# The Quest for Low Loss High Refractive Index Dielectric Materials for UV Photonic Applications
## 5 Conclusions  
We have explored the possibilities of a selection of semiconductors--of the low loss High Refractive Index kind--to form nanoparticles with interesting applications in the UV region. The behavior we have considered of interest includes acting as HRI nanoantennas or behaving as unit cells of more complex metamaterials. The analyzed materials include some important semiconductors like AIP, AlAs, AlN, diamond, CeO\({}_{2}\) and TiO\({}_{2}\). When studying its near field--averaged over the surface of the nanoparticle--some important values of the enhancement have been observed within the UV range in most of the considered materials. In the far field, the possibility of using nanoparticles of these materials to generate light directionality effects has been explored by means of the zero-backward efficiency, which accounts for both the scattering efficiency and the backward-to-forward scattering  
Figure 5: Near field \(\left|\left.E\right|\right./\left|E0\right|\) (**top** row) and temperature difference \(\Delta\)T (**bottom** row) maps for a diamond and Al/Al2O3 dimers with gap = 20 nm. Both dimers are illuminated at resonance (photon energy indicated as a inset), with a p-polarized beam E and wave vector k. \(E_{photon}\) corresponds to the photon energy of the illuminating beam. The chosen values of \(E_{photon}\) are those that produce the maximum near-field enhancement at the center of the gap.  
ratio. In fact, all the analyzed materials are better options than Si for scattering directionality applications, both in the VIS and UV ranges. Finally, the near-field enhancement and local temperature effects have been studied for these materials when forming dimers, reaching high values of the near field, similar to the response of well-known semiconductors used in VIS and near-IR (Si, GaAs, and Ge).  
Based on these analyses, some of the studied compounds can be considered as promising High Refractive Index dielectrics in the UV. On the one hand there is diamond, along with AlN, that show loss-less behavior below 6 eV, so they have HRI dielectric character in the entire optical regime (from near-IR to UV). They exhibit the highest values of \(Q_{ZB}\), only matched by CeO\({}_{2}\), but with moderate values of \(\left|\,E\,\right|/\left|\,E_{0}\,\right|\)  all along the UV range. On the other hand, TiO\({}_{2}\), along with AlP, AlAs and CeO\({}_{2}\), present losses above \(\approx 3.5\) eV. Between 3 and 3.5 eV they present high values of \(\left|\,E\,\right|/\left|\,E_{0}\,\right|\)  but lower \(Q_{ZB}\) values than AlN and diamond.  
Finally, the analysis of the thermal response in the case of dimers shows that, for both TiO\({}_{2}\) and diamond, high values of \(\left|\,E\,\right|/\left|\,E_{0}\,\right|\)  can be generated at energies above 3 eV without any losses and consequently no heat.  
[PERSON] and [PERSON] conceived the original idea. [PERSON] carried out the numerical calculations and wrote the paper. All authors analyzed the results and reviewed the manuscript. [PERSON] and [PERSON] supervised the study.  
This research has been supported by the Army Research Laboratory under Cooperative Agreement Number W911 NF-17-2-0023 and by SODERCAN (Sociedad para el Desarrollo de Cantabria) through the Research Vicerrectorate of the University of Cantabria.  
[PERSON] wants to thank the University of Cantabria for her FPU grant. [PERSON] also acknowledges funding from the Ramon y Cajal Fellowship RYC-2016-20831.  
The authors declare no conflict of interest.