Semiconducting Binary and Alloyed Silver Chalcogenide Quantum Dots structural morphological and optical band gap tuning

Abstract

The eco-friendly quantum dots (QDs) are useful for the conversion of solar radiations to electrical energy due to their unique properties i.e. multiple electron generation, effective charge transfers, bandgap tuning. Silver-based QDs are comparatively eco-friendly than lead and cadmium based QDs. Silver selenide (Ag2Se) QDs are synthesized by optimizing various parameters in co-precipitation approach. The bandgap of Ag2Se decreases from 1.8 eV to 0.99 eV with the increase in the size from 5 nm to 31.6 nm. The hydrothermal approach is also tested but the size obtained is beyond QD size. So, co-precipitation approach is used for further synthesis. The size of co-precipitated silver sulphide (Ag2S) changes from 24.1 ± 10 nm to 4.8 ± 0.75 nm with synthesis time from 5 minutes to 60 minutes. The size calculated by transmission electron microscopy (TEM) and Brus equation is in good agreement. Quantum confinement (QC) arises with the phase-change as confirmed by X-ray diffraction (XRD) and Raman spectra. The size of co-precipitated selenium alloyed Ag2SexS1-x (x = 0, 0.4, 0.6 and 1.0) QDs calculated using Williamson-Hall plot, TEM and Brus equation is in good agreement. The redshift in first exciton peak of UV-VIS-NIR spectroscopy indicate QC. The bandgap (Tauc plot) of Ag2SexS1-x QDs decrease from 1.3 eV to 0.88 eV showing QC depends upon size and composition. Raman spectra show the formation of the desired alloyed structure. The synthesized QDs may be suitable for devices requiring QC that are influenced by even a little change in size. newline