Fabrication And Characteristics Of Rare Earth Compounds Micro/Nanostructures With Special Morphologies

Rare earth compounds have great significance in many fields,such as display devices,rubbers,luminescent probes,and optical imaging.Rare earth ion doped compounds have become the mainstream phosphors of research and application in the field of luminescence due to their excellent luminescent properties.Thereinto,down-conversion luminescence materials are widely used for the production of phosphor-converted white light emitting diodes?LEDs?.Because excellent morphology and controllable size can equip micro/nanostructure materials with special chemical,physical,and luminescent properties,the preparation techniques of rare earth luminescent materials with special morphology have become important subject of study.In this thesis,we focused our attention on the preparation and luminescent properties of several rare earth luminescent materials.1.Special morphological La₂O₂CN₂ samples with uniform rod-like,umbrella-like,cauliflower-like and mushroom-like microarchitectures have been successfully synthesized by combining a simple hydrothermal route with cyanamidation technology.The morphological regulation of the products is realized via simply adjusting a series of experimental parameters including amount of sodium citrate,reaction temperature,and pH value of the initial solution.Simultaneously,the growth mechanisms of different morphologies have been proposed.Under ultraviolet light excitation,the mushroom-like La₂O₂CN₂:RE³⁺?RE=Eu,Dy,Tb,Tm?samples exhibit downconversion emissions showing different fluorescent colors.Additionally,upon 980 nm laser excitation,La₂O₂CN₂:Yb³⁺/Er³⁺phosphors have strong upconversion emissions.Therefore,as-synthesized La₂O₂CN₂:RE³⁺samples have potential applications in fluorescent lamps,field emission displays,biological labeling,and catalysis.2.A set of 3D umbrella-like LaOCl:Tm³⁺,Eu³⁺phosphors was synthesized via a facile hydrothermal method and subsequent chlorination process.The energy transfer between Tm³⁺and Eu³⁺ions was observed in LaOCl:Tm³⁺,Eu³⁺system.The mechanism of energy transfer from Tm³⁺to Eu³⁺was discussed in detail.Under ultraviolet light excitation at 229nm,a relatively large range of adjustable white light emission can be obtained due to the energy transfer from Tm³⁺to Eu³⁺.The finding clarifies these materials as promising for potential application in near ultraviolet based white light emitting diodes.3.A class of Tb³⁺,Sm³⁺activated LaOCl samples possessing 3D umbrella-like structure was successfully fabricated by a conventional hydrothermal approach followed by further chloration process.The energy transfer process occurs in co-doped phosphors.Meanwhile,the energy transfer mechanism is determined to be a dipole-dipole interaction,and the critical distance and energy transfer efficiency between Tb³⁺and Sm³⁺are also calculated.Excited by ultraviolet light,color hue from cool white light to warm white light is acquired via modulating the concentration of Sm³⁺in the LaOCl:0.5%Tb³⁺,z%Sm³⁺system.These results manifest that the as-synthesized samples can be good candidates for LEDs with great potential.