  We report on the evidenced orbital mediated electron phonon coupling and band
gap tuning in HoFe1-xCrxO3 compounds. From the room temperature Raman
scattering, it is apparent that the electron-phonon coupling is sensitive to
the presence of both the Fe and Cr at the B-site. Essentially, an Ag like local
oxygen breathing mode is activated due to the charge transfer between Fe3+ -
Cr3+ at around 670 cm-1, this observation is explained on the basis of
Franck-Condon (FC) mechanism. Optical absorption studies infer that there
exists a direct band gap in the HoFe1-xCrxO3 compounds. Decrease in band gap
until x = 0.5 is ascribed to the broadening of the oxygen p orbitals as a
result of the induced spin disorder due to Fe3+ and Cr3+ at B site. In
contrast, the increase in band gap above x = 0.5 is explained on the basis of
the reduction in the available unoccupied d - orbitals of Fe3+ at the
conduction band. We believe that above results would be helpful for the
development of the optoelectronic devices based on the ortho-ferrites.
