Ultrafast carrier dynamics and radiative recombination in multiferroic   BiFeO$_{3}$
  We report a comprehensive study of ultrafast carrier dynamics in single crystals of multiferroic BiFeO$_{3}$. Using femtosecond optical pump-probe spectroscopy, we find that the photoexcited electrons relax to the conduction band minimum through electron-phonon coupling with a $\sim$1 picosecond time constant that does not significantly change across the antiferromagnetic transition. Photoexcited electrons subsequently leave the conduction band and primarily decay via radiative recombination, which is supported by photoluminescence measurements. We find that despite the coexisting ferroelectric and antiferromagnetic orders in BiFeO$_{3}$, the intrinsic nature of this charge-transfer insulator results in carrier relaxation similar to that observed in bulk semiconductors. 
Y. M. Sheu, S. A. Trugman, Y.-S. Park, S. Lee, H. T. Yi, S.-W. Cheong,   Q. X. Jia, A. J. Taylor, and R. P. Prasankumar
cond-mat.mtrl-sci