Variations énergétiques de l'absorption optique du lanthane et du praséodyme pris en couches minces

Under static ultrahigh vacuum (10(-9) torr), we have studied the optical properties of lanthanum and praseodymium thin films. It is shown that these films behave similarly in the 2000-8000 A spectral range. Results are identical for other light rare-earth thin films. We suggest that indirect transitions are responsible for the presence of a maximum in the optical absorption near 5,8 eV.