Polychromatic light-emitting diodes with a fluorescent nanosphere opal coating
– KN Hui, WY Fu, WN Ng, CH Leung, PT Lai, KKY Wong, and HW Choi
device
Nanotechnology, vol. 19, 35, pp. 355203 (2008)
A hexagonally close-packed array consisting of fluorescent nanospheres was coated onto short-wavelength GaN light-emitting diodes to demonstrate polychromatic white light emission. The spherical particles self-assemble into ordered three-dimensional opal structures, performing the role of color conversion to generate a polychromatic spectrum with smooth and uniform emission patterns. Different ratios of green and orange-red fluorescent nanospheres were mixed and coated onto high-extraction-efficiency micro-LEDs. Four devices with different shades of white emission were demonstrated. Device A, with a high content of orange-red nanospheres, offers the highest CRI value of 80, whereas device C with a well-balanced ratio of green and orange-red nanospheres exhibits color characteristics closest to ideal white with CIE coordinate at (0.34, 0.34). At 20 mA driving current, the luminous efficacy of the devices A, B, C, and D are 40.5 lm W−1, 57.7 lm W−1, 63.1 lm W−1, and 67.2 lm W−1 respectively, while the correlated color temperatures (CCTs) of the corresponding devices are 3587, 4778, 5271, and 13 000 K.
DOI: 10.1088/0957-4484/19/35/355203
