High quality factor metasurfaces for two-dimensional wavefront manipulation.

The strong interaction of light with micro- and nanostructures plays a critical role in optical sensing, nonlinear optics, active optical devices, and quantum optics. However, for wavefront shaping, the required local control over light at a subwavelength scale limits this interaction, typically leading to low-quality-factor optical devices. Here, we demonstrate an avenue towards high-quality-factor wavefront shaping in two spatial dimensions based on all-dielectric higher-order Mie-resonant metasurfaces. We design and experimentally realize transmissive band stop filters, beam deflectors and high numerical aperture radial lenses with measured quality factors in the range of 202-1475 at near-infrared wavelengths. The excited optical mode and resulting wavefront control are both local, allowing versatile operation with finite apertures and oblique illumination. Our results represent an improvement in quality factor by nearly two orders of magnitude over previous localized mode designs, and provide a design approach for a new class of compact optical devices.

Amorphous silicon carbide high contrast gratings as highly efficient spectrally selective visible reflectors.

We report spectrally selective visible wavelength reflectors using hydrogenated amorphous silicon carbide (a-SiC:H) as a high index contrast material. Beyond 610nm and through the near infrared spectrum, a-SiC:H exhibits very low loss and exhibits an wavelength averaged index of refraction of n = 3.1. Here we design, fabricate, and characterize such visible reflectors using a hexagonal array of a-SiC:H nanopillars as wavelength-selective mirrors with a stop-band of approximately 40 nm full-width at half maximum. The fabricated high contrast grating exhibits reflectivity R >94% at a resonance wavelength of 642nm with a single layer of a-SiC:H nanopillars. The resonance wavelength is tunable by adjusting the geometrical parameters of the a-SiC:H nanopillar array, and we observe a stop-band spectral center shift from 635 nm up to 642 nm. High contrast gratings formed from a-SiC:H nanopillars are a promising platform for various visible wavelength nanophotonics applications.

Carbene metal amide photoemitters: tailoring conformationally flexible amides for full color range emissions including white-emitting OLED.

Conformationally flexible "Carbene-Metal-Amide" (CMA) complexes of copper and gold have been developed based on a combination of sterically hindered cyclic (alkyl)(amino)carbene (CAAC) and 6- and 7-ring heterocyclic amide ligands. These complexes show photoemissions across the visible spectrum with PL quantum yields of up to 89% in solution and 83% in host-guest films. Single crystal X-ray diffraction and photoluminescence (PL) studies combined with DFT calculations indicate the important role of ring structure and conformational flexibility of the amide ligands. Time-resolved PL shows efficient delayed emission with sub-microsecond to microsecond excited state lifetimes at room temperature, with radiative rates exceeding 106 s-1. Yellow organic light-emitting diodes (OLEDs) based on a 7-ring gold amide were fabricated by thermal vapor deposition, while the sky-blue to warm-white mechanochromic behavior of the gold phenothiazine-5,5-dioxide complex enabled fabrication of the first CMA-based white light-emitting OLED.