PPM level gaseous ammonia detection using laser Induced fluorescence on vapochromic coordination polymers

The detection of ammonia in parts per millions range has been challenging in sensors research and is of great importance for industrial applications. This thesis document efforts to develop and test a low-cost optical detection system for ppm level ammonia measurements utilizing a Vapochromic Coordination Polymer (VCP) Zn[Au(CN)2]2 as the sensing material. Upon high concentration ammonia exposure, the polymer's fluorescent peak under near-UV stimulation undergoes a spectral shift from 470nm to 530nm, while the intensity increases by 3~4X. At ammonia concentrations < 1000ppm, the spectral shift becomes hidden within the overall changing fluorescent spectrum shape so simple detection methods do not work. The key point in this analysis is to note the way the spectrum changes in each wavelength bins varies in different ammonia concentration exposures. We then developed two customized spectral processing techniques named Spectral Region Subtraction (SRS) method and Sum of Integrated Emissions (SIE) method to characterize hidden changes in spectral shape for concentrations < 1000ppm. Both methods give excellent sensitivity between 0 – 50 ppm and > 300 ppm. For wide-range concentration detection, a combination of two metrics have to be used together.