Deposition of fluorescent organic coatings by glow discharge induced sublimation

The glow discharge induced sublimation (GDS) is a solvent-free coating deposition method used for the growth of organic thin films on solid substrates. This method involves the sublimation of organic molecules in a vacuum chamber and their condensation onto the substrate. The sublimation is obtained by using a radio frequency magnetron sputtering equipment: the organic compound is placed on the sputtering source and bombarded by low energy noble gas ions, which transfer their energy to the organic molecules. The synthesis of pyromellitic dianhydride-4,4′-oxydianiline polyimide thin coatings by this technique has been previously detailed [1]. This work investigated the deposition of thin coatings consisting of the 3-hydroxyflavone (3-HF) fluorescent organic molecule. 3-HF is widely used in organic scintillators owing to the large Stokes shift due to the intramolecular excited-state proton transfer (ESIPT) process. Plasma sampling mass spectrometry is used to study the sublimation of the 3-HF molecules and their gas–phase interactions with plasma ions and electrons. FT-IR spectroscopy and Ion Beam Analysis (RBS and ERDA) have been performed in order to determine the chemical structure and the composition of the deposited coatings. The spectroscopic properties of the deposited coatings, as related to the ESIPT mechanism, have been analysed by UV–Visible spectrofluorimetry, in order to study the chemical surroundings of the 3-HF molecules in the deposited films. Preliminary results on the synthesis and characterisation of SiO2/3-HF bilayer structures deposited by GDS and sputtering are also reported.