Tandon, S. P., M. P. Bhutra, and A. Gupta. “Absorption Spectra of Ternary Complexes of Rare Earths”. Rev. Téc. Fac. Ing. Univ. Zulia, Vol. 7, no. 2, 1, https://mail.produccioncientificaluz.org/index.php/tecnica/article/view/5125.