The Optical Module Encapsulation Based On The Gradient Refractive Index And Multilayer Structure With Improved Light Extraction Efficiency And Color Temperature Uniformity Of LED

The ever-increasing applications of LED in the market have lead to the improving demands for LED luminescence properties. It is largely accepted that LED is a kind of monochromatic light source, and therefore, it needs to be converted to the white light to satisfy the various requirements of our daily life. To date, the most highly employed conversion is realized by packing the Y3Al5O12:Ce3+(YAG:Ce) yellow phosphor on the GaInN/GaN blue chips. Many factors, however, cause that the white light is trapped within the LED chip as well as device fabricated through above method, thus indicating the low light extraction efficiency. Even worse, the uneven distribution of fluorescent powder may result in various problems (e.g. the nonuniform distribution of the LED color temperature). In light of this situation, the following methods were developed to improve these problems.Firstly, multilayer encapsulation structure with gradient refractive index was constructed by adding nanoscattering agents with high refractive index. The YAG phosphors and several nanoscattering agents, including nano-SiO2,-TiO2,-Si3N4, with different proportions were mixed into silica gel to obtain an uniform material, which were then packaged on LED chips with one layer or multilayer. The attention was focused on the improvement of the light extraction efficiency by changing the type and concentration of nanoscattering agents, together with the number of encapsulation layers. The results suggested that the LED luminous intensity was enhanced with the addition of nanoscattering agent and the enhancement increased with current. In addition, the light extraction efficiency could also be improved by designing multilayer encapsulation structure with gradient refractive index. In particular, when the white LED devices employed nano-SiO2 as scattering regent and the bilayer encapsulation structure, the luminescence increasement up to 50%was obtained compared with the traditional monolayer LED at 50 mA.Secondly, the double lens structure with gradient refractive index was also used to improve the uniformity of the LED color temperature. Primarily, the LED performances were explored by changing the phosphors distribution, which was implemented via altering the LED direction during the dry process. As indicated by the examined results, the phosphors distribution played an important role in the LED luminescence properties. The silica gel formed concave lens structure by the gravity on the chip, and then the phosphors was coated on the structure to form a convex lens structure. Thus the LED double lens structure was prepared. It could be observed that this two-lens structure changed the location and distribution of the phosphor in LED devices, and the gradient refractive index of the structure was conduce to the improvement of LED light extracted efficiency.Ultimately, the light extraction efficiency was greatly enhanced through roughening the upper surface of the packaged silica gel. During the packing process, the roughen surface was obtained by employing the patterned sapphire to press the packaged silica gel. LED devices with high light extraction efficiency were thus fabricated by means of this facile method.