ORMOSIL's layers as luminophores' matrices in an UV optical fibre's sensor

Abstract

The paper concerns the results of optical fibre's ultraviolet sensors' investigation. The cladding of the optical fibre's sensing part was removed and substituted with an active layer containing a coumarin's derivative designated with the number 3609. The dye acted as a transducer converting ultraviolet into visible radiation which could be easily detected. The theoretical modeling with the use of genetic algorithms proved that the best sensitivity of the sensor is achieved when the refractive indices of the active layer and the core are equal. Organically Modified Silica (ORMOSIL) matrices satisfy that condition as their refractive indices may be controlled and reach a value characteristic for the fused silica glass. However it may be expected that both the structure and the composition of ORMOSIL matrices may influence the organic dye's behaviour. The aim of the experiment presented in the paper was to measure the sensitivity of optical fibre sensors comprising the active layers composed of three alkoxysilanes which were methyltriethoxysilane (MTES), phenyltriethoxysilane (PhTES) and tetraethoxysilane (TEOS) as far as the sensitivity of the sensors with silica active layer derived from pure TEOS. Moreover, the influence of hydrolysis and condensation's time on the intensity of dye's luminescence both in active layers and sols' solutions was investigated. The results proved that hydrolysis time and gel's composition may influence a sensitivity of the sensor. Despite the initial decrease of luminescence's signal the long-lasting stability of UV/VIS conversion has been noticed which creates a possibility of the future practical application of the described sensors.