Enhanced near infrared luminescence in Ag@Ag2S core-shell nanoparticles.

Graphical abstract Highlights • Ag@Ag 2 S core shell nanoparticles were synthesized by soft chemical route. • SPR of Ag NPs blue shifts from 408 to 378 nm with increasing sulfur ion concentration. • Ag@Ag 2 S CSNPs exhibit tunable (1.43–1.50 eV) NIR luminescence with increasing sulfur ion concentration. Abstract Ag-Ag 2 S core-shell nano-structured particles, prepared by soft chemical route, were found to be luminescent in the near-infrared (NIR) range. The silver nanoparticles were pre-synthesized with size control by poly-vinyl-pyrrolidone (PVP) polymer capping from silver nitrate solution, by reduction using sodium borohydride in solution, which were further subjected to reaction with sulfur ions in the later stage by mixing controlled amount of Na 2 S in the solution. With increasing concentration of sulfur ions, the plasmonic peak of Ag showed progressive blue shift and damping, leading to final diminishment. Enhanced NIR luminescence obtained from Ag@Ag 2 S core-shell nanoparticles were found to be asymmetric and blue shifting with reduced intensity and increasing sulfur ion concentration. The mechanism behind such a behavior is predicted due to formation of composite layer of Ag 2 S-Ag both at the surface and the volume, with Ag core at the center, diminishing in size with increasing sulfur concentration. The structure, chemical composition, morphology and final core-shell structure formation were further established by combination of X-ray diffractometry (XRD), X-ray Photoelectron Spectroscopy (XPS) and Transmission Electron Microscopy (TEM) analysis. [ABSTRACT FROM AUTHOR]