The Preparation And Luminescent Properties Of Rare Earth Doped Tantalum Based Pyrochlore Oxides

As a kind of photoluminescent material,upconversion luminescence materials can have strong luminescence under the excitation of visible light,ultraviolet light or infrared light.Because of the excellent physical and chemical properties,pyrochlore oxides are promising and can be treated as a matrix material in upconversion luminescent materials.Based on the layered arrangements of octahedral TaO₆^7-,Sr₂Ta₂O₇ and Ca₂Ta₂O₇ have strong and wide charge transfer absorption band,which can transfer energy to activator quickly and accurately through their own non radiative transition.There are many kinds of pyrochlore oxides,and they have excellent physical and chemical properties even in extreme environment.Therefore,these remarkable characteristics of TaO₆^7-can provide excellent energy-level transition conditions for rare earth ions,and will be studied in this thesis.In this thesis,a series of Sr₂Ta₂O₇,Ca₂Ta₂O₇,Sr_2-xEu_xTa₂O₇:Eu³⁺and Sr_2-xCe_xTa₂O₇:Ce⁴⁺were synthesized by high temperature solid state method.The as-prepared samples were characterized by XRD,Raman,high pressure Raman and XRF.The crystal structure stability and doping effects on the luminescent properties were studied.The following results were obtained:1?By high temperature solid state method,Sr₂Ta₂O₇?Ca₂Ta₂O₇?Sr_2-xEu_xTa₂O₇:Eu³⁺and Sr_2-xCe_xTa₂O₇:Ce⁴⁺were synthesized.It was found that these samples were pure,and the doped ions of Eu³⁺and Ce⁴⁺were in a free state in the lattice.2?The ambient and high pressure Raman spectrum were carried out,and the vibrational modes of Sr₂Ta₂O₇ and Ca₂Ta₂O₇ were identified.It was found that the pressure-induced phase transition might occur in hexagonal Ca₂Ta₂O₇,while orthorhombic Sr₂Ta₂O₇ remained stable.3?Through the analysis of fluorescence spectra,we found that the photoluminescence performance of the samples increased gradually with the increase of doping concentration.The results showed that the energy-level transitions of Eu³⁺and Ce⁴⁺weren't affected by the parent materials.It indicated that the pyrochlore oxides with special TaO₆^7-could provide a very suitable energy-level activity condition for the transition between the f-f forbidden energy levels of rare earth ions.