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CCT- and CRI-tuning of white light-emitting diodes using three-dimensional non-close-packed colloidal photonic crystals with photonic stop-bands

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Abstract

This study exhibited the correlated color temperature (CCT)- and color-rendering index (CRI)-tuning behavior of light emission from white light-emitting diodes (WLEDs) using three-dimensional non-close-packed (3D NCP) colloidal photonic crystals (CPhCs). The CCT of approximately 5300 K (characteristic of cold WLEDs) of white light propagated through the NCP CPhCs dropped to 3000 K (characteristic of warm WLEDs) because of the photonic stop-bands based on the photonic band structures of NCP CPhCs. This study successfully developed a novel technique that introduces lower-cost CCT- and CRI-tuning cold WLEDs with a CRI of over 90 that of warm WLEDs by using 3D NCP CPhCs.

©2013 Optical Society of America

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Supplementary Material (1)

Media 1: MOV (3694 KB)     

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Figures (4)

Fig. 1
Fig. 1 (a) Schematic diagram of the 3D NCP CPhCs deposited onto the 5630 WLED package. The inset shows the OM image of c-WLEDs with 3D NCP CPhCs. (b) The fcc Brillouin zone with symmetry points. The z-axis is along the [111] direction.
Fig. 2
Fig. 2 FESEM images of the 3D NCP CPhCs prepared using PS nanospheres with D of (a) 225 nm, and (b) 250 nm. (c) The FESEM surface images of the NCP CPhCs showing that the nanospheres stack with a well-organized (111) plane and fcc structures. The first Brillouin zone with the symmetry points indicated. Inset: cross-section of the NCP CPhCs into domains along the (110) plane. (d) Schematic showing the NCP CPhC of the fcc structure viewed along the (100) plane.
Fig. 3
Fig. 3 (a) Current-dependent luminous flux and luminous efficiency of the four types of WLEDs. (b) Luminescence spectra of the four types of WLEDs. The WLEDs have an input power of approximately 0.384 W.
Fig. 4
Fig. 4 (a) and (c) Unpolarized angular-resolved transmission measurements of the c-WLEDs with NCP CPhC of a = 349 nm (Media 1) and 385 nm. (b) and (d) The photonic dispersion curves determined from the data shown in (a) and (c) and compared with the photonic band structures. Inset: The photonic band structure of the infinite NCP CPhCs of the fcc structure calculated using the PWE method. With respect to mirror symmetry, the continuous blue lines represent asymmetric bands, and the dashed red lines represent symmetric bands.

Tables (1)

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Table 1 The optical characteristics of the four types of WLEDs.

Equations (4)

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λ R ( D )=2 d 111 n eff 2 sin 2 θ 111
d 111 = a 3 = 2 3 ( D+x )
n eff 2 = n PS 2 f PS + n air 2 ( 1 f PS )
f PS = 4 V sphere V cubic = 4 2 3 π [ D 2( D+x ) ] 3
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