Valence changes and semiconductor-to-metal transitions in Tm1-xEuxSe and TmSe1-xTex B. Batlogg, E. Kaldis et P. Wachter J. Phys. Colloques, 40 C5 (1979) C5-370-C5-371 DOI: 10.1051/jphyscol:19795131