In this work, the effects of nitrogen addition on the properties of a-C:H:F films produced by rf plasma enhanced chemical vapor deposition at different temperatures are reported. The structural and optical properties were investigated by x-ray photoelectron spectroscopy, Raman spectroscopy, ultraviolet-visible transmittance and ellipsometry measurements. The dependence of both fluorine and nitrogen incorporation in the carbon matrix on the deposition temperature was analyzed. The main effect of progressive nitrogen incorporation is a decrease of transmittance and optical band gap of the samples grown at room temperature and at 400 degreesC. Raman spectra evidence that for films deposited at 400 degreesC a sudden loss of sp(3) carbon bonding occurs. In particular, at fixed plasma composition, the decrease of the optical band gap is interpreted as a clustering of the existing sp(2) carbon sites. Ellipsometry characterization indicates that nitrogen incorporation for the samples deposited at room temperature induces an increase of the refractive index while films deposited at 400 degreesC are characterized by a reduction of the refractive index; this has been correlated to changes in the graphitic cluster size of the network. In particular, the increase in the deposition temperature produces an increase in the size of the graphitic clusters.