Abstract
We present a simple and intriguing device that generates highly circularly polarized white light. It comprises white polymer light-emitting diodes (WPLEDs) attached to a wideband cholesteric liquid crystal (CLC) reflector with a wide photonic bandgap (PBG) covering the visible range. The degree of circular polarization realized is very high over the visible range. The wide PBG was realized by introducing a gradient in pitch of the cholesteric helix by controlling the twisting power within the CLC medium. WPLEDs fabricated using a ternary (red, green, and blue) fluorescent polymer blend with the same moiety showed a low turn-on voltage, high brightness, high efficiency, and good color stability.
Highlights
White polymer light-emitting diodes (WPLEDs) have attracted considerable attention because of their several advantages in a wide range of potential applications such as solid-state lighting [1,2], flat-panel display backlights [3], and flexible optoelectronic devices
The emissive polymer blend consisted of three polymers, namely, M-blue (Merck Co.) as the blue emitter, super yellow (SY) (Merck Co.) as the green emitter, and M-red (Merck Co.) as the red emitter; the proportions of the red, green, and blue (RGB) fluorescent polymers were adjusted to realize white emission, i.e., Commission Internationale de L’Eclairage (CIE) coordinates (x, y) of (0.33, 0.33)
Compatibility among the polymers in the blend is another key issue that determines the stability of white light emission
Summary
White polymer light-emitting diodes (WPLEDs) have attracted considerable attention because of their several advantages in a wide range of potential applications such as solid-state lighting [1,2], flat-panel display backlights [3], and flexible optoelectronic devices. CLCs exhibit wavelength- and polarization-selective reflection due to the helical arrangement of the molecules; that is, CLCs selectively reflect CP light with the same handedness as the helix This feature makes CLCs one of the most interesting onedimensional self-assembled photonic crystals (PCs) [20,21]. We present a simple and intriguing device structure that generates highly CP white light from WPLEDs incorporating a single PCLC reflector with a wide photonic bandgap (PBG). Our fabricated WPLED showed low turn-on voltage, high brightness, high efficiency, and good color stability
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