth ion, this kind ofnanocrystals have optical/magnetic multifunctional properties and will realizeoptical–magnetic dual-modal biomedical imaging and improve the imaging resolutionwhen it be used as biological labels. Hence it is very important to prepared size, shape,and property-tunable rare earth ion doped fluoride nanocrystals. On the basis of ourprevious stdudis, in this thesis, we achieved some results on controllable synthesis,paramagnetic and photoluminescence properties of rare earth doped UC nanocrystals.The main content are described as follows:1. Controlable synthesis of hexagonal NaLnF4(Ln=Y, Gd, Yb) nanocrystals isrealized via in situ cation-exchange reaction using a hydrothermal method. By simplyadjusting the Na+concentrations, the crystal phase and size of hexagonal NaLnF4withuniform composition can be effectively controlled and hexagonal NaLnF4nanocrystals with tunable size from100to10nm is obtained. A seriers of experimentsare designed to investigate the growth mechanism and it is found that during the insitu cation exchange, the stable hexagonal NaLnF4particles serving as the seed nucleiplay a key role in the final crystal phase and size of the NCs The in situ cationexchange approach provides not only valuable insights into the growth dynamics ofLn3+doping-induced size tuning and phase transformation in NaYF4, but also amethod to prepare high-quality multifunctional NaLnF4NCs with tunableparamagnetism and multi-color upconversion emission.2. Magnetic Ln3+(Ln3+=Yb3+/Er3+, Yb3+/Tm3+, Yb3+/Ho3+and Yb3+/Er3+/Tm3+)doped NaGdF4nanocrystals are synthesized by a thermal decomposition method.Watere-soluble nanocrystals is obtained after the removing of OA on the surface ofNaGdF4by acid treatment. Enhanced multi-color upconversion emissions as preparednanocrystals by acid treatment are observed under the excitation of a980nm laser diode. In addition, white upconversion emission is realized by adjusting different Ln3+doping cencertrations.