Amplifying persistent luminescence in heavily doped nanopearls for bioimaging and solar-to-chemical synthesis

Lanthanides are widely co-doped in persistent luminescence phosphors to elevate defect concentration and enhance luminescence efficiency. However, the deleterious cross-relaxation between activators and lanthanides inevitably quench persistent luminescence, particularly in heavily doped phosphors. Herein, we reported a core-shell engineering strategy to minimize the unwanted cross-relaxation but retain the charge-trapping capacity of heavily doped persistent luminescence phosphors by confining the activators and lanthanides in the core and shell, respectively. As a proof of concept, we prepared a series of codoped ZnGa ₂ O ₄ :Cr, Ln (CD-Ln, Ln = Nd, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb) and core-shell structured ZnGa ₂ O ₄ :Cr@ZnGa ₂ O ₄ :Ln (CS-Ln) nanoparticles. First-principle investigations suggested that lanthanide doping elevated the electron trap concentration for enhanceing persistent luminescence, but the energy transfer (ET) from Cr ³⁺ to Ln ³⁺ ions quenched the persistent luminescence. The spatial separation of Cr ³⁺ and Ln ³⁺ ions in the core-shell structured CS-Ln nanoparticles suppressed the ET from Cr ³⁺ to Ln ³⁺ . Due to the efficient suppression of deleterious ET, the optimal doping concentration of Ln in CS-Ln was elevated 50 times compared to CD-Ln. Moreover, the persistent luminescence intensity of CS-5%Ln was up to 60 times that of the original ZnGa ₂ O ₄ :Cr. The CS-5%Ln displayed significantly improved signal-to-noise ratios in bioimaging. Further, the CS-Ln was interfaced with the lycopene-producing bacteria Rhodopseudomonas Palustris for solar-to-chemical synthesis and the lycopene productivity was increased by 190%. This work provides a reliable solution to fulfill the potential of lanthanides in enhancing persistent luminescence and opens opportunities for persistent luminescence phosphors in biomedicine and solar-to-chemical synthesis.