Controllable Synthesis And Upconversion Emission Properties Of SrF₂-GdF₃ System Nanocrystals

During past decades, the search for highly emitting and efficient luminescent fluorescent materials has been a hot research field. Rare-earth upconversion nanocrystals?UCNCs? exhibit a unique narrow photoluminescence with high energy when excited by continuous-wave near-infrared light. Among them, lanthanide doped inorganic nanocrystals?NCs? were chosen as one of the major objects for the potential boilogical application because they possess good stability, are free of toxicity and have high upconversion?UC? luminescence properties compared to some organic dyes and semiconductor quantum dots. The special upconversion emission makes UCNCs as promising probes for biomedical imaging with attractive features, such as no auto-fluorescence from biological samples, large penetration depth, tumor-targeted imaging, vascular imaging, cell tracking, and even multifunctional nanoscale carriers for integrated imag ing and therapy. ?-NaYF₄ is considered to be the most important host material due to its highest UC efficiency among all the hosts of UC materials, but the size of ?-NaYF₄ hardly is tuned to sub-10 nm. The smaller crystal size of UCNCs usually means weaker UC emission intensity, so, how to synthesize sub-10 nm UCNCs with intense UC emission for biomedical imaging always be challenging.In the dissertation, The influence of rare-earth ions content on the phase structure, crystal size and morphology of SrF₂-GdF₃ system and upconversion emission properties were studied.The main conclusion listed as follows:1. A series of Sr_1-xGd_xF_2+x nanocrystals were synthesized by solvothermal methods using oleic acid as capping ligands. Under the condition of fixed reaction time and temperature, by changing the molar ratio of reactants, tetragonal phase Sr₂GdF₇ NCs were synthesized. The upconversion emission of pure phase Sr₂GdF₇ nanocrystals were measured.2. The different kinds of capping ligands was used. A series of Sr1-xGdx F2+x NCs were synthesized by solvothermal methods by a hydrothermal method using polyvinyl-pyrrolidone?PVP? as capping ligands. The influence of different kinds of capping ligands on the phase structure, crystal size, morphology and the molar ratio of reactants of SrF₂-GdF₃ system were studied.3. The Yb³⁺/Er³⁺, Yb³⁺/Er³⁺/Tm³⁺ and Yb³⁺/Ho³⁺/Tm³⁺ doped Sr₂GdF₇ materials were synthesized by a hydrothermal method using oleic acid as capping ligands. The influences of different doped rare-earth ions and different concentration of doped rareearth ions on upconversion emission are studied.