LASER-SELECTIVE EXCITATION-SPECTRA OF HO3+ IONS IN BAF2 CRYSTALS

Crystal-field energy levels for five multiplets of the dominant Ho3+ c entre in BaF2:Ho3+ crystals have been derived from the centre's select ive excitation and fluorescence spectra. The centre is deduced to be o f trigonal symmetry and irrep labels of the C-3v point group are assig ned to the energy levels. The splittings of up to 5.5 cm(-1) observed for transitions involving the gamma(3) (doublet) symmetry levels are e vidence of some distortion at the Ho3+ site from exact C-3v symmetry. The centre exhibits strong up-conversion fluorescence in the 0.1% Ho3-doped crystals. A minor centre, characterised by fluorescence transit ions of much lower energies compared to the dominant centre, is also p resent. (C) 1998 Elsevier Science B.V. All rights reserved.