Luminescence of plasma-treated polymer surfaces at ambient temperature

The aim of the present work is to detect the light emitted by a polypropylene film at ambient temperature once its surface has been subjected to a cold plasma, in other words plasma-induced luminescence (PIL). The general topics is to develop a tool for investigating surface polymer transformation. Kinetic and spectral features of PIL emission were recorded after discharge switch off, thanks to a photomultiplier and a liquid-nitrogen-cooled CCD camera. Three spectral components were clearly identified with their own excitation processes. The two fastest luminescence decay processes are due to radiative de-excitation of energy levels populated during plasma contact, termed as ‘direct excitation mechanisms’. They are related to the short wavelength range of the PIL spectrum which mainly characterizes chromophores initially present in the material. The third one, called a ‘carrier-recombination mechanism’, corresponds to a slow luminescence decay which becomes more and more dominant with the increase of the treatment duration.