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.