Abnormal Raman spectra in Er‐doped BaTiO₃ ceramics

Abstract

Greatly enhanced and abnormal Raman spectra were discovered in the nominal (Ba 1 − x Er x )Ti 1 − x /4 O 3 ( x = 0.01) (BET) ceramic for the first time and investigated in relation to the site occupations of Er 3+ ions. BaTiO 3 doped with Ti‐site Er 3+ mainly exhibited the common Raman phonon modes of the tetragonal BaTiO 3 . Er 3+ ions substituted for Ba sites are responsible for the abnormal Raman spectra, but the formation of defect complexes will decrease spectral intensity. A large increase in intensity showed a hundredfold selectivity for Ba‐site Er 3+ ions over Ti‐site Er 3+ ions. A strong EPR signal at g = 1.974 associated with ionized Ba vacancy defects appeared in BET, and the defect chemistry study indicated that the real formula of BET is expressed by (Ba 1 − x Er 3 x /4 )(Ti 1 − x /4 Er x /4 )O 3 . These abnormal Raman signals were verified to originate from a fluorescent effect corresponding to 4 S 3/2 → 4 I 15/2 transition of Ba‐site Er 3+ ions. The fluorescent signals were so intense that they overwhelmed the traditional Raman spectra of BaTiO 3 . The significance is that the abnormal Raman spectra may act as a probe for the Ba‐site Er 3+ occupation in BaTiO 3 co‐doped with Er 3+ and other dopants. A new broad EPR signal at g = 2.23 was discovered, which originated from Er 3+ Kramers ions. Copyright © 2014 John Wiley & Sons, Ltd.