title: Improved color coordinates of green monochromatic pc-LED capped with a band-pass filter.
abstract: This study introduces a "greener" green monochromatic phosphor-converted light-emitting diode (pc-LED) using a band-pass filter (BPF) combined with a long-pass dichroic filter (LPDF) and a short-pass dichroic filter (SPDF) to improve the color quality of our previously developed LPDF-capped green pc-LED. This can also address the drawbacks of III-V semiconductor-type green LEDs, which show a low luminous efficacy and a poor current dependence of the efficacy and color coordinates compared to blue semiconductor-type LEDs. The optical properties of green monochromatic pc-LEDs using a BPF are compared with those of LPDF-capped green pc-LEDs, which have a broad band spectrum, and III-V semiconductor-type green LEDs by changing the transmittance wavelength range of the BPF and the peak wavelength of the green phosphors. BPF-capped green monochromatic pc-LEDs provide a high luminous efficacy (134 lm/W at 60 mA), and "greener" 1931 Commission Internationale d'Eclairage (CIE; CIEx, CIEy) color coordinates (0.24, 0.66) owing to the narrowed emission spectrum. We also propose a two-dimensional (2D) polystyrene (PS) microbead (2-μm diameter) monolayer as a scattering layer to overcome the poor angular dependence of the color coordinates of the transmitted light through a nano-multilayered dichroic filter such as an LPDF or BPF. The 2D PS scattering layer improves the angular dependence of the green color emitted from a BPF-capped green pc-LED with only 3% loss of luminous efficacy.
authors.affiliation: Department of Chemistry, Kookmin University, Seoul 136-702, South Korea.
authors.forename: Ji Hye
authors.initials: JH
authors.lastname: Oh
authors.forename: Su Ji
authors.initials: SJ
authors.lastname: Yang
authors.forename: Yeon-Goog
authors.initials: YG
authors.lastname: Sung
authors.forename: Young Rag
authors.initials: YR
authors.lastname: Do
mesh_terms: D003116:Color; D004867:Equipment Design; D019544:Equipment Failure Analysis; D005374:Filtration / Q000295:instrumentation*; D008029:Lighting / Q000295:instrumentation*; D055096:Optical Devices; D012031:Refractometry / Q000295:instrumentation*; D012666:Semiconductors