LUMINESCENCE IN ONE-DIMENSIONAL CHAINS OF CLOSED-SHELL TRANSITION-METAL OXOCOMPLEXES

The luminescence of undoped and doped Ln3MO7 (Ln = Y, La, Gd; M = Nb, Ta) and Ba2WO5 is reported and discussed. Dopants are Eu3+ and Nb5+ (f or Ta5+). The crystal structures are characterized by chains consistin g of closed-shell transition-metal oxocomplexes sharing corners. The l uminescence results show that the excited state in these chains is del ocalized. Energy transfer to the dopants is strongly counteracted by d efect sites in the crystal structure which trap the excitation energy before it reaches the intentionally added activator. Therefore, these types of crystal structures do not offer potential as the basis for ef ficient luminescent materials. The luminescence of La3TaO7 is especial ly remarkable, because it seems to show the shortest-wavelength emissi on (almost-equal-to 280 nm) known for tantalates and a small Stokes sh ift (almost-equal-to 8000 cm-1).