Study On The Synthesis And Optical Properties Of Rare Earth-doped Perovskite Composite Oxides

Rare earth ions have stable physical and chemical properties, abundant levelstructure and longer lifetime.Under proper near UV or blue light excitation, rare earthions can be doped into appropriate host as the activator, to get excellent luminescenceproperties. Rare earth doped phosphors is an important class of function materials,and the rare eath doped oxides phosphors could be widely used in the field ofillumination and displays. With the advance of science and technology, and the basictheoretical study goes deeper and wider, people make higher demand on theluminescence properties of optical materials. The optical properities of rare earth ionsshow strong dependce on the compositon and structure of matrix materials, because oftheir unique4f intraconfiguration,4f5d configuration and the charge transfer bandstructure. Therefore, in the exploration of new phosphors, a selection of new hostmaterials to enhance the optical properties is a major concern.Perovskite oxides are one of the most studied groups of materials, owing to theirwidely technological applications. In recent years, the optical properties of rareearth-doped perovskie oxides have attracted more and more interest of scientist.Furthermore, an incredibly high versatility of structures and phases with totallydifferent functions can be obtained depending upon the combination of chemicalelements into the formula ABO₃. So the optical properties of rare earth-dopedperovskite composite oxides show well research value and potential applications.In this thesis, we systematically investigated on the synthesis and opticalproperties of rare earth-doped perovskite composite oxides. We synthesized a serielsof rare-earth-doped-perovskite composite oxides through sol-gel method and high temperature solid state reaction method, study on the optical properties of the rareearth ions (mainly Eu³⁺) doped in different host materials. The main experimentalresearch includes photoluminescence excitation and emission spectra, concentrationquenching, lifetime and high resolution laser spectra. The experimental data weresummarized, analyzed and followed by partial theoretical calculation and analysis, toinvestigate the relation between composition, structure and luminescent properties.The thesis mainly consists of three parts, as follows:Firstly, the preparation and analysis of Eu³⁺-doped LnAlO₃（Ln=Gd, La）.LnAlO₃（Ln=Gd, La） are typical A³⁺B³⁺O₃perovskites. In this part, Eu³⁺-dopedLaAlO₃and GdAlO₃phosphors were synthesized with sol-gel method. Thecrystallization processes of the phosphors were characterized by X-ray diffraction（XRD） and thermogravimetry-differential scanning calorimetry （TG-DSC）, and theoptical properties were investigated in details. The influences of doping concentrationand annealing temperature on the luminescent intensity were investigated, and finallywe got the optimal doping concentration and calcining temperature for the twophosphors. Under appropriate UV-radiation, the reddish orange light emitted fromGdAlO₃:Eu³⁺was brighter than that from LaAlO₃:Eu³⁺. Such a brightly luminescentphosphor could be considered as an ideal optical material for the development of newoptical display systems. As can be seen from the PLE spectra of Eu³⁺-doped LaAlO₃and GdAlO₃, the CT band energy of Eu³⁺―O2-was strongly influenced by the hostmaterials. Correspondingly, we calculated the bond lengths and bond covalency ofLa-O and Gd-O based on the chemical bond theory to investigate relations betweenthe CT band energy and bond convalency. Furthermore, the site-selective laserspectroscopy and luminescence decay of Eu³⁺-doped GdAlO₃and LaAlO₃preparedby sol-gel method have been investigated at room temperature. As can be seen fromthe site-selective excitation spectra in the7F0â†'5D0region, there were threecrystallographic sites for Eu³⁺in LaAlO₃:Eu³⁺, and one crystallographic site for Eu³⁺in GdAlO₃:Eu³⁺. Secondly, preparation and tunable spectra of CaRlO₃:Ln (R=Zr, Ti; Ln=Pr³⁺, Eu³⁺),Tb³⁺, Tm³⁺, Dy³⁺, Sm³⁺).CaZrO₃and CaTiO₃are typical A2+B4+O₃perovskites. In this part, CaRlO₃:Ln(R=Zr, Ti; Ln=Pr³⁺, Eu³⁺, Tb³⁺, Tm³⁺, Dy³⁺, Sm³⁺) phosphors were prepared byconventional solid state reaction. We investigated luminescent properties thePr3+/Eu³⁺-doped CaRlO₃:Ln （R=Zr, Ti） through photoluminescence spectrameasurement, although CaZrO₃and CaTiO₃both possess orthorhombic structure,their luminescent properties were different. Furthermore, the tunable spectra ofCaZrO₃were investigated by changing the doped rare earth ions. As a result, CaZrO₃is a kind of well host materials, under appropriate UV or blue light excitation, CaZrO₃could get tunable color light emission, can be exploited as potential host materials foroptical display systems to get better color light output.Thirdly, synthesis and investigation of luminescence properties of Eu³⁺-dopedcubic perovskite Ba₃Y₂WO₉.In the above two sections, we investigated the optical properties of rare earthdoped simple perovskite oxides. In this part, we focused on the luminescenceproperties of A(B′_2/3B″_1/3)O₃type complex provskiteoxides, and the study on theoptical properties of this kind of provskite oxides is limited at present. Eu³⁺-dopedcubic Ba₃Y₂WO₉phosphors were synthesized by sol-gel method. The preparedsamples were characterized by XRD and field emission-scanning electron microscopy（FE-SEM）. The luminescence excitation emission spectra in the UV region, thesite-selective laser spectra along with luminescence decay were measured in the5D0-7F0region were used to characterize the luminescence properties and the sitedistributions of Eu³⁺in Ba₃Y₂WO₉. As the result, the Ba₃Y₂WO₉:Eu³⁺phosphorsexhibit strong orange-red luminescence, and the optimal concentration of Eu³⁺in thehost of cubic Ba₃Y₂WO₉is30mol%; Eu³⁺ions replace both theY³⁺and Bs²⁺ions,and the Eu³⁺in Bs²⁺sites accompanied by a charge-compensating defect leading tothe disordered surrounding.