Scalable Synthesis of Thermally Robust Carbon Dot-Silica Microspheres Enabling High-Temperature Polymer Processing and Multifunctional Luminescent Composites

Carbon dots (C-dots) are promising fluorescent nanomaterials, yet their inherent thermal and environmental instability, coupled with challenges in achieving independent control over emission wavelength, intensity, and composite transparency in polymer matrices, severely limit their practical utility. Here, we present a scalable spray-drying strategy to synthesize C-dot-embedded silica (SiO₂) microspheres featuring a dense shell with low accessible porosity. This unique, dense SiO₂ shell effectively encapsulates C-dots, providing remarkable thermal stability up to 350 °C. Our method also enables precise tuning of emission wavelength from blue to yellow by simply adjusting the C-dot concentration within the spheres during synthesis. Crucially, the incorporation of these C-dot-embedded SiO₂ microspheres into PMMA matrices allows for independent control of composite transparency and fluorescence intensity by varying the microsphere loading, all without altering the emission wavelength. Demonstrating their unprecedented industrial applicability, these robust microspheres are fully compatible with high-temperature injection molding processes (up to 250 °C), previously unsuitable for C-dots, enabling the formation of complex 3D fluorescent objects. Furthermore, this approach facilitates a "hidden-to-revealed" functionality, where an embedded fluorescent object remains invisible under ambient light but brightly emerges upon UV illumination, offering vast potential for advanced security features, interactive displays, and innovative consumer products. This work significantly broadens the applicability of inherently sensitive C-dots to widely utilized industrial polymer processing techniques, paving the way for their large-scale integration into high-performance, versatile luminescent materials.