Electrical properties and light up conversion effects in Bi3.79Er0.03Yb0.18Ti3-xWxO12 ferroelectric ceramics

Modified ceramic compositions of Bi3.79Er0.03Yb0.18Ti3-xWxO12 with fixed Er and Yb content, and a varying W content (x=0.0, 0.01, 0.03, 0.06 and 0.10) are prepared. The site selectivity of Er3+, Yb3+, and W6+ cations is analyzed, and their influence on the electrical and light up conversion properties is studied. Formation of single phase orthorhombic structure is confirmed with enhanced grain growth up to x=0.03, and for (x >= 0.04-0.10) the grain growth is inhibited, and the orthorhombic distortion is relaxed. Raman spectroscopy reveals W6+ cation substitutes preferentially at the B-site replacing Ti4+ ions in the Bi4Ti3O12 lattice structure. Increasing W6+ donor concentration reduces the conductivity effects by lowering the oxygen vacancies. Reduced dielectric losses (tan delta=0.003) and dispersion with frequency in the range (10(-2)-10 Hz) are observed, and improvements in the remnant polarization (2P(r)= 28.86 mu C/cm(2)) are seen up to an optimum content of x=0.03. At higher W content (x > 0.03), the properties tend to degrade due to structural relaxation and microstructural changes. Up conversion photoluminescence (UC-PL) under 980 nm excitation shows strong emission in the green and red bands due to enhanced crystal field around the Er3+ ions for an optimum W content of x=0.06. A weak blue emission band around (similar to 492 nm) is observed by cooperative emission (CE) due to radiative relaxation of an excited Yb-Yb pair from a virtual level. Variation of UC emission intensity with pump-power confirms a two-photon mechanism for the up conversion process. (C) 2015 Elsevier Ltd and Techna Group S.r.l. All rights reserved.