Lanthanides-based multifunctional luminescent films for ratiometric humidity sensing, information storage, and colored coating

Multifunctional luminescent materials have attracted great attention because of their widely potential applications, however, fabrication of luminescent films are still great challenge. Herein, a new type of luminescent films have been developed by way of facile fabrication of solution casting method on the base of the reaction of hyaluronic acid (HA) with lanthanide ions (Tb3+ and/or Eu3+). The coordination interactions between HA and lanthanides were confirmed by FT-IR and XPS analysis. Luminescent spectra and luminescent decay curves supported the energy transfer from Tb3+ to Eu3+ ions, and the emission color of Tb-Eu co-doped films can be tuned by water molecules. Thus, HA-(Tb0.3Eu0.7) film was applied as a self-referencing and ratiometric luminescent sensor for humidity detection, where the corresponding variable colors can be observed by the naked eyes. Moreover, the HA-(Tb0.3Eu0.7) film for humidity sensing exhibited good reversibility and repeatability. Further, the luminescent films were applied as information carrier by using water as inks, and the writing and erasing was reversible. In addition, the luminescent films were also applied as colored coating. Therefore, this approach may provide a facile way for fabrication of luminescent films, which are of potential applications in sensing, information transmission, and colored coating.