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The sol–gel process has emerged as a powerful synthetic strategy for tailoring the physicochemical properties of zinc oxide (ZnO) nanomaterials through controlled metal doping. This review provides a comprehensive and critical analysis of metal-doped ZnO nanoparticles synthesized via sol–gel routes, emphasizing the fundamental mechanisms governing dopant incorporation, defect chemistry, and microstructural evolution. Attention is given to transition-metal, noble-metal, and rare-earth dopants and their influence on crystallographic structure, lattice strain, grain growth, oxygen vacancy formation, and band structure modification. Key sol–gel parameters, including precursor chemistry, chelating agents, hydrolysis and condensation kinetics, pH control, aging conditions, dopant concentration, and calcination temperature, are systematically examined to elucidate their role in dopant dispersion, phase purity, and nanoparticle morphology. The interplay between synthesis conditions and functional performance is critically discussed, highlighting band-gap engineering, charge carrier dynamics, magnetic ordering, and surface reactivity. The review further correlates structure–property relationships with multifunctional applications, including photocatalysis, gas sensing, optoelectronic devices, energy conversion systems, antimicrobial coatings, and biomedical technologies. Current limitations such as dopant segregation, secondary phase formation, and reproducibility challenges are identified, and future directions for scalable, defect-controlled sol–gel fabrication are proposed. This work aims to provide a mechanistic framework and practical guidelines for designing high-performance metal-doped ZnO nanomaterials through sol–gel chemistry.
Perovskite oxides such as LaFeO₃ are promising for various functional applications, with performance significantly enhanced by targeted doping strategies. This study reports the synthesis of La₀.₈Sr₀.₁Ba₀.₁Fe₁₋ₓNiₓO₃ (x = 0.05 and 0.1) compounds via the sol–gel method, followed by systematic structural, microstructural, electrical, and dielectric characterizations using X-ray diffraction (XRD), scanning electron microscopy (SEM), Raman spectroscopy, Fourier-transform infrared spectroscopy (FTIR), and impedance spectroscopy. XRD results confirmed the formation of a single-phase rhombohedral perovskite structure. SEM analysis revealed a homogeneous microstructure, with average grain size decreasing from 171 nm (x = 0.05) to 119 nm (x = 0.1), attributed to the grain growth pinning effect of Ni. Raman and FTIR spectroscopies indicated that Ni substitution induces local lattice distortion. Electrical characterization showed semiconducting behavior across compositions, with DC conductivity analysis revealing temperature-dependent conduction mechanisms: Mott Variable Range Hopping (VRH) at low temperatures, Greaves VRH at intermediate, and Small Polaron Hopping (SPH) at higher temperatures. Activation energy decreased with increasing Ni doping. AC conductivity analysis demonstrated correlated barrier hopping (CBH) conduction for x = 0.05 and overlapping large polaron tunneling (OLPT) for x = 0.1 at high frequencies. Dielectric measurements showed reduced dielectric constant and loss upon Ni substitution, while impedance spectroscopy revealed non-Debye relaxation processes dominated by grain and grain boundary contributions. These findings establish that Ni doping effectively modulates structural order, defect chemistry, and charge transport in La₀.₈Sr₀.₁Ba₀.₁FeO₃ perovskites, improving their electrical performance and dielectric properties and making them promising candidates for applications in solid oxide fuel cells, gas sensors, and electronic devices.
This work presents a comprehensive analysis of the eigenenergy structure and intersubband optical transitions of Al0.3Ga0.7N/AlN cylindrical core–shell quantum dots embedded in an HfO₂ host matrix, aiming to enhance the design and optimization of mid-infrared intersubband optoelectronic devices operating under combined thermal and pressure constraints. The Schrödinger equation is solved using the finite difference method to evaluate confinement energies, dipole matrix elements, nonlinear absorption coefficients, and refractive index changes as functions of structural and environmental parameters. The HfO2 coating significantly enhances dielectric confinement through polarization-induced band redistribution, increasing the intersubband transition energy ΔE by approximately 25–30
Our current study establishes the synthesis and the spectroscopic attributes of a two five-coordinated iron(II) picket fence porphyrin with the formula [Na(2,2,2-crypt)][FeII(TpivPP)(NCO)] (Fe2NCO) and [K(2,2,2-crypt)][FeII(TpivPP)(NCS)] (Fe2NCS) where TpivPP is the (α,α,α,α-terakis(o-pivalamidophenyl)(porphinato) anion and (2,2,2-crypt) is the cryptand-222). The two complexes are characterized in solution by UV-visible and IR spectroscopies. The molecular structures of the two compounds are determined and described using single-crystal X-ray diffraction analysis and Hirshfeld surface area derivations. Our complexes crystallize in the monoclinic system with space group C2 and P21/n, respectively. The average distance between the central Fe(II) ion and the nitrogen atoms in the equatorial position is 2.120(2) Å and 2.104(2) Å, respectively, while the FeII–N(axial ligand) distances from the cyanate and thiocyanate ligand are 2.005(3) Å and 2.042(2) Å, respectively. In each compound, the crystal packing cohesion is stabilized by unconventional intramolecular C–H…O and C–H…N hydrogen bonds. Furthermore, several important physical attributes were numerically examined to deliver an in-depth analysis of the electron charge migration pathways of the iron(II) porphyrin complex using Density Functional Theory (DFT) at the B3LYP-D3/LanL2DZ level. This includes the analysis of frontier molecular orbitals (FMOs) and associated reactivity descriptors, molecular electrostatic potential (MEP), non-covalent interaction (NCI) analysis through reduced density gradient (RDG) surfaces, and bond critical points (BCPs), as well as electron localization function (ELF), localized orbital locator (LOL), and Hirshfeld surface characterization.
In this research, we have focused to examine en detail the microstructural, magneto-optical and photocatalytic properties of the spinel chromite Ni0.5Cd0.5Cr2O4. SEM analysis revealed an average crystallite size of approximately 73 µm. Magnetic characterization, based on hysteresis loop measurements, enabled the determination of key parameters including the saturation magnetization (MS), coercivity (Hc), anisotropy constant (K), and squareness ratio (SQ). The band gap energy (Eg) was estimated to be 2.52 eV using multiple methods, including the Tauc plot and the derivative method. The superposition of the absorbance and reflectance spectra reveals an optical singularity around 895 nm. Cauchy dispersion parameters were derived from the variation of the refractive index with wavelength, and the dispersion energy was evaluated using the Wemple–DiDomenico relation. Additional optical parameters—such as penetration depth, extinction coefficient, electrical conductivity, and plasma frequency—were analyzed as functions of wavelength. Finally, the photocatalytic activity of Ni0.5Cd0.5Cr2O4 was assessed through the degradation of methylene blue, confirming its potential for environmental remediation. Overall, this comprehensive study provides valuable insights into the multifaceted physicochemical behavior of Ni0.5Cd0.5Cr2O4 and underscores its applicability in functional and environmental applications.
