Enhanced near infrared luminescence in Ag@Ag<SUB>2</SUB>S core-shell nanoparticles

International audienceAg-Ag2S core-shell nano-structured particles, prepared bysoft chemical route, were found to be luminescent in the near-infrared(NIR) range. The silver nanoparticles were pre-synthesized with sizecontrol by poly-vinyl-pyrrolidone (PVP) polymer capping from silvernitrate solution, by reduction using sodium borohydride in solution,which were further subjected to reaction with sulfur ions in the laterstage by mixing controlled amount of Na2S in the solution.With increasing concentration of sulfur ions, the plasmonic peak of Agshowed progressive blue shift and damping, leading to finaldiminishment. Enhanced NIR luminescence obtained from Ag@Ag2Score-shell nanoparticles were found to be asymmetric and blue shiftingwith reduced intensity and increasing sulfur ion concentration. Themechanism behind such a behavior is predicted due to formation ofcomposite layer of Ag2S-Ag both at the surface and thevolume, with Ag core at the center, diminishing in size with increasingsulfur concentration. The structure, chemical composition, morphologyand final core-shell structure formation were further established bycombination of X-ray diffractometry (XRD), X-ray PhotoelectronSpectroscopy (XPS) and Transmission Electron Microscopy (TEM) analysis