Broadband Near-Infrared Light Excitation Generates Long-Lived Near-Infrared Luminescence in Gallates.

Persistent luminescence describes the phenomenon whereby luminescence remains after the stoppage of excitation. Recently, upconversion persistent luminescence (UCPL) phosphors that can be directly charged by near-infrared (NIR) light have gained considerable attention due to their promising applications ranging from photonics to biomedicine. However, current lanthanide-based UCPL phosphors show small absorption cross sections and low upconversion charging efficiency. The development of UCPL phosphors faces challenges due to the lack of flexible upconversion charging pathways and poor design flexibility. Herein, we discovered a lattice defect-mediated broadband photon upconversion process and the accompanying NIR-to-NIR UCPL in Cr-doped zinc gallate nanoparticles. The zinc gallate nanoparticles can be directly activated by broadband NIR light in the 700-1000 nm range to produce persistent luminescence at about 700 nm, which is also readily enhanced by rationally tailoring the lattice defects in the phosphors. This proposed UCPL phosphor achieved a signal-to-background ratio of over 200 in bioimaging by efficiently avoiding interference from autofluorescence and light scattering. Our work reported a lattice defect-mediated photon upconversion phenomenon, which significantly expands the horizons for the flexible design of UCPL phosphors toward broad applications ranging from bioimaging to photocatalysis.

Hierarchical Electrode Architecture Enabling Ultrahigh-Capacity LiFePO4 Cathodes with Low Tortuosity.

Thickening electrodes are expected to increase the energy density of batteries. Unfortunately, the manufacturing issues, sluggish electrolyte infiltration, and restrictions on electron/ion transport seriously hamper the development of thick electrodes. In this work, an ultrathick LiFePO4 (LFP) electrode with hierarchically vertical microchannels and porous structures (I-LFP) is rationally designed by combining the template method and the mechanical channel-making method. By using ultrasonic transmission mapping technology, it is proven that the open and vertical microchannels and interconnected pores can successfully overcome the electrolyte infiltration difficulty of conventional thick electrodes. Meanwhile, both the electrochemical and simulation characterizations reveal the fast ion transport kinetics and low tortuosity (1.44) in the I-LFP electrode. As a result, the I-LFP electrode delivers marked improvements in rate performance and cycling stability even under a high areal loading of 180 mg cm-2. Moreover, according to the results of operando optical fiber sensors, the stress accumulation in the I-LFP electrode is effectively alleviated, which further confirms the improvement of mechanical stability.