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The present work reports a simple fluorescence based tapered fiber optic probe for fluoride ion having a detection range of 2.08 × 10 -6 -2.005×10 -4 M. The performance of the tapered probe is evaluated with respect to probes that consist of combinations of bare un-cladded multimode optical fibers. The effect of fluorescence quenching of a natural dye Curcumin in the presence of fluoride ion is used in the implementation of the probes. The probe effectively uses multiple mechanisms for the excitation and collection of fluorescence from the medium enabling higher sensitivity compared to conventional spectrophotometry especially at very low concentrations of fluoride.

The present work describes an energy-transfer-based fluoride sensor using the highly photo-stable Coumarin 540a (C540a)-Rhodamine 6g (Rh6g) dye pair. Rh6g exhibits a decrease in fluorescence emission, whereas C540a shows no change in response to fluoride. The increase in fluoride concentration decreases the energy transfer efficiency between the C540a donor and Rh6g acceptor in acetonitrile, leading to a subsequent recovery of fluorescence emission from C540a molecules. The sensing mechanism using fluorescence resonance energy transfer is found to be highly specific towards fluoride detection when compared to the response towards other anions. The fluorescence emission of both dyes is monitored to enable fluoride detection within a broad range.

The present work describes the enhanced photochemical degradation of natural dye Curcumin in acetonitrile-water mixture in the presence of fluoride upon irradiation with light. The strong basicity of fluoride modifies the solvent environment around Curcumin molecule leading to alkaline mediated degradation of Curcumin which is further accelerated by irradiation with light. The photochemical degradation of Curcumin is studied using absorption and fluorescence spectroscopy and verified using infrared spectroscopy and fluorescence lifetime studies. The results of the work indicate that the method of Curcumin irradiation can be used as a sensing technique for fluoride detection in a wide range.

Fluorescence based fiber optic sensor for fluoride in acetonitrile is implemented using Curcumin dye as the sensing reagent.Curcumin complexes with fluoride ion leading to considerable decrease in fluorescence intensity with increase in fluoride ion concentration OCIS codes: (060.0060) Fiber optics and optical communications; (120.0120) Instrument, measurement and metrology; (230.0230) Optical devices; (280.0280) Remote sensing and sensors