Amorphous carbon dot and chitosan based composites as fluorescent inks and luminescent films

A composite of self-passivated amorphous carbon dots (CDs) and chitosan has been developed and utilized to form fluorescent inks and luminescent films. The ink is invisible under visible light but glows brightly under external excitation. Cross-linking between the numerous surface groups present in the highly disordered CDs and chitosan, endow the inks and films with enhanced optical and mechanical properties. The amorphous CD based ink is capable of writing on nearly all types of surfaces and exhibits excellent anti-clogging and anti-smearing properties. The luminescent films on the other hand are characterized by good mechanical strength (σUTS ≈ 61.3 MPa) along with high luminescence efficiency. The luminescence yield, ultimate tensile stress, hydrophobicity and glass transition temperature of the films were found to scale similarly with the concentration of CDs in chitosan. All the parameters initially improved with increasing CD concentration but then deteriorated beyond some optimal CD loading due to agglomeration effect. We demonstrate that the amorphous carbon dot-based inks and films outperform all other carbon-based fluorescent inks and films prepared from the more expensive crystalline structures.