  Despite of useful applications of Ag, it is hazardous to health and
environment and hence early detection is required. Crystal defects influencing
optical property is less likely utilized for Ag detection using prevalent
UV-Vis technique. Quantum dots (QDs) ZnS prepared by soft chemical route are
exploited for the detection of Ag ions in aqueous solution for nM to mM
concentrations. UV-Vis and photoluminescence (PL) measurements reveal quantum
confinement effect and presence of defects in ZnS nanoparticles (NPs).
Controlled synthesis of ZnS NPs allows appearance of defects related peak at
400-550 nm in UV-Vis spectra. A plausible mechanism is presented and elucidated
by XRD and PL studies for chemical interaction between ZnS with Ag ion. The
interaction affects prominently and defects related absorption of ZnS NPs and
allows single step Ag ion detection in aqueous medium. This absorption method
is extended to other ions (Na, K, Mg, Ca, Ba ions) including S prone heavy and
toxic ions like Pb, Hg and Cd. Among them, Ag ion shows the best response with
ZnS NPs. This demonstration using a portable and cost effective technique with
no organic component opens up possibility for other inorganic materials.
