# The Quest for Low Loss High Refractive Index Dielectric Materials for UV Photonic Applications
## 1 Introduction
This area has experienced a great development in the last decade. In photocatalysis, photons are used to activate chemical reactions by offering product selectivity. This effect can be enhanced by plasmonic metals by using metal-semiconductor nanostructures, like Au-TiO\({}_{2}\) decorated particles [27; 28]. However, more recently it was demonstrated that metallic NPs can drive chemical reactions on their own [29]. Most of these studies on UV plasmonics have been done using metals with strong UV plasmonic response such as aluminum, magnesium, gallium, or rhodium [20; 30], but, to the best of our knowledge, HRI dielectric NPs have not been explored in this spectral range yet. Here we present a numerical analysis of several candidate dielectric materials that show HRI dielectric properties at energies above 3 eV. The dielectric materials chosen for this study are aluminum phosphide (AIP), aluminum arsenide (AlAs), aluminum nitride (AlN), diamond, cerium dioxide (CeO\({}_{2}\)), and titanium dioxide (TiO\({}_{2}\)). TiO\({}_{2}\) and CeO\({}_{2}\) are commonly used in photocatalysis [31; 32]. AlN, AlP, and AlAs have undergone extensive study because of their potential use in the fabrication of light-emitting diodes (LEDs) [33]. In fact, in 2010 an AlN LED was presented with an emission wavelength of 210 nm, the shortest ever reported [34]. AlP and AlAs are materials commonly alloyed with GaP and GaAs to form AlGaP and Al\({}_{x}\)G\({}_{1-x}\)As for their use in LED design. Nanodiamonds are being used in several areas of research and for various applications that include catalysis, drug delivery, and biomedical imaging [35]. The analysis of the aforementioned materials consists in a detailed numerical investigation of their directionality properties and their near-field enhancement in the UV. For the sake of comparison, we specifically consider isolated spheres of different sizes. It is worth mentioning that the results obtained for the spheres can be generalized for other NP's shapes. To mimic common typical experimental conditions, interaction effects in dimers are explored by comparing the near-field enhancement and the temperature generated in the nanoparticles and its surroundings. This work is aimed to introduce some HRI dielectric materials that can offer high quality directional properties and high near-field enhancement without heat generation in the UV regime. These features are closely connected with UV light-trapping applications and sensing. We envision that this study can open a new landscape for optimizing the efficiency of solar energy harvesting, photocatalysis, photodetection, and spectroscopic techniques in the UV regime. The work is organized as follows. In Section 2, we briefly review the theoretical concepts and methods used to perform the electromagnetic and temperature calculations. In Section 3, we describe the criteria used to select the analyzed materials. In addition, the optical properties of these materials are presented. Section 4 includes the results and discussion of this research: an analysis of the near-field enhancement, directionality properties and cooperative effects in spherical NPs made of the selected materials. Finally, in Section 5 the main conclusions of this work are summarized.