Observation of the characteristics of Tm2+ and Tm3+ in homogeneous and inhomogeneous TmSe G. Chouteau, F. Holtzberg, O. Peña, T. Penney et R. Tournier J. Phys. Colloques, 40 C5 (1979) C5-361-C5-363 DOI: 10.1051/jphyscol:19795128