Integrated structural, optical and dielectric analysis of low-loss α-Al₂O₃ nanoparticles for UV photonic and dielectric applications.

High-purity α-Al2O3 nanoparticles were synthesised using a modified Pechini sol-gel method and calcinated at 1100 °C. Their structural, optical, and dielectric properties were thoroughly examined. Structure research utilizing X-ray diffraction and advanced Rietveld refinement showed that adding the axial divergence asymmetry pseudo-Voigt function improves refinement quality and produces more precise crystallographic parameters for the R-3c corundum structure. A stress-free crystalline framework was confirmed by a size-strain plot showing a volume-weighted crystallite size of ~ 24.4 nm and low lattice strain. The HR-TEM revealed spherical polycrystalline aggregates with an average particle size of ~ 100 nm, while FTIR confirmed phase purity and complete organic precursor elimination. UV-Vis diffuse reflectance spectroscopy determined the refractive index, extinction coefficient, absorption coefficient, and complex dielectric function. The Kubelka-Munk formalism estimated the optical band gap at ~ 4.29 eV, indicating wide-band-gap insulating behaviour. In the visible-near-infrared region, the real part of the dielectric constant showed substantial photon energy dispersion, but the imaginary part remained extremely low (≤ 0.03), indicating minimal optical losses. The dielectric loss tangent was extremely low (~ 10-4-10-6), indicating strong electronic polarization and minimal dissipation. The lattice dielectric constant (εₗ = 7.97), low plasma frequency, and minimal free-carrier contribution support the intrinsic insulation of α-Al2O3. Researchers found a strong correlation between structural perfection and low-loss optical response, making α-Al2O3 nanoparticles promising for high-transparency, dielectric-stable applications such as optical coatings, ultraviolet optoelectronic devices, and high-frequency photonics.