Synthesis And Luminescence Properties Of Rare Earth Borates, Molybdates And Tungstates

In recent years, the designable and controllable synthesis of micro/nano materials withregular morphologies and tunable sizes is one of hot topics in the field of material science,because the properties of the materials are much related with the size, shape, and dimensionality.Therefore, a facile, fast and efficient method is appreciated in the synthesis of micro/nanostructured material in nanomaterial science and engineering. Wet chemical method is easier tocontrol the morphology and composition of the synthetic products. Moreover,microwave-assisted process is a popular way to synthesize inorganic micro/nano structuredmaterials. Compared with the conventional hydrothermal procedure, it has been proved to be afast and green technology with high yields and reproducibility. The microwave dielectric heatingmechanism can heat samples from the inside to the exterior and eliminate the wall effect causedby inverted temperture gradient. Furthermore, it is convenient to combine microwave irradiationwith available liquid synthesis technique, including hydrothemal method, solvothermal method,template synthesis and sol-gel chemistry. Up to now, mocrowave-assisted routes have been usedto synthesize a great deal of inorganic materials such as metallic nanostructures, metal oxide,metal chalcogenides, metal fluoride and metal phosphates. The as-obtained materials havepotential applications in electricity, optics, catalysis and biomedicine. However, we are mostinterested in the microwave-assisted method for the synthesis of the luminescent materials withspecial morphologies and special optical properties. The main contents of the thesis are asfollows:1. Self-assembly of LaBO3:Eu twin microspheres synthesized by a facile hydrothermalprocess and their tunable luminescence properties. The LaBO3:Eu twin microspheres, composedof nanorods with high crystallinity, were synthesized by a facile hydrothermal process. Tunableluminescence property, which was observed by varying the excitation wavelength of the samples,was studied. Near white light can be generated for exciting at³70and390nm. Because of surface defect, the LaBO3twin microspheres present blue emission under the excitationwavelength of³30nm. Our work is a profitable approach to synthsis white light material.2. Microwave synthesis of NaLa(MoO4)2microcrystals and their near-infrared luminescentproperties with lanthanide ion (Er³⁺, Nd³⁺, Yb^3-) doping. The doubled metal molybdateNaLa(MoO4)2microcrystals with various morphologies have been synthesized using microwaveassisted hydrothermal method without any organic additives or surfactants. Its morphology andsize can be tuned by the initial concentrations of the reagents and the reaction temperatures.Remarkably, the morphologies were the rod, the highly branched dendrite, the ellipsoid-like,when the initial concentration of the precursors was increased from0.01to0.05M at180°C;The morphology can be changed from the octahedral bipyramid to the dendrite when the reactiontemperature was increased from100to180°C at the reagents concentration of0.02M. Theluminescent properties of the lanthanide ion (Nd³⁺, Er³⁺, Yb³⁺) doped NaLa(MoO4)2microcrystals were studied, and all of them exhibited strong near-infrared luminescenceemissions.3. Micro-nano self-assembled NaY(WO₄)₂hierarchial dumbbells have been synthesized bya microwave-assisted hydrothermal approach, followed by a heat treatment. The growthmechanism of the precursor has been investigated, it was found that the amount of trisodiumcitrate play a crucial role in the assembly process of the precursor. Under980nm excitation,Yb³⁺/Er³⁺, Yb³⁺/Tm³⁺), and Yb³⁺/Ho³⁺co-doped NaY(WO₄)₂samples exhibit strong green, blue,and yellow emissions, respectively. The luminescence colors of Yb³⁺/Ho³⁺/Tm^3-tri-dopedNaY(WO4)2samples can be tuned from blue through white to yellow by simply adjusting thedoping concentrations of the activator ions under980nm excitation. The tunable luminescencemay potentially applied in fields such as light display systems and multicolor biological labeling.