Unravelling the Impact of Annealing Time on the Structural, Optical, Spectroscopic and Morphological Aspects of Sm-doped TiO2 Quantum Dots (QDs): A Probable Material for Optoelectronic Applications

In an assortment of light-mediated optoelectronic applications, the possibility of manipulating the bandgap in semiconductor nanostructures from ultraviolet to visible is a highly significant endeavor. In this work, Sm 3+ -doped TiO 2 quantum dots (QDs) were tailored to have a narrow bandgap by varying the annealing time. The dislocation density of the sample annealed at 350 °C for 3 h (5.67 × 10 -3 nm −2 ) is less than that of the samples annealed at 1 and 2 h (12.23 × 10 -3 nm − 2 and 5.74 × 10 -3 nm −2 , respectively), according to the XRD results, which demonstrate a decrease in dislocation density that is prompted by an increase in crystallite size. The TEM image of the sample of QDs that were annealed at 350 °C for 3 h shows the distribution of almost identical ultra-fine particles. Based on the TEM image, the average grain size distribution is calculated to be 4.35 ± 0.13 nm. The Sm 3+ oxidation state of Sm atoms is indicated by a broad peak centered at 1082.35 eV in the XPS spectrum of the QDs that were annealed for 3 h at 350 °C. The reduction in luminescence intensity observed in the PL spectra of these nanoparticles is most likely caused by the long-lived carriers and efficient electron–hole separation of QDs annealed at 350 °C for 3 h. The bandgap has decreased from 3.54 eV to 3.40 eV as a result of the longer annealing period. Furthermore, after 3 h of annealing at 350 °C, Sm-doped TiO 2 exhibits a reduced optical bandgap and an elevated absorption edge value, indicating that it could be applied for the production of optoelectronic devices.