Raman system for monitoring dye doping to hybrid polymer network

Being a relatively low-temperature technique, the sol-gel technology enables the synthesis of hybrid polymers doped by organic dyes. In order to ensure the required properties of the final product, however, the mixing of sol and dye must be strictly controlled to avoid unwanted chemical reactions between them. Raman spectroscopic in-sit monitoring of the process was used to address this problem. Problems encountered in spectroscopic studies of non-transparent dye-doped sols, arising from intensive scattering, attenuation of the Raman signal inside the investigated material, and fluorescence induced by the laser beam, are discussed. The Raman measuring system constructed for the research presented in this paper uses a diode laser and a compact spectrometer connected to a reaction glass vessel by a fibre optic probe. Proper selection of the excitation beam wavelength and suitable design of the opto-mechanical setup results in an increase of the Raman signal and improved rejection of interfering signals. The system presented does not require access inside the vessel. In-situ monitoring was carried out for the process conducted at room temperature and up to 87 °C. As the intensity of the Raman bands assigned to the dye did not change during the process, it can be concluded that dye does not decompose.