Study On Preparation And Characterization Of Niobate Luminescent Materials

Rare earth (RE) luminescent material is one of the most important functional material which has many applications like photo-electronic displays, fluorescence detecting and X-ray imaging. Niobate is an excellent luminescent host material because of its outstanding physical and chemical properties and superior optical characteristics. At present, it is very common to use solid state reaction method to synthesize niobates powder, however, this method has some disadvantages as needing a great amount of energy consumption. In this thesis, we used sol-gel combustion method to prepare LaNbO4and KLaNb2O7powders, and studied different rare earth ions doped LaNbO4:Ln3+(Ln3+=Eu3+,Er3+,Tb3+,Tm3+,Pr3+) powders’luminescence properties and mechanisms.The main contents of this dissertation are surnmarized as follows:1. We used sol-gel combustion method which nitrate as oxidizing agent and citric acid as complexant to prepare LaNbO4powder. We characterized the luminescent properties, crystal structure and microscopic topography of LaNbO4powder. The results show that the LaNbO4samples crystallize in both monoclinic and tetragonal phase, and the monoclinic phase dominate in the mix phases. As the calcination temperature increases, tetragonal phase converts to monoclinic phase gradually. The most appropriate temperature to prepare LaNbO4powder by sol-gel combustion method is1000℃, and LaNbO4powder crystallizes completely at this temperature. LaNbO4powder is self-activation luminescent material, the emission spectrum of LaNbO4sample contains a broad band with a maximum at445nm. The metal-to-ligand charge-transfer transition (MLCT) in NbO6groups causes the luminescence of LaNbO4powder.2.We used sol-gel combustion method to prepare KLaNb2O7precursors and characterized KLaNb2O7precursors by XRD、TG-DSC、SEM. Accord ing to the results, the best heat treatment temperature to prepare KLaNb2O7is1100℃. K evaporates when temperature increases. LaNbO4phase appeares in the calcined product when temperature increases to1200℃.3. Different Ln3+(Ln3+=Eu3+,Er3+,Tb3+,Tm3+,Pr3+) doped LaNbO4powders have been successfully prepared by sol-gel combustion process. We studied the photoluminescence properties and mechanisms of all the LaNbO4-based phosphors systemically. It is foud that the excitation spectrum of LaNbO4:Ln3+contations two parts:the strong band is caused by the O2-�'Nb5+charge-transfer transition, and some weak peaks at longer wavelength are corresponding to f-f transition within Ln3+. The appearance of the niobate band in the excitation spectrum shows that energy transfer possibly occurs from niobate groups to Ln3+ 4.The relationship between the luminous intensity of LaNbO4:Ln3+(Ln3+=Eu3+,Er3+,Tb3+,Tm3+,Pr3+) and Ln3+doping concentration shows that when Ln3+doping concentration increases, the luminous intensity of LaNbO4:Ln3+doesn’t increase at the same time, there is a best value.The process of energy transfer and concentration quenching compete all the time which cause the best value appear.