Han, W., T. Wu, and S. Zhu. “Effect of Reduced Grapheme Oxide in Enhancing the Photocatalytic Activity of β-NaYF4:Ho3+@TiO2”. Thematics Journal of Geography, Vol. 7, no. 8, Aug. 2018, https://mail.thinkindiaquarterly.org/index.php/tjg/article/view/8244.