Exploration on the Mechanism and Expansibility of the MOFs-Template-Removal Method for Synthesizing Smaller and Brighter Persistent Luminescent Nanoparticles

ZnGa2O4:Cr3+ (ZGC) long-persistent luminescent (PersL) nanomaterial is a potential bioimaging contrast agent without autofluorescence. However, the existing synthetic methods such as the hydrothermal method, solid-state method, and sol–gel method are generally struggling to reconcile the contradiction between small particle size and high PersL intensity, which hinder the clinical application of ZGC. In this study, ZGC nanoparticles are prepared via an “MOFs-template-removal” method. Their hydrodynamic size distribution exhibits a peak at 160 nm. The PersL intensity reaches 5.7-fold that of its hydrothermal ZGC counterparts. Mechanisms of size control and PersL enhancement via the “MOFs-template-removal” method are thoroughly investigated using PXRD, XPS, PersL decay curves, UV–vis DRS, elemental analysis, etc. The results show that the nanoscale dimension of the MOF template, with its abundant internal pores, facilitates the formation of smaller ZGC particles. Furthermore, the copious shallow electron traps on the surface are vital for enhancing the PersL intensity of ZGC-mofs. The wide bandgap (4.88 eV) of ZGC-mofs allows for the efficient absorption of 254 nm ultraviolet light in aqueous environments, promoting the PersL emission. Additionally, the experimental results also suggest that this method holds potential for controlling the size of ZnX2O4-type (X = Al, In) metallic oxides, not only broadening its application scope but also inspiring the development of bioimaging materials.