Spatiotemporal control of photochromic upconversion through interfacial energy transfer.

Dynamic control of multi-photon upconversion with rich and tunable emission colors is stimulating extensive interest in both fundamental research and frontier applications of lanthanide based materials. However, manipulating photochromic upconversion towards color-switchable emissions of a single lanthanide emitter is still challenging. Here, we report a conceptual model to realize the spatiotemporal control of upconversion dynamics and photochromic evolution of Er3+ through interfacial energy transfer (IET) in a core-shell nanostructure. The design of Yb sublattice sensitization interlayer, instead of regular Yb3+ doping, is able to raise the absorption capability of excitation energy and enhance the upconversion. We find that a nanoscale spatial manipulation of interfacial interactions between Er and Yb sublattices can further contribute to upconversion. Moreover, the red/green color-switchable upconversion of Er3+ is achieved through using the temporal modulation ways of non-steady-state excitation and time-gating technique. Our results allow for versatile designs and dynamic management of emission colors from luminescent materials and provide more chances for their frontier photonic applications such as optical anti-counterfeiting and speed monitoring.

High-efficiency photocatalytic CO2 reduction enabled by interfacial Ov and isolated Ti3+ of g-C3N4/TiO2 Z-scheme heterojunction.

Exploring the real force that drives the separation of Coulomb-bound electron-hole pairs in the interface of heterojunction photocatalysts can establish a clear mechanism for efficient solar energy conversion efficiency. Herein, the formation of oxygen vacancy (Ov) and isolated Ti3+ was precisely regulated at the interface of g-C3N4/TiO2 Z-scheme heterojunction (g-C3N4/Ov-Ti3+-TiO2) by optimizing the opening degree of the calcination system, showing excellent production rate of CO and CH4 from CO2 photoreduction under visible light. This photocatalytic system also exhibited prominent stability. Combining theoretical calculation and characterization, the introduction of Ov and isolated Ti3+ on the interface could construct a charge transfer channel to break the forbidden transition of n â†’ π*, improving the separation process of photoexcited electron-hole pairs. The photoexcited electrons weakened the covalent interaction of CO bonds to promote the activation of adsorbed inert CO2 molecules, significantly reducing the energy barrier of the rate-limiting step during CO2 reduction. This work demonstrates the great application potential of reasonably regulating heterojunction interface for efficient photocatalytic CO2 reduction.

Cross Relaxation Enables Spatiotemporal Color-Switchable Upconversion in a Single Sandwich Nanoparticle for Information Security.

Smart control of ionic interaction dynamics offers new possibilities for tuning and editing luminescence properties of lanthanide-based materials. However, it remains a daunting challenge to achieve the dynamic control of cross relaxation mediated photon upconversion, and in particular the involved intrinsic photophysics is still unclear. Herein, this work reports a conceptual model to realize the color-switchable upconversion of Tm3+ through spatiotemporal control of cross relaxation in the design of NaYF4:Gd@NaYbF4:Tm@NaYF4 sandwich nanostructure. It shows that cross relaxation plays a key role in modulating upconversion dynamics and tuning emission colors of Tm3+. Interestingly, it is found that there is a short temporal delay for the occurrence of cross relaxation in contrast to the spontaneous emission as a result of the slight energy mismatch between relevant energy levels. This further enables a fine emission color tuning upon non-steady state excitation. Moreover, a characteristic quenching time is proposed to describe the temporal evolution of cross relaxation quantitatively. These findings present a deep insight into the physics of ionic interactions in heavy doping systems, and also show great promise in frontier applications including information security, anti-counterfeiting and nanophotonics.

Photocatalytic C-N bond construction toward high-value nitrogenous chemicals.

The construction of carbon-nitrogen bonds is vital for producing versatile nitrogenous compounds for the chemical and pharmaceutical industries. Among developed synthetic approaches to nitrogenous chemicals, photocatalysis is particularly prominent and has become one of the emerging fields due to its unique advantages of eco-sustainable characteristics, efficient process integration, no need for high-pressure H2, and tunable synthesis methods for developing advanced photocatalytic materials. Here, the review focuses on potential photocatalytic protocols developed for the construction of robust carbon-nitrogen bonds in discrepant activation environments to produce high-value nitrogenous chemicals. The photocatalytic C-N bond construction strategies and involved reaction mechanisms are elucidated.

Novel supramolecular deep eutectic solvent-enabled in-situ lignin protection for full valorization of all components of wheat straw.

Lignin is usually deemed as an inhibitor to enzymatic hydrolysis of cellulose due to its physical barrier, non-productive adsorption, and steric hindrance. Herein, a novel supramolecular deep eutectic solvent (SUPRADES), comprising ethylene glycol and citric acid in 5:1 M ratio, and ß-cyclodextrin (ß-CD) in a concentration of 3.5% (w/w), was developed to be efficient for pretreating wheat straw. The delignification rate, cellulose enzymatic digestibility, and hemicellulose removal reached 90.45%, 97.36% and 87.24%, respectively, which may be attributed to the introduction of ß-CD with superior ability of both adsorption and in-situ lignin protection to efficiently remove lignin with intact structure from cellulose surface. The mechanisms of high-efficiency lignin extraction/protection were systematically illustrated by adsorption kinetics. Moreover, Trichosporon cutaneum grown on the hemicellulose and cellulose fractions after pretreatment afforded 8.8 g total lipids from 100 g wheat straw. The green SUPARDES pretreatment strategy offers a new avenue for upgrading lignocellulose to biofuels.

Tunable and Efficient Photoluminescence of Lanthanide-Doped Cs2NaScCl6 Double Perovskite Single Crystals toward Multifunctional Light-Emitting Diode Applications.

Lead-free halide double perovskite, as one of the promising candidates for lead halide perovskite materials, shows great potential in light-emitting diodes (LEDs), benefiting from its environmental friendliness and high chemical stability. However, the poor regulation of the emission spectra severely limits its application range. Herein, various lanthanide ions were successfully doped in Cs2NaScCl6 double perovskite single crystals (DPSCs) to yield effective and stable emissions spanning from visible to near-infrared (NIR) regions. Notably, efficient energy transfer from the host to the dopants enables tunable emissions with good chromaticity, which is rarely reported in the field of lead-free double perovskite. Moreover, density functional theory calculations reveal that the high local electron density around the [LnCl6]3- octahedron in DPSCs plays a key role in the improvement of photoluminescence quantum yields (PLQYs). The optimal PLQYs are up to 84%, which increases around 3 times over that of the undoped sample. Finally, multicolor and NIR LEDs based on Ln3+-doped Cs2NaScCl6 DPSCs were fabricated and had different application functions. Specifically, the single-composite white LED shows adjustable coordinates and correlated color temperatures, while the NIR LED shows good night vision imaging. This work provides new inspiration for the application of efficient multifunctional LEDs based on lead-free double perovskite materials.

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.

Multi-wavelength excitable mid-infrared luminescence and energy transfer in core-shell nanoparticles for nanophotonics.

2 µm mid-infrared (MIR) light sources have shown great potential for broad applications in molecular spectroscopy, eye-safe lasers, biomedical systems and so on. However, previous research studies were mainly focused on conventional materials such as glasses, glass-ceramics and crystals, limiting the luminescence intensity and miniaturization of photonic devices. Here we report a new strategy to realize the multiple excitation wavelength responsive MIR emission in a single nanoparticle by employing an erbium sublattice as the sensitizing host. Intense 2 µm emission of Ho3+ from its 5I7 → 5I8 optical transition was observed under 808, 980 and 1530 nm excitations. The possible energy transfer mechanism between Er3+ and Ho3+ ions was discussed. We also designed a core-shell-shell nanostructure by inserting an NaYF4:Yb interlayer to maximize the absorption of 980 nm photons and enhance the 2 µm emission. The MIR luminescence under 808 nm excitation can be further improved by introducing Nd3+ into the outermost shell and attaching indocyanine green dyes. These results present an efficient way for the development of MIR luminescent nanomaterials with great potential in the fields of MIR gain devices, nanosized MIR light sources, and nanophotonics.

Photothermal technique-enabled ambient production of microalgae biodiesel: Mechanism and life cycle assessment.

Thermocatalytic (trans)esterification of oils/lipids to produce biodiesel is generally energy-consuming, reversible, and controlled by the equilibrium law. Herein, a light-induced photothermal process was illustrated to be highly efficient for biodiesel production (96.8 % yield) from microalgae lipids at room temperature enabled by a biomass-based SO3H-functionalized graphene-like heterogeneous catalyst (S-NGL-600), as optimized by response surface methodology. Infrared thermal imaging indicated that interfacial solar heating led to forming a local photothermal catalytic system, reaching 72.2 °C in 2 min. The local light heating was conducive to evaporation and removal of water from acid sites, resulting in local excess of microalgae lipids to facilitate the forward reaction. Notably, the photothermal catalyst was highly recyclable and exhibited a significantly higher conversion rate of microalgae lipids than industrially used catalyst H2SO4. Life cycle assessment suggested energy-saving advantage (0.87 MJ/MJ) and environmental protection (-89.42 CO2eq/MJ) of the photothermal-driven protocol for microalgae biodiesel production.

Oxidative C-C bond cleavage of lignin via electrocatalysis.

Lignin, which is an important component of biomass in nature and is constantly produced in industry, becomes potential raw material for sustainable production of fine chemicals and biofuels. Electrocatalysis has been extensively involved in the activation of simple molecules and cleavage-recasting of complex scaffolds in an elegant environment. As such, electrocatalytic cleavage of C-C(O) in ß-O-4 model molecules of lignin to value-added chemicals has received much attention in recent years. This mini-review introduces various anodes (e.g., Pb, Pt, Ni, Co., and Ir) developed for electro-oxidative lignin degradation (EOLD) under mild conditions. Attention was placed to understand the conversion pathways and involved reaction mechanisms during EOLD, with emphasis on the product distribution caused by different electrodes.

Efficient and tunable photoluminescence for terbium-doped rare-earth-based Cs2NaYCl6 double perovskite.

Lead-free double perovskite materials with efficient and stable self-trapped exciton (STE) emissions show enormous potential for next-generation solid-state lighting. However, the low-emission efficiency and difficulty of spectral regulation are two major obstacles to their application. Here, all-inorganic rare-earth-based double perovskite Cs2NaYCl6 single crystals with strong blue emissions were reported as effective hosts to accommodate lanthanide ion doping. By controlling the introduction of Tb3 + ions and efficient energy transfer from the STEs to the dopants, the emission color of Cs2NaYCl6 single crystals was flexibly modulated from blue to green. The quantum yields were also significantly improved from 10% to 78.81% by optimizing the Tb3 + ion concentration. Further, stable light-emitting diode prototypes based on Cs2NaYCl6 color conversion materials were fabricated to demonstrate the practical applications of rare-earth-based double perovskite.

Multichannel Control of PersL/Upconversion/Down-Shifting Luminescence in a Single Core-Shell Nanoparticle for Information Encryption.

Persistent luminescence (PersL) has been attracting substantial attention in diverse frontier applications such as optical information security and in vivo bioimaging. However, most of the reported PersL emissions are based on the dopants instead of the host matrix, which also plays an important role. In addition, there are few works on the PersL-based multifunctional nanoplatform in nanosized materials. Here, we report a class of novel nanostructure designs with PersL, upconversion, and down-shifting luminescence to realize the fine-tuning of emission colors under different excitation modes including steady-state irradiation, time-gating, and PersL generation. Blue, orange, and green emissions were easily achieved in such a single nanoparticle under suitable excitation modes. Moreover, the physical origin of the PersL of the CaF2 matrix was discussed by simulating the energy band structure with CaxFy defects. Our results provide new opportunities for the design of a new class of multifunctional materials, showing great promise in the field of information encryption security and multilevel anticounterfeiting.

Activating Ultrahigh Thermoresponsive Upconversion in an Erbium Sublattice for Nanothermometry and Information Security.

Thermal activation of upconversion luminescence in nanocrystals opens up new opportunities in biotechnology and nanophotonics. However, it remains a daunting challenge to achieve a smart control of luminescence behavior in the thermal field with remarkable enhancement and ultrahigh sensitivity. Moreover, the physical picture involved is also debatable. Here we report a novel mechanistic design to realize an ultrasensitive thermally activated upconversion in an erbium sublattice core-shell nanostructure. By enabling a thermosensitive property into the intermediate 4I11/2 level of Er3+ through an energy-migration-mediated surface interaction, the upconverted luminescence was markedly enhanced in the thermal field together with a striking thermochromic feature under 1530 nm irradiation. Importantly, the use of non thermally coupled red and green emissions contributes to the thermal sensitivity up to 5.27% K-1, 3 times higher than that obtained by using conventional thermally coupled green emissions. We further demonstrate that the controllable surface interaction is a general approach to the thermal enhancement of upconversion for a series of lanthanide-based nanomaterials. Our findings pave a new way for the development of smart luminescent materials toward emerging applications such as noncontact nanothermometry, information security, and anticounterfeiting.

Switching the NIR upconversion of nanoparticles for the orthogonal activation of photoacoustic imaging and phototherapy.

Phototheranostics based on upconversion nanoparticles (UCNPs) offer the integration of imaging diagnostics and phototherapeutics. However, the programmable control of the photoactivation of imaging and therapy with minimum side effects is challenging due to the lack of ideal switchable UCNPs agents. Here we demonstrate a facile strategy to switch the near infrared emission at 800 nm from rationally designed UCNPs by modulating the irradiation laser into pulse output. We further synthesize a theranostic nanoagent by combining with a photosensitizer and a photoabsorbing agent assembled on the UCNPs. The orthogonal activation of in vivo photoacoustic imaging and photodynamic therapy can be achieved by altering the excitation modes from pulse to continuous-wave output upon a single 980 nm laser. No obvious harmful effects during photoexcitation was identified, suggesting their use for long-term imaging-guidance and phototherapy. This work provides an approach to the orthogonal activation of imaging diagnostics and photodynamic therapeutics.

Research Progress on the Photo-Driven Catalytic Production of Biodiesel.

Biodiesel considered a green, environmentally friendly, and renewable energy source is one of the most promising candidates to replace fossil fuels to supply energy for the world. The conventional thermocatalytic methods have been extensively explored for producing biodiesel, while inevitably encountering some drawbacks, such as harsh operating conditions and high energy consumption. The catalytic production of biodiesel under mild conditions is a research hotspot but with difficulty. Photocatalysis has recently been highlighted as an eco-friendly and energy-saving approach for biodiesel production. This mini-review summarizes typical photocatalysts for biodiesel production and discusses in detail the catalytic mechanism and strategies of the photo-driven (trans)esterification to produce biodiesel. The current challenges and future opportunities of photo-driven catalysis to prepare biodiesel are also outlined, in steps towards guiding the design of advanced photocatalysts for biodiesel production.

Reductive Upgrading of Biomass-Based Levulinic Acid to γ-Valerolactone Over Ru-Based Single-Atom Catalysts.

With the great adjustment of world industrialization and the continuous improvement of energy consumption requirements, the selective conversion of biomass-based platform molecules to high-value chemicals and biofuels has become one of the most important topics of current research. Catalysis is an essential approach to achieve energy-chemical conversion through the "bond breaking-bond formation" principle, which opens a broad world for the energy sector. Single-atom catalysts (SACs) are a new frontier in the field of catalysis in recent years, and exciting achievements have been made in biomass energy chemistry. This mini-review focuses on catalytic conversion of biomass-based levulinic acid (LA) to γ-valerolactone (GVL) over SACs. The current challenges and future development directions of SACs-mediated catalytic upgrading of biomass-based LA to produce value-added GVL, and the preparation and characterization of SACs are analyzed and summarized, aiming to provide theoretical guidance for further development of this emerging field.

A Highly Effective Biomass-Derived Solid Acid Catalyst for Biodiesel Synthesis Through Esterification.

Efficient valorization of renewable liquid biomass for biodiesel production using the desirable biomass-based catalysts is being deemed to be an environmentally friendly process. Herein, a highly active biomass-based solid acid catalyst (SiO2@Cs-SO3H) with renewable chitosan as raw material through sulfonation procedure under the relatively mild condition was successfully manufactured. The SiO2@Cs-SO3H catalyst was systematically characterized, especially with a large specific surface area (21.82 m2/g) and acidity (3.47 mmol/g). The catalytic activity of SiO2@Cs-SO3H was evaluated by esterification of oleic acid (OA) and methanol for biodiesel production. The best biodiesel yield was acquired by Response Surface Methodology (RSM). The optimized reaction conditions were temperature of 92°C, time of 4.1 h, catalyst dosage of 6.8 wt%, and methanol to OA molar ratio of 31.4, respectively. In this case, the optimal experimental biodiesel yield was found to be 98.2%, which was close to that of the predicted value of 98.4%, indicating the good reliability of RSM employed in this study. Furthermore, SiO2@Cs-SO3H also exhibited good reusability in terms of five consecutive recycles with 87.0% biodiesel yield. As such, SiO2@Cs-SO3H can be considered and used as a bio-based sustainable catalyst of high-efficiency for biodiesel production.

Ultrasensitive Thermochromic Upconversion in Core-Shell-Shell Nanoparticles for Nanothermometry and Anticounterfeiting.

Upconversion nanoparticle based ratiometric nanothermometry has shown many advantages including high relative sensitivity, fast temperature response, and high spatial resolution. However, most of the existing designs are on the basis of thermally coupled upconversion emissions, and it remains a challenge to improve the thermo-sensitivity. Here, we report a new nanoplatform of NaYF4:Yb/Er/Ce@NaYF4@NaYF4:Yb/Tm core-shell-shell nanostructure to improve the thermal sensitivity through the nonthermally coupled upconversion emissions. With the increase of temperature, the green upconversion of Er3+ shows a decline while the blue upconversion of Tm3+ exhibits a rapid increase, leading to a huge contrast in both intensity ratio and emission colors. The maximum relative sensitivity can reach up to 9.86% K-1 at 303 K. It is further found that introducing Ce3+ is able to improve the sensitivity and expand the thermochromic green-to-blue gamut greatly. These results show great potential in ultrasensitive lanthanide-based nanothermometry and anticounterfeiting.

Controlling upconversion in emerging multilayer core-shell nanostructures: from fundamentals to frontier applications.

Lanthanide-based upconversion nanomaterials have recently attracted considerable attention in both fundamental research and various frontier applications owing to their excellent photon upconversion performance and favourable physicochemical properties. In particular, the emergence of multi-layer core-shell (MLCS) nanostructures offers a versatile and powerful tool to realize well-defined matrix compositions and spatial distributions of the dopant on the nanometer length scale. In contrast to the conventional nanomaterials and commonly investigated core-shell nanoparticles, the rational design of MLCS nanostructures allows us to deliberately introduce more functional properties into an upconversion system, thus providing unprecedented opportunities for the precise manipulation of energy transfer channels, the dynamic control of upconversion processes, the fine tuning of switchable emission colours and new functional integration at a single-particle level. In this review, we present a summary and discussion on the key aspects of the recent progress in lanthanide-based MLCS nanoparticles, including the manipulation of emission and lifetime, the switchable multicolour output and the lanthanide ionic interactions on the nanoscale. Benefitting from the multifunctional and versatile luminescence properties, the MLCS nanostructures exhibit great potential in diversities of frontier applications such as three-dimensional display, upconversion laser, optical memory, anti-counterfeiting, thermometry, bioimaging, and therapy. The outlook and challenges as well as perspectives for the research in MLCS nanostructure materials are also provided. This review would be greatly helpful in exploring new structural designs of lanthanide-based materials to further manipulate the upconversion phenomenon and expand their application boundaries.