Mesoporous Confinement of Fluorescent Dyes in Ultra-Transparent Silica Aerogel Films via Tailored Sol-Gel Kinetics

Silica aerogel films are highly promising matrices for advanced optical applications, yet balancing ultra-high transmittance with structural stability during functionalization remains a critical challenge. Directly incorporating organic dyes often leads to aggregation and severe photodegradation, necessitating a robust host-guest encapsulation strategy. Herein, we report the fabrication of ultra-transparent, fluorescent silica aerogel films via precisely tailored acid/base two-step sol-gel kinetics and dip-coating. The optimized pure silica matrix achieves a peak visible transmittance of 97.4% and sub-nanometer surface smoothness (RMS = 276.7 pm). By utilizing this pristine network, Rhodamine 6G (Rh6G) and Rhodamine B (RhB) dyes were effectively confined within the amorphous mesoporous pores. Notably, RhB exhibited superior matrix integration, indicated by an H4 hysteresis loop transition and a significantly reduced pore volume (0.019 cm³/g). This mesoporous confinement successfully suppressed dye quenching, prolonging the fluorescence lifetimes to 5.22 ns and 5.36 ns for Rh6G and RhB, respectively. Crucially, we elucidate that the electrostatic and hydrogen-bonding interactions between the silica pore walls and the dye's xanthene rings elevate the excited-state energy, inducing a distinct matrix-driven emission blue shift. This work provides a scalable pathway for high-performance optical coatings and offers deep insights into host-guest interfacial coupling in gel networks.