Carbon dots (CDs) have emerged as a promising class of carbon-based nanomaterials due to their unique properties and versatile applications. Carbon dots (CDs), also known as carbon quantum dots (CQDs) or graphene quantum dots (GQDs), are nanoscale carbon-based materials with dimensions typically less than 10 nanometers. They exhibit intriguing optical, electronic, and chemical properties, making them attractive for a wide range of applications, including sensing, imaging, catalysis, and energy conversion, among many others. Both bottom-up and top-down synthesis approaches are utilized for the synthesis of carbon dots, with each method impacting their physicochemical characteristics. Carbon dots can exhibit diverse structures, including amorphous, crystalline, or hybrid structures, depending on the synthesis method and precursor materials used. CDs have diverse chemical structures with modified oxygen, polymer-based, or amino groups on their surface. These structures influence their optical and electronic properties, such as their photoluminescence, bandgap, and charge carrier mobility, making them tunable for specific applications. Various characterization methods such as HRTEM, XPS, and optical analysis (PL, UV) are used to determine the structure of CDs. CDs are cutting-edge fluorescent nanomaterials with remarkable qualities such as biocompatibility, low toxicity, environmental friendliness, high water solubility, and photostability. They are easily adjustable in terms of their optical properties, making them highly versatile in various fields. CDs find applications in bio-imaging, nanomedicine, drug delivery, solar cells, photocatalysis, electrocatalysis, and other related areas. Carbon dots hold great promise in the field of solar cell technology due to their unique properties, including high photoluminescence, high carbon quantum yield (CQY), and excellent charge separation.

This study uses the Quantum ESPRESSO code to introduce Hubbard correction (U) to the density functional theory (DFT) in order to examine the effects of non-metals (C, F, N, and S) doping on the structural, electronic, and optical characteristics of rutile TiO₂. Rutile TiO₂ is a substance that shows promise for use in renewable energy production, including fuels and solar energy, as well as environmental cleanup. Its wide bandgap, however, restricts their uses to areas with UV light. In order to move the rutile TiO₂ absorption edge toward visible light, one atom of each dopant was substituted at oxygen atom locations in this work. The calculated band structures yielded a bandgap of 3.03 eV for pure rutile TiO₂, which is in good agreement with the experimental measurement. The bandgap of all doped materials, with the exception of F-doped TiO₂, displayed a redshift. The absorption edges in C, N, and S-doped TiO₂ are displaced toward the visible area, as indicated by the imaginary component of the dielectric function peaks. The appropriateness of C, N, and S-doped TiO₂ for photocatalysis applications is demonstrated by the shift in the absorption coefficient to the highest wavelength. The presence of extra charges that attenuate the transmission of light in materials is shown by the increase in refractive index following doping. Furthermore, this discovery is crucial for experimentalists since it helps them understand how non-metal doping affects the characteristics of rutile TiO₂ for photocatalysis applications.

Tin dioxide (SnO₂) nanoparticles doped with varying concentrations of copper were synthesized and characterized using various techniques. The X‐ray diffraction analysis revealed that all doped and undoped SnO₂ samples had a rutile‐type tetragonal structure. The average crystalline size of the doped samples estimated using Scherrer’s formula and the Williamson–Hall plot decreased as dopant concentration increased. Images from scanning electron microscopy revealed spherical grains in the samples. The transmission electron microscope was used to examine the particle nature, and nearly spherical particles were discovered. The energy‐dispersive X‐ray spectroscopy analyses confirmed that the synthesized nanoparticles were nearly stoichiometrically composed of the expected elements copper, oxygen, and tin. The bandgap energy of doped and undoped SnO₂ nanoparticles was determined using UV–visible diffuse reflectance spectra, and it was found to decrease as Cu²⁺ ion concentration increased. The photoluminescence study at the excitation wavelength of 300 nm revealed defect‐oriented emissions between 350 and 500 nm. All the obtained results showed that the physical properties of SnO₂ can be easily engineered through Cu doping for various optoelectronic applications using a low‐cost coprecipitation method.

The growth temperature of semiconducting nanoparticles is well known to be an essential factor in determining their structure and quality of characteristics. To create high-quality ZnO nanostructures, it is critical to optimize the growth temperature. The sol-gel approach is used to render ZnO NPs at different growth temperatures in this report. The influence of growth temperature on the material properties of ZnO nanoparticles has been extensively investigated. The scanning electron microscopy (SEM) images show needle-like structures when synthesized at low temperatures (35 and 45 °C) that transformed into spherical particles as the temperature of the growing medium increased to 75 °C. X-ray diffraction (XRD) analysis displays an increase in crystallinity with annealing temperatures. The average crystallite sizes of ZnO nanoparticles rose with increasing growth temperature and varied from 28 to 34 nm. The XRD peaks positions shift slightly towards lower 2θ angles with the growth temperatures brought about by a change in lattice parameters. The Fourier transform infrared spectroscopy (FTIR) study revealed the presence of a Z–O bond at around 680 cm⁻¹. The intensity of the defect level emission (DLE) band decreased, as the growth temperature exceeded 35 °C. The photoluminescence (PL) study further demonstrated that the prepared nanoparticles had a strong emission peak at 546 nm. PL measurements confirm that with increasing growth temperature, the excitonic peak intensity increases, indicating that the quality of ZnO nanoparticles improves. The estimated bandgap changed from 3.31 to 3.24 eV with the growth temperature.