Haranath, D., S. Mishra, A. G. Joshi, S. Sahai, and V. Shanker. “Effective Doping of Rare-Earth Ions in Silica Gel: A Novel Approach to Design Active Electronic Devices”. Nano-Micro Letters, vol. 3, no. 3, Aug. 2011, pp. 141-5, doi:10.1007/BF03353664.