Boosting Persistent Luminescence with Spatially Confined Ion Doping for Profiling Bacterial-Environment Interactions

Ion doping is widely employed to introduce defects in persistent luminescence nanoparticles (PLNPs) to enhance the luminescence efficiency. However, the influence of ion doping on persistent luminescence remains insufficiently studied, and current doping strategies require further optimization. In this study, we systematically investigated the effects of heterovalent K⁺ doping on the persistent luminescence of CaSc₂O₄:Tb PLNPs and further refined the doping strategy. Results indicate that the luminescence enhancement in CaSc₂O₄:Tb,K via K⁺ doping is seriously constrained by concentration quenching, with an optimal K⁺ doping ratio of only 1.5%. To further improve the doping-enhanced persistent luminescence, we designed two types of core-shell structured PLNPs: CaSc₂O₄:Tb@CaSc₂O₄:K (Tb@K) and CaSc₂O₄:K@CaSc₂O₄:Tb (K@Tb). In these architectures, the luminescent center Tb³⁺ and dopant K⁺ are spatially separated, which increases the optimal K⁺ doping ratio to 7%. Notably, the persistent luminescence intensities of Tb@K and K@Tb reach up to 1.9 and 2.2 times those of codoped CaSc₂O₄:Tb,K, respectively. Furthermore, by coating the surface-confined persistent luminescent K@Tb with a coordination network composed of Fe²⁺/³⁺ and tannic acid (TA), we constructed a reversible K@Tb@Fe-TA nanoprobe for monitoring bacterial-environment interactions. Shewanella putrefaciens (S. putrefaciens) reduces Fe³⁺ to Fe²⁺ in K@Tb@Fe-TA, leading to attenuation of the persistent luminescence. Using this probe, we observed that the intensity of the S. putrefaciens-environment interaction varies with the bacterial growth stage. This work presents a superior ion-doping strategy to boost persistent luminescence efficiency and offers a promising approach for tracking bacterial-environment interactions. Moreover, it also opens exciting possibilities for the development and biomedical applications of PLNPs.