Study On Phosphor Coating For High Power LED Packaging

In this paper, the phosphor films are prepared by different parameters. We have designed the white LED with reflective glass structure and fixed the phosphor film away from the blue-chip for a special distance. After that, its optical efficiency, color rendering index and other properties were characterized. Optical microscope, scanning electron microscopy (SEM), electron diffraction (XRD), Raman spectroscopy, Zhejiang University Tri-color LED Tester and other analysis or detection methods were used in this experiment. The composition of the phosphor particles, phosphor particles in the silicone, particles'precipitation and its dispersion in the matrix problem, distribution issues, different concentration, thickness of the phosphor film are all discussed in this article. We have made a conclusion that a good optical efficiency with high Color Index of the LED corresponding to the preparation parameters of the phosphor film.Phosphor film microstructure observation showed that the YAG phosphor film phosphor particles (Y₃Al₅O₁₂) is more evenly distributed, no significant precipitation. When participating into the red phosphor, the red nitride particles (Sr₂Si₅N₈) reunion obviously that this will lead to output light unevenly. In order to avoid the phosphor generating bubbles, we use ultrasonic agitation with vacuum environment to removal bubbles. Phosphor film mechanical analysis showed that the phosphor particle surface is angular. For the surface tension, the interfacial bonding strength between the silicone matrix and the phosphor particles is low.Raman spectra showed that with the increase in phosphor film's thickness, white LED's light intensity is also on the rise. While using same thickness of the phosphor film, the yellow light's peak strength is also increased with the increasing of yellow phosphor's content, and vice versa. The incorporation of the red phosphor make the red light segment increased in the Raman spectrum. Its light intensity increase and the optical power diagram become wider and fuller. Also the color rendering index increases with photosynthetic efficiency decrease slightly.We have selected series of White LED of different phosphor concentration film's thickness and phosphor composition to observe their lighting color. Its efficiency, color coordinates, color rendering index, color temperature and other optical properties were measured by Zhejiang tricolor LED-201. Comprehensive analysis with phosphor to silicone ratio of 1:3:3(yellow phosphor:8866A silicone:8866B silicone) and participation in red phosphor ratio of 1/60 (red phosphor mass/yellow phosphor mass) is obtained. We can find out that the 315μm thickness of these series LED's light performance is better, and its color index is 79.7, light efficiency is 36.52lm/W. While not participating in red phosphor in the LED, the optimal ratio is 1:3:3(phosphor to silicone ratio) with its thickness of 315μm, and its color coordinates is (0.3248, 0.2830), light efficiency is 69.65lm/W, but its color index is only 74.2.