Preparation Of Ce:YAG Transparent Ceramics By Reactive Sintering Method And Its Application For White LEDs

White leds,as the fourth-generation lighting source,have a great advantage in light efficiency,longevity,brightness and energy efficiency compared with traditional lighting source.The study of white LED devices shows that phosphors has a great impact on the performance of traditional phosphor white LED devices.In this packaging structure,the phosphor powders and epoxy resin can not be fully blended,making that the optical homogeneity cannot achieve the theoretical value.Although LED is known as the cold light source because of its high electro-optic conversion efficiency,in the working process of the high-power LED device,it will produce significant heat.And in case of the effect of coating epoxy resin which can also work as lens,it's difficult for heat dissipation.And it will result in a decline in performance of phosphor powder,and makes epoxy aging,or even fall off.A new type of fluorescent material is urgently needed to overcome the problem.This paper uses Ce:YAG transparent ceramics which have good heat dissipation performance as a fluorescent body,and the ceramics is designed to overcome the problem of heat dissipation for LED devices.Currently,the preparation of Ce:YAG transparent ceramics mainly includes two ways: one is to synthesis Ce:YAG nano-powder,and then prepare transparent ceramics by solid-state sintering method.The other is by a direct reaction sintering in vacuum or atmosphere.Compared with the former way,the second one can save time and resources,which is beneficial to the industrialization of production.The Ce:YAG transparent ceramics is prepared by direct reaction sintering method in vaccum and at atmospheric pressure.And a series of analysis characterization has been done.According to X-ray diffraction phase structure analysis of the prepared ceramics,the product of both sintering methods only concludes YAG phase without others.And the hardness of Ce:YAG transparent ceramics is more than 1400kg/mm2.It can be found that according to the analysis of SEM analysis and transmittance analysis,the density of transparent ceramics prepared by vacuum reaction sintering method is higher than prepared by pressureless reaction sintering method,the internal porosity is less,and the ceramics have a certain transmittance.The excitation spectrum and emission spectrum detection of the Ce:YAG transparent ceramics shows that two peaks of excitation spectrum are at 340 nm and 458 nm,the peak of emission spectrum is at 545 nm and the range of emission spectrum is from 490 nm to 675 nm.It means that the transparent ceramics can produce yellow light which excited by blue light.It can be used as a fluorescent body for white LED devices,and the quantum efficiency of Ce:YAG transparent ceramics is more than 60%.The transparent ceramic pieces are packaged into WLED devices for the test of light color electrical parameters which includes luminous flux and luminous efficiency,chromaticity coordinates and color temperature,color rendering index and color difference.And YAG:Ce³⁺ phosphor is also packaged into WLED devices for the same test.And the WLED is compared with that packaged by transparent ceramics.In case of that the human eye is more sensitive to the yellow light which the wave length is near 555 nm,therefore,increasing the amount of Ce3 + and the thickness of the ceramic chips can increase the luminous flux and luminous efficiency within a certain range.The color rendering index and chromaticity coordinates test shows that,the color of the white LED device packaged by transparent ceramics which Ce/?Ce+Y?doping ratio is 0.25% and 0.5% is yellow compare with the pure white light.It is resulted from the over-thick ceramic pieces and the higher content of Ce³⁺.comparing the performance Comprehensively,the white LED devices packaged by the transparent ceramics sintered at 1750°C which Ce/?Ce+Y?doping ratio is 0.25% and the thickness is 0.4mm show the highest photosynthetic efficiency,better optical performance.However,the color difference test of the white LED device was found to be much more than the market demand.