Hoi, P.V., Huy, B. and Chi, D.T. 2012. Effect of Excitation Migration and Upconversion in Highly Erbium-doped Glass Micro-sphere Lasers. Communications in Physics. 20, 2 (Aug. 2012), 143. DOI:https://doi.org/10.15625/0868-3166/20/2/2168.