Synthesis, Structural Characterization, and Photoluminescence Properties of Germanium Oxide Nanoparticles: Experimental and DFT Study

Nanocrystalline germanium metal oxide (GeO2) is a highly promising inorganic nanoparticle for use in electrochemical, electronic, optical, and optoelectronic devices. In this work, germanium metal oxide nanoparticles with uniform and tunable size, crystallinity, and surface chemistry content were synthesized via a nonaqueous sol–gel route. To support and interpret the experimental findings, first-principles density functional theory (DFT) calculations were performed on hexagonal GeO2. The optical properties of the germanium metal oxide nanoparticles and their composite materials, which are optically active in the Ultra-Visible@red, respectively, are presented. The germanium metal oxide nanoparticles demonstrated exceptional optical emission characteristics within ultravisible, highlighting their potential for applications in optoelectronic communication. Electronic structure analysis revealed a wide direct band gap of approximately 3.5 eV, with valence bands dominated by the O 2p orbitals and conduction bands composed mainly of Ge 4s/4p states. Moreover, quantum theory of atoms in molecules (QTAIM) analysis based on the electron density topology confirmed the polar-covalent character of Ge–O bonds, consistent with the bonding environment inferred from experiments.