Synthesis,Color-Tunable And Energy Transfer Of Rare Earth Niobate And Tantalate Luminescent Materials

The rare-earth niobate and tantalate have excellent chemical stability,and NbO₄^3-and TaO₄^3-groups have strong charge transfer bands in the ultraviolet region.Therefore,as luminescent matrix materials,rare-earth niobate and tantalate can transfer the absorbed energy to the doped rare earth ions and enhance the luminescence performance of rare earth ions.In this dissertation,using YTaO₄,Gd TaO₄ and YNbO₄ as hosts and different rare earth ions(Tb³⁺,Eu³⁺,Dy³⁺,Sm³⁺ and Er³⁺)as doped ions,the phosphors with tunable color were obtained by sol-gel method.Photoluminescence properties,energy transfer and adjustable color were studied.The main contents are as follows:1.A series of YTaO₄:Eu³⁺,Tb³⁺ phosphors were synthesized by sol-gel method.The obtained YTaO₄ phosphors are spherical particles with the diameter of about 18 nm.It is found from the luminescence spectra of the phosphor that the charge transfer bands of O^2--Tb³⁺/Eu³⁺ and O^2--Ta⁵⁺ contribute to the emission of Tb³⁺ and Eu³⁺.Under 270 nm excitation,YTaO₄:Eu³⁺ phosphor exhibits red emission,YTaO₄:Tb³⁺ phosphor shows green emission,and the optimum doping concentrations are 0.07 and 0.02,respectively.By adjusting the doping ratio of Tb³⁺ and Eu³⁺ ions,the YTaO₄: Tb³⁺,Eu³⁺ phosphor can achieve the multi-color emitting.2.A series of YNbO₄:Tb³⁺,Sm³⁺ phosphors were synthesized by sol-gel method.The obtained phosphors are spherical particles with the diameter of about 0.78 μm.NbO₄^3-group can absorb ultraviolet light and transfer energy to Tb³⁺ and Sm³⁺,then enhance the luminescene intensity of the phosphor.For YNbO₄:Sm³⁺ phosphor,the optimum excitation and emission wavelengths are 290 and 609 nm,respectively.Under the excitation of 290 nm,green emission of Tb³⁺ and orange red emission of Sm³⁺ are presented in the emission spectrum of YNbO₄:Tb³⁺,Sm³⁺.Therefore,the emitting color can be adjusted by changing the doping concentration of Sm³⁺.3.A series of GdTaO₄:Dy³⁺,Eu³⁺ phosphors were prepared by sol-gel method.According to the fluorescence spectra of Gd TaO₄:Dy³⁺,Eu³⁺ phosphor,under the excitation of 352 nm near UV light,the TaO₄^3-group and Gd³⁺ ions can absorb energy and transfer it to Dy³⁺ and Eu³⁺,then the phosphors show the characteristic yellow and blue light emission of Dy³⁺ and the characteristic red light emission of Eu³⁺.The polychromatic emission of the samples can be controlled by changing the concentration of Dy³⁺ and Eu³⁺ ions.Therefore,the as-prepared Gd TaO₄:Dy³⁺,Eu³⁺ phosphors have important applications in the fields of LED display,color display and biological tissue imaging.4.A series of YTaO₄:Er³⁺,Eu³⁺ phosphors were synthesized by sol-gel method,and the morphology,luminescence properties,energy transfer process and emitting light colors of the phosphors were investigated.It is confirmed that there is the energy transfer process of Er³⁺→Eu³⁺ ions,and at the same time,the YTaO₄ host can transfer the absorbed energy to Er³⁺ and Eu³⁺.Under near-ultraviolet excitation at 378 nm,YTaO₄:Er³⁺ and YTaO₄:Eu³⁺ phosphors can emit the characteristic green emission of Er³⁺ and the characteristic red emission of Eu³⁺,respectively.The tunable color of the phosphors can be realized by changing the ratio of Er³⁺ and Eu³⁺ ions and the excitation wavelengths.