One-pot solvothermal conversion of polysilazane to fluorescent nanoparticles for anticounterfeiting and Ag⁺ sensing...

Silicon-based fluorescent nanoparticles are now of significant interest for sensing and security applications; however, their synthesis often depends on multiple complex precursors and processes. Herein, we report a one-pot solvothermal strategy for the synthesis of fluorescent polysilazane-derived nanoparticles using polysilazane as a single-source precursor at 200 °C. The solvothermal treatment introduces controlled oxidation-condensation and partial crosslinking of the polysilazane backbone, yielding amorphous hybrid nanoparticles composed of a disordered Si-O-C-N network with residual Si-rich domains and very few organic surface functionalities. The visible fluorescence origin is attributed to the defect-related states associated with oxygen-rich siloxane networks and surface electronic states within the structure, supported by structural and spectroscopic analyses. The nanoparticles show strong excitation-dependent visible fluorescence with high photostability and long-term storage stability. The nanoparticles demonstrate selective and concentration-dependent fluorescence quenching toward Ag⁺ ions at a low concentration of 0.55 µM via their surface chemistry, enabling sensitive detection in aqueous media. The intense and durable fluorescence further enables their use as anti-counterfeiting inks, where printed patterns remain invisible under ambient light and become clearly visible under UV illumination, showing performance durability. This work establishes polysilazane-derived fluorescent nanoparticles as a new class of polymer-derived ceramic nanomaterials, offering a scalable platform for multifunctional applications in sensing, security labeling, and smart surface technologies.