Detailed Study on Pulse-Sprayed Conformal Phosphor Configurations for LEDs

We report an investigation of the optical performance of a conformal-shaped phosphor coating fabricated using pulsed spray techniques on horizontal LED chips. Both the nitride and YAG:Ce phosphor mixed configuration and the multilayer configuration were studied. Also, 3535-packaged LED devices with the two typical phosphor configurations were prepared and analyzed. The results revealed that the LED devices with multilayer phosphor configurations emitted an average of 5.6% more radiant flux than those with mixed phosphor configurations. However, such LED devices presented an interesting reversed tendency in the luminosity measurements, which were 0.3 lm and 6 lm lower at 10 mA and 350 mA, respectively. Finally, the color rendering index (CRI) and correlated color temperature (CCT) homogeneity of the LED devices were further analyzed. A twofold reduction in CCT variation was observed compared with the conventional phosphor coating methods. It was found that the mixed phosphor LED devices demonstrated outstanding angular CCT distributions for viewing angles ranging from -80° to 0°, and a CCT variation of only 45 K was detected, while the multilayer phosphor coating had higher color rendering capabilities, reaching a CRI_general value as high as 85.6. A promising guideline found through this work is that the pulse-sprayed conformal phosphor configuration would particularly be able to improve the light quality of LED devices by a significant amount: the mixed phosphor configuration achieves excellent CCT homogeneity, and the multilayer phosphor configuration reveals a novel concept for fabricating a low-CCT and high-CRI LED device with less nitride phosphor. The findings of our research should provide valuable insight to LED industries.