Boosting NIR-to-NIR persistent luminescence by nanoscale spatial confinement for bioimaging

Core-shell spatial confinement breaks concentration quenching in ion doping. • A universal boosting strategy for NIR-to-NIR persistent luminescence. • Core-shell engineering achieves 6.5-fold enhancement of persistent luminescence. Near-infrared-to-near-infrared (NIR-to-NIR) persistent luminescence nanoparticles (PLNPs) hold great promise for biomedical applications, yet their practical use is severely limited by low persistent luminescence efficiency. In this study, we demonstrate that introducing traps via heavily doped ions, combined with spatial separation of luminescent centers (confined in the core) from heavily doped ions (confined in the shell), effectively enhances NIR-to-NIR persistent luminescence. Using ZnGa 2 O 4 :Cr (ZGO:Cr) as a model system exhibiting NIR-to-NIR upconversion persistent luminescence (UCPL), we synthesized co-doped ZnGa 2 O 4 :Cr,Eu (Cr Eu) and ZnGa 2 O 4 :Cr,Ca (Cr Ca) PLNPs. Both systems emitted persistent luminescence at 695 nm upon 700 nm excitation, with optimal enhancement observed at 0.7% Eu and 0.5% Ca, yielding 1.9- and 1.3-fold intensity increases relative to ZGO:Cr, respectively. To overcome the concentration quenching effect, we further designed core-shell structured ZnGa 2 O 4 :Cr@ZnGa 2 O 4 :Eu (Cr@Eu) and ZnGa 2 O 4 :Cr@ZnGa 2 O 4 :Ca (Cr@Ca) PLNPs, in which Cr 3+ luminescent centers are confined in the core while Eu 3+ or Ca 2+ ions are heavily doped in the shell. These core-shell PLNPs exhibited persistent luminescence at ∼695 nm after charging with 700 or 800 nm LED light, lasting over 30 min. Remarkably, the NIR-to-NIR persistent luminescence intensities of Cr@Eu and Cr@Ca reached 5.6 and 6.5 times that of ZGO:Cr, respectively, with optimal doping concentrations elevated to 3% and 5%. In in vivo bioimaging tests, Cr@Eu exhibited signal-to-background ratios over 3 times greater than that of ZGO:Cr. This work establishes a universal paradigm for enhancing NIR-to-NIR persistent luminescence in PLNPs, paving the way for their biomedical applications. Download: Download high-res image (113KB) Download: Download full-size image