Charge-Transfer Bands in Crystals of Alkaline Earth Fluorides with Eu~(3+) and Yb~(3+1)

摘要

The absorption, luminescence, and excitation spectra of CaF_(2), SrF_(2), and BaF_(2) crystals with EuF_(3) or YbF_(3) impurity have been investigated in the range 1-12 eV. In all cases, strong wide absorption bands (denoted as CT_(1)) were observed at energies below the 4f~(n)-4f~(n-1)5d absorption threshold of impurity ions. Weaker absorption bands (denoted as CT_(2)) with energies 1.5-2 eV lower than those of the CT_(1) bands have been found in the spectra of CaF_(2) and SrF_(2) crystals with EuF_(3) or YbF_(3) impurities. The fine structure of the luminescence spectra of CaF_(2) crystals with EuF_(3) impurities has been investigated under excitation in the CT bands. Under excitation in the CT_(1) band, several Eu centers were observed in the following luminescence spectra: C_(4v), O_(h), and R aggregates. Excitation in the CT_(2) bands revealed luminescence of only C_(4v) defects.