Continuous Flow Synthesis of Persistent Luminescent Chromium-Doped Zinc Gallate Nanoparticles

Near-Infrared Luminescent Materials Incorporating Rare Earth/Transition Metal Ions: From Materials to Applications

The spotlight has shifted to near-infrared (NIR) luminescent materials emitting beyond 1000 nm, with growing interest due to their unique characteristics. The ability of NIR-II emission (1000-1700 nm) to penetrate deeply and transmit independently positions these NIR luminescent materials for applications in optical-communication devices, bioimaging, and photodetectors. The combination of rare earth metals/transition metals with a variety of matrix materials provides a new platform for creating new chemical and physical properties for materials science and device applications. In this review, the recent advancements in NIR emission activated by rare earth and transition metal ions are summarized and their role in applications spanning bioimaging, sensing, and optoelectronics is illustrated. It started with various synthesis techniques and explored how rare earths/transition metals can be skillfully incorporated into various matrixes, thereby endowing them with unique characteristics. The discussion to strategies of enhancing excitation absorption and emission efficiency, spotlighting innovations like dye sensitization and surface plasmon resonance effects is then extended. Subsequently, a significant focus is placed on functionalization strategies and their applications. Finally, a comprehensive analysis of the challenges and proposed strategies for rare earth/transition metal ion-doped near-infrared luminescent materials, summarizing the insights of each section is provided.

Persistent luminescent nanoparticles for plant imaging: toward exploring the distribution of nanoparticles in plants

Nanotoxicology on plants has raised great concerns about the prevalence of nanoparticles (NPs) in ecosystems, and the most fundamental aspect is to assess the fate of NPs in plants. Nonetheless, the lack of high-sensitivity tracking techniques in vivo constraints intensive research on NP distribution in plants. Herein, we have overcome this limitation by first introducing persistent luminescent nanoparticles (PLNPs) as an imaging probe, which can detect the distribution of NPs in whole plants with high sensitivity by completely eliminating interference from autofluorescence. We synthesized two differently surface-charged PLNPs with excellent biosafety and then exposed these NPs to plants in the hydroponic medium. Persistent luminescence (PersL) images visually showed the disparate accumulation of PLNPs in plants. PersL signals of positively charged PLNPs were observed in the whole exposed portion of the plant roots, while negatively charged PLNPs were mainly in the root collars instead of the exposed portion. With prolonged exposure, the presence of PersL signals in leaves indicated the long-distance translocation of differently charged PLNPs from roots to leaves via hypocotyls. For further confirmation of imaging results, the distribution of NPs in plants was investigated using electron microscopy. Based on their unique optical properties, PLNPs provide a promising strategy for tracking NP's fate in plants.

Design of need-based phosphors and scintillators by compositional modulation in the ZnGa2-xAlxO4:Cr3+ spinel: pure compound versus solid solutions

Materials that can depict persistent deep red light under both ultraviolet (UV) and X-ray illumination can be a boon to sustainable economy, particularly for optical imaging, solid state lighting, and anticounterfeiting applications. Herein, we have made a series of compounds starting from ZnGa₂O₄:Cr³⁺ to ZnAl₂O₄:Cr³⁺ (individual spinel) by substituting the varied concentration of Al³⁺ in place of Ga³⁺ in ZnGa_2-xAl_xO₄:Cr³⁺ (solid solution). By virtue of the structural and defect engineering doping strategy, the photo and radioluminescence are expected to be improved. Both Cr and Al doping was found to be energetically favorable in ZnGa₂O₄, where the same does not hold true for Ga doping in ZnAl₂O₄, as indicated by the DFT-calculated defect formation energies. There seems to be ordering around the dopant ion in the solid solutions compared to either ZnGa₂O₄ or ZnAl₂O₄ and is also reflected to as lower persistent luminescence (PerL) lifetimes. PerL under UV, in general. was found to be lower with the enhancement in the Al³⁺ content endowed by the formation of Cr-Cr ion pair, lower probability of antisite formation, and widening band gap. On the other hand, X-ray excited emission enhances in the solid solution due to the decrease in cation inversion and associated defects. Confocal Microscopy showed that larger particles depicted much brighter deep red emission but failed to percolate to the human cells to a detectable limit; hence, future work is needed for the functionalization of the ZnGa_2-xAl_xO₄:Cr³⁺ spinel. This work could be of great implication in designing need-based materials, where UV and X-ray excitation is required, for deep red emission with persistent characteristics from chromium-doped spinels.