Electronic excitations and optical properties of YbFe2O4 thin films

We present the structural, optical properties, and electronic excitation spectra of the YbFe2O4 thin film deposited on (0001) sapphire substrates. The optical spectra of a YbFe2O4 thin film show several electronic transitions, dominated by Fe d to d on-site electronic transitions as well as O 2p to Fe 3d, Yb 6s, and Yb 5d charge-transfer electronic transitions. The direct energy band gap of YbFe2O4 has been found to be 1.40 +/- 0.01 eV at 300 K. Moreover, the electronic transitions centered at 1.75 eV and 2.41 eV exhibit strong temperature dependence with a discontinuity at similar to 190 +/- 10 K, indicating evidence for a structural instability in the system. The optical spectra of YbFe2O4 have been analyzed and also compared with that of isostructural YbFe2O4 and LuFe2O4.