Polychromatic emission from fluorescent-microsphere-coated LEDs

Abstract

White light LEDs using fluorescent microspheres as color conversion agents are demonstrated. The hexagonal ordered arrays of green and red fluorescence microspheres were coated on the blue micro-hexLED centered at 480 nm by microspheres coating technique. At optimal mixed portion of green and red microspheres, white light emission is generated by a combination of blue light from LED and down conversion of fluorescence emission of green and red microspheres by blue excitation light. An overall efficiency of more than 70% is obtained by this new approach. The enhanced efficiency is attributed to two main properties of ordered micropsheres arrays: (1) efficient color conversion and (2) efficient light out-coupling via volumetric light scattering. The resultant LED has lumnious efficiency of 31.8 lm/W with CIE coordinates of (0.30, 0.31). We have demonstrated an alternative solution of producing white light emission, apart from existing down conversion of yellow phosphor with blue or UV LED and multichip LEDs. © 2008 Wiley-VCH Verlag GmbH & Co. KGaA.