A new silver metaniobate semiconductor of Ag_0.5La_0.5Nb₂O₆ with defect-perovskite structure

Silver-containing lanthanum metaniobate Ag_0.5La_0.5Nb₂O₆ nanoparticles were synthesized by sol-gel polymerized complex method. A typical defect-perovskite structure was confirmed by XRD Rietveld refinements. The surface characteristics of the sample were tested by SEM, TEM and EDS measurements. SEM and TEM show that the sample presents ball-like particles with the diameters of 100nm to 400nm. The sample shows both self-activated luminescence and photocatalytic activities. Ag_0.5La_0.5Nb₂O₆ has a direct transition with band energy of 2.85eV. The Ag4d-O2p hybridization in the valence band contributes to the narrowed band gap. The luminescence properties of Ag_0.5La_0.5Nb₂O₆ have been investigated for the first time. The luminescence is characterized by two emission centers with maximum wavelength near 460 and 530nm. The emission and excitation spectra, decay curves and the thermal quenching mechanism were discussed. Ag_0.5La_0.5Nb₂O₆ shows the efficient photocatalytic activities and the photodegradation rate for methylene blue dye (MB) can reach about 95% under visible light (>420nm) irradiation in 5h. The trapped experiments for the active species were tested and discussed, which verified that OH radicals could be the major active species in photocatalysis.