Photoluminescent Lanthanide Coordination Polymers for Ammonia Gas Detection at Ambient Temperature and Humidity

Aiming at ammonia gas detection at ambient temperature, phenoxyacetic acid (Hpoa) and 2,5-pyridinedicarboxylic acid (H2pydc) were employed to construct the isostructural [LnIII(poa)(2,5-pydc)(H2O)2]·3H2O (LnIII = EuIII (I), GdIII (II), and TbIII (III)). Their single crystal structures and photophysical properties as well as the triplet state energies of the sensitizers were characterized. Robustness and responses of I and its composite film with poly(vinyl alcohol) (I/PVA) toward water, ammonia, and common volatile organic compounds were examined. The substantial quenching of EuIII:5D0 → 7FJ by only ammonia was disclosed, and the underlying mechanism was postulated based on experimental and computational studies. Referring to EuIII:5D0 → 7F2, the response R parameter was defined. Under ambient temperature (25–35 °C) and humidity (45–55% RH), a linear dependence of R on ammonia concentration (0.50–10.0 ppm) was obtained from I/PVA. Based on the calibration method, the sensitivity (4.04%·ppm–1), detection limit (0.14 ppm), percentage recoveries (103–111% for 3.50, 6.50, and 8.50 ppm), and relative standard deviation (1.5–8.2%) were determined. The reuse of the film for at least 10 cycles was demonstrated with 95–97% repeatability. Limitation of the detection by extreme humidity was presented.