title: Polychromatic light-emitting diodes with a fluorescent nanosphere opal coating.
abstract: 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.
authors.affiliation: Department of Electrical and Electronic Engineering, University of Hong Kong, Hong Kong.
authors.forename: K N
authors.initials: KN
authors.lastname: Hui
authors.forename: W Y
authors.initials: WY
authors.lastname: Fu
authors.forename: W N
authors.initials: WN
authors.lastname: Ng
authors.forename: C H
authors.initials: CH
authors.lastname: Leung
authors.forename: P T
authors.initials: PT
authors.lastname: Lai
authors.forename: K K Y
authors.initials: KK
authors.lastname: Wong
authors.forename: H W
authors.initials: HW
authors.lastname: Choi