Controllable Synthesis And Photoluminescence Of Rare Earth Fluoride Nanocrystals Containing Alkaline Earth Ions

Monodisperse rare earth (RE) fluoride nanocrystals with excellent photoluminescence and paramagnetism present great real and potential applications in optical devices, color display, laser anti-counterfeit, solar cell, biolabels and bioimaging et al. It is important and interesting to research deeply the newly RE fluoride nanocrystals, study their growth mechanisms and improve their properties. Especially, the research and development of RE materials is not only of scientific values, but also of strategic values to transform the nation from a wealthy RE resource nation to a wealthy advanced RE science and technology nation.Compared with organic dyes, quantum dots and noble metal nanocrystals in the applications of bioimaging, biolabels and biomacromolecule probes, upconversion nanocrystals possess advantages such as narrow emission peaks, excellent photostability, absence of autofluorescence and low photodamage. Bioimaging includes the intracellular bioimaging and extracellular bioimaging. Ultrasmall nanocrystals have potential applications in the intracellular bioimaging, and can also be applied in extracellular bioimaging and other applications. Other nanocrystals with large size can be applied in extracellular bioimaging and biomacromolecule probes. To satisfy these targets, the first aim centers how to synthesize the nanocrystals which can be applied in these applications. So, the main work of this dissertation focused on the synthesis, the growth mechanisms and the structure and property characterization of monodisperse RE fluoride nanocrystals with different shapes. These nanocrystals were synthesized via solvothermal method with the existence of alkaline earth ions (including Ca2+, Sr2+and Ba2+). The main contents of this dissertation concern the following.(1) A series of xMF2-yLnF3(M=Ba, Sr) monodisperse ultrasmall nanocrystals with the size of sub-10nm (few has the size of sub-20nm) were synthesized with solvothermal method. Their crystalline structures, controllable photoluminescence and paramagnetic property of partial samples were systemically studied. Many types of xMF2-yLnF3nanocrystals with the same size (sub-10nm) present more efficient photoluminescent than NaLnF4nanocrystals. We found the diluted hydrochloric acid can protonate the oleate which capped on the surface of the as-synthesized ultrasmall nanocrystals, and then remove the oleit acid from the surface of the nanocrystals and make the nanocrystals hydrophilic. Further surface modification of these nanocrystals made them have potential applications in bioimaging and biolabels.(2) A series of ultrathin single-crystalline nanoplates with large area, which are of stoichiometric formula BaLn4F14(Ln=Ho, Er, Tm, Yb, Lu, Y) and space group C2/m (12). We had systematically discussed their crystalline structure (including crystalline constants, space group) and their Ostwald ripening with the case of BaLu4F14Intense upconversion can be realized in BaLn4F14(Ln=Yb, Lu, Y) with definitely defined lanthanide doping, which confirms that the series of BaLn4F14are nice host matrix materials for infraredâ†'infrared upconversion luminescence. So, these nanoplates can be applied in the infrared upconversion bioimaging and macromolecule probes. In addition, this type of BaLn4F14nanoplates for their ultrathin and big area structure can be used as building blocks of other composite nano-materials and composite nano-structures.(3) With the existence of Ca2+or Sr2+, a series of NaCeF4and NaLaF4nanocrystals (including nanorods, nanoplates, ultralong nanowires) were synthesized through solvothermal method. The doping of other RE ions with smaller radius than Ce3+and La3+plays an important role in the controllable synthesis of NaCeF4and NaLaF4nanocrystals with different shapes. However, Yb3+and Er3+can not be doped in NaLaF4nanocrystals with high doping concentration for big difference from the radius of La3+. High efficient photoluminescence can be obtained in Tb3+doped NaCeF4and Tb3+/Ce3+codoped NaLaF4nanocrystals under the ultraviolet excitation, so these two types of nanocrystals can also be used in bioimaging and as macromolecule probes.(4) Some special growth mechanisms of nanocrystals were revealed in the synthesis of these fore-mentioned three series of nanocrystals. In fact, the system of oleic acid, alcohol and water are mixed together to form the microemulsion, in which the oleic acid acts as solvent, the alcohol acts as the assistant solvent and the water as solute. We first discussed the growth mechanism of the monodisperse ultrasmall nanocrystals, and then discussed the doping of lanthanide ions with smaller radius facilitating the growth of nanocrystals to a certain size with the case of Ba2LaF7and LaF3nanocrystals. In addition, by taking BaY4F14nanoplates as an example, we had discovered the growth mechanism of that the ultrasmall nanocrystals can be self-assembled into2D array and then annexed together to form the ultrathin (sub-10nm) nanoplates with large area.