Renuka Bokolia | University of Delhi (original) (raw)
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![Research paper thumbnail of Effect of particle size on the thermoluminescence properties of Ba[sub 0.97]Ca[sub 0.03]SO[sub 4]:Cu](https://a.academia-assets.com/images/blank-paper.jpg)
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Modified ceramic compositions of Bi3.79Er0.03Yb0.18Ti3−xWxO12 with fixed Er and Yb content, and a... more 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 δ=0.003) and dispersion with frequency in the range (10−2–10 Hz) are observed, and improvements in the remnant polarization (2Pr=28.86 μC/cm2) 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 (~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.
Structural, electrical, and light up conversion properties of Erbium (Er) substituted bismuth tit... more Structural, electrical, and light up conversion properties of Erbium (Er) substituted bismuth titanate (Bi 4 À x Er x Ti 3 O 12 ) ceramics have been investigated. Formation of single phase Bi 4 Ti 3 O 12 with orthorhombic unit cell is confirmed, and orthorhombic distortion is found to decrease with increasing erbium content (x). Presence of Bi 2 Ti 4 O 11 secondary phase ( o5 wt%) is detected due to bismuth loss, and is found to decrease with increasing erbium content (x). A randomly oriented plate like microstructure with increasing grain size is found to change abruptly at higher erbium content x 4 0.2. Raman spectroscopy reveals that (Bi 2 O 2 ) 2 þ layers remain unaffected in the modified compositions, and Er 3 þ substitution for Bi 3 þ occurs predominantly at the A-site in the perovskite blocks leading to cationic disorder and a decrease in the TiO 6 octahedral distortion. Increasing Er substitution results in reduced dielectric losses and reduced dispersion in ε 0 and tan δ over a wide frequency range (10 À 2 to 10 6 Hz). Strong UC luminescence at 527, 548 and 662 nm is seen under an excitation of 980 nm for an optimum erbium content (x ¼0.2) and is attributed to the transitions 2 H 11/2 -4 I 15/2 , 4 S 3/2 -4 I 15/2 and 4 F 9/2 -4 I 15/2 respectively. Increasing Er content (x 4 0.2) exhibits pronounced luminescence quenching due to cross-relaxation (CR) process, and degrades the ferroelectric properties. However the electrical conductivity, dielectric losses and dielectric dispersion reduce considerably with increasing Er content up to x ¼0.3.
Modified ceramic compositions of Bi3.79Er0.03Yb0.18Ti3−xWxO12 with fixed Er and Yb content, and a... more 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 δ=0.003) and dispersion with frequency in the range (10−2–10 Hz) are observed, and improvements in the remnant polarization (2Pr=28.86 μC/cm2) 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 (~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.
Structural, electrical, and light up conversion properties of Erbium (Er) substituted bismuth tit... more Structural, electrical, and light up conversion properties of Erbium (Er) substituted bismuth titanate (Bi 4 À x Er x Ti 3 O 12 ) ceramics have been investigated. Formation of single phase Bi 4 Ti 3 O 12 with orthorhombic unit cell is confirmed, and orthorhombic distortion is found to decrease with increasing erbium content (x). Presence of Bi 2 Ti 4 O 11 secondary phase ( o5 wt%) is detected due to bismuth loss, and is found to decrease with increasing erbium content (x). A randomly oriented plate like microstructure with increasing grain size is found to change abruptly at higher erbium content x 4 0.2. Raman spectroscopy reveals that (Bi 2 O 2 ) 2 þ layers remain unaffected in the modified compositions, and Er 3 þ substitution for Bi 3 þ occurs predominantly at the A-site in the perovskite blocks leading to cationic disorder and a decrease in the TiO 6 octahedral distortion. Increasing Er substitution results in reduced dielectric losses and reduced dispersion in ε 0 and tan δ over a wide frequency range (10 À 2 to 10 6 Hz). Strong UC luminescence at 527, 548 and 662 nm is seen under an excitation of 980 nm for an optimum erbium content (x ¼0.2) and is attributed to the transitions 2 H 11/2 -4 I 15/2 , 4 S 3/2 -4 I 15/2 and 4 F 9/2 -4 I 15/2 respectively. Increasing Er content (x 4 0.2) exhibits pronounced luminescence quenching due to cross-relaxation (CR) process, and degrades the ferroelectric properties. However the electrical conductivity, dielectric losses and dielectric dispersion reduce considerably with increasing Er content up to x ¼0.3.