Ordered and flexible lanthanide complex thin films showing up-conversion and color-tunable luminescence

Polarized and up-conversion luminescent films have great potential for use in the design of various optical devices. In this work, we report transparent and flexible thin films based on alternate layer-by-layer assembly of sulfonated Eu- and Tb-based lanthanide complexes (LCs) and Mg-Al-layered double hydroxide (LDH) nanosheets. UV-visible absorption and fluorescence spectroscopy showed an orderly growth of the two types of thin films (TFs) upon increasing the number of deposition cycles. XRD, AFM and SEM measurements indicated that the films feature periodic layered structures as well as uniformsurface morphology. Moreover, by combining the assembly of both the Eu- and/or Tb-based LC systems, these TFs can exhibit well-defined one- and two-color polarized fluorescence with high polarization anisotropy. In addition, it was observed that the two TFs exhibited obvious red and green up-conversion emission upon excitation by near-IR laser light. Therefore, this work provides a facile way to develop new types of LC TFs with both up-conversion and color-tunable luminescence, which have great potential applications for the design of various LC-based optical films and flexible devices.