Efficient Deep-Blue Light-Emitting Diodes from Highly Luminescent Eu2+-Doped Alkali Metal Halide Nanocrystals via Lattice Field Modulation.

Lead-halide perovskite nanocrystals (NCs) are promising for fabricating deep-blue (<460 nm) light-emitting diodes (LEDs), but their development is plagued by low electroluminescent performance and lead toxicity. Herein, the synthesis of 12 kinds of highly luminescent and eco-friendly deep-blue europium (Eu2+)-doped alkali-metal halides (AX:Eu2+; A = Na+, K+, Rb+, Cs+; X = Cl-, Br-, I-) NCs is reported. Through adjustment of the coordination environment, efficient deep-blue emission from Eu-5d → Eu-4f transitions is realized. The representative CsBr:Eu2+ NCs exhibit a high photoluminescence quantum yield of 91.1% at 441 nm with a color coordinate at (0.158, 0.023) matching with the Rec. 2020 blue specification. Electrically driven deep-blue LEDs from CsBr:Eu2+ NCs are demonstrated, achieving a record external quantum efficiency of 3.15% and half-lifetime of ∼1 h, surpassing the reported metal-halide deep-blue NCs-based LEDs. Importantly, large-area LEDs with an emitting area of 12.25 cm2 are realized with uniform emission, representing a milestone toward commercial display applications.

Thermally Enhanced Phosphorescent Carbon Nanodots for Monitoring Cold-Chain Logistics.

Room-temperature phosphorescent materials, renowned for their long luminescence lifetimes, have garnered significant attention in the field of optical materials. However, the challenges posed by thermally induced quenching have significantly hindered the advancement of luminescence efficiency and stability. In this study, thermally enhanced phosphorescent carbon nanodots (CND) are developed by incorporating them into fiber matrices. Remarkably, the phosphorescence lifetime of the thermally enhanced CND exhibits a twofold enhancement, increasing from 326 to 753 ms, while the phosphorescence intensity experienced a tenfold enhancement, increasing from 25 to 245 as the temperature increased to 373 K. Rigid fiber matrices can effectively suppress the non-radiative transition rate of triplet excitons, while high temperatures can desorb oxygen adsorbed on the surface of the CND, disrupting the interaction between the CND and oxygen. Consequently, a thermally enhanced phosphorescence is obtained. In addition, benefiting from the thermally enhanced phosphorescence property of CND, a warning indicator with an anti-counterfeiting function for monitoring cold-chain logistics is demonstrated based on CND.

Entropy-Dominated Triplet Exciton Emission in Carbon Dots.

Phosphorescence in carbon dots (CDs) from triplet exciton radiative recombination at room temperature has achieved significant advancement. Confinement and nanoconfinement, serving as valuable techniques, are commonly utilized to brighten triplet exciton in CDs, thereby enhancing their phosphorescence. However, a comprehensive and universally applicable physical description of confinement-enhanced phosphorescence is still lacking, despite efforts to understand its underlying nature. In this study, the dominance of entropy is revealed in triplet exciton emission from CDs through the establishment of a microscopic vibration state model. CDs with varying entropy levels are studied, indicating that in a low entropy system, the multi-energy triplet exciton emission in CDs exhibits enhanced brightness, accompanied by a corresponding increase in their lifetimes. The product of lifetime and intensity in CDs serves as a descriptor for their phosphorescence properties. Moreover, an entropy-dependent information variation system based on the CDs is demonstrated. Specifically, in a low-entropy system, information is retained, whereas the corresponding information is erased in a high-entropy system. This work elucidates the underlying physical nature of confinement-enhanced triplet exciton emission, offering a deeper understanding of achieving ultralong phosphorescence in the future.

Uncooled Mid-Infrared Sensing Enabled by Chip-Integrated Low-Temperature-Grown 2D PdTe2 Dirac Semimetal.

Next-generation mid-infrared (MIR) imaging chips demand free-cooling capability and high-level integration. The rising two-dimensional (2D) semimetals with excellent infrared (IR) photoresponses are compliant with these requirements. However, challenges remain in scalable growth and substrate-dependence for on-chip integration. Here, we demonstrate the inch-level 2D palladium ditelluride (PdTe2) Dirac semimetal using a low-temperature self-stitched epitaxy (SSE) approach. The low formation energy between two precursors facilitates low-temperature multiple-point nucleation (∼300 °C), growing up, and merging, resulting in self-stitching of PdTe2 domains into a continuous film, which is highly compatible with back-end-of-line (BEOL) technology. The uncooled on-chip PdTe2/Si Schottky junction-based photodetector exhibits an ultrabroadband photoresponse of up to 10.6 µm with a large specific detectivity. Furthermore, the highly integrated device array demonstrates high-resolution room-temperature imaging capability, and the device can serve as an optical data receiver for IR optical communication. This study paves the way toward low-temperature growth of 2D semimetals for uncooled MIR sensing.

Supramolecular Aggregation of Carbon Nanodots.

Supramolecular aggregation has provided the archetype concept to understand the variants in an emerging systems property. Herein, we have achieved the supramolecular assembly of carbon nanodots (CDs) for the first time and employ supramolecular aggregation to understand their alteration in photophysical properties. In detail, we have employed the CDs as a block to construct the supramolecular assembly of aggregates in the CDs' antisolvent of ethanol. The CD-based aggregates exhibit complex and organized morphologies with another long-wavelength excitation-dependent emission band. The experimental results and density functional theoretical calculations reveal that the supramolecular assembly of CDs can decrease the energy gap between the ground and excited states, contributing to the new long-wavelength excitation-dependent emission. The supramolecular aggregation can be employed as one universal strategy to manipulate and understand the luminescence of CDs. These findings cast new light to build the emerging systems and understand the light emission of CDs through supramolecular chemistry.

Highly Antibacterial and Antioxidative Carbon Nanodots/Silk Fibroin Films for Fruit Preservation.

The issues of fruit waste and safety resulting from rot have spurred a demand for improved packaging systems. Herein, we present highly antibacterial and antioxidative carbon nanodot/silk fibroin (CD/SF) films for fruit preservation. The films are composed of CDs and SF together with a small amount of glycerol via hydrogen bonding, exhibiting outstanding biosafety, transparency, and stretchability. The films effectively integrate key functionalities (atmosphere control, resistance to food-borne pathogens, and antioxidation properties) and can be manufactured in large sizes (about 20 × 30 cm), boasting a transmission rate of 13 183 cm3/m2·day for oxygen and 2860 g/m2·day for water vapor, favoring the preservation of fresh fruits. A convenient dip-coating method enables in situ fabrication of films with a thickness of approximately 14 µm directly on the fruits' surface providing comprehensive protection. Importantly, the films are washable and biodegradable. This work presents a promising technology to produce multifunctional and eco-friendly antibacterial packaging systems.

Enhanced Phosphorescence of Carbon Nanodots via Double Confinement for 3D Artworks with Long Emission Lifetimes.

Phosphorescent materials as block elements to build artwork incorporating the time and emission, enable them with spectacular lighting effects. In this work, enhanced phosphorescence of carbon nanodots (CNDs) is demonstrated via double confinement strategy, which silica and epoxy resin are used as the first and the second order confinement layer. The multi-confined CNDs show an enhanced phosphorescence quantum yield up to 16.4%, with enduring emission lifetime up to 1.44 s. Delicately, the plasticity of the epoxy resin enables them easily to be designed for 3D artworks with long emission lifetimes in different shapes. The efficient and eco-friendly phosphorescent CNDs may arouse intense interest both in the academic community and markets.

In Situ Confining Citric Acid-Derived Carbon Dots for Full-Color Room-Temperature Phosphorescence.

Room-temperature phosphorescence has received much attention owing to its potential applications in information encryption and bioelectronics. However, the preparation of full-color single-component-derived phosphorescent materials remains a challenge. Herein, a facile in situ confining strategy is proposed to achieve full-color phosphorescent carbon dots (CDs) through rapid microwave-assisted carbonization of citric acid in NaOH. By tuning the mass ratio of citric acid and NaOH, the obtained CDs exhibit tunable phosphorescence wavelengths ranging from 483 to 635 nm and alterable lifetimes from 58 to 389 ms with a synthesis yield of up to 83.7% (>30 g per synthesis). Theoretical calculations and experimental results confirm that the formation of high-density ionic bonds between cations and CDs leads to efficient afterglow emission via the dissociation of CD arrangement, and the evolution of the aggregation state of CDs results in redshifted phosphorescence. These findings provide a strategy for the synthesis of new insights into achieving and manipulating room-temperature phosphorescent CDs, and prospect their applications in labeling and information encryption.

Ga2O3-Based Solar-Blind Position-Sensitive Detector for Noncontact Measurement and Optoelectronic Demodulation.

As a kind of photodetector, position-sensitive-detectors (PSDs) have been widely used in noncontact photoelectric positioning and measurement. However, fabrications and applications of solar-blind PSDs remain yet to be harnessed. Herein, we demonstrate a solar-blind PSD developed from a graphene/Ga2O3 Schottky junction with a 25-nanometer-thick Ga2O3 film, in which the absorption of the nanometer-thick Ga2O3 is enhanced by multibeam interference. The graphene/Ga2O3 junction exhibits a responsivity of 48.5 mA/W and a rise/decay time of 0.8/99.8 µs at zero bias. Moreover, the position of the solar-blind spot can be determined by the output signals of the PSD. Using the device as a sensor of noncontact test systems, we demonstrate its application in measurement of angular, displacement, and light trajectory. In addition, the position-sensitive outputs have been used to demodulate optical signals into electrical signals. The results may prospect the application of solar-blind PSDs in measurement, tracking, communication, and so on.

Regulating the Singlet and Triplet Emission of Sb3+ Ions to Achieve Single-Component White-Light Emitter with Record High Color-Rendering Index and Stability.

The rapid development of solid-state lighting technology has attracted much attention for searching efficient and stable luminescent materials, especially the single-component white-light emitter. Here, we adopt a facile ion-doping technology to synthesize vacancy-ordered double perovskite Cs2ZrCl6:Sb. The introduction of Sb3+ ions with a 5s2 active lone pair into Cs2ZrCl6 host stimulates the singlet (blue) and triplet (orange) states emission of Sb3+ ions, and their relative emission intensity can be tuned through the energy transfer from singlet to triplet states. Benefiting from the dual-band emission as a pair of perfect complementary colors, the optimum Cs2ZrCl6:1.5%Sb exhibits a high-quality white emission with a color-rendering index of 96. By employing Cs2ZrCl6:1.5%Sb as the down-conversion phosphor, stable single-component white light-emitting diodes with a record half-lifetime of 2003 h were further fabricated. This study puts forward an effective ion-doping strategy to design single-component white-light emitter, making practical applications of them in lighting technologies a real possibility.

Brighten Triplet Excitons of Carbon Nanodots for Multicolor Phosphorescence Films.

Triplet excitons usually do not emit light under ambient conditions due to the spin-forbidden transition rule, thus they are called dark excitons. Herein, triplet excitons in carbon nanodots (CNDs) are brightened by embedding the CNDs into poly(vinyl alcohol) (PVA) films; flexible multicolor phosphorescence films are thus demonstrated. PVA chains can isolate the CNDs, and excited state electron or energy transfer induced triplet exciton quenching is thus reduced; while the formed hydrogen bonds between the CNDs and PVA can restrict vibration/rotation of the CNDs, thus further protecting the triplet excitons from nonradiative recombination. The lifetimes of the flexible multicolor phosphorescence films can reach 567, 1387, 726, and 311 ms, and the longest-lasting phosphorescence film can be observed by naked eyes for nearly 15 s even after bending 5000 times. The phosphorescence films can be processed into various patterns, and a dynamic optical signature concept has been proposed and demonstrated based on the phosphorescence films.

Superhydrophobic Nanodiamond-Functionalized Melamine Sponge for Oil/Water Separation.

Fabrication of absorbent materials foroil/water separation is an important ecological pursuit for oil spill clean-up and organic pollutants' removal. In this study, nanodiamonds (NDs), a promising member of the carbon family, were functionally modified by the covalent linking of octadecylamine (ODA). Subsequently, the superhydrophobic sponge with hierarchical microstructures was fabricated by embedding ND-ODA into a melamine sponge (MS) skeleton via a simple immersion-drying process. The as-prepared sponge (ND-ODA@PDMS@MS) showed superhydrophobic properties with a water contact angle of 155 ± 2°. For various oils and organic solvents, ND-ODA@PDMS@MS possesses excellent absorption capacity (26.65-55.64 g/g) and oil/water separation efficiency (above 98.6%). Furthermore, the adsorption capacity to crude oil remained relatively stable in highly acidic, alkaline, and salty conditions, ensuring the application in the clean-up of industrial oily sewages and marine oil spills. Besides absorbing oil for a single time, ND-ODA@PDMS@MS also exhibited satisfactory performance in continuous oil/water separation. Therefore, this work provides a facile strategy to produce robust and efficient absorbent materials for oil/water separation in large-scale oil and organic solvent clean-ups.

Deep-Ultraviolet Emissive Carbon Nanodots.

Deep-ultraviolet (DUV) emissive carbon nanodots (CNDs) have been designed theoretically and demonstrated experimentally based on the results of first-principles calculations using the density functional theory method. The emission of the CNDs is located in the range from 280 to 300 nm, which coincides well with the results of theoretical calculation results. The photoluminescence (PL) quantum yield (QY) of the CNDs is up to 31.6%, and the strong emission of the CNDs originates from core-state (π-π*) carriers' radiative recombination and surface passivation. Benefiting from the core-state emission and surface group passivation, the emission of the CNDs is independent of the excitation wavelength and ambient solvent. DUV light-emitting diodes (LEDs) have been fabricated based on the DUV emissive CNDs, and the LEDs can be used as the excitation source to excite blue, green, and red CNDs, indicating their potential application in DUV light sources. This work may provide a clue for the designing and realizing of DUV emissive CNDs, thus promising the potential application of CNDs in DUV light-emitting sources.

Oleylamine-assisted and temperature-controlled synthesis of ZnO nanoparticles and their application in encryption.

A temperature-controlled synthesis process for ZnO nanoparticles (NPs) with the assist of oleylamine (OAm) has been demonstrated, and the ZnO NPs show bright fluorescence under ultraviolet illumination. In this process, zinc nitrate was firstly converted to zinc nitrate hydroxide (Zn5(OH)8(NO3)2) sheets with the assist of OAm, then the Zn5(OH)8(NO3)2 was decomposed into fluorescent ZnO NPs by increasing the ambient temperature. Furthermore, information encryption has been realized based on this process. For encryption, the encrypted information cannot be observed, while the encrypted information appears when they are proceeded in the temperature of 120 °C for about one minute. The results shown in this work provide a controllable way for the synthesis of ZnO NPs by adjusting the reaction temperature, and this may inspire wide applications of ZnO in information encryption.

Transparent ultraviolet photovoltaic cells.

Photovoltaic cells have been fabricated from p-GaN/MgO/n-ZnO structures. The photovoltaic cells are transparent to visible light and can transform ultraviolet irradiation into electrical signals. The efficiency of the photovoltaic cells is 0.025% under simulated AM 1.5 illumination conditions, while it can reach 0.46% under UV illumination. By connecting several such photovoltaic cells in a series, light-emitting devices can be lighting. The photovoltaic cells reported in this Letter may promise the applications in glass of buildings to prevent UV irradiation and produce power for household appliances in the future.

Ammonia reduced graphene oxides as a hole injection layer for CdSe/CdS/ZnS quantum dot light-emitting diodes.

In this study, we report quantum-dot light-emitting devices (QD-LEDs) using ammonia reduced graphene oxide (rGO) as a hole injection layer (HIL). Compared with pristine GO, QD-LEDs employing rGO as a HIL show higher maximum luminance (936 cd m(-2) versus 699 cd m(-2)) and lower turn-on voltage (V th, 5.0 V versus 7.5 V). The improved performance can be attributed to the synergistic effect of the improved conductivity (1.27 µS cm(-1) versus 0.139 µS cm(-1)) and decreased work function (5.27 eV versus 5.40 eV) of the GO after the reduction process. The above results indicate that ammonia functionalized graphene may be a promising hole injection material for QD-LEDs.

Black-colored ZnO nanowires with enhanced photocatalytic hydrogen evolution.

Black-colored ZnO nanowires have been prepared in a metal-organic chemical vapor deposition system by employing a relatively low growth temperature and oxygen-deficient conditions. X-ray photoelectron spectroscopy reveals the incorporation of carbon into the nanowires. The photocatalytic hydrogen evolution activity of the black-colored ZnO nanowires is over 2.5 times larger than that of the pristine ZnO nanowires under simulated solar illumination conditions, and the enhanced photocatalytic activity can be attributed to the higher absorption of visible light by the black color and better carrier separation at the ZnO/carbon interface.

Towards the design of efficient quantum dot light-emitting diodes by controlling the exciton lifetime.

Time-resolved photoluminescence and electroluminescence measurements were used to explore the emission characteristics of excitons in quantum dot light-emitting diodes (QD-LEDs). It is found that the lifetime of excitons in the QDs can be varied by adjusting the distance between the excitons and metal Al mirror, which is due to the effect of local density of optical states (LDOS) on the exciton decay rate. QD-LEDs with different hole transport layer (HTL) thickness, i.e., different distance between QDs and Al reflective anode, have been fabricated and it is found that the HTL thickness affects the device efficiency performance greatly, and the optimal HTL thickness for the red QD-LED (emission peak is at 621 nm) is 80 nm. These results shed light on the factors affecting the efficiency and efficiency roll-off in QD-LEDs, thus may provide a clue for high performance QD-LEDs.

Improved performance of ZnO light-emitting devices by introducing a hole-injection layer.

ZnO p-n homojunction light-emitting devices (LEDs) have been fabricated, and by introducing a p-type GaN as the hole-injection layer, the output power of the LEDs can reach 18.5 µW when the drive current is 60 mA, which is almost three orders of magnitude larger than the pristine LEDs without the hole-injection layer. The improved performance can be attributed to the extra holes injected into the p-ZnO layer from the p-GaN hole-injection layer.

Pure ultraviolet emission from ZnO nanowire-based p-n heterostructures.

Well-aligned ZnO nanowires have been prepared on sapphire substrate, and structural and optical characterizations indicate that the nanowires are of single crystalline and have relatively high luminescent quality. By employing the ZnO nanowires as an active layer, p-Zn0.68Mg0.32O:N/n-ZnO nanowire heterostructure light-emitting devices (LEDs) have been fabricated. The LEDs show pure ultraviolet emission when a forward bias is applied, while the deep-level emission frequently observed in ZnO p-n junctions is almost totally invisible. The devices can work continuously for over 27 h under the injection of a current density of 500 mA/cm2, indicating their good stability.