Morphology does not matter: WSe2 luminescence nanothermometry unravelled.

Transition metal dichalcogenides, including WSe2, have gained significant attention as promising nanomaterials for various applications due to their unique properties. In this study, we explore the temperature-dependent photoluminescent properties of WSe2 nanomaterials to investigate their potential as luminescent nanothermometers. We compare the performance of WSe2 quantum dots and nanorods synthesized using sonication synthesis and hot injection methods. Our results show a distinct temperature dependence of the photoluminescence, and conventional ratiometric luminescence thermometry demonstrates comparable relative thermal sensitivity (0.68-0.80% K-1) and temperature uncertainty (1.3-1.5 K), irrespective of the morphology of the nanomaterials. By applying multiple linear regression to WSe2 quantum dots, we achieve enhanced thermal sensitivity (30% K-1) and reduced temperature uncertainty (0.1 K), highlighting the potential of WSe2 as a versatile nanothermometer for microfluidics, nanofluidics, and biomedical assays.

Insights into NdIII to YbIII Energy Transfer and Its Implications in Luminescence Thermometry.

This work challenges the conventional approach of using NdIII 4F3/2 lifetime changes for evaluating the experimental NdIII → YbIII energy transfer rate and efficiency. Using near-infrared (NIR) emitting Nd:Yb mixed-metal coordination polymers (CPs), synthesized via solvent-free thermal grinding, we demonstrate that the NdIII [2H11/2 → 4I15/2] → YbIII [2F7/2 → 2F5/2] pathway, previously overlooked, dominates energy transfer due to superior energy resonance and J-level selection rule compatibility. This finding upends the conventional focus on the NdIII [4F3/2 → 4I11/2] → YbIII [2F7/2 → 2F5/2] transition pathway. We characterized Nd0.890Yb0.110(BTC)(H2O)6 as a promising cryogenic NIR thermometry system and employed our novel energy transfer understanding to perform simulations, yielding theoretical thermometric parameters and sensitivities for diverse Nd:Yb ratios. Strikingly, experimental thermometric data closely matched the theoretical predictions, validating our revised model. This novel perspective on NdIII → YbIII energy transfer holds general applicability for the NdIII/YbIII pair, unveiling an important spectroscopic feature with broad implications for energy transfer-driven materials design.

Exploring the Luminescence, Redox, and Magnetic Properties in a Multivariate Metal-Organic Radical Framework.

Persistent neutral organic radicals are excellent building blocks for the design of functional molecular materials due to their unique electronic, magnetic, and optical properties. Among them, triphenylmethyl radical derivatives have attracted a lot of interest as luminescent doublet emitters. Although neutral organic radicals have been underexplored as linkers for building metal-organic frameworks (MOFs), they hold great potential as organic elements that could introduce additional electronic properties within these frameworks. Herein, we report the synthesis and characterization of a novel multicomponent metal-organic radical framework (PTMTCR@NR-Zn MORF), which is constructed from the combination of luminescent perchlorotriphenylmethyl tricarboxylic acid radical (PTMTCR) and nonemissive nonradical (PTMTCNR) organic linkers and Zn(II) ions. The PTMTCR@NR-Zn MORF structure is layered with microporous one-dimensional channels embedded within these layers. Kelvin probe force microscopy further confirmed the presence of both organic nonradical and radical linkers in the framework. The luminescence properties of the PTMTCR ligand (first studied in solution and in the solid state) were maintained in the radical-containing PTMTCR@NR-Zn MORF at room temperature as fluorescence solid-state quenching is suppressed thanks to the isolation of the luminescent radical linkers. In addition, magnetic and electrochemical properties were introduced to the framework due to the incorporation of the paramagnetic organic radical ligands. This work paves the way for the design of stimuli-responsive hybrid materials with tunable luminescence, electrochemical, and magnetic properties by the proper combination of closed- and open-shell organic linkers within the same framework.

Deciphering Density Fluctuations in the Hydration Water of Brownian Nanoparticles via Upconversion Thermometry.

We investigate the intricate relationship among temperature, pH, and Brownian velocity in a range of differently sized upconversion nanoparticles (UCNPs) dispersed in water. These UCNPs, acting as nanorulers, offer insights into assessing the relative proportion of high-density and low-density liquid in the surrounding hydration water. The study reveals a size-dependent reduction in the onset temperature of liquid-water fluctuations, indicating an augmented presence of high-density liquid domains at the nanoparticle surfaces. The observed upper-temperature threshold is consistent with a hypothetical phase diagram of water, validating the two-state model. Moreover, an increase in pH disrupts the organization of water molecules, similar to external pressure effects, allowing simulation of the effects of temperature and pressure on hydrogen bonding networks. The findings underscore the significance of the surface of suspended nanoparticles for understanding high- to low-density liquid fluctuations and water behavior at charged interfaces.

Extending the Palette of Luminescent Primary Thermometers: Yb3+/Pr3+ Co-Doped Fluoride Phosphate Glasses.

The unique tunable properties of glasses make them versatile materials for developing numerous state-of-the-art optical technologies. To design new optical glasses with tailored properties, an extensive understanding of the intricate correlation between their chemical composition and physical properties is mandatory. By harnessing this knowledge, the full potential of vitreous matrices can be unlocked, driving advancements in the field of optical sensors. We herein demonstrate the feasibility of using fluoride phosphate glasses co-doped with trivalent praseodymium (Pr3+) and ytterbium (Yb3+) ions for temperature sensing over a broad range of temperatures. These glasses possess high chemical and thermal stability, working as luminescent primary thermometers that rely on the thermally coupled levels of Pr3+ that eliminate the need for recurring calibration procedures. The prepared glasses exhibit a relative thermal sensitivity and uncertainty at a temperature of 1.0% K-1 and 0.5 K, respectively, making them highly competitive with the existing luminescent thermometers. Our findings highlight that Pr3+-containing materials are promising for developing cost-effective and accurate temperature probes, taking advantage of the unique versatility of these vitreous matrices to design the next generation of photonic technologies.

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.

Exploring the intra-4f and the bright white light upconversion emissions of Gd2O3:Yb3+,Er3+-based materials for thermometry.

Upconversion broadband white light emission driven by low-power near-infrared (NIR) lasers has been reported for many materials, but the mechanisms and effects related to this phenomenon remain unclear. Herein, we investigate the origin of laser-induced continuous white light emission in synthesized nanoparticles (Gd0.89Yb0.10Er0.01)2O3 and a mechanical mixture of commercial oxides with the same composition 89% Gd2O3, 10% Yb2O3, and 1% Er2O3. We report their photophysical features with respect to sample compactness, laser irradiation (wavelength, power density, excitation cycles), pressure, temperature, and temporal dynamics. Despite the sensitizer (Yb3+) and activator (Er3+) being in different particles for the mechanical mixture, efficient discrete and continuous upconversion emissions were observed. Furthermore, the synthesized nanoparticles were developed as primary luminescent thermometers (upon excitation at NIR) in the 299-363 K range, using the Er3+ upconversion 2H11/2 → 4I15/2/4S3/2 → 4I15/2 intensity ratio. They were also operating as secondary ones in the 1949-3086 K, based on the blackbody distribution of the observed white light emission. Our findings provide important insights into the mechanisms and effects related to the transition from discrete to continuous upconversion emissions with potential applications in remote temperature sensing.

Lanthanide-based logic: a venture for the future of molecular computing.

Managing the continuous and fast-growing volume of information, the progress in the Internet-of-Things, and the evolution from digitalization to networking are huge technological chores. Si-based integrated chips face increasing demands as they strive to meet these challenges. However, there is growing recognition that information processing and computing based on molecules performing logic operations may play a decisive role in shaping the future of the computer industry. Molecular logic gates are molecular counterparts of electronic devices that, instead of exclusively by electrical signals, can be stimulated by diverse chemical or physical input signals that produce optical outputs according to a well-defined logical transfer function. Several materials have been applied for molecular logic, however, the Ln3+-based ones appear to be a commendable choice, as they can respond to both chemical and physical stimuli, presenting unique photophysical properties that make them quite popular for photonics applications. Here we critically review illustrative molecular logic systems based on Ln3+ ions and discuss their potential for integration in future molecular photonic-electronic hybrid logic computing systems.

Local Temperature Increments and Induced Cell Death in Intracellular Magnetic Hyperthermia.

The generation of temperature gradients on nanoparticles heated externally by a magnetic field is crucially important in magnetic hyperthermia therapy. But the intrinsic low heating power of magnetic nanoparticles, at the conditions allowed for human use, is a limitation that restricts the general implementation of the technique. A promising alternative is local intracellular hyperthermia, whereby cell death (by apoptosis, necroptosis, or other mechanisms) is attained by small amounts of heat generated at thermosensitive intracellular sites. However, the few experiments conducted on the temperature determination of magnetic nanoparticles have found temperature increments that are much higher than the theoretical predictions, thus supporting the local hyperthermia hypothesis. Reliable intracellular temperature measurements are needed to get an accurate picture and resolve the discrepancy. In this paper, we report the real-time variation of the local temperature on γ-Fe2O3 magnetic nanoheaters using a Sm3+/Eu3+ ratiometric luminescent thermometer located on its surface during exposure to an external alternating magnetic field. We measure maximum temperature increments of 8 °C on the surface of the nanoheaters without any appreciable temperature increase on the cell membrane. Even with magnetic fields whose frequency and intensity are still well within health safety limits, these local temperature increments are sufficient to produce a small but noticeable cell death, which is enhanced considerably as the magnetic field intensity is increased to the maximum level tolerated for human use, consequently demonstrating the feasibility of local hyperthermia.

Multimodal Tuning of Synaptic Plasticity Using Persistent Luminescent Memitters.

Mimicking memory processes, including encoding, storing, and retrieving information, is critical for neuromorphic computing and artificial intelligence. Synaptic behavior simulations through electronic, magnetic, or photonic devices based on metal oxides, 2D materials, molecular complex and phase change materials, represent important strategies for performing computational tasks with enhanced power efficiency. Here, a special class of memristive materials based on persistent luminescent memitters (termed as a portmanteau of "memory" and "emitter") with optical characteristics closely resembling those of biological synapses is reported. The memory process and synaptic plasticity can be successfully emulated using such memitters under precisely controlled excitation frequency, wavelength, pulse number, and power density. The experimental and theoretical data suggest that electron-coupled trap nucleation and propagation through clustering in persistent luminescent memitters can explain experience-dependent plasticity. The use of persistent luminescent memitters for multichannel image memorization that allows direct visualization of subtle changes in luminescence intensity and realization of short-term and long-term memory is also demonstrated. These findings may promote the discovery of new functional materials as artificial synapses and enhance the understanding of memory mechanisms.

Hexagonal-phase NaREF4 upconversion nanocrystals: the matter of crystal structure.

The hexagonal-phase (ß) of NaREF4 upconversion nanocrystals (RE = rare earth elements) has been widely employed because of the outstanding luminescence performance, yet less is known about the essence of this superior property. The current understanding of this issue is raised from the advantage of weak electron-vibration interactions in fluoride systems, while the interpretability of this statement is controversial and contradictory results are commonly reported. One feasible way to solve this puzzle is from the aspect of "structure-property" relationship, yet even after decades of investigation, the structural details of ß-NaREF4 are still under debate. Herein, the reported results relevant to this topic are reviewed, and the conflicting viewpoints are summarized. The similarities and differences between different lattice templates are assessed, and the reasons underlying the divergence are analysed. Based on these discussions, it is realized that the crystal structure of ß-NaREF4 should be more reliably depicted as one flexible lattice framework with complex characteristics, and the structural disorder induced by atom displacements in the lattice is probably the key to supporting the superior luminescence properties of ß-NaREF4 nanocrystals.

Controlling the thermal switching in upconverting nanoparticles through surface chemistry.

Photon upconversion taking place in small rare-earth-doped nanoparticles has been recently observed to be thermally modulated in an anomalous manner, showing thermal enhancement of the emission intensity. This effect was proved to be linked to the role of adsorbed water molecules as surface quenchers. The surface capping of the particles has a direct influence on the thermal dynamics of water adsorption and desorption, and therefore on the optical properties. Here, we show that the upconversion intensity of small-size (<25 nm) nanoparticles co-doped with Yb3+ and Er3+ ions, and functionalized with different capping molecules, presents clear irreversibility patterns upon thermal cycling that strongly depend on the chemical nature of the nanoparticle surface. By performing temperature-controlled luminescence measurements we observed the formation of a thermal hysteresis loop, resembling an optical switching phenomenon, whose shape and trajectory depend on the hydrophilicity of the surface. Additionally, an intensity overshoot takes place immediately after turning off the heating source, affecting each radiative transition differently. We performed numerical modelling to understand this effect considering non-radiative energy transfer from the surface defect states to the Er3+ ions. These findings are relevant for the comprehension of nanoparticle-based luminescence and the interplay between the surface and volume effects, and more generally, for applications involving UCNPs such as nanothermometry and bioimaging, and the development of optical encoding systems.

Thermal enhancement of upconversion emission in nanocrystals: a comprehensive summary.

Luminescence thermal stability is a major figure of merit of lanthanide-doped nanoparticles playing an essential role in determining their potential applications in advanced optics. Unfortunately, considering the intensification of multiple electron-vibration interactions as temperature increases, luminescence thermal quenching of lanthanide-doped materials is generally considered to be inevitable. Recently, the emergence of thermally enhanced upconversion luminescence in lanthanide-doped nanoparticles seemed to challenge this stereotype, and the research on this topic rapidly aroused wide attention. While considerable efforts have been made to explore the origin of this phenomenon, the key mechanism of luminescence enhancement is still under debate. Here, to sort out the context of this intriguing finding, the reported results on this exciting topic are reviewed, and the corresponding enhancement mechanisms as proposed by different researchers are summarized. Detailed analyses are provided to evaluate the contribution of the most believed "surface-attached moisture desorption" process on the overall luminescence enhancement of lanthanide-doped nanoparticles at elevated temperatures. The impacts of other surface-related processes and shell passivation on the luminescence behaviour of the lanthanide-doped materials are also elaborated. Lack of standardization in the reported data and the absence of important experimental information, which greatly hinders the cross-checking and reanalysis of the results, is emphasized as well. On the foundation of these discussions, it is realized that the thermal-induced luminescence enhancement is a form of recovery process against the strong luminescence quenching in the system, and the enhancement degree is closely associated with the extent of luminescence loss induced by various quenching effects beforehand.

Thermal properties of lipid bilayers derived from the transient heating regime of upconverting nanoparticles.

Heat transfer and thermal properties at the nanoscale can be challenging to obtain experimentally. These are potentially relevant for understanding thermoregulation in cells. Experimental data from the transient heating regime in conjunction with a model based on the energy conservation enable the determination of the specific heat capacities for all components of a nanoconstruct, namely an upconverting nanoparticle and its conformal lipid bilayer coating. This approach benefits from a very simple, cost-effective and non-invasive optical setup to measure the thermal parameters at the nanoscale. The time-dependent model developed herein lays the foundation to describe the dynamics of heat transfer at the nanoscale and were used to understand the heat dissipation by lipid bilayers.

Exploring Single-Nanoparticle Dynamics at High Temperature by Optical Tweezers.

The experimental determination of the velocity of a colloidal nanoparticle (vNP) has recently became a hot topic. The thermal dependence of vNP is still left to be explored although it is a valuable source of information allowing, for instance, the discernment between ballistic and diffusive regimes. Optical tweezers (OTs) constitute a tool especially useful for the experimental determination of vNP although they have only been capable of determining it at room temperature. In this work, we demonstrate that it is possible to determine the temperature dependence of the diffusive velocity of a single colloidal nanoparticle by analyzing the temperature dependence of optical forces. The comparison between experimental results and theoretical predictions allowed us to discover the impact that the anomalous temperature dependence of water properties has on the dynamics of colloidal nanoparticles in this temperature range.

Inert Shell Effect on the Quantum Yield of Neodymium-Doped Near-Infrared Nanoparticles: The Necessary Shield in an Aqueous Dispersion.

Lanthanide-doped nanoparticles (LnNPs) are versatile near-infrared (NIR) emitting nanoprobes that have led to their growing interest for use in biomedicine-related imaging. Toward the brightest LnNPs, high photoluminescence quantum yield (PLQY) values are attained by implementing core/shell engineering, particularly with an optically inert shell. In this work, a thorough investigation is performed to quantify how an outer inert shell maintains the PLQY of Nd3+-doped LnNPs dispersed in an aqueous environment. Three relevant quantitative findings affecting the PLQY of Nd3+-doped LnNPs are identified: (i) the PLQY of core LnNPs is improved 3-fold upon inert shell coating; (ii) PLQY decreases with increasing Nd3+ doping despite the inert shell; and (iii) solvent quenching has a major influence on the PLQY of the LnNPs, though it is relatively lessened for high Nd3+ doping. Overall, we shed new light on the impact of the LnNP architecture on the NIR emission, as well as on the quenching effects caused by doping concentration and solvent molecules.

Real-Time Intracellular Temperature Imaging Using Lanthanide-Bearing Polymeric Micelles.

Measurement of thermogenesis in individual cells is a remarkable challenge due to the complexity of the biochemical environment (such as pH and ionic strength) and to the rapid and yet not well-understood heat transfer mechanisms throughout the cell. Here, we present a unique system for intracellular temperature mapping in a fluorescence microscope (uncertainty of 0.2 K) using rationally designed luminescent Ln3+-bearing polymeric micellar probes (Ln = Sm, Eu) incubated in breast cancer MDA-MB468 cells. Two-dimensional (2D) thermal images recorded increasing the temperature of the cells culture medium between 296 and 304 K shows inhomogeneous intracellular temperature progressions up to ∼20 degrees and subcellular gradients of ∼5 degrees between the nucleolus and the rest of the cell, illustrating the thermogenic activity of the different organelles and highlighting the potential of this tool to study intracellular processes.

Decoding a Percolation Phase Transition of Water at ∼330 K with a Nanoparticle Ruler.

Liquid water, despite its simple molecular structure, remains one of the most fascinating and complex substances. Most notably, many questions continue to exist regarding the phase transitions and anomalous properties of water, which are subtle to observe experimentally. Here, we report a sharp transition in water at 330 K unveiled through experimental measurements of the instantaneous Brownian velocity of NaYF4:Yb/Er upconversion nanoparticles in water. Our experimental investigations, corroborated by molecular dynamics simulations, elucidate a geometrical phase transition where a low-density liquid (LDL) clusters become percolated below 330 K. Around this critical temperature, we find the sizes of the LDL clusters to be similar to those of the nanoparticles, confirming the role of the upconversion nanoparticle as a powerful ruler for measuring the extensiveness of the LDL hydrogen-bond network and nanometer-scale spatial changes (20-100 nm) in liquids. Additionally, a new order parameter that unequivocally classifies water molecules into two local geometric states is introduced, providing a new tool for understanding and modeling water's many anomalous properties and phase transitions.