• Journal of the Korean Ceramic Society
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• v.44 no.3 s.298
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• pp.147-151
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• 2007

An improvement for the efficiency of the $Sr_{2}SiO_{4}:Eu$ yellow phosphor under the $450{\sim}470\;nm$ excitation range have been achieved by adding the co-doping element ($Mg^{2+}\;and\;Ba^{2+}$) in the host. White LEDs were fabricated through an integration of an blue (InGaN) chip (${\lambda}_{cm}=450\;nm$) and a blend of two phosphors ($Mg^{2+},\;Ba^{2+}\;co-doped\;Sr_{2}SiO_{4}:Eu$ yellow phosphor+CaS:Eu red phosphor) in a single package. The InGaN-based two phosphor blends ($Mg^{2+},\;Ba^{2+}\;co-doped\;Sr_{2}SiO_{4}:Eu$ yellow phosphor+CaS:Eu red phosphor) LEDs showed three bands at 450 nm, 550 nm and 640 nm, respectively. The 450 nm emission band was due to a radiative recombination from an InGaN active layer. This 450 nm emission was used as an optical transition of the $Mg^{2+},\;Ba^{2+}\;co-doped\;Sr_{2}SiO_{4}:Eu$ yellow phosphor+CaS:Eu red phosphor. As a consequence of a preparation of white LEDs using the $Mg^{2+},\;Ba^{2+}\;co-doped\;Sr_{2}SiO_{4}:Eu$ yellow phosphor+CaS:Eu red phosphor yellow phosphor and CaS:Eu red phosphor, the highest luminescence efficiency was obtained at the 0.03 mol $Ba^{2+}$ concentration. At this time, the white LEDs showed the CCT (5300 K), CRI (89.9) and luminous efficacy (17.34 lm/W).

• Korean Journal of Optics and Photonics
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• v.32 no.4
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• pp.163-171
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• 2021

Conventional white light-emitting diodes (LEDs) for lighting applications consist of blue LEDs and yellow phosphors, the spectrum of which lacks deep red. To improve the color-rendering characteristics of white LEDs, a red quantum-dot film was applied to the diffuser plate of LED lighting. The mean free paths of the quantum dots and the concentration of the TiO₂ particles in the diffuser plate were adjusted to optimize the optical structure of the lighting. The color-rendering index (CRI) was greater than 90 for most conditions, which demonstrates that adoption of the red quantum-dot film is an effective way for improving the color-rendering properties of conventional white LEDs. The angular dispersion of color coordinates could be removed by utilizing the optical cavity formed between the diffuser plate and the reflector on the bottom of the lighting, where multiple passages of the light through the quantum-dot film reduced the differences in optical path length depending on the viewing angle.