  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.
