Optical properties of a-C:H and a-C:H:N films subjected to UV and proton irradiations have been investigated by photoluminescence (PL) and spectral ellipsometry (SE) methods. It was shown that the optical properties and PL mechanism of a-C:H:N films depend strongly on nitrogen concentration in the films. a-C:H:N films with high nitrogen content are more tolerant to UV-treatment. In all cases, proton implantation leads to some quenching of luminescence due to introduction of non-radiative recombination centers.