Research On Fluorescent Composite Materials For White LED

WLED,as a new type of light source with energy saving and environmental protection,has been widely used in various lighting fields.At present,The most widely used WLED is made by mixing YAG:Ce phosphors with organic polymers such as silica gel/epoxy resin and coating them directly on blue light chips.However,the organic polymer material that directly contacts with LED chips can result in the heat generated by the LED chip to collect in the phosphors and the organic polymer material,thus reduces the luminous efficiency of the phosphor and accelerates the aging and yellowing of the organic polymer material.Therefore,in this paper,the secondary melting method and the bulk polymerization method are used to prepare inorganic matrix and organic matrix fluorescent composite materials,respectively,and the materials are subjected to remote packaging experiments and related tests.The main research contents and results are as follows:1.Inorganic matrix fluorescent composite was prepared by the secondary melting method,and orthogonal test was utilized to study the effects of commercial YAG:Ce phosphors doping amount,secondary sintering temperature,holding time and the thickness of the composites on the fluorescent light emitting properties.Based on the analysis of the results of two orthogonal experiments and the verification experiments,the optimal doping amount of the commercial YAG:Ce phosphor for the inorganic matrix fluorescent composite material is 0.2wt%,the sintering temperature is 820℃,the holding time is 30 minutes,and the thickness is 0.8mm,WLED has the best optical performance With the values of CCT,CRI and SDCM are 4776 K,73.6 and 2.7,respectively.2.The effects of phosphor doping amount and particle size on optical properties of fluorescent composites were studied.YAG:Ce phosphors were prepared by high-temperature solid-state method.YAG:Ce phosphors with different particle sizes were prepared by ball milling process.The center particle diameter was D50=3.6μm,7.4μm,12.3μm,18.4μm and22.8μm,respectively.Fluorescent composite was prepared by mixing phosphors and glass powder with different doping amount and particle size according to the optimal sintering temperature,holding time and thickness.The experimental results showed that grinding would damage the surface morphology of phosphors and the intensity of emission spectrum decreases with the decrease of particle size,and the change of YAG:Ce phosphors doping amount and particle size would lead to the change of optical properties of fluorescent composites.3.Organic matrix fluorescent composites were prepared by bulk polymerization method of methyl methacrylate（MMA）,and the influence of the doping amount of commercial YAG:Ce phosphors on the optical properties of fluorescent composites was studied.The results showed that the transmittance of the fluorescent composite decreased greatly with the increase of the doped amount of phosphor,but the emission intensity of the fluorescent composite increased.The fluorescent composite was performed by LED Photochromic test and the experimental results showed that the white LED encapsulated by fluorescent composite had the best optical performance when the doping amount of fluorescent powder was 0.2wt%.4.In order to improve the color rendering performance of white LED and achieve low color temperature and high color rendering index white light output,based on the above experiment of single-doped YAG:Ce,the optical performance change of double-doped fluorescent composite was studied by changing the amount of SrAlSiN₃:Eu red phosphor.The experimental results showed that the emission spectrum intensity of the fluorescent composite decreased with the increase of the doping amount of SrAlSiN₃:Eu red phosphor.However,the results of LED photochromic electric test showed that the color coordinates shifted to the red light region,color temperature decreased,color development index increased,and the optimal doping amount of SrAlSiN₃:Eu was 0.02wt%.Compared with YAG:Ce,the CCT decreased by 1875K and the CRI increased by 7.9.