| White LED is one kind of complex optoelectronic device, which has many key technologies to be solved, such as thermal management technology, phosphor technology and packaging technology. Only when the problems are solved, can the White LEDs replace the traditional light sources, giving full play to their strong points:high luminous efficiency, long lifetime and high stability. Therefore, great efforts have been made to optimize the packaging structure, heat dissipation structure, phosphor coating methods and novel packaging materials to enhance the optical performance by using numerical calculation and computer simulation. As we all know,the way of using a blue or ultraviolet LED chip coated with YAG phosphor to produce white light LED is widely used with the advantages of simple structure, easy to make and low cost. The dissertation mainly focus on how to enhance the luminous efficiency and the heat dissipation capacity, studying the key issues in the optical simulation, optical design and optimizing process of packaging structure, phosphor and heat dissipation structure and achieving some innovative works as following:1) A light scattering model of nanoparticles inside epoxy was proposed based on the Mie Scattering theory and Rayleigh scattering cross section theory. The model revealed the effect of concentration, nanoparticle radius and refractive index of the nanoparticle on the optical scattering length, which will be effective for designing the optimal thickness of the encapsulate film.Furthermore, the optimal refractive index producing maximum transmittance was calculated by using Monte Carlo method and a graded-refractive-index encapsulation structure of G layers with nanocomposites based on ray propagation theory of gradient index, Three-dimensional optical ray-tracing simulations demonstrated that high light-extraction could be achieved through the encapsulation structure. The structure of 3 layers presented a 5.98% increase in output luminous flux when compared with traditional encapsulation structure with single layer.2) A novel YVO4:Eu3+@YPO4 nano core-shell phosphor was designed based on electronic structure calculation and an efficient process for preparing YVO4:Eu3+@YPO4 nano core-shell phosphor with hydrothermal method was studied. X-ray diffraction, transmission electron microscopy, and photoluminescence spectra were used to characterize the feature of YVO4:Eu3+@YPO4 core-shell phosphor. The TEM images indicate that the core-shell phosphor possessed the diameter of 10～30 nm and shell thickness of 5-10 nm, regular crystalline morphologies, highly uniform in size and distribution, high degree of crystallinity. The XRD images indicated the the synthetic products contained the YVO4:Eu3+cores and YPO4 shells.The photoluminescence spectra show that the luminous efficiency of YVO4:Eu3+@YPO4 core-shell phosphor was 66.75% higher than that of YVO4:Eu3+phosphor, which also had high color purity. Finally, the first principle calculation was also used to calculate the band-structure of the YVO4 and YPO4 crystal. Furthermore, the relationship between the electron transition and the luminance was illustrated.3) Based on Computational Fluid Dynamics(CFD), a complete field 3D model containing LED chips,baseboard,radiator and exterior fluid space was built.It has taken conduction-convection-radiation coupled heat transfer into consideration according to the characteristics of LED natural convection. Natural convection of LED array was simulated with the model. It comes to some result that:①flow pattern is a consequential fact affecting heat transfer characteristics of fins. Heat transfer rate varies with different fins in a radiator. It also varies with different positions on fins. There is a visible relationship between heat transfer characteristics and flow rate distribution. Thus, flow pattern of exterior space must be taken into consideration to analyze LED heat transfer;②Effects of radiation play an important role in this case. It reduced thermal resistance and lowered down the junction temperature while homogenizing the temperature field and raising heat transfer efficiency. As discussed in this paper, comparing to the case neglecting radiation, when the radiator surface was severely oxidized to enhance the radiation, the heat emitted by radiation was as much as 38.7% of the whole heat rejection. The temperature of baseboard was lowered down by 6.4℃. Therefore, it is an effective way to improve LED radiator performance by enhancing the radiation.4) A visible orientation sensitivity problem exists in parallel plate fin LED radiator. The performance ranking of different orientations is 90°> 0°> 180°>270°. CFD computation indicated that it was the different flow patterns in each flow field that resulted in different performance in different orientations. Strip fin radiator keeped the same bottom up natural convection flow pattern in all orientations; so that the orientation sensitivity was weaken.5) Analysis based on field synergy principle indicated that the improvements on LED radiator structure which were composed of strip fin and hole drilling result from the reformation of the exterior natural convection flow pattern around LED, that was, to decrease the angle between the velocity and heat flux vectors which leaded to the improvements of the synergy between velocity and heat flux vectors. Thus, it is also an effective way to improve LED radiator performance by synergy principle design aiming at a flow field with better synergy. Under the conditions of this research, for the strip fin radiator, the heat transfer coefficient was increased by 67.5% and the highest temperature was reduced by 8℃comparing with that of parallel plate fin radiator. For the hole drilling case, the heat transfer coefficient was increased by 54.8% while the highest temperature drops about 7℃.
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