Dual-wavelength superscattering in plasmonic core-shell nanostructures for transparent structural color

Structural coloration generates some of the most vibrant colors in nature and has numerous applications. Inspired by the recently reported transparent displays relying on wavelength-selective scattering, we address the novel problem of transparent structural color, which requires nanoparticles to have a narrow-band and broad-angle scattering response. Although superscattering beyond the single-channel limit has important prospects for enhancing transparent displays, it has not yet been reported. Here, we propose a simple dielectric-gold core-shell nanoparticle capable of superscattering at blue (lambda = 450 nm) and green (lambda = 532 nm) wavelengths, along with a dipolar surface plasmon resonance (SPR) at the red wavelength (lambda = 640 nm), making it suitable for full-color transparent displays. We demonstrate that the superscattering at lambda = 450 nm arises from the overlap of the epsilon-near-zero (ENZ) dipolar and quadrupolar modes. Furthermore, the coupling of conventional quadrupolar and dipolar modes can also enhance the scattering efficiency at lambda = 532 nm, breaking the single-channel limit. Lastly, we show that the optimized nanoparticles can confine the scattering light within the forward hemisphere at lambda = 450 nm and 532 nm, due to the interaction of quadrupolar and dipolar modes. Additionally, they exhibit dipole far-field radiation characteristics at lambda = 640 nm with a wide angular beamwidth > 60 degrees. The simple structural nature and unique scattering properties of proposed dielectric-gold core-shell nanoparticles hold promise applications in full-color transparent displays, spectroscopy, and biomedical imaging.