The role of Li⁺ and Yb³⁺ in modulating the electronic structure and luminescence of MgGeO₃:Mn²⁺ nanoparticles

Inorganic persistent luminescence (PersL) nanoparticles (NPs) emitting at the deep-red and near-infrared (NIR) are promising candidates for applications in the biomedical field, such as optical imaging, sensing and therapy. The emission wavelength is closely related to the identity of the light activators (i.e. metal ion dopant), and the local environment they occupy in the host crystal lattice. In this paper, PersL nanoparticles with dual emission bands based on MgGeO3 was investigated. These nanoparticles exhibit one emission band at the deep-red region when doped with Mn2+. Introducing Yb3+ as a second dopant enables a deepred-to-NIR energy transfer, producing dual-emission at both deep-red and NIR. The NIR emission can be further enhanced by the addition of Li+. A detailed spectroscopy study is performed to investigate the local structure around the light activators Mn2+ and Yb3+, and how it is influenced by the Li+ co-dopant. We found that adding the Yb3+ and Li+ changes the preferred site of occupancy for Mn2+, and when Mn2+ is shifted to a site that emits deep-red less efficiently, it acts as an electron trap to extend the PersL of the NIR-II emission. The mechanism for the deep-red-to-NIR energy transfer is proposed.(c) 2023 Elsevier B.V. All rights reserved.