Study On Preparation And Luminescence Properties Of KSrY?BO₃?₂ Phosphors For WLED

WLED have been widely used in daily life due to small size,long life,high efficiency,environmentally friendly and so on.Conventional WLED was a blue chip combined with yellow phosphors to obtain white light.The white light obtained by this method has higher color temperature and lower color rendering index,and prolonged exposure will cause retinal damage.Therefore,it is of great value to explore the phosphors that have high efficiency,high color purity,low color temperature and can be excited by near-ultraviolet LED chips.In this thesis,we selected KSrY?BO₃?₂ as the host material of phosphors,and prepared three kinds of rare earth ions(Sm³⁺/Eu³⁺/Dy³⁺)doped KSrY?BO₃?₂phosphors by solid-state method.The prepared samples were characterized by X-ray diffraction,UV-Vis absorbance,as well as Photoluminescence techniques.Main research were listed as follow:?1?The optimal preparation conditions of phosphors were explored.KSrY?BO₃?₂:0.03Sm³⁺phosphors were prepared at different calcination temperatures?750?,800?,850?,900??and different holding times?6 h,8 h,10 h?,where the pre-calcination temperature and time remained unchanged.The optimal calcination temperature of the phosphors was determined to be850?and the holding time was 8 h by analyzing the XRD and fluorescence spectra.The Rietveld structure refinement results indicated that the crystal structure of KSrY?BO₃?₂ belonged to the monoclinic system with a space group of P2₁/m.The combination of first-principles calculation with UV-Vis absorption spectrum confirmed the direct band gap characteristic of KSrY?BO₃?₂.?2?The effect of the doping amount of Sm³⁺ions on the luminescence properties of KSrY?BO₃?₂:Sm³⁺phosphors was investigated.The excitation-emission spectra showed that the optimum doping concentration of the Sm³⁺was0.01,after which the concentration quenching effect occurred due to the dipole-dipole interaction between the Sm³⁺ions.The CIE chromaticity coordinates of all samples were located at the orange light region,the color purity were above 90%and the correlated color temperatures were lower than3000 K.The relevant parameters of KSrY?BO₃?₂:0.01Sm³⁺were calculated by J-O theory,such as the radiative transition probabilities,oscillator strengths,intensity parameters,fluorescence branching ratios and quantum efficiency.The results showed that Sm³⁺ions might occupied symmetric sites in the crystal lattice and the bond between Sm³⁺ions and O^2-ions were covalent.?3?The effect of the doping amount of Eu³⁺ions on the luminescence properties of KSrY?BO₃?₂:Eu³⁺phosphors was investigated.Under the excitation of near-ultraviolet light,the emission intensity of the phosphors was the highest when the Eu³⁺ions doping concentration was 0.40,and then the concentration quenching effect was caused by the multipole interaction between Eu³⁺ions.By analyzing the relative intensity relationship of ⁵D₀?⁷F₁ and⁵D₀?⁷F₂ transitions in the fluorescence emission spectra of the samples,it was found that the symmetry around the Eu³⁺sites varied with the doping concentration.It was proved by J-O theory that excessive incorporation of Eu³⁺ions would reduce sites symmetry.The CIE coordinates of the samples gradually moved from the orange to the red region with the increase of Eu³⁺ions doping concentration,and the color purity of all samples were up to over 96%,and the correlated color temperatures were lower than 3000 K.In addation,the quantum efficiency of KSrY?BO₃?₂:0.40Eu³⁺phosphors was as high as 81.38%.?4?The effect of the doping amount of Dy³⁺ions on the luminescence properties of KSrY?BO₃?₂:Dy³⁺phosphors was investigated.Under the excitation of near-ultraviolet light at 351 nm,the emission spectra showed radiation transitions of ⁴F_9/2?⁶H_15/2 and ⁴F_9/2?⁶H_13/2.The intensity ratio of the two transitions could be varied by adjusting the Dy³⁺concentration such that the phosphors achieved white light emission.Concentration quenching occured when the doping concentration of Dy³⁺exceeded 0.05,mainly due to the energy transfer through dipole-dipole interactions between Dy³⁺ions.The CIE chromaticity coordinates of KSrY?BO₃?₂:Dy³⁺phosphors was located at?0.3097,0.3161?,which was close to standard white light,its color purity was 76.85%,and the correlated color temperature was 5908.38 K.