Publications by authors named "Ray J H Ng"

LEDs offer a wide range of spectral output with high efficiencies. However, the efficiencies of solid-state LEDs with green and yellow wavelengths are rather low due to the lack of suitable direct bandgap materials. Here, we introduce and develop perylene-enhanced green LEDs that produce a higher wall-plug efficiency of 48% compared to 38% for a solid-state green LED.

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While structural colors are ubiquitous in nature, saturated reds are mysteriously absent. This long-standing problem of achieving Schrödinger's red demands sharp transitions from "stopband" to a high-reflectance "passband" with total suppression of higher-order resonances at blue/green wavelengths. Current approaches based on nanoantennas are insufficient to satisfy all conditions simultaneously.

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Dielectric optical nanoantennas are promising as fundamental building blocks in next generation color displays, metasurface holograms, and wavefront shaping optical devices. Due to the high refractive index of the nanoantenna material, they support geometry-dependent Mie resonances in the visible spectrum. Although phase change materials, such as the germanium-antimony-tellurium alloys, and post-transition metal oxides, such as ITO, have been used to tune antennas in the near-infrared spectrum, reversibly tuning the response of dielectric antennas in the visible spectrum remains challenging.

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Article Synopsis
  • This paper explores how UV-C LED light can effectively inactivate SARS-CoV-2 on surfaces, utilizing a custom-built ray-tracing simulator for this purpose.
  • The simulator is validated against real experiments and a commercial software program, confirming its reliability and user-friendliness for modeling UV-C applications.
  • The study includes a practical example involving a food court in Singapore to analyze how environmental factors impact the effectiveness of UV-C irradiation in eliminating the virus, ultimately offering guidance for the efficient design of UV-C systems.
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Article Synopsis
  • Efficient anti-Stokes emission can lead to ultracompact photonic devices with various applications.
  • Researchers integrate lanthanide-activated nanocrystals in gold nanotrenches using self-assembly to enhance light emission.
  • The study shows that this method significantly boosts emission rates and upconversion efficiency, suggesting future uses in sensors and lasers.
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When a microlens array is aligned and overlaid on an array of patterns with similar periodicity, a highly magnified image of the patterns is observed. This effect, known as moiré magnification, is used to reveal micropatterns that are unresolvable by the naked eye. These patterns are typically limited by print resolution to single color patterns.

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The coloration of some butterflies, Pachyrhynchus weevils, and many chameleons are notable examples of natural organisms employing photonic crystals to produce colorful patterns. Despite advances in nanotechnology, we still lack the ability to print arbitrary colors and shapes in all three dimensions at this microscopic length scale. Here, we introduce a heat-shrinking method to produce 3D-printed photonic crystals with a 5x reduction in lattice constants, achieving sub-100-nm features with a full range of colors.

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Through numerical simulations, we investigate the correlation between the absorption cross-section and the color saturation of plasmonic nanostructures of varying density. Understanding this correlation, enables the prediction of an optimal nanostructure separation, or combinations of different nanostructure sizes for plasmonic color printing applications. Here, we use metal-insulator-metal (MIM) aluminum nanostructures that support gap-plasmons.

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Color printing with plasmonic resonators can overcome limitations in pigment-based printing approaches. While layering in pigment-based prints results in familiar color mixing effects, the color effects of stacking plasmonic resonator structures have not been investigated. Here, we demonstrate an experimental strategy to fabricate a 3-tiered complex superlattice of nanostructures with multiple sets of building blocks.

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All-metal structures consisting of nanoprotrusions on a bulk silver layer are theoretically investigated and shown to have narrow near-perfect absorption peaks (>95%). Within the constraints of constant nanostructure height (50 nm) and pitch (250 nm), these peaks are tunable across the visible spectrum by adjusting the width and shape of the protrusion. The peaks are caused by localized surface plasmon resonances leading to dissipation on the surface of the protrusions.

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