Preparation And Luminescence Properties Of NaYSnMoO₇ Based Phosphors For WLED

Due to the small size,the low heat generation,the energy saving,the high efficiency and the long life,the WLED are regarded as a new generation of illumination sources.In order to make up for the shortcomings of the lack of red light components,high color temperature and low luminous intensity in the current WLED phosphors,therefore,it is a hot spot research to search the red phosphor with low color temperature and high quantum conversion efficiency.In this thesis,quaternary pyrochlore NaYSnMoO₇ were used as the matrix to dope different rare earth ions and study their photoluminescence properties.The synthesized samples were measured and characterized by the X-ray diffraction,Rietveld structural refinement,Field emission scanning electron microscope,UV-Vis-NIR spectrophotometer,Raman spectrometer and photoluminescence spectrometer.Main research were listed as follow:?1?In order to explore the optimal preparation process of NaYSnMoO₇-based phosphors,the effects of calcination temperature,holding time and flux H₃BO₃content on the crystallinity and luminescence intensity of NaYSnMoO₇:Eu³⁺phosphors were investigated by orthogonal experiment.Based on this study,the effect of single variable H₃BO₃ content on the crystallinity and luminescence intensity of NaYSnMoO₇:Eu³⁺phosphors were studied.The optimum preparation process for NaYSnMoO₇-based phosphors were as follows:the calcination temperature is 1300°C,the holding time 6 h,the H₃BO₃ content is 5wt%.?2?Using Eu³⁺ions as fluorescent structure probes,a series of NaYSnMoO₇:xEu³⁺phosphors were prepared.The relationship between matrix structure and luminescence properties was investigated.Structural refinement results indicated that the doping-ions didn't change the crystalline phase.The emission spectra of NaYSnMoO₇:Eu³⁺phosphors were composed of a series of characteristic transition peaks corresponding to ⁵D₀?⁷F_J?J=1,2,3,4?of the Eu³⁺ions.The electric dipole transition of ⁵D₀?⁷F₂ had the highest intensity,which indicated that the Eu³⁺ions occupied the asymmetric position in the NaYSnMoO₇ crystal.The optimal doping concentration of Eu³⁺ions was 0.30mol,and the concentration quenching was caused by electrostatic multi-level interaction.?3?The photoluminescence properties of NaYSnMoO₇:Eu³⁺phosphors were verified by Judd-Ofelt theory.The increase in luminous intensity was due to an increase in the probability of radiation transitions and a decrease in the probability of non-radiative transitions.The Judd-Ofelt parameters?₂>?₄ indicated that the Eu³⁺ions occupied the asymmetric position in NaYSnMoO₇.The quantum efficiency of the phosphor was up to 83.83%.The best color coordinate was?0.6481,0.3483?,the color purity was 90.81%,and the color temperature was2577K.It is a potential candidate for high color purity and high efficiency red phosphors for WLED in the future.?4?A series of NaYSnMoO₇:xSm³⁺phosphors were prepared by using Sm³⁺ions as the activator.The relationship between the occupying site of Sm³⁺and luminescence properties was investigated.There are characteristic transitions of Sm³⁺ions which corresponded to ⁴G_5/2?⁶H_J?J=5/2,7/2,9/2 and 11/2?in the NaYSnMoO₇:Sm³⁺phosphors emission spectra.The electric dipole-dominated transitions intensity is higher than that of the magnetic dipole,which indicated that the Sm³⁺ions occupied the asymmetric positions in the NaYSnMoO₇ matrix.The concentration quenching of NaYSnMoO₇:Sm³⁺phosphors was caused by dipole-dipole interaction with an optimum doping concentration of 0.07mol.?5?The optical properties of NaYSnMoO₇:0.07Sm³⁺phosphors were verified by Judd-Ofelt analysis.The Judd-Ofelt parameters?₄>?₆>?₂ confirmed that the Sm³⁺ions also occupied an asymmetrical position in the NaYSnMoO₇ lattice,and the matrix structure was stable and rigid.The quantum efficiency was as high as 63.73%.The fluorescence branching ratios of ⁴G_5/2?⁶H_7/2 transition and ⁴G_5/2?⁶H_9/2 transition were 53.56%and 34.51%,respectively,which were the dominant factor that caused the phosphors to be orange-red color.The color coordinate of phosphor was?0.5329,0.4532?,the color purity was 79.45%,and the color temperature was 2207K,which were the potential low color temperature and high efficacy WLED-pumped orange-red phosphors.