Study On The Up-conversion Luminescence Properties Of Er³⁺，Yb³⁺ Doped Rare-earth Stannate Nanocrystals

Many excellent optical, electrical, magnetic, superconducting properties of rare earth compoundsexhibit have and rare earth ions on special4f electronic configuration and4f5d energy level structure,especially rare earth elements has spectral properties of general elements are incomparable, so rare earthluminescent materials has become the preferred materials in the field of information processing, stereodisplay, fluorescence marker, the present study of rare earth luminescent material is causing widespreadconcern and interest. The nanometer luminescent materials because of its special properties and is verylikely to become the new luminescent materials for the next generation. In many of the nanostructuredluminescent materials, the pyrochlore structure composite oxide as the host material has the most attractivefor rare earth doped material matrix. Because of the very good physical and chemical stability whichpyrochlore structure composite oxide has so it also has excellent luminescent properties, and now has beenwidely applied to information display, lighting engineering, optical communication and other realms.Multiple complex oxides of rare earth stannate belongs to the pyrochlore structure, which has excellentthermal, electrical, magnetic and catalytic properties, so they show great potential applications in ionconductor, fluorescence, lithium battery, catalyst and radiation field. Rare earth ions, especially Er³⁺ionswhich has rich radiation level, the long excited level service life, easy to be direct excitated by low photonenergy, conversion efficiency is very high and other advantages, they very suitable as up-conversionluminescence materials center. So, in order to find the excellent luminescent materials, we use rare earthstannate as matrix materials, the Er³⁺ion as fluorescent center. In this thesis, we use sol-gel methodcombining several stannate nanocrystal materials, and systematic study on the luminescence properties.The main content of this thesis and the conclusions obtained are as follows:1. We successfully prepared nanocrystal Er³⁺doped La₂Sn₂O₇phosphors by the sol-gel method. Theresults show that: La₂Sn₂O₇: Er³⁺nanocrystals are cubic pyrochlore structure, the crystal morphologysimilar as octahedral. We can observe that all these nanocrystals can give the green emission （517-575nm）and red emission （644-690nm）, which are attributed to the intra-4f transition of4H11/2,4S3/2→4I15/2and4F9/2→4I15/2of Er³⁺ions, respectively. The optimal doping concentration of Er³⁺is found to be7mol%, the optimal annealing temperature is1150℃.2. This chapter we prepared Gd₂Sn₂O₇: Er³⁺nanocrystals by Sol-gel method with different annealingtemperature and different Er³⁺doping concentration. The up-conversion emission spectrum of the samplesare measured under the excitation of a980nm continuous wave diode laser under the room temperature,which can produce three strong upconversion emission peak around527,563,661nm. Analysis of theoptimal doping content and annealing temperatures of Er³⁺are found to be5mol%and1050℃.3. Er³⁺and Yb³⁺ions co-doped La₂Sn₂O₇nanocrystals are synthesized by sol-gel method. Analysis ofthe influence of crystal structure of different substrates on the up-conversion emission intensity we find thatthe best luminescence is the La₂Sn₂O₇as the substrate. The up-conversion luminescence intensity of Er³⁺ions is enhanced greatly by addition of various contents of Yb³⁺ions, and the optimal doping concentrationis3mol%of Yb³⁺ions.4. We prepared La₂Sn₂O₇:Er³⁺//SnO₂nanocrystals by sol-gel method. The structure and morphology ofthe samples which are characterized by XRD and SEM, the results show that the sample is a mixture ofLa₂Sn₂O₇and SnO₂. At the same time we compare and explain the excitation of a980nm continuous wavediode laser which at different temperature, we can see that the up-conversion luminescence intensity isdifferent, and the optimal annealing temperature is1100℃. We also explore the surface photovoltageproperties of the samples, the induced electric field can enhance its optical voltage value, but thephotovoltage spectrum broadening is not to visible region.