Full colour mixing with plasmonic nanorods

February 10, 2020 //By Julien Happich
Researchers from ETH Zürich have demonstrated the use of interleaved arrays of plasmonic nanorods to create continuous transitions between RGB colours.

The method described in the ACS Nano journal under the title “A Plasmonic Painter’s Method of Color Mixing for a Continuous Red−Green−Blue Palette” goes beyond the typical sub-pixel colour mixing approach whereby red, green and blue pixels are periodically arranged in arrays of colour-tunable pixels.

Here, the researchers used numerical full wave simulations to design plasmonic nanorods meeting specific resonance conditions for a given colour. Etched out of an evaporated silver film on an anti-reflection-coated glass substrate, the nanorods structures described in the paper are just 45nm tall with a length varying from 63 to 143nm and a width ranging from 54 to 57nm depending on the represented colour. Smooth colour transitions were obtained by spatially multiplexing the nanorod lattices of the different primary colours on a single pixel, without increasing the pixel size, the authors explain, covering 39% of the standard red-green-blue (sRGB) colour gamut with the possibility to set colour luminance independently of chromaticity (through in-plane geometric parameter adjustments).

As a demonstration, the researchers reproduced colour and grayscale photographs with multiplexed nanorod lattices creating colour pixels just 1.28x1.28μm in size. The authors anticipate that such a colour-mixing approach could be applied to a broad range of scatterer designs and materials and could also find use cases a multi-wavelength colour filters for dynamic photorealistic displays.

Another interesting benefit of these interleaved plasmonic colours is that they are polarization sensitive. When illuminated with light polarized perpendicular to the long axis of the nanorods, reflected light intensity is near zero. This particular property could be used to create active tunable colours or for the polarization encoding of multiple pieces of information in a single image, the authors conclude, for example for anti-counterfeiting applications.

ETH Zürich – www.ethz.ch

Related articles:

Plasmonic nanorods as ultra-fast switching colour pixels

Plasmonic nanolaser can be stretched to different wavelengths

Photo-grade plasmonic colour printing: back to silver

Spray-on plasmonics enable tunable colours at video rate

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