Tuning the physical properties of SnO₂ quantum dots via Ag-doping for fabricating efficient photodetectors

In order to satisfy the increasing demand for affordable photodetectors in the sectors of flexible electronics and contemporary medical devices in this decade, researchers are looking for efficient semiconducting nanomaterials globally. Ag-doped SnO₂ quantum dots (QDs) with varying Ag ion concentrations were synthesized via chemical co-precipitation for efficient photodetector fabrication. The impact of Ag dopants on SnO₂ QDs properties was analyzed through multiple characterization techniques. X-ray diffraction and Raman spectra confirmed an impurity-free crystal structure. Crystallite sizes (2.9-3.4 nm), calculated using Scherrer's formula, were below the Bohr excitonic diameter, validating their quantum dot nature. TEM images aligned with crystallite sizes, further confirming QD formation. The observed blue shift in band gaps with increasing Ag dopants is attributed to quantum confinement due to the reduction in mean particle size. Theoretically, the estimated values of absorption cross sections and electric field intensity of SnO₂ QDs and Ag-doped SnO₂ QDs using the finite time domain method were found to be in harmony with UV-Vis spectroscopy results. The obtained FTIR spectra of all the QDs demonstrated distinct peaks corresponding to different chemical bonds, further validated the phase purity. Ag-doped SnO₂ QDs show lower PL intensity than pure SnO₂, indicating better charge separation and less recombination. Including photodetector application, the highest Ag-doped SnO₂ QD sample is expected to have more active sites and be more suitable for various applications, such as photocatalytic and antioxidant capabilities, because of its higher specific surface area. Room temperature Hall effect experiments revealed that the pure SnO₂ QDs showed the p-type semiconducting nature, whereas, with the addition of metal Ag ions, electrons became the majority charge carriers and the doped samples turned into n-type semiconductors. We have fabricated photodetectors using as-prepared samples and found that 6% Ag-doped SnO₂ QDs showed better performance when compared with the other two samples. In addition to that, the free-radical scavenging activities of all the QDs were determined and it was found that SnO₂ QDs doped with Ag ions have better antioxidant properties than pure SnO₂ QDs. Consequently, these Ag-doped SnO₂ QDs were found to be effective for photodetector application and reducing the oxidative stress.