Charge carrier trapping management in Bi³⁺ and lanthanides doped Li(Sc,Lu)GeO₄ for x-ray imaging, anti-counterfeiting, and force recording

Discovering energy storage materials with rationally controlled trapping and de-trapping of electrons and holes upon x-rays, UV-light, or mechanical force stimulation is challenging. Such materials enable promising applications in various fields, for instance in multimode anti-counterfeiting, x-ray imaging, and non-real-time force recording. In this work, photoluminescence spectroscopy, the refined chemical shift model, and thermoluminescence studies will be combined to establish the vacuum referred binding energy (VRBE) diagrams for the LiSc_1−xLu_xGeO₄ family of compounds containing the energy level locations of Bi²⁺, Bi³⁺, and the lanthanides. The established VRBE diagrams are used to rationally develop Bi³⁺ and lanthanides doped LiSc_1−xLu_xGeO₄ storage phosphors and to understand trapping and de-trapping processes of charge carriers with various physical excitation means. The thermoluminescence intensity of x-ray irradiated LiSc_0.25Lu_0.75GeO₄:0.001Bi³⁺,0.001Eu³⁺ is about two times higher than that of the state-of-the-art x-ray storage phosphor BaFBr(I):Eu²⁺. Particularly, a force induced charge carrier storage phenomenon appears in Eu³⁺ co-doped LiSc_1−xLu_xGeO₄. Proof-of-concept non-real-time force recording, anti-counterfeiting, and x-ray imaging applications will be demonstrated. This work not only deepens our understanding of the capturing and de-trapping processes of electrons and holes with various physical excitation sources, but can also trigger scientists to rationally discover new storage phosphors by exploiting the VRBEs of bismuth and lanthanide levels.