Controllable Synthesis And Luminescent Properties Of Rare-earth Downconversion Nanophosphors

In recent years, rare-earth downconversion nanophosphors have triggered widespread attention owing to their excellent photoluminescent properties and applications in display, lighting and biomedical fields. However, selecting a mature and universal method that can achieve phase, morphology and size control of rare-earth downconversion nanophosphors has become a new scientific problem. The strategies used for preparation of rare-earth downconversion nanophosphors include thermal decomposition method, hydrothermal method, sol-gel method, co precipitation method, etc. Among them, hydrothermal method and coprecipitation method do not require high temperature and long reaction time. Moreover, it is easier to control phase composition, morphology and size of nanocrystalline via the two methods aforementioned, and which are considered as the mildest and most friendly synthesis methods. As a consequence, this paper is to synthesize rare-earth downconversion nanophosphors with high quality, monodispersity, and uniformed crystalline phase, morphology and size through choosing the suitable lanthanide ions and concentration in certain matrix hosts. And then, systematical investigation towards the photoluminescent characteristics and the corresponding mechanisms has been discussed in detail. The main research contents of this work are as follows:1. A one-step hydrothermal synthesis method has used for fabrication of Tb3+,Dy3+, or Mn2+doped CePO4 downconversion nanophosphors. Due to efficient energy transfer between Ce3+ and Tb3+/Dy3+/Mn2+, the nanophosphors can realize tunable multicolor output and white light emission under the ultraviolet excitation. It is the first time that obtains white light emission using a single doping of Dy3+or Mn2+in CePO4 matrix.2. A typical hydrothermal route has utilized for preparing lanthanide ions(Eu3+,Dy3+, or Tb3+) doped NaCeF4 nanocrystals with monodispersity and hexagonal phase.The photoluminescent properties, including excitation and emission spectra, quantum yields, lifetime decay curves, cathode luminescence curves, and energy transfer mechanisms have been systematically studied. Muticolor tuning and white emission can be obtained by singly tuning doping ions and concentrations. Achievement of white emission via doping Eu3+ in NaCeF4 matrix host is for the first time, providing a simple method for white emission.3. Urchin-like Ce3+/Tb3+co-doped GdPO4 downconversion microspheres with hollow structure have been synthesized using a self-sacrificing template method(one of the co-precipitation method) with some modification. The phase, microstructure,and luminescent nature of the precursor Gd(OH)CO3:Ce3+/Tb3+and the final product of GdPO4:Ce3+/Tb3+ were analyzed and studied in detail. The hollow structure of the products makes it potential in drug delivery and targeting cancer therapy.