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The problem in fluorescence detection of gases like ammonia over a wide range from Parts Per Millions (ppm) to 10,000’s ppm (saturation) is that often at <1000 ppm the spectra show almost no peak wavelength shift or intensity change and only subtle fluorescence spectrum alterations, so new metrics are needed. We are exploring two Vapochromic Coordination Polymers (VCP): Zn[Au(CN)2]2, which emits light when exposed to NH3, shifting its peak from 470 nm to green 530 nm under high concentration while the intensity grows 3-5X. A second VCP In2[Pt(CN)4]3 shifts from 560 nm (yellow) to 530 nm. To enhance spectral changes we use a 405 nm laser diode excitation source’s narrow (4nm) stimulation which is clearly separated from the spectral peak for 1000ppm. Focusing the emission on a USB portable spectrometer we enhance the subtle spectra changes with a method that gives unique all ppm values by dividing the spectrum into 10 nm bins, integrate the emission in each bin, relative to that of 0 ppm emission, then sum all the bins (Sum of Integrated Emissions, SIE). This emphasizes wavelength regions that have rapid relative changes at different ammonia ppm exposures. For Zn[Au(CN)2]2 VCP SIE gives excellent sensitivity between 0-100 ppm and >400 ppm, but has poor accuracy in the 100-500 ppm range. At mid ppm ranges some SIE bins decline while others increase so we switch to a second metric, Limited Range SIE, that covers only the 430-470 nm bins which show an accurate linear response. In many spectral fluorescence cases, in the region where the longer wavelength peak begins to dominate, it is best to focus on regions outside of the peak maxima. At higher ppm where the longer peak begins to dominate the full SIE again works best. The SIE also works for the opposite shift from In2[Pt(CN)4]3 showing that it is a very sensitive metrics for different behaving materials, but not for <40 ppm exposures.
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