Behavior of tunable ZnO quantum dots (QDs) stabilized by surfactant-free silica nanofluids in their visible luminescence spectra

This research explores the impact of ZnO quantum dots (QDs) physical characteristics, stabilized by cationic surfactants hexadecyltrimethylammonium bromide (CTAB) and embedded in silica alcogel networks, on their optical properties as photomaterials. Using the sol–gel method with ethanol dispersants, the synthesized ZnO QDs displayed varying optical characteristics based on the stabilizer type. When stabilized with cationic surfactants, the ZnO QDs exhibited photoluminescence (PL) emissions in the visible spectrum, specifically green emission at 536 nm with a band gap energy of 2.31 eV, which closely resembled those of pure ZnO QDs. However, these cationic surfactant-stabilized ZnO QDs demonstrated a significant PL intensity decline of 86 % within the first 24 h, suggesting a limited shelf life. As an alternative, silica nanofluids were utilized as stabilizers within a transparent solid matrix, showing a stabilizing effect on the ZnO nanoparticle size, which remained under 10 nm even as the alcogel composite bulk scaled to micrometer dimensions. This study varied the concentration of ZnO and the pH of silica nanofluids during the ZnO/SiO₂ nanocomposite formation, which significantly influenced the photoluminescence performance, transmittance, and stability. After being storage for 14 days at ambient temperature, the silica-stabilized ZnO QDs remarkably showed a PL emission intensity more than a thousand times higher at a pH 10 of silica nanofluids than ZnO QDs stabilized by the cationic surfactant CTAB. This enhancement underscores the efficacy of silica nanofluids as stabilizers, whose pH can be adjusted to optimize PL emissions within specific visible light spectra, showcasing potential for tailored photomaterial applications.