Tuning the Surface Plasmon Resonance of Lanthanum Hexaboride to Absorb Solar Heat: A Review.

While traditional noble metal (Ag, Au, and Cu) nanoparticles are well known for their plasmonic properties, they typically only absorb in the ultraviolet and visible regions. The study of metal hexaborides, lanthanum hexaboride (LaB₆) in particular, expands the available absorbance range of these metals well into the near-infrared. As a result, LaB₆ has become a material of interest for its energy and heat absorption properties, most notably to those trying to absorb solar heat. Given the growing popularity of LaB₆, this review focuses on the advances made in the past decade with respect to controlling the plasmonic properties of LaB₆ nanoparticles. This review discusses the fundamental structure of LaB₆ and explains how decreasing the nanoparticle size changes the atomic vibrations on the surface and thus the plasmonic absorbance band. We explain how doping LaB₆ nanoparticles with lanthanide metals (Y, Sm, and Eu) red-shifts the absorbance band and describe research focusing on the correlation between size dependent and morphological effects on the surface plasmon resonance. This work also describes successes that have been made in dispersing LaB₆ nanoparticles for various optical applications, highlighting the most difficult challenges encountered in this field of study.