Flux growth and optical spectra of NdTa7O19 crystals

Phase formation in the region of NdTa7O19 (NHT) stability of the Nd2O3-Ta2O 5-Li2B4O7 system has been studied. Single crystals of NHT have been grown f rom fluxed melts based on the lithium tetraborate by spontaneous nucleation method. These crystals belong to 6/m class of symmetry, and they have stro ngly developed faces of pinacoid, hexagonal prism and two hexagonal pyramid s. The typical sizes of the hexagonal NHT plate-like crystals with no signi ficant inclusions were up to 3 x 3 x 1 mm(3). The optical spectra of NdTa7O 19 are presented and discussed. They are strongly affected by the presence of optically active ions at different, non-equivalent host sites. In fact, the number of components of the low temperature absorption and emission ban ds often exceeds that expected from the crystal field splitting of the elec tronic states of a single Nd3+ ion. At room temperature the bands become qu ite broad, and this should favour both pumping operations and tunability in case of laser applications. The lifetime of the F-4(3/2) emitting level is about 140 mus independently on the temperature, indicating that non-radiat ive multiphonon relaxation processes are ineffective for this compound. (C) 2001 Elsevier Science B.V. All rights reserved.