Luminescence of Yb3+ ions in calcium tetraborate with charge transfer

The luminescent properties of Yb3+ ions in calcium tetraborate CaB4O7 under x-ray (similar to30 kV) and UV (3.5-15 eV) excitations are studied. Apart from the IR luminescence associated with the F-2(5/2) --> F-2(7/2) transitions occurring in the Yb3+ ions, the x-ray excitation of CaB4O7:Yb3+ at room temperature gives rise to a broadband luminescence at 330 nm with a large Stokes shift and a decay time of similar to30 ns. On the basis of analysis of the experimental results and their comparison with data from the literature, it is shown that this broadband luminescence is caused by radiative decay of charge transfer states of the Yb3+ ions. (C) 2003 MAIK "Nauka/Interperiodica".