The effect of plasma treatment and subsequent oxygen annealing on the critical temperature of superconducting transition T(c) and optical properties of high-T(c) superconducting GdBa2Cu3O7-x, films was studied. The optimal treatment conditions for a substantial increase of T(c) were found. The behavior of typical peculiarities in the epsilon2(HomegaBAR)) spectra (2.5 eV and 3.7-4 eV bands) was shown to correlate well with T(c) changes.