Fig. 1: Overview of the sample design and energy levels.

a Illustration of how the nanocomposite film is built up layer by layer. Terephthalic acid molecules are shown attaching to the surface, while TbF₃ and SmF₃ layers are shown in green and orange, respectively. b Energy-level diagram of the sample design, showing UV absorption in the aromatic acid (Ar), energy transfer to Tb³⁺, migration towards Sm³⁺ and finally Sm³⁺ emission. Note that some energy levels have been omitted for clarity. c Photograph of the 100Sm sample on a silica substrate in room light (top) and 254 nm UV light (bottom). d Energy-level diagram of Tb³⁺, Eu³⁺ and Sm³⁺, including names of the energy levels involved in radiative transitions. These transitions are shown with arrows with colours corresponding to the emitted photon.