Z. Pei, G. Dirksen, G. Blasse
May 1, 1994
Materials Chemistry and Physics
Abstract The luminescence of undoped and doped Ln 3 MO 7 (Ln = Y, La, Gd; M = Nb, Ta) and Ba 2 WO 5 is reported and discussed. Dopants are Eu 3+ and Nb 5+ (for Ta 5+ ). The crystal structures are characterized by chains consisting of closed-shell transition-metal oxocomplexes sharing corners. The luminescence results show that the excited state in these chains is delocalized. Energy transfer to the dopants is strongly counteracted by defect 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 efficient luminescent materials. The luminescence of La 3 TaO 7 is especially remarkable, because it seems to show the shortest-wavelength emission (≈ 280 nm) known for tantalates and a small Stokes shift (≈ 8000 cm −1 ).