Charge transfer luminescence of Yb3+

A systematic study of charge transfer (CT) luminescence from Yb3+ is presented. CT luminescence was observed in LiYF4 (approximate to 7 eV), aluminates, phosphates, oxides (approximate to 4 eV) and oxysulfides (approximate to 3 eV). In all cases the CT emission bands are broad and the Stokes shifts are large, ranging from 7000 cm(-1) in oxysulfides and LiYF4 and up to 17 000 cm(-1) in aluminates. The influence of the size of the host lattice cation site on the charge transfer luminescence was investigated. A. shift to longer wavelengths of the CT emission bands with increasing size of the cation site was observed. Typical (radiative) decay times for the CT luminescence are between 100 and 200 ns. The quenching of the Yb3+ CT luminescence in the various host lattices was investigated and compared with the quenching of the Eu3+ emission under CT excitation in the same lattices. A good correlation was found. The quenching temperatures of the Eu3+ emission are much higher than that of the Yb3+ CT luminescence. In lattices where Eu3+ emission quenches at very high temperatures (>500K) Yb3+ CT luminescence could be observed. (C) 2000 Elsevier Science B.V. All rights reserved.