Preparation And Photoelectric Properties Of Red Fluorescent Materials For White LEDs

Currently,commercial white LEDs are mainly fabricated by combining 460 nm blue chip with a mixture of YAG:Ce yellow phosphor and epoxy resin.However,since the emission spectra of Ce³⁺ions does not have continuous spectral characteristics and lacks red light components,resulting in a low color rendering index（CRI）and a high correlation color temperature（CCT）,so the warm white light emission cannot be achieved.Moreover,the epoxy resin used in packaging is a low thermal conductivity material and has poor chemical stability,indicating such device is not suitable for high-power white LED.In addition,this method of coating a phosphor dispersed in an epoxy resin on a blue chip has foreign patent barriers.Therefore,this paper proposes to adopt the all-solid transparent fluorescent material,including fluorescent film,glass-ceramic,single crystal,instead of the traditional epoxy resin package,which not only can effectively supplement the red light,but also can effectively improve the thermal stability,physical stability,and luminescence stability.The main research contents and results are as follows:1.CuInS₂/ZnS/water-borne epoxy resins（WER）and CdSe/ZnS/WER light quantum dot films were prepared by spin coating method.Ulteriorly,we obtained a CuInS₂/ZnS/WER/GaAG:Ce phosphor film-based white LED with a CRI of 95,a CCT of 5119 K,a LE of 44.52lm/W and a CdSe/ZnS/WER/GaAG:Ce phosphor film-based white LED with a CRI of 80,a CCT of 4154 K,a LE of 36.73 lm/W,respectively.2.CdSe_xS_1-x quantum dot glass ceramics were prepared by melt-quenching method with borosilicate glass as a host.The emission of yellow to red wavelength is adjustable by controlling the quantum dot size and and component content.The photoluminescence quantum efficiency（PL QY）of CdSe_xS_1-x quantum dot glass ceramics was improved by doping Eu³⁺ion.In addition,its application in white LED was discussed in detail.3.Transparent red-emitting YAG:Cr³⁺single crystal（SC）was grown by the Czochralski method.Compared with commercial red phosphors,YAG:Cr³⁺SC display excellent thermal stability and high PL QY of 92%.By combining YAG:Cr³⁺SC and YAG:Ce SC with a 460 nm blue light chip,the CRI of the as-encapsulated white LED was increased from 67.5to 76.5,and the CCT was reduced from 6225 K to 5236 K.In addition,the white light generated from such device was relatively stable when used in high-power white LED.