Optical absorption related to Co-3d bands in sol–gel grown LiCoO2 films

The d–d transition related to the Co-3d bands in sol–gel grown LiCoO2 films was studied using an optical absorption method. The crystallinity of the films was confirmed by the observation of two Raman active modes, A1g (495 cm−1) and Eg (601 cm−1), attributed to the space group (R3m) of the layered rock-salt structure. A prominent optical absorption was observed at ∼2.1 eV, reflecting a peak energy of the density of states for the conduction band related to two Co-eg bands. The Co-eg bands in LiCoO2, viewed as Li substitution into CoO, show the downshift in comparison with that (∼2.3 eV) of CoO, supporting the prediction that the eg bands shift down by Li intercalation.