The Controllable Preparation Of Rare-earth Tungstates And Oxides And The Research Of Optical Properties

In modern chemistry and materials science, the ability to prepare nano-andmicrostructures with well-defined morphology and excellent monodispersity in bulkscale is an essential requirement for applications of materials. It is well know thatthe chemical and physical properties of the materials are related not only to theirchemical composition, but also to their morphology, size and monodispersity.As a class of important luminescent materials, rare earth （RE） ions dopedluminescent materials have received much attention for their wide applications in thefields of solid-state lasers, solar cells, and flat-panel displays. Luminescent materialsbased on alkali rare earth tungstates with the general formula RE₂（WO₄）₃andARE（WO₄）₂and （A represents alkali metal ions; RE represents rare earth ions） haveattracted particular interest since they are good laser crystal materials. In addition,Y₂O₃is a promising alternative host matrix for luminescence, due to its high chemicalstability and phonon energy.In the present work, NaLa（WO₄）₂,Y₂（WO₄）₃and Y₂O₃microcrystals with diversemorphologies, sizes and dimensions have been controllable synthesized by ahydrothermal process and precipitation process, respectively. The luminescentproperties of these samples were systematically investigated. The main works in ourpaper are as follows:（1） We systematically studied the morphologies and architectures of NaLa（WO₄）₂through a mild and manageable hydrothermal method using PVP as the surfactant.The morphology, structure and size of the NaLa（WO₄）₂microcrystals can be tuned ina controlled manner by altering the PVP amount, pH value of the initial solution andthe reaction time. The crystal growth was thoroughly investigated, and the possibleformation mechanism was proposed. We take the as-prepared NaLa（WO₄）₂spindle-like microcrystals as a representation to investigate the down-conversion ofNaLa（WO₄）₂:Ln³⁺（Ln=Eu, Tb） and the up-conversion luminescent properties ofNaLa（WO₄）₂:Yb³⁺/Ln³⁺（Ln=Er, Tm, Ho）. Furthemore, we also systemataciallyinvestigated the dependence of NaLa（WO₄）₂:Tb³⁺luminescence intensity on differentmorphologies, structures and sizes. （2） Yttrium tungstate precursors with novel3D hierarchical architectures assembledfrom nanosheet building blocks were controllable synthesized by a hydrothermalmethod with the assistance of sodium dodecyl benzenesulfonate （SDBS）. Themorphology and dimension of the as-prepared precursors can be effectively tuned byaltering the amounts of organic SDBS and the reaction time, and the possibleformation mechanism was also proposed. After a further heat treatment in air, theemission of Y₂（WO₄）₃:xmol%Eu³⁺microcrystals can be tuned, and the dopingconcentration of Eu³⁺ has been optimized. Furthermore, the up-conversion （UC）luminescence properties as well as the emission mechanisms of Y₂（WO₄）₃:Yb³⁺/Ln³⁺（Ln=Er, Tm, Ho） microcrystals were systematically investigated. Moreover, thedoping concentration of the Yb³⁺has been optimized under fixed concentration of Er³⁺for the UC emission of Y₂（WO₄）₃: x%Yb³⁺/1%Er³⁺（3） We systematically studied the morphologies and structures of Y（OH）₃through afacile and mass production precipitation process using sodium citrate as theshape-control agent. The morphologies and dimensioned evolution for theas-synthesized Y（OH）₃under different reaction conditions have been studied in detail,and a formation mechanism was proposed on the basis of a series of time-dependentexperiments. After a further heat treatment in air, the as-synthesized Y（OH）₃precursor was transformed into Y₂O₃without changing their original morphology. TheUC emission properties of the hexagonal microprisms are investigated. By tuning thedoped Yb³⁺concentrations in Y₂O₃:x%Yb³⁺/1%Ln³⁺（Ln=Er, Tm, Ho）, we canprecisely manipulate the relative emission intensities and the output colors. Inaddition, the dependence of Y₂O₃:1%Yb³⁺/1%Ho³⁺luminescence intensity ondifferent morphologies and sizes have been investigated in detail.