Advances in understanding the mechanisms of luminescence in lanthanide-doped upconverting nanoparticles can guide researchers in developing brighter materials. This review discusses the latest developments in the field and suggests routes to improvements.

Modulating the emission wavelengths of materials has always been a primary focus of fluorescence technology. Nanocrystals (NCs) doped with lanthanide ions with rich energy levels can produce a variety of emissions at different excitation wavelengths. However, the control of multimodal emissions of these ions has remained a challenge. Herein, we present a new composition of Er3+‐based lanthanide NCs with color‐switchable output under irradiation with 980, 808, or 1535 nm light for information security. The variation of excitation wavelengths changes the intensity ratio of visible (Vis)/near‐infrared (NIR‐II) emissions. Taking advantage of the Vis/NIR‐II multimodal emissions of NCs and deep learning, we successfully demonstrated the storage and decoding of visible light information in pork tissue.

Because of their unique physicochemical properties, lanthanide-doped upconverting nanoparticles (Ln-UCNPs) have exceptional potential for biological applications. However, the use in biological systems is hampered by the limited understanding of their bionano interactions. Our multidisciplinary study has generated these insights through in-depth and quantitative analyses. The Ln-UCNPs examined here are spherical, monodisperse, and stable in aqueous environments. We show that Ln-UCNPs were associated with HeLa (cervical cancer) and LLC-PK1 (renal proximal tubule) cells and were nontoxic over a wide concentration range. Multiple biomarkers were assessed to monitor the cellular homeostasis in Ln-UCNP-treated cells. To this end, we evaluated the nuclear lamina, nucleoli, and nuclear transport factors. Single-cell analyses quantified the impact on Nrf2 and NF-κB, two transcription factors that control stress and immune responses. Moreover, we measured Ln-UCNP-induced changes in the abundance of molecular chaperones. Collectively, in vitro studies confirmed that Ln-UCNPs are nontoxic and trigger minor cellular stress responses. This lack of toxicity was verified in vivo, using the model organism Caenorhabditis elegans. The compatibility with biological systems prompted us to assess Ln-UCNPs as potential contrast agents for magnetic resonance imaging. We demonstrated that the Ln-UCNPs examined here were especially suitable as T 2 contrast agents; they clearly outperformed the clinically used Gadovist. Taken together, our interdisciplinary work provides robust evidence for the nontoxicity of Ln-UCNPs. This sets the stage for the translation of Ln-UCNP for use in complex biological systems.

Luminescent metal−organic frameworks (MOFs) are of interest for sensing, theranostics, dosimetry, and other applications. The use of lanthanoids in MOF nodes allows for intrinsic metal-based luminescence. In this work, a facile route for modulating the photoluminescent and radioluminescent properties of Tb(III)-based MOFs is reported. By using Tb(III) cluster nodes as X-ray attenuators, and organic linkers with varying excited state energies as sensitizers, MOFs with metalbased, linker-based, and metal+linker-based photo-and radioluminescence are reported.