dx.doi.org/10.1016/s0022-2313(02)00648-8
J. Lumin.
Photonic Materials

Isshiki, H, Polman, A, & Kimura, T. (2003). Fine structure in the Er-related emission spectrum from Er-Si-O matrices at room temperature under carrier mediated excitation. J. Lumin., 102-103, 819–824. doi:10.1016/s0022-2313(02)00648-8