**6. Conclusions**

We demonstrated that low-cost, low-tech techniques such as blade coating out of aqueous based dispersions offer an interesting alternative for producing thin, homogeneous, and well controlled nanoporous coatings. While this has been known for years, we demonstrated here the benefit of using dispersions of CeO2, an oxide possessing a high refractive index and which results in nanoporous coatings with a high refractive index. These coatings are then interesting candidates for use as an intermediate layer between air and substrates, such as silicon with a even higher refractive index for providing, for instance, anti-reflection features. Eventually, we believe the UV-blocking of the coating could be of potential interest for protecting organic sub-layers and we think the catalytic capabilities of CeO2could add even more functionalities to the final material.

**Author Contributions:** J.L. and L.J.R. conceived the experiments, analysed and modelled the data, and wrote the paper; L.J.R. performed experiments with the help of S.K. and C.P. for mid-IR imaging; L.D.A. provided nanoparticle samples.

**Funding:** The authors thank funding from Solvay and Agence Nationale de la Recherche (ANR) within the EVAPEC gran<sup>t</sup> 13-BS09-0010-01. The financial support from the CPER CAMPUSB project funded by the French state and the Région Nouvelle-Aquitaine is gratefully acknowledged.

**Acknowledgments:** The authors thank J.-B. Salmon, Ch. Loussert, M. 2 Lehtihet for fruitful help and support.

**Conflicts of Interest:** The authors declare no conflict of interest.
