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a b s t r a c tWe show in our work that very narrow (FSR $ 0.09 nm) lasing modes can be formed from Rhodamine 6G solution confined within quartz (SiO 2 ) cuvette with suitable pumping scheme by Q switched Nd:YAG laser. With introduction of silver nanoparticles of different concentrations in Rhodamine 6G we show that such lasing modes can be modulated as well as tuned in intensity, band spacing and emission wavelength. We also show that this system maintains a very high Q value 46.4*10 3 irrespective to change in other parameters.

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.