Hydrothermal Synthesis And Its Optical Properties Of Er³⁺,Yb³⁺ Co-doped Molybdate

With the development of science and technology, the demands for material performance are getting higher in many fields, especially for low thermal stress property. Low and tailored thermal expansion coefficient and prolonged-life devices have becoming important investigations in material fields. The multi-fuctions investigtion of materials with near zero or negative thermal expansion are attracting more and more attentions.This paper investigates the preparation technology with hydrothermal method and thermal and optical properties of Fe2Mo3O12, Y2Mo3O12and Er3+, Yb3+co-doped Fe2-xYxMo3O12(x=2.0,1.8,1.6,1.4,1.2,1.0,0.8,0.6,0.4,0.2and0). The structure, phase transition and hygroscopicity of the materials are analyzed by X-ray diffraction, Raman spectroscopy, scanning electron microscope, and meanwhile the fluorescence spectrum and up-conversion luminescence of Er3+, Yb3+co-doped Fe2-xYxMo3O12are explored by using fluorescence spectrometer.1. Fe2Mo3O12and Y2Mo3O12are synthesized with solid state method and hydrothermal method, then measured with X-ray diffraction, Raman spectroscopy and scanning electron microscopy. It is found that the hydrothermal method can produce smaller particles and more uniform distributed particles. After a series of experiments, the optimum process conditions for the preparation of Fe2Mo3O12and Y2Mo3O12by using hydrothermal method are obtained. Hydrothermal method is also a kind of method worth spreading as its preparation temperature is reduced to about200℃less than that of solid state method (900℃). Especially, under high pressure and temperature, the morphous of particles change greatly, which favors novel particles for novel properties. And at room temperature Fe2Mo3O12crystllizes in monoclinic phase structure, without negative thermal expansion characteristic; Y2Mo3O12presents a orthorhombic structure, whereas its strong hygroscopicity feature at room temperature affects its negative thermal expansion characteristic.2. Er3+, Yb3+co-doped Fe2-xYxMo3O12are prepared by hydrothermal method. X-ray diffraction results show that when x≤0.6, the sample presents monoclinic phase.With increasing the content of Y3+ions to substitute Fe3+ions, the lattice constant becomes larger and the density gets smaller and the intervals between the molecules increase to result in high hygroscopicity. When x≥0.8, the samples begin to show orthorhombic structure, which implies that phase transition takes place within the scope of0.6<x<0.8. In addition, according to Raman spectrum, the Raman peaks change obviously between x=0.6and x=0.8; when x<0.6near the wave number of992cm-1a small Raman peak appears, which means the sample is monoclinic phase structure; when x≥0.8this small Raman peak disappears indicating an orthorhombic phase structure. It is aslo found that with the increase of Y3+ion content, the average particle sizes of the sample decrease, and the morphology becomes more and more regular. When x<1.4, the particles are not so regular, especially when the samples Fe0.4Y1.6Mo3012take on the shape of superimposed sheets with the thickness of about0.1μm. Fe0.2Y1.8Mo3O12crystallizes in cylindrical particles with diameter3μm and height4μm.3. The fluorescence emission and up-conversion luminescence of Er3+, Yb3+co-doped Fe2-xYxMo3O12are investigated. The fluorescence emission is attributed to the Er3+ion energy level transitions. Violet-blue light is attributed to4G11→4I15/2、4F3/2→4I15/2、4F5/2→4I15/2transition, blue light is produced by2H11/2→4I15/2transition and red light is given out by4F9/2→4I15/2transition near the broadband at394nm respectively. The upconversion luminescence of the sample is stronger than fluorescence emission. It is noted that the morphology of the particles has a great influence on luminescence and upconversion emisson:the smaller the particles in the sample, the better the luminescent properties; especially, sheetlike particles present strong luminescence properties and upconversion emission.