A Study On Multi-layer Phosphor Coating Structure Of White Light Pc-LEDs

Solid state lighting is a new lighting technology and has become the mainstream of lighting.With high brightness,low cost,low energy consumption,pollution-free and other advantages.The most common semiconductor solid light source is the light-emitting diode,or LED.The new coating technology of phosphor powder and the optimization design of coating structure are also concerned.The most common way to achieve white LED is the pc-LEDs,namely coating the blue LED chip based on gallium nitride with YAG:Ce yellow phosphor powder to output white light.However,due to some factors,this kind of implementation will lead to the low efficiency of light absorption and light output in the interiort.And phosphor powder coating is not uniform,easy to make the Angle of light intensity distribution is not uniform,obviously in the current packaging structure still can not get rid of low light efficiency and uneven color temperature and other shortcomings.It is a hot spot to design and optimize the pc-leds packaging structure and improve the performance parameters.This subject mainly studies the influence of the coating structure of phosphor and silica gel on the optical properties.The gradient refractive index structure was designed by adding nano-oxide with high refractive index to reduce the total reflection of light inside the package,improve the light extraction rate,and optimize the design to obtain the phosphor coating structure with the best luminous efficiency and spatial color temperature distribution uniformity.The main contents of this paper are as follows:（1）Adding nano SiO₂.The traditional approach is to add micro-particles,but the scattering is severe,so it is considered to uniformly mix different proportions of nano-SiO2 particles in the silica gel phosphor system.The results show that the luminous flux of white light is only increased by 4.5%after the addition of SiO₂ particles.Considering that the refractive indices of SiO₂ and silica gel are similar,the mixed refractive index system hardly changes,so TiO₂ having a refractive index higher than that of SiO₂ is added,The experimental results showed that the luminous efficiency increased by up to 16.3%.The experiment measured the two-layer structure and the three-layer structure according to the gradient of the doping of the added nanoparticles.The double layer structure obtained the highest lumen,reaching 135 lm.It is 22.7%higher than undoped.And when comparing in the 5000k color temperature range,the data shows that the higher the number of doped layers,the better the spatial color temperature uniformity.（2）Considering that there are two ways to improve the refractive index,one is the nanoparticle with high refractive index.The second is to introduce high index atoms or organic groups into the material through chemical bonds at the molecular level.Surface-modified ZrO₂ nanoparticles（m-ZrO₂）with functional groups were prepared by a sol-gel reaction.The surface-modified ZrO₂ was reacted with silica gel to synthesize m-ZrO₂/AB composite,and the composite was applied to the pc-LEDs coating structure.（3）The synthesized material m-ZrO2/AB was exposed to the surface of the chip using a self-exposure process in the laboratory.The experiment measured the effect on the light efficiency under different exposure times.It was finally determined that the light efficiency of blue light was improved by 27%in the case of 10 times of exposure,and the spatial light intensity distribution of blue light was optimized.（4）Adaptive coating double layer structure.Exposing m-ZrO2/AB as a remote layer using adaptive techniques.The remote layer blocks the contact between the chip and the phosphor silica gel mixing system,which reduces the effect of heat released by the chip on the conversion efficiency of the phosphor,and also reduces the absorption of light by total reflection.Experiments show that the m-ZrO2/AB is used as the remote layer,and then the phosphor layer is exposed.The junction temperature is reduced by 13.94%,and the light efficiency is improved at the same time.