Power Both Within And Outside The White Led Phase Plane Structure Of The Phosphor Coating Study

Because of advantages of LEDs, more and more attentions had been paid to the LEDs industry by world wide governments and companies. With the development of the technology of semiconductor and process, the luminous efficiency is increasing and the production cost is increasing. The excellent performance of LEDs is shown in many application fields.The first blue LED was realized in 1993 and subsequently white-LED in 1996 was fabricated, which made the all hue of visible light come true. The increasing luminous efficiency of white LEDs lead the application field shift from the direction light to lighting light. The white LEDs will substitute for incandescent lamp and fluorescent lamp, and then be fourth generation lighting source. Therefor, the white LEDs has been a hot issue.White light can be generated by LEDs with one of three ways or approaches. The first is through combining light of red, green, and blue LEDs. The second approach is to use a UV LED emitter to excite red, green, and blue phosphors—the same way fluorescent lamps generate white light. The most common approach for producing white LEDs has been to use a broadband yellow-emitting phosphor such as YAG:Ce³⁺ which largely absorbs mostly 460nm blue light and emits 560nm yellow light with a blue LED chip. Nowadays, the typically phosphor coating process is that phosphor-containing silica gel is dropped on the surface of a blue LED chip. There are three disadvantages to the white LEDs fabricated with this method. First, the production efficiency is lower, which cannot fit the modern industrial production; second, the thickness of phosphor layer is non-uniformity, which introduce non-uniformity within the light spot of LED; third, the chromaticity deviation among LEDs is inevitable. In light of above issues, a conformal phosphor coating method, i.e. the slurry method, was employed in our experiment, which firstly used for color CRT production. A conformal-coating phosphor layer covered LED chip emitting surface was realized by slurry method based on a self-developed phosphor suspension in a water-soluble photoresist. The emulsion, in which water is both dispersant and developer, debases the production cost and has a excellent performance.According to the above problems, the new conformal coating technology is employed. Some interesting conclusions from the work are listed as follows:1. The sensitometric performance of the emulsion is investigated, and it is thought that the UV source and the blue light could make the emulsion exposed.2. Taking the luminous efficiency and output light uniformity of white LED as the evaluating indicator, the concentration and ratio of ingredients in slurry are researched. The parameters are investigated and some advices, which are suggested to improve the performance, are proven to be effective in our experiment. In the slurry, the typical concentration of PVA, ADC and phosphor is 2%, 0.02% and 250mg/ml, respectively.3. A silica gel-internal and PVA-external emulsion, which can improve the performance of phosphor layer further, is advanced.4. The study on the stability of emulsion of PVA and silica gel show PVA is both a filmer and a emulsifier for achieving the silica gel-internal and PVA-external emulsion. What's more, some non-ion or cation surfactant in slurry can make for the further stabilization of emulsion.5. Testings, such as output light uniformity, spectrum, life and so on ,are carried out on the packaged LED.