Controllable Synthesis And Luminescence Property Of BaLnF₅（Ln=Lu,La,Sc） Upconversion Nanocrystals

Upconversion fluorescence rare earth materials possess unique anti-stokes optical properties. Among these materials, fluorides have great potential application in solid laser, color display, biological medicine. This is because the fluorides possess low phonon energy(<400 cm-1) and high optical and chemical stability. Now, due to the trivalent lanthanide ions doping rare earth fluorides simultaneously have unique optical and magnetic properties, and these materials as bioprobes in bioimaging are studied widely. Nanoparticles as ideal bioprobes in bioimaging, especially in the cell level bioimaging, must have ultra-small size, good uniformity and excellent luminescence property. Therefore, it is important to find a simple method to synthesize nanocrystals with good dispersion and uniformity, tunable morphology and size and excellent upconversion luminescence. In this paper, several ultra-small rare earth fluorides with good monodispersity were controllable synthesized by the solvothermal method. The morphology, size, crystal phase and upconversion luminescence of nanoparticles are tuned by changing the dopant content. The main content listed as follows:1. Ultra-small BaLuF5 nanocrystals with average size of 10 nm were synthesized tunably by solvothermal methods. Under the condition of fixed reaction time and temperature, the size, morphology and luminescence of the Yb3+/Er3+ co-doped BaLuF5 nanoparticles at different contents of Mn2+ were studied. The upconversion spectrogram of Gd3+/Tm3+/Yb3+ co-doped BaLuF5 nanocrystals was measured with changing the ratio of Gd3+ and Tm3+ ions. BaLu F5 nanocrystals with 30% Gd3+ and 1% Tm3+ can emit the strongest near-infrared light.2. A series of ultra-small BaLa F5:Yb3+/Er3+/Mn2+ nanoparticles with good monodispersity were synthesized by hydrothermal methods. The crystal phase, morphology, size and upconversion luminescence of the products with different Mn2+ contents were studied,respectively. Moreover, the luminescence mechanism of the BaLaF5 nanocrystals was studied. The luminescence color of BaLaF5 nanocrystals can be tuned from pure yellow to yellow-green by changing the Mn2+ content.3. A group of Yb3+/Er3+/Mn2+ tri-doped BaScF5 nanocrystals were prepared via the solvothermal methods with the ligand of oleic acid. We studied the influence of the Mn2+ content on the crystal phase, morphology, size and upconversion luminescence of the BaScF5 nanocrystals. When the content of Mn2+ was not more than 10%, the nanocrystals consisted of only small nanoparticles and big nanosheets. By increasing the Mn2+ content, the nanocrystals were mostly pure ultra-small BaScF5 nanoparticles. The nanocrystals with 10% Mn2+ can emit strong red visible lights because some NaMnF3 nanoparticles existed in the nanocrystals.