F. J. Al-maliki, “Synthesis of Nanosilica Glass Activated by Erbium Ions, Spectroscopic studies”, IJP, vol. 7, no. 8, pp. 85–92, Dec. 2009, Accessed: Dec. 19, 2024. [Online]. Available: https://ijp.uobaghdad.edu.iq/index.php/physics/article/view/921