Photoluminescence quenching in ligand free CdS nanocrystals due to silver doping along with two high energy surface states emission

Uncapped CdS and Ag doped CdS (CdS/Ag) nanocrystals have been prepared through chemical method, which are spherical in shape with an average size of 5 nm and 7 nm respectively. X-ray diffraction (XRD) pattern indicates that these nanocrystals are cubic zinc blende in structure. Further, Nuclear Magnetic Resonance (NMR) study verifies that CdS and CdS/Ag nanocrystals are ligand free stable nanocrystals (NCs). Both the prepared samples exhibit absorption band in the ultraviolet-visible range with absorption hump around 475 nm and 480 nm respectively. Photoluminescence (PL) study gives three emission peaks at 418 nm, 486 nm and 526 nm for CdS NCs and at 416 nm, 483 nm and at 529 nm for CdS/Ag NCs, which clearly indicates red shift of peak positions due to silver doping. But, Ag doping on CdS quenches the emission intensity at 529 nm, with enhancement of the intensity for the peaks at 483 nm and at 416 nm. An extra peak at 380 nm has been observed for CdS/Ag NCs, when excited with 300 nm of wavelength, which originates due to the surface interstitial defects. - Graphical abstract: For CdS/Ag, a quenching effect has been observed for the low energy peaks with an enhancement of intensity for the higher energy peaks.