The Coming of Age of Neodymium: Redefining Its Role in Rare Earth Doped Nanoparticles

NIR-II upconversion nanomaterials for biomedical applications

As a nonlinear optical phenomenon, upconversion (UC) occurs when two or more low-energy excitation photons are sequentially absorbed and emitted. Upconversion nanomaterials exhibit superior photostability, non-invasiveness, a unique near-infrared anti-Stokes shift, and enhanced tissue penetration capability. However, general upconversion nanomaterials typically utilize visible light (400-700 nm) for excitation, leading to limited tissue penetration, background signal interference, limited excitation efficiency and imaging quality issues due to tissue absorption and scattering. The increasing use of upconversion nanomaterials in the near-infrared one-region (NIR-I) window (700-900 nm) offers benefits such as enhanced penetration into biological tissues, relatively improved imaging resolution, and lower spontaneous luminescence, although these materials are still susceptible to background signals, limiting their effectiveness in high signal-to-noise ratio imaging. This distinctive wavelength conversion endows upconversion nanomaterials in the NIR-II region with extraordinary potential for diverse applications. Biomedical research has primarily focused on biomedical imaging for disease diagnosis and treatment, as well as biomarker detection. Nonetheless, studies specifically targeting the NIR-II window remain limited. This paper summarizes the latest research progress on upconversion nanomaterials in the NIR-II region. It begins by introducing the preparation methods for these materials in the NIR-II, followed by their applications in imaging and biological contexts. Lastly, it discusses the primary challenges and future prospects of upconversion materials in NIR-II, aiming to promote their development.

Nanoparticles-Based Optical Chemosensors for Lead Acetate Sensing in Water: ZnO, Zn0.97Ce0.03O, and Zn0.97Nd0.03O

This study reports the synthesis, characterization, and optical properties of ZnO, Zn0.97Ce0.03O, and Zn0.97Nd0.03O nanoparticles and their interactions with lead acetate solutions. X-ray diffraction (XRD) confirmed that the nanoparticles were synthesized in a single-phase hexagonal structure, with crystallite sizes of 12.48 nm, 50.79 nm, and 39.00 nm, respectively. Doping ZnO with Ce and Nd ions significantly enhanced its paramagnetic properties, as evidenced by squareness ratios of 11.18 × 10-3, 41.60, and 20.25 for ZnO, Zn0.97Ce0.03O, and Zn0.97Nd0.03O, respectively. UV-Vis absorption spectra revealed a redshift in lead acetate upon interaction with ZnO, indicating the formation of new chemical species. Ce and Nd doping further modified the optical properties by introducing additional absorption peaks and altering spectral profiles. Significant enhancement in photoluminescence (PL) intensity is observed due to the addition of ZnO, Zn0.97Ce0.03O, and Zn0.97Nd0.03O nanoparticles, as compared to the pure PbC2H3O2​ solution across various concentrations. The incorporation of ZnO nanoparticles increases the PL intensity by approximately tenfold (from 13 to over 100 a.u.). Similarly, Zn0.97Ce0.03O exhibits a comparable level of enhancement. Notably, the introduction of Zn0.97Nd0.03O nanoparticles achieves a remarkable 100-fold increase in PL intensity, establishing it as a highly effective material for detecting lead contamination in water. This exceptional performance highlights its potential for environmental monitoring and water quality applications. These results highlight the potential of ZnO, Zn0.97Ce0.03O, and Zn0.97Nd0.03O nanoparticles as sensitive and effective chemosensors for detecting trace lead levels in environmental samples.

Manipulating energy migration in nanoparticles toward tunable photochromic upconversion

Smart control of energy interactions plays a key role in manipulating upconversion dynamics and tuning emission colors for lanthanide-doped materials. However, quantifying the energy flux in particular energy migration in the representative sensitizer-activator coupled upconversion system has remained a challenge. Here we report a conceptual model to examine the energy flux in a single nanoparticle by designing an interfacial energy transfer mediated nanostructure. We show that energy migration indeed occurs simultaneously with energy transfer in a sensitizer-activator system and the competition between them can be quantified by proposing a characteristic ratio parameter. Moreover, this model is also able to realize the color-switchable photochromic upconversion by temporal control of up-transition processes. These findings offer a deep insight into the understanding of upconversion dynamics and provide a versatile approach to manipulating the energy flux in nanostructures with tunable emission colors, showing great promise in applications of logic operation and information security.

Defect-Mediated Energy Transfer Mechanism by Modulating Lattice Occupancy of Alkali Ions for the Optimization of Upconversion Luminescence

The performance optimization of photoluminescent (PL) materials is a hot topic in the field of applied materials research. There are many different crystal defects in photoluminescent materials, which can have a significant impact on their optical properties. The luminescent properties and chemical stability of materials can be effectively improved by adjusting lattice defects in crystals. We systematically studied the effect of doping ions on the energy transfer upconversion mechanism in different defect crystals by changing the matrix alkali metal ions. Meanwhile, the influence mechanism of crystal defect distribution on luminescence performance is explored by adjusting the ratio of Na-Li. The PL spectra indicate that changing the alkaline ions significantly affects the luminescence performance and efficiency of UCNPs. The change in ion radius leads to substitution or gap changes in the main lattice, which may alter the symmetry and strength of the crystal field around doped RE ions, thereby altering the UCL performance. Additionally, we demonstrated the imaging capabilities of the synthesized upconversion nanoparticles (UCNPs) in cellular environments using fluorescence microscopy. The results revealed that Na0.9Li0.1LuF4-Yb, Er nanoparticles exhibited significantly enhanced fluorescence intensity in cell imaging compared to other compositions. We further investigated the mechanism by which structural defects formed by doping ions in UCNPs with different alkali metals affect energy transfer upconversion (ETU). This work emphasizes the importance of defect regulation in the ETU mechanism to improve the limitations of crystal structure on the luminescence performance and promote the future application of upconversion nanomaterials, which will provide important theoretical references for the exploration of high-performance luminescent materials in the future.

Ultrafast upconversion superfluorescence with a sub-2.5 ns lifetime at room temperature

Photon upconversion through lanthanide-doped nanoparticles is of great significance for various applications. However, the current development of upconversion nanoparticles is hindered by the low quantum efficiency and long radiative lifetimes of lanthanide ions, restricting their applications in time-dependent nanophotonics. Herein, we report ultrafast upconversion superfluorescence with a lifetime of sub-2.5 ns in lanthanide-doped nanoparticles at room temperature. Upon excitation with an 800-nm fs-pulsed laser, we achieve a large number (N = 912) of correlated dipoles in Nd3+-concentrated nanoparticles, resulting in collective coherent emission with two orders of magnitude amplification in intensity and more than three orders of magnitude improvement in the radiative decay rate. Furthermore, we demonstrate that the control of excitation power and emitting sample length enables the lifetime manipulation of upconversion emission in a wide range from μs to sub-ns, accompanied by the typical superfluorescence signature of Burnham-Chiao ringing. These findings may benefit applications in many advanced technologies such as quantum counting and high-speed super-resolution bioimaging.

Advances in Lanthanide-Based NIR-IIb Probes for In Vivo Biomedical Imaging

The past decades have witnessed the significant development and practical interest of in vivo biomedical imaging technologies and optical materials in the second-near infrared (NIR-II, 1000-1700 nm) window. Imaging with the extended emission wavelength toward the long-wavelength end (NIR-IIb, 1500-1700 nm) further offers micrometer imaging resolution and centimeter tissue penetration depth by taking advantage of the much-reduced photon scattering and near-zero tissue autofluorescence background, which have become a very hot research area. This review focuses on the recent advances in the development of lanthanide-based NIR-IIb probes for in vivo biomedical applications. The progress including ratiometric imaging, multiplexed imaging for wide-field and microscopy, lifetime multiplexing and sensing, persistent luminescence, and multimodal imaging is summarized. Challenges and future directions concerning the investigation of the photophysical and photochemical properties of NIR-IIb probes, the selection of near-infrared cameras as well as the potential extension of the NIR-IIb imaging sub-window are pointed out. This review will inspire readers who have a strong interest in developing optical imaging technology and long-wavelength fluorescence probes for high-contrast in vivo biomedical applications.

Electronic Structure of a Neodymium(III) Tris(oxidiacetate) Complex from Luminescence Data and Ab Initio Calculations

Neodymium(III) is a near-infrared emissive and magnetic ion, which has found use in various high-technology applications. Yet, accurate predictions of the luminescent and magnetic properties of neodymium(III) based on the coordination environment remain to be done. Guidelines exist, but to build structure-property relationships for this element, more data are needed. Herein, we present a high-symmetry starting point. The tris(oxidiacetate) complex of neodymium(III) was prepared and crystallized, and access to the experimentally determined structure allowed us to quantify the symmetry of the compound and to perform calculations directly on the same structure that is investigated experimentally. The luminescent properties were determined and the electronic structure was computed using state-of-the-art ab initio methods. All electronic transitions in the range from 490 to 1400 nm were mapped experimentally. Using a Boltzmann population analysis, the combination of the excitation and emission spectra revealed the crystal field splitting of the 18 lowest-energy Kramers levels that experimentally could be unambiguously resolved. This assignment was supported by ab initio calculations, and the crystal field splitting was well reproduced. The electronic structure reported for the tris(oxidiacetate) complex was used to deduce the coordination structure in aqueous solution. Finally, the results are compared to empirical trends in the literature for the electronic structure of neodymium(III).

Toward Accurate Photoluminescence Nanothermometry Using Rare-Earth Doped Nanoparticles for Biomedical Applications

ConspectusPhotoluminescence nanothermometry can detect the local temperature at the submicrometer scale with minimal contact with the object under investigation. Owing to its high spatial resolution, this technique shows great potential in biomedicine in both fundamental studies as well as preclinical research. Photoluminescence nanothermometry exploits the temperature-dependent optical properties of various nanoscale optical probes including organic fluorophores, quantum dots, and carbon nanostructures. At the vanguard of these diverse optical probes, rare-earth doped nanoparticles (RENPs) have demonstrated remarkable capabilities in photoluminescence nanothermometry. They distinguish themselves from other luminescent nanoprobes owning to their unparalleled and versatile optical properties that include narrow emission bandwidths, high photostability, tunable lifetimes from microseconds to milliseconds, multicolor emissions spanning the ultraviolet, visible, and near-infrared (NIR) regions, and the ability to undergo upconversion, all with excitation of a single, biologically friendly NIR wavelength. Recent advancements in the design of novel RENPs have led to new fundamental breakthroughs in photoluminescence nanothermometry. Moreover, driven by their excellent biocompatibility, both in vitro and in vivo, their implementation in biomedical applications has also gained significant traction. However, these nanoprobes face limitations caused by the complex biological environments, including absorption and scattering of various biomolecules as well as interference from different tissues, which limit the spatial resolution and detection sensitivity in RENP temperature sensing.Among existing approaches in RENP photoluminescence nanothermometry, the most prevalent implemented mechanisms either leverage the changes in the relative intensity ratio of two emission bands or exploit the lifetimes of various excited states. Photoluminescence intensity ratio (PLIR) nanothermometry has been the mainstream method owing to the readily available spectrometers for photoluminescence acquisition. Despite offering high temperature sensitivity and spatial resolution, this technique is restricted by tedious calibration and undesirable fluctuation in photoluminescence intensity ascribed to factors such as probe concentration, excitation power density, and biochemical surroundings. Lifetime-based nanothermometry uses the lifetime of a specific transition as the contrast mechanism to infer the temperature. This modality is less susceptible to various experimental factors and is compatible with a broader range of photoluminescence nanoprobes. However, due to relatively expensive and complex instrumentation, long data acquisition, and sophisticated data analysis, lifetime-based nanothermometry is still breaking ground with recently emerging techniques lightening its path.In this Account, we provide an overview of RENP nanothermometry and their applications in biomedicine. The architectures and luminescence mechanisms of RENPs are examined, followed by the principles of PLIR and lifetime-based nanothermometry. The in-depth description of each approach starts with its basic principle of accurate temperature sensing, followed by a critical discussion of the representative techniques, applications as well as their strengths and limitations. Special emphasis is given to the emerging modality of lifetime-based nanothermometry in light of the important new developments in the field. Finally, a summary and an outlook are provided to conclude this Account.

Enhancing the Output Performance of Triboelectric Nanogenerator Through Regulation of its Internal Nano-Architecture

Triboelectric Nanogenerator (TENG) has proven highly effective in converting mechanical energy into electrical energy. Previous research on manipulating microstructure for performance enhancement primarily focused on the surface of TENGs. In this study, an innovative bottom-up strategic design to control the internal nano-architecture for the enhanced output of TENG is proposed. This multiscale structural design strategy consists of defect chemistry (angstrom-scale), surface modification (nano-scale), and spatial regulation of nanoparticles (meso-scale), which helps explore the optimal utilization of TENG's internal structure. After fine-tuning the nano-architecture, the output voltage is significantly increased. This optimized TENG serves as a robust platform for developing self-powered systems, including self-powered electrochemical chlorination systems for sterilization. Additionally, through the utilization of multiscale simulations (density functional theory, all-atom molecular dynamics, and dissipative particle dynamics), the underlying mechanisms governing how the optimized nanoparticle-polymer interface and spatial arrangement of nanoparticles influence the storage and transfer of charges are comprehensively elucidated. This study not only demonstrates the effectiveness of manipulating internal nano-architecture to enhance TENG performance for practical applications but also provides invaluable insights into structural engineering for TENG advancement.

Summary of the Research Progress on Advanced Engineering, Processes, and Process Parameters of Rare Earth Green Metallurgy

The addition of rare earth metals to aluminum alloys can effectively improve their corrosion resistance and has been widely used in the aerospace and military industries. However, the current methods for the preparation of rare earth metals involve long processing steps, high energy consumption, and high carbon emissions, which severely constrains the development of aluminum alloys. Its output is further developed. To this end, this paper reviews mainstream rare earth production processes (precipitation methods, microemulsion methods, roasting-sulfuric acid leaching methods, electrochemical methods, solvent extraction methods, and ion exchange methods) to provide basic information for the green smelting of rare earth metals and help promote the development of green rare earth smelting. Based on the advantages and disadvantages of each process as well as recent research results, the optimal process parameters and production efficiency were summarized. Studies have concluded that the precipitation method is mostly used for the recovery of rare earth elements and related valuable metals from solid waste; the microemulsion method is mostly used for the preparation of nanosized rare earth alloys by doping; the roasting-sulfuric acid leaching method is mostly used for the treatment of raw rare earth ores; and the molten salt electrolysis method is a more specific method. This is a green and environmentally friendly production process. The results of this study can provide direction for the realization of green rare earth smelting and provide a reference for improving the existing rare earth smelting process.

Lanthanide-based nanomaterials for temperature sensing in the near-infrared spectral region: illuminating progress and challenges

Being first proposed as a method to overcome limitations associated with conventional contact thermometers, luminescence thermometry has been extensively studied over the past two decades as a sensitive and fast approach to remote and minimally invasive thermal sensing. Herein, lanthanide (Ln)-doped nanoparticles (Ln-NPs) have been identified as particularly promising candidates, given their outstanding optical properties. Known primarily for their upconversion emission, Ln-NPs have also been recognized for their ability to be excited with and emit in the near-infrared (NIR) regions matching the NIR transparency windows. This sparked the emergence of the development of NIR-NIR Ln-NPs for a wide range of temperature-sensing applications. The shift to longer excitation and emission wavelengths resulted in increased efforts being put into developing nanothermometers for biomedical applications, however most research is still preclinical. This mini-review outlines and addresses the challenges that limit the reliability and implementation of luminescent nanothermometers to real-life applications. Through a critical look into the recent developments from the past 4 years, we highlight attempts to overcome some of the limitations associated with excitation wavelength, thermal sensitivity, calibration, as well as light-matter interactions. Strategies range from use of longer excitation wavelengths, brighter emitters through strategic core/multi-shell architectures, exploitation of host phonons, and a shift from double- to single-band ratiometric as well as lifetime-based approaches to innovative methods based on computation and machine learning. To conclude, we offer a perspective on remaining gaps and where efforts should be focused towards more robust nanothermometers allowing a shift to real-life, e.g., in vivo, applications.

Behavior of Microstrain in Nd3+-Sensitized Near-Infrared Upconverting Core-Shell Nanocrystals for Defect-Induced Tailoring of Luminescence Intensity

In an attempt to optimize the upconversion luminescence (UCL) output of a Nd3+-sensitized near-infrared (808 nm) upconverting core-shell (CS) nanocrystal through deliberate incorporation of lattice defects, a comprehensive analysis of microstrain both at the CS interface and within the core layer was performed using integral breadth calculation of high-energy synchrotron X-ray (λ = 0.568551 Å) diffraction. An atomic level interpretation of such microstrain was performed using pair distribution function analysis of the high-energy total scattering. The core NC developed compressive microstrain, which gradually transformed into tensile microstrain with the growth of the epitaxial shell. Such a reversal was rationalized in terms of a consistent negative lattice mismatch. Upon introduction of lattice defects into the CS systems upon incorporation of Li+, the corresponding UCL intensity was maximized at some specific Li+ incorporation, where the tensile microstrain of CS, compressive microstrain of the core, and atomic level disorders exhibited their respective extreme values irrespective of the activator ions.

Customized Lanthanide Nanobiohybrids for Noninvasive Precise Phototheranostics of Pulmonary Biofilm Infection

A noninvasive strategy for in situ diagnosis and precise treatment of bacterial biofilm infections is highly anticipated but still a great challenge. Currently, no in vivo biofilm-targeted theranostic agent is available. Herein, we fabricated intelligent theranostic alginate lyase (Aly)-NaNdF4 nanohybrids with a 220 nm sunflower-like structure (NaNdF4@DMS-Aly) through an enrichment-encapsulating strategy, which exhibited excellent photothermal conversion efficiency and the second near-infrared (NIR-II) luminescence. Benefiting from the site-specific targeting and biofilm-responsive Aly release from NaNdF4@DMS-Aly, we not only enabled noninvasive diagnosis but also realized Aly-photothermal synergistic therapy and real-time evaluation of therapeutic effect in mice models with Pseudomonas aeruginosa biofilm-induced pulmonary infection. Furthermore, such nanobiohybrids with a sheddable siliceous shell are capable of delaying the NaNdF4 dissolution and biodegradation upon accomplishing the therapy, which is highly beneficial for the biosafety of theranostic agents.

Short-wave Infrared Photoluminescence Lifetime Mapping of Rare-Earth Doped Nanoparticles Using All-Optical Streak Imaging

The short-wave infrared (SWIR) photoluminescence lifetimes of rare-earth doped nanoparticles (RENPs) have found diverse applications in fundamental and applied research. Despite dazzling progress in the novel design and synthesis of RENPs with attractive optical properties, existing optical systems for SWIR photoluminescence lifetime imaging are still considerably restricted by inefficient photon detection, limited imaging speed, and low sensitivity. To overcome these challenges, SWIR photoluminescence lifetime imaging microscopy using an all-optical streak camera (PLIMASC) is developed. Synergizing scanning optics and a high-sensitivity InGaAs CMOS camera, SWIR-PLIMASC has a 1D imaging speed of up to 138.9 kHz in the spectral range of 900-1700 nm, which quantifies the photoluminescence lifetime of RENPs in a single shot. A 2D photoluminescence lifetime map can be acquired by 1D scanning of the sample. To showcase the power of SWIR-PLIMASC, a series of core-shell RENPs with distinct SWIR photoluminescence lifetimes is synthesized. In particular, using Er3+ -doped RENPs, SWIR-PLIMASC enables multiplexed anti-counterfeiting. Leveraging Ho3+ -doped RENPs as temperature indicators, this system is applied to SWIR photoluminescence lifetime-based thermometry. Opening up a new avenue for efficient SWIR photoluminescence lifetime mapping, this work is envisaged to contribute to advanced materials characterization, information science, and biomedicine.

Dysprosium-containing Cobalt Sulfide Nanoparticles as Anticancer Drug Carriers

BACKGROUND

Among various materials designed for anticancer drug transport, sulfide nanoparticles are uniquely intriguing owing to their spectral characteristics. Exploration of newer nanoscale copper sulfide particles with dysprosium doping is reported herein. It leads to a change in the physicochemical properties of the sulfide nanoparticles and hence the difference in drug release and cytotoxicity.

OBJECTIVE

We intend to purport the suitably engineered cobalt sulfide and dysprosium-doped cobalt sulfide nanoparticles that are magnetic and NIR-absorbing, as drug delivery vehicles. The drug loading and release are based on the supramolecular drug complex formation on the surface of the nanoparticles.

METHOD

The nanomaterials are synthesized employing hydrothermal procedures, coated with a biocompatible poly-β-cyclodextrin, and characterized using the methods of diffractometry, microscopy, spectroscopy, thermogravimetry and magnetometry. The sustained drug release is investigated in vitro. 5-Fluorouracil is loaded in the nanocarriers. The empty and 5-fluorouracil-loaded nanocarriers are screened for their anti-breast cancer activity in vitro on MCF-7 cells.

RESULTS

The size of the nanoparticles is below 10 nm. They show soft ferromagnetic characteristics. Further, they show broad NIR absorption bands extending up to 1200 nm, with the dysprosium-doped material displaying greater absorbance. The drug 5-fluorouracil is encapsulated in the nanocarriers and released sustainably, with the expulsion duration extending over 10 days. The IC50 of the blank and the drug-loaded cobalt sulfide are 16.24 ± 3.6 and 12.2 ± 2.6 μg mL-1, respectively. For the drug-loaded, dysprosium-doped nanocarrier, the IC50 value is 9.7 ± 0.3 μg mL-1.

CONCLUSION

The ultrasmall nanoparticles possess a size suitable for drug delivery and are dispersed well in the aqueous medium. The release of the loaded 5-fluorouracil is slow and sustained. The anticancer activity of the drug-loaded nanocarrier shows an increase in efficacy, and the cytotoxicity is appreciable due to the controlled release. The nanocarriers show multi-functional characteristics, i.e., magnetic and NIR-absorbing, and are promising drug delivery agents.

Spotlight on Luminescence Thermometry: Basics, Challenges, and Cutting-Edge Applications

Luminescence (nano)thermometry is a remote sensing technique that relies on the temperature dependency of the luminescence features (e.g., bandshape, peak energy or intensity, and excited state lifetimes and risetimes) of a phosphor to measure temperature. This technique provides precise thermal readouts with superior spatial resolution in short acquisition times. Although luminescence thermometry is just starting to become a more mature subject, it exhibits enormous potential in several areas, e.g., optoelectronics, photonics, micro- and nanofluidics, and nanomedicine. This work reviews the latest trends in the field, including the establishment of a comprehensive theoretical background and standardized practices. The reliability, repeatability, and reproducibility of the technique are also discussed, along with the use of multiparametric analysis and artificial-intelligence algorithms to enhance thermal readouts. In addition, examples are provided to underscore the challenges that luminescence thermometry faces, alongside the need for a continuous search and design of new materials, experimental techniques, and analysis procedures to improve the competitiveness, accessibility, and popularity of the technology.

Large-Scale Synthesis of Tunable Fluorescent Carbon Dots Powder for Light-Emitting Diodes and Fingerprint Identification

The emergence and fast development of carbon dots (CDs) provide an unprecedented opportunity for applications in the field of photoelectricity, but their practicability still suffers from complicated synthesis procedures and the substrate dependence of solid-state fluorescence. In this study, we design a unique microwave-assisted solid-phase synthesis route for preparing tunable fluorescent CD powders with yellow, orange, and red fluorescence (Y-CDs, O-CDs, R-CDs) by simply adjusting the mass ratio of reactants, a method which is suitable for the large-scale synthesis of CDs. The Y-/O-/R-CDs were systematically characterized using physics and spectroscopy techniques. Based on the perfect solid-state fluorescence performance of the proposed fluorescent CD powders, the Y-/O-/R-CDs were successfully applied for the construction of multi-color and white light-emitting diode devices at low cost. Furthermore, the Y-CDs displayed much higher yield and luminous efficiency than the O-CDs and R-CDs and were further used for fingerprint identification on the surfaces of glass sheets and tinfoil. In addition, the R-CD aqueous solution fluorescence is sensitive to pH, suggesting its use as a pH indicator for monitoring intracellular pH fluctuations. The proposed series of fluorescent powders composed of CDs may herald a new era in the application of optical components and criminal investigation fields.

Recent advances of lanthanide nanomaterials in Tumor NIR fluorescence detection and treatment

Lanthanide nanomaterials have garnered significant attention from researchers among the main near-infrared (NIR) fluorescent nanomaterials due to their excellent chemical and fluorescence stability, narrow emission band, adjustable luminescence color, and long lifetime. In recent years, with the preparation, functional modification, and fluorescence improvement of lanthanide materials, great progress has been made in their application in the biomedical field. This review focuses on the latest progress of lanthanide nanomaterials in tumor diagnosis and treatment, as well as the interaction mechanism between fluorescence and biological tissues. We introduce a set of efficient strategies for improving the fluorescence properties of lanthanide nanomaterials and discuss some representative in-depth research work in detail, showcasing their superiority in early detection of ultra-small tumors, phototherapy, and real-time guidance for surgical resection. However, lanthanide nanomaterials have only realized a portion of their potential in tumor applications so far. Therefore, we discuss promising methods for further improving the performance of lanthanide nanomaterials and their future development directions.

Selectively Manipulating Interactions between Lanthanide Sublattices in Nanostructure toward Orthogonal Upconversion

Smart control of ionic interactions is a key factor to manipulate the luminescence dynamics of lanthanides and tune their emission colors. However, it remains challenging to gain a deep insight into the physics involving the interactions between heavily doped lanthanide ions and in particular between the lanthanide sublattices for luminescent materials. Here we report a conceptual model to selectively manipulate the spatial interactions between erbium and ytterbium sublattices by designing a multilayer core-shell nanostructure. The interfacial cross-relaxation is found to be a leading process to quench the green emission of Er³⁺, and red-to-green color-switchable upconversion is realized by fine manipulation of the interfacial energy transfer on the nanoscale. Moreover, the temporal control of up-transition dynamics can also lead to an observation of green emission due to its fast rise time. Our results demonstrate a new strategy to achieve orthogonal upconversion, showing great promise in frontier photonic applications.

Optimizing Upconversion Nanoparticles for FRET Biosensing

Upconversion nanoparticles (UCNPs) are some of the most promising nanomaterials for bioanalytical and biomedical applications. One important challenge to be still solved is how UCNPs can be optimally implemented into Förster resonance energy transfer (FRET) biosensing and bioimaging for highly sensitive, wash-free, multiplexed, accurate, and precise quantitative analysis of biomolecules and biomolecular interactions. The many possible UCNP architectures composed of a core and multiple shells doped with different lanthanoid ions at different ratios, the interaction with FRET acceptors at different possible distances and orientations via biomolecular interaction, and the many and long-lasting energy transfer pathways from the initial UCNP excitation to the final FRET process and acceptor emission make the experimental determination of the ideal UCNP-FRET configuration for optimal analytical performance a real challenge. To overcome this issue, we have developed a fully analytical model that requires only a few experimental configurations to determine the ideal UCNP-FRET system within a few minutes. We verified our model via experiments using nine different Nd-, Yb-, and Er-doped core-shell-shell UCNP architectures within a prototypical DNA hybridization assay using Cy3.5 as an acceptor dye. Using the selected experimental input, the model determined the optimal UCNP out of all theoretically possible combinatorial configurations. An extreme economy of time, effort, and material was accompanied by a significant sensitivity increase, which demonstrated the powerful feat of combining a few selected experiments with sophisticated but rapid modeling to accomplish an ideal FRET biosensor.