@article{gonçalves_messaddeq_atik_ribeiro_1999,  title={Optical properties of ZrO2, SiO2 and TiO2-SiO2 xerogels and coatings doped with Eu3+ and Eu2+},  volume={2},  ISSN={1516-1439},  url={https://doi.org/10.1590/S1516-14391999000100003},  DOI={10.1590/S1516-14391999000100003},  number={1},  journal={Materials Research},  publisher={ABM, ABC, ABPol},  author={Gonçalves, Rogéria R. and Messaddeq, Younes and Atik, Mohamed and Ribeiro, Sidney J.L.},  year={1999},  month={Jan},  pages={11–15} }