Photoluminescence in electronic ferroelectric Er_{1-x}Yb_xFe_2O_4
  Strong Stark splitting, which is nearly independent of the R-ions replacement, has been observed through the photoluminescence investigation of electronic ferroelectric Er1-xYbxFe2O4 (x=0, 0.8, 0.9 and 0.95). Initially multiple radiative decay channels have been investigated, especially the visible transition 4F9/2-->4I15/2, of which a quenching effect has been observed. A series of small non-Raman peaks have been observed superimposed on a broadband photoluminescence spectrum, of which we tentatively assign Stark splitting to be the cause. The splitting of the 4F9/2 and 4I15/2 levels is found to be 54meV and 66meV, respectively. This unusually large Stark splitting at visible range indicates the existence of strong local field originated from the W-layer in the charge-frustrated ErFe2O4. 
R. Wang, H. X. Yang, Y. B. Qin, B. Dong, J. Q. Li, and Jimin Zhao
cond-mat.str-el cond-mat.mtrl-sci