Dielectric, ferroelectric and photoluminescence properties of Er3+ doped Bi4Ti3O12 ferroelectric ceramics

Structural, electrical, and light up conversion properties of Erbium (Er) substituted bismuth titanate (Bi4-xErxTi3O12) ceramics have been investigated. Formation of single phase Bi4Ti3O12 with orthorhombic unit cell is confirmed, and orthorhombic distortion is found to decrease with increasing erbium content (x). Presence of Bi2Ti4O11 secondary phase (< 5 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>0.2. Raman spectroscopy reveals that (Bi2O2)(2+) layers remain unaffected in the modified compositions, and Er3+ substitution for Bi3+ occurs predominantly at the A-site in the perovskite blocks leading to cationic disorder and a decrease in the TiO6 octahedral distortion. Increasing Er substitution results in reduced dielectric losses and reduced dispersion in epsilon' and tan delta over a wide frequency range (10(-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=0.2) and is attributed to the transitions H-2(11/2) -> I-4(15/2), S-4(3/2) -> I-4(15/2) and F-4(9/2) -> I-4(15/2) respectively. Increasing Er content (x > 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=0.3. (C) 2015 Elsevier Ltd and Techna Group S.r.l. All rights reserved.