@article{tessler_1999,  title={Erbium in a-Si:H},  volume={29},  ISSN={0103-9733},  url={https://doi.org/10.1590/S0103-97331999000400003},  DOI={10.1590/S0103-97331999000400003},  number={4},  journal={Brazilian Journal of Physics},  publisher={Sociedade Brasileira de Física},  author={Tessler, Leandro R.},  year={1999},  month={Dec},  pages={616–622} }