Synthesis And Modification Of Silicate Or Aluminate Matrix Phosphors For Blue-light LEDs

Silicate and aluminate systems were widely used as matrix materials for transparent scintillating ceramics or white LED phosphors due to the abundent source of raw materials,good physicochemical stability and various crystal field environments.Phosphorscent powders made from the two matrix systems can be perfectly combined with the current mainstream LED chips to achieve white light when rare earth or other exciting ions doped in owing to the good absorption in the ultraviolet and visible blue regions.However,silicate-based or aluminate-based phosphors,like other oxide-based phosphors combined with LED chips,have higher relatively color temperature and lower color index due to the lack of red light in emission spectra.As mentioned above,full-spectrum phosphors with excellent performance and high color index prepared by ions doping will greatly enrich the choice of white light illumination for LED.Generally,the kind of phosphor is mostly prepared by the traditional high-temperature solid-state reaction method.The preparation process and luminescent properties of powders are closely related to the starting materials,synthetic atmosphere,flux and firing system（such as temperature,sintering time,etc.）,which have always been a hotspots in the field of material synthesis and lighting research and attracted much attention of scientific researchers.In this paper,using high temperature solid state reaction and optimizing the initial raw materials or flux,the synthesis process and doping modification of silicate or aluminate based phosphors were studied in detail.The phase,morphology,luminescent properties and color parameters of the samples were characterized by X-ray powder diffraction（XRD）,scanning electron microscopy（SEM）,fluorescence spectroscopy（PL）and color coordinates（CIE）simulation.The experimental results show that AlF₃·3H₂O can be used as another alternative flux for high temperature synthesis of this kind of fluorescent materials,and ions doped can improve the luminescent properties and the color of the powders.Specific manifestations are as follows:（1）Aluminate-based phosphors: Optimizing cerium trifluoride as the starting material,Y3-x（Al1-y Cry）5 O12-3x/2F3x: x Ce³⁺（YACG: Ce）and Lu3-x（Al1-2y Mny Ry）5O12-3x/2F3x: x Ce³⁺（Lu AMG: Ce）were synthesized in nitrogen and activated carbon atmosphere respectively.Among them,the optimum synthesis process of YACG: Ce is that the powder with good phase can be obtained by sintering at 1560℃ for 4-6h with Al F3 ·3H2O as flux in nitrogen atmosphere.A small amount of Cr³⁺ cannot affect the phase composition of the sample,but can realize the energy transfer between Ce³⁺ and Cr³⁺,which makes the emission spectrum show dark red composition near 708 nm and improves the color rendering index of the powder similar to that of YACG: Ce³⁺.Nevertheless,the synthesis conditions of Lu AMG:Ce³⁺ is slightly different from those of YACG:Ce³⁺.The synthesis condition is activated carbon as a protective atmosphere,without adding any flux at 1540℃,sintering for 4-5h.The doping of Mn4+ does not change the phase composition of samples,but can make.（2）Silicate-based phosphors: based on yellow phosphors stimulated by Europium Divalent,were synthesized and their luminescent properties were optimized.The results show that the optimum synthesis process is to use AlF₃·3H₂O as flux,reduce the amount of SiO₂ properly,and keep it at1350 ℃ for 4h under reducing atmosphere to obtain yellow phosphor Sr3-x Si1-m O5-2m:x Eu²⁺.Among them,the amount of Al F3 ·3H2O is 2wt.%,m = 0.04mol;the sample emits single peak under the blue light（λ=460nm）,and the main peak is located at λ=584nm.When Ba2+ is doped,because the radius of Ba2+ is slightly larger than Sr²⁺ and the substitution of similar substances occurs,the cell volume enlarges.When stimulated emission occurs,the main emission peak appears bright red shift to orange red region,and when Ba2+=0.2655 mol,λ=598 nm,the maximum red shift is 15 nm.