Two-Photon Absorption Carbon Quantum Dot Composite Films for Optical Limiting Applications

The widespread use of high-energy lasers creates an urgent demand for optical limiting materials with both ultrafast response times and broad wavelength band adaptability. Carbon quantum dots (CQDs) have emerged as ideal candidates owing to their strong two-photon absorption, but their solid-state performance is hampered by aggregation. To address this, a composite film strategy combining two-photon absorption CQDs with various film-forming agents ((N-(β-aminoethyl)-γ-aminopropyltrimethoxysilane (KH792), poly(vinyl alcohol), and polyvinylpyrrolidone) was proposed. The results show that the CQDs/KH792 films exhibit excellent thermal stability, attributed to the formation of a protective SiO2 network structure by hydrolysis. More importantly, Z-scan measurements under 532 nm femtosecond laser irradiation reveal that the CQDs/KH792 films exhibit a strong two-photon absorption effect and self-focusing property, with optical limiting performance comparable to CQDs in solution. Further modulation of CQD concentration in the films shows that the optical limiting performance of the films is enhanced with the increase of CQD content. By effectively preventing CQD agglomeration, this work establishes a viable pathway for developing high-performance solid-state optical limiting materials for femtosecond laser protection.