Emergent Opportunities with Magnesium for Green Photonics

Structural color generation exploiting nanophotonics or plasmonic behaviors has burgeoning applications in displays, lasers, sensors and other optical sources due to promising advantages such as durability, environmental friendliness, and compatible integration with monolithic fabrication compared to traditional pigments and dyes. While conventional metals (e.g., Au, Ag and Cu) and their alloys are the focus of current optical research, magnesium (Mg) as an earth-abundant material, with biodegradability and CMOS compatibility, has not been fully explored in photonic applications. In our present works [1, 2], we have already established a novel platform for transient color filters/superabsorbers based on Mg and other dielectric thin films with angle-insensitive response and capabilities for fast fading of single vivid hues when exposed to water. These results motivate us to now pursue the realization of sophisticated 3D nanostructures that will form the building blocks of degradable/biocompatible devices. Based on our preliminary optical simulations using Finite-Difference Time-Domain (FDTD) for selected nanostructure configurations [3], all of the structures exhibit pronounced blueshift of their scattering peak frequency with decreased sizes (i.e. due to the etching process of Mg in water). These resonance shifts beget a plethora of applications in photonic devices. For example, it can produce a smooth transition of hues in color display devices for dynamic color tuning. Besides, we perform near-field scattering measurements with Mg nanostructures <i>in situ</i> to experimentally demonstrate the transient behavior as the Mg dissolves in a controlled manner. This helps us to achieve our long-term goal of realizing Mg-based devices for next-generation CMOS-compatible and green photonic devices.<br/><br/>1. Gong, T., P. Lyu, and M.S. Leite, Scalable Superabsorbers and Color Filters Based on Earth-Abundant Materials. ACS Applied Optical Materials, 2023. 1(4): p. 825-831.<br/>2. Lyu, P., et al., Transient Structural Colors with Magnesium-Based Reflective Filters. Advanced Optical Materials, 2022. 10(13): p. 2200159.<br/>3. Farinha, T.G., et al., Selective etching properties of Mg thin films and micro/nanostructures for dynamic photonics [Invited]. Optical Materials Express, 2021. 11(5): p. 1555-1565.