Ammonia vapor sensor based on CdSe/SiO₂ core-shell nanoparticles embedded in sol-gel matrix

A high-performance ammonia vapor sensor is proposed comprising CdSe/SiO₂ core-shell nanoparticles embedded in a sol-gel matrix immobilized on the tip of an optical fiber. The experimental results show that the luminescence intensity of the CdSe/SiO₂ nanoparticles reduces significantly when exposed to ammonia vapor. The fluorescence quenching effect is thought to be caused by the adsorption of the ammonia molecules at the trapped sites on the surface of the CdSe quantum dots (QDs). In addition, the proposed sensor exhibits good linearity for ammonia vapor concentrations between 10 and 400 ppm, and has a detection limit of as little as 1.2 ppm. Moreover, the sensor has a response time of 6.1 s when switching from pure N₂ to a mixed N₂-ammonia vapor and 942.2 s when switching in the reverse direction. Importantly, the signal changes are fully reversible when switching repeatedly between the two gaseous environments. Overall, the results show that the proposed sensor has many key advantages compared to optical sensors based on organic sensitive dye, including a higher response (I₀/I), an improved chemical stability, and full reversibility.