Large Energy Research Articles

Missing energy plus jet in the SMEFT

We study the production of dineutrinos in proton-proton collisions, with large missing transverse energy and an energetic jet as the experimental signature. Recasting a search from the ATLAS collaboration we work out constraints on semileptonic four-fermion operators, gluon and electroweak dipole operators and Z-penguins in the SMEFT. All but the Z-penguin operators experience energy-enhancement. Constraints on gluon dipole operators are the strongest, probing new physics up to 14 TeV, and improve over existing ones from collider studies. Limits on FCNC four-fermion operators are competitive with Drell-Yan production of dileptons, and improve on those for tau final states. For left-handed |∆s| = |∆d| = 1 and right-handed |∆c| = |∆u| = 1 transitions these are the best available limits, also considering rare kaon and charm decays. We estimate improvements for the 3000 fb−1 High Luminosity Large Hadron Collider.

Room temperature polariton spin switches based on Van der Waals superlattices

Transition-metal dichalcogenide monolayers possess large exciton binding energy and a robust valley degree of freedom, making them a viable platform for the development of spintronic devices capable of operating at room temperature. The development of such monolayer TMD-based spintronic devices requires strong spin-dependent interactions and effective spin transport. This can be achieved by employing exciton-polaritons. These hybrid light-matter states arising from the strong coupling of excitons and photons allow high-speed in-plane propagation and strong nonlinear interactions. Here, we demonstrate the operation of all-optical polariton spin switches by incorporating a WS2 superlattice into a planar microcavity. We demonstrate spin-anisotropic polariton nonlinear interactions in a WS2 superlattice at room temperature. As a proof-of-concept, we utilize these spin-dependent interactions to implement different spin switch geometries at ambient conditions, which show intrinsic sub-picosecond switching time and small footprint. Our findings offer new perspectives on manipulations of the polarization state in polaritonic systems and highlight the potential of atomically thin semiconductors for the development of next generation information processing devices.

Anchoring mechanical characteristics of Ductile-Expansion bolt

The application of ductile rock bolts has been a crucial method for solving the problems of large deformations, energy absorption and stability control issues in deep rock masses. To study the anchoring mechanism of the key expansive structure, this paper proposes a novel type of bolt — the Ductile-Expansion bolt, and conducts research on anchoring mechanics, energy absorption characteristics, and failure modes of the bolt. In addition, this paper defines the concept of load-volume ratio of metal rock bolts and proves the Ductile-Expansion bolt is capable of better improving the unit volume bearing capacity of the bolt material. Furthermore, laboratory and field tests verify the Ductile-Expansion bolt had better anchoring effect than the traditional rebar bolt, with the expansion structure favorably enhancing the ductility and energy absorption performance of the bolt. Finally, this paper microscopically analyzes the crack propagation and distribution morphology of the bolts by establishing a 3D coupled numerical model based on FDM-DEM. Numerical results illustrate the interface at the variable diameter of the Ductile-Expansion bolt serves as the transition zone between high and low stress levels. The expansion structure can impose radial compression on the medium around the bolt, which can improve the bolt anchorage performance.

Selection of the Lubricating Oil Components Based on the Molecular Adsorption Characteristics

Abstract The adsorption characteristics of the lubricating oil near the solid surface play crucial roles in the lubricating performance. In this paper, the molecular dynamics simulation implemented by MS software was carried out to reveal the adsorption properties of different lubricants on Fe2O3 surfaces. Several kinds of lubricating oil molecules were employed, namely, n-eicosane, 2, 6, 11, 15-tetramethylhexadecane, 2-decyldecahydronaphthalene and tetradecylcyclohexane. The results show that 2, 6, 11, 15-tetramethylhexadecane and 2-decyldecahydronaphthalene are relatively more favorable as the lubricant components. This is because they both have relatively high adsorption density, low molecular diffusivity and large adsorption energy. These results can provide a theoretical basis for the selection of future lubricant components as well as lubricant performance enhancement for blending.

Two-dimensional Cr2Cl3S3 Janus magnetic semiconductor with large magnetic exchange interaction and high-TC

Abstract The two-dimensional (2D) Janus monolayers are promising in spintronic device application due to their enhanced magnetic couplings and Curie temperatures. Van der Waals CrCl3 monolayer has been experimentally proved to have an in-plane magnetic easy axis and a low Curie temperature of 17 K, which will limit its application in spintronic devices. In this work, we propose a new Janus monolayer Cr2Cl3S3 based on the first principles calculations. The phonon dispersion and elastic constants confirm that Janus monolayer Cr2Cl3S3 is dynamically and mechanically stable. Our Monte Carlo simulation results based on magnetic exchange constants reveal that Janus monolayer Cr2Cl3S3 is an intrinsic ferromagnetic semiconductor with T C of 180 K, which is much higher than that of CrCl3 due to the enhanced ferromagnetic coupling caused by S substitution. Moreover, the magnetic easy axis of Janus Cr2Cl3S3 can be tuned to the perpendicular direction with a large magnetic anisotropy energy (MAE) of 142 μeV/Cr. Furthermore, the effect of biaxial strain on the magnetic property of Janus monolayer Cr2Cl3S3 is evaluated. It is found that the Curie temperature is more robust under tensile strain. This work indicates that the Janus monolayer Cr2Cl3S3 presents increased Curie temperature and out-of-plane magnetic easy axis, suggesting greater application potential in 2D spintronic devices.

M/BiOCl-(M=Pt, Pd, and Au) Boosted Selective Photocatalytic CO2 Reduction to C2 Hydrocarbons via *CHO Intermediate Manipulation.

Selective CO2 photoreduction to C2 hydrocarbons is significant but limited by the inadequate adsorption strength of the reaction intermediates and low efficiency of proton transfer. Herein, an ameliorative *CO adsorption and H2O activation strategy is realized via decorating bismuth oxychloride (BiOCl) nanostructures with different metal (Pt, Pd, and Au) species. Experimental and theoretical calculation results reveal that distinct *CO binding energies and *H acquisition abilities of the metal cocatalysts mediate the CO2 reduction activity and hydrocarbon selectivity. The relatively moderate *CO adsorption and *H supply over Pd/BiOCl endows it with the lowest free energy to generate *CHO, leading to its highest activity of hydrocarbon production. Specifically, the Pt cocatalyst can efficiently participate in H2O dissociation to deliver more *H for facilitating the protonation of the *CHO and *CHOH, thereby favoring CH4 production with 76.51% selectivity. A lower *H supply over Pd/BiOCl and Au/BiOCl results in a large energy barrier for *CHO or *CHOH protonation and thus a more thermodynamically favored OC─CHO coupling pathway, which endows them with vastly increased C2 hydrocarbon selectivity of 81.21% and 92.81%, respectively. The understanding of efficient C2 hydrocarbon production in this study sheds light on how materials can be engineered for photocatalytic CO2 reduction.

An off-energy multipole kicker injection scheme designed with an acceptance analysis method for a diffraction-limited storage ring

Diffraction-limited storage rings (DLSRs) have restricted dynamic apertures (DAs) due to their ultralow emittances and very strong nonlinearity. Off-energy multipole kicker injection (MKI) scheme, in which off-energy beam is injected onto the corresponding off-energy orbit, can reduce the requirement of DAs. However, it requires relatively large energy acceptance and high dispersion bumps. For a DLSR lattice with relatively large energy acceptance and off-momentum DAs, off-energy beam can be injected into the off-momentum DA but with an additional offset from the off-energy closed orbit to increase the total offset of the injected beam from the on-energy closed orbit, which is favorable to the application of the off-energy MKI. In this paper, such an off-energy MKI is designed for a DLSR, and an acceptance analysis method based on 6D particle tracking is utilized to design and optimize this injection scheme. Detailed simulation is carried out, and the results demonstrate the feasibility of this injection scheme.

Additive Manufacturing of Grid Reservoir-Integrated Anodes for Dendrite-Free, Safe, and Ultra-Low Voltage Zinc-Ion Batteries.

This work reports a novel 3D printed grid reservoir-integrated mesoporous carbon coordinatedsilicon oxycarbide hybrid composite (3DP-MPC-SiOC) to establish the zincophile interphase for controlling the dendrite formation. The customized 3D printed grid patterned structure inhibits Zn dendrite growth and achieves long-term stability with reduced voltage polarization due to homogeneous electric field distribution. The hybrid composite consisting of SiOC interpenetrated within carbon constructs a high zinc nucleation interphase, hence promoting uniform Zn2+ deposition and enhancing ionic diffusion with dendrite-free growth and a reduced nucleation energy barrier. As a result, the 3DP-MPC-SiOC@Zn symmetrical cell affords a highly reversible Zn plating/stripping and dendrite-free structure over 198h with an ultra-low voltage polarization. These inspiring performances endow the 3DP anode with a 3DP-VO cathode as a full battery, which shows a retention capacity of 78.8mAhg-1 (Coulombic efficiency: 94.04%) at 0.1Ag-1 and a large energy density of 41Whkg-1 at a power density of 1.2Wkg-1 (based on the total mass of electrode) after 120 cycles. This newly developed 3D printing of hybrid composite as an electrode is straightforward and scalable and provides a novel concept for realizing dendrite-free and stable rechargeable Zn-ion batteries.

Floating solar photovoltaics in the Mediterranean Sea: Mapping and sensitivity analysis of the levelised cost of energy

In this work, the levelised cost of energy (LCOE) from floating solar photovoltaics (PV) is calculated and mapped in the Mediterranean Sea. A breakdown of the factors that influence the LCOE is presented, including site-specific aspects such as distance to shore, water depth and solar resources. To address the uncertainties inherent to any novel technology, a sensitivity analysis is conducted, in which the effects on the LCOE of variations in its factors are quantified. With respect to the numerator of the LCOE (the costs), the results indicate that installation costs, which increase rapidly with distance to shore, play the main role. With respect to the denominator (the energy output), the substantial solar resources of the Mediterranean Sea translate into large annual energy productions overall – a clear advantage for the development of floating solar PV. Going into greater detail, LCOE values are found to be particularly sensitive to: (i) parameters directly linked to the production of energy, e.g., panel capacity and number of panels per structure; (ii) general project and project finance parameters, e.g., number of structures, project lifetime and discount rate; (iii) sources of costs, e.g., structure weight and installation of components. The lowest LCOEs occur in nearshore areas of Libya and Egypt. The Iberian Peninsula presents LCOE values in the range 340–380 €/MWh, and Italy, in the range 380–400 €/MWh. In the Aegean Sea there is high spatial variability, with LCOE values ranging from 320 €/MWh to 500 €/MWh. These results help to identify optimal locations for the deployment of floating PV in the Mediterranean Sea and indicate the key parameters for reducing its cost in future.

Evaluation of the energy flow characteristics and efficiency of photothermal functional phase change materials for efficient solar thermal harvesting

Photothermal functional phase change materials (PCMs) have attracted considerable attention due to their large energy density, which can solve the inherent imbalance defects of solar energy. However, the efficiency determination of the PCM-based photothermal utilization process (including photon absorption, photothermal conversion, thermal storage, and thermal release) is still unclear, especially with different or even contradictory quantitative indexes for the same process, resulting in inaccurate photothermal utilization performance and unfair comparison in various efforts. Herein, we clarified the photothermal utilization sub-processes of phase change composites via optical characterizations and photothermal conversion experiments and highlighted the energy dissipation mechanism of photothermal conversion process by fluorescence and femtosecond transient absorption examination. Besides, the energy flow features of these sub-processes were explored by determining the energy flow and optical/thermal losses. More importantly, we standardized the efficiency of the four sub-processes by proposing evaluation indexes and established the relationship among the four sub-processes to derive the total photothermal utilization efficiency. This work provides a paradigm for a comprehensive investigation of PCM-based photothermal utilization systems, especially establishing consistent criteria for subsequent efficiency determination, laying a solid foundation for developing and quantifying solar thermal utilization systems.

The signal quality improvement of laser-induced breakdown spectroscopy due to the microwave plasma torch modulation

BackgroundLaser-induced breakdown spectroscopy (LIBS) is a versatile analytical technique for element determination in solids, liquids, and gases. However, LIBS suffers from low detection sensitivity and high relative standard deviation (RSD), restricting its large-scale applications. the process of a physical sampling can, in some cases, compromise the mechanical strength of the component under examination. It should be considered that too large laser energy is bound to cause damage to samples which cannot be tolerated in the process of safe production in the nuclear industry. It is necessary to find a method to obtain high elemental signal intensity in low energy laser. ResultsHere, we present a novel approach by integrating microwave plasma torch (MPT) with LIBS, referred to as MPT-LIBS, which effectively addresses the limitations associated with traditional LIBS. The MPT-LIBS technique is evaluated using Cu samples with a low laser pulse energy of 0.55 mJ. A remarkable enhancement factor of over 70 for Cu I 521.82 nm line is demonstrated, while that of Cu I 324.75 nm and 327.40 nm lines exceeding two orders of magnitude. Furthermore, the RSDs of all Cu spectral lines are reduced, especially for Cu I 521.82 nm, which is decreased from 11.48 % to 1.36 %. This indicates a significant improvement in signal stability. Characterization of the tested samples using con-focal microscopy reveals that the ablation area of MPT-LIBS is only 1.36 times of that of LIBS. The limit of detection of Cu I 324.75 nm line is reduced from 52.8 ppk to 319 ppm. Significance and noveltyThis study not only offers valuable guidance for improving signal stability and the limit of detection in LIBS, but also demonstrates minimal sample damage due to its low ablation amount. Consequently, the proposed methodology has the potential to significantly advance LIBS technology, expanding its applicability in industrial applications.

Effect of element doping on the structural stability, magnetic properties and electronic structure of SmCo5-based rare earth permanent magnets

Doping transition metals has been proven as an effective method to enhance the performance of Sm-Co based rare earth permanent magnets. However, due to the complex interactions involved, the specific effects on magnetic properties, atomic occupancy preferences and structural stability mechanisms are still to be further investigated. In this study, we systematically investigated the influence of various transition metal dopants on the structural stability, magnetic properties and electronic structure of SmCo5 rare earth permanent magnet using first-principles calculations. Our calculations show that Ti, V, Cr, Mn, Ni, Cu, Zn elements preferentially occupy the 3 g site, while Sc and Zr tend to occupy the 1a site, and Fe elements have a preference for the 2c site. Regarding structural stability, doping with Sc, Cr, Mn, Fe, Ni, Cu, Zn and Zr all contribute to enhancing structural stability, while Ti and V doping exhibit adverse effects. Magnetic calculations indicate that doping with Mn and Fe significantly increases the total magnetic moment of the SmCo5 system. Notably, at a high doping concentration of 60 at%, the Ni and Zn-doped systems exhibit an exceptionally large magnetocrystalline anisotropy energy Additionally, a change in the magnetic easy axis direction occurs when the doping concentrations of Cr, Fe, Cu and Zn reach 60 at%, 40 at%, 40 at% (and 60 at%), 40 at% (and 60 at%), respectively. Our work provides important theoretical guidance for further optimizing the performance of Sm-Co based rare earth permanent magnets.

Urban Geothermal Resource Potential Mapping Using Data-Driven Models—A Case Study of Zhuhai City

Geothermal energy, with its promise of sustainability and a minimal environmental impact, offers a viable alternative to fossil fuels that can allow us to meet the increasing energy demands while mitigating concerns over climate change. Urban areas, with their large energy consumption, stand to benefit significantly from the integration of geothermal systems. With the growing need to harness renewable energy sources efficiently, the detection of urban subsurface resources represents a critical frontier in the pursuit of sustainability. The Guangdong Bay area, known for its abundant geothermal resources, stands at the forefront of this green energy revolution, so, in our study, we chose to evaluate Zhuhai City, which is a city representative of the resource-rich area of Guangdong. With the progress of geographic information system (GIS) technology, the land surface temperature (LST) has been used to monitor the spatial distribution characteristics of geothermal anomalies. However, relatively few studies have been conducted in the field of urban geothermal resources. In this study, we calculated the LST of Zhuhai City using Landsat 8 remote sensing data and then investigated the distributions of geothermal hot springs. Spatial data layers were constructed, including the geological structure, DEM and derivatives, lithology, and urban regions, and, based on technology with the integration of machine learning, their spatial correlations with geothermal anomalies were analyzed. The support vector machine (SVM) and the multilayer perceptron (MLP) were employed to produce maps of potential geothermal resources, and their susceptibility levels were divided into five classes: very low, low, moderate, high, and very high. Through model interpretation, we found the moderate-susceptibility class to dominate at 26.90% (SVM) and 46.27% (MLP) according to the two models. Considering the influence of artificial areas, we also corrected the original LST by identifying urban areas of thermal anomalies via the urban thermal anomaly leapfrog fusion extraction (UTALFE) method; following this augmentation, the results shifted to 24.16% (SVM) and 28.67% (MLP). Meanwhile, the area under the curve (AUC) values of all results were greater than 0.65, showing the superior performance and the high applicability of the chosen study area. This study demonstrates that data-driven models integrating thermal infrared remote sensing technology are a promising tool for the mapping of potential urban geothermal resources for further exploration. Moreover, after correction, the reclassified LST results of urban areas are more authentic and suitable for the mapping of potential geothermal resources. In the future, the method applied in this study may be considered in the exploration of more southeastern coastal cities in China.

Spin-polarized second-order nonlinear Hall effect in 8-Pmmn monolayer borophene

The second-order nonlinear Hall effect in 8-Pmmn monolayer borophene under the influence of an out-of-plane electric field and intrinsic spin–orbit interaction is reported. This unconventional response sensitive to the breaking of discrete and crystal symmetries can be tuned by the applied electric field, which can vary the bandgap induced by spin–orbit coupling. It is described by a Hall conductivity tensor that depends quadratically on the applied electric field. We find that the nonlinear Hall effect strongly depends on the spin polarization. In particular, it exhibits out of the phase character for spin-up and spin-down states. Remarkably, it undergoes a phase flip in the spin-up state at a large out-of-plane electric field that generates a staggered sublattice potential greater than the spin–orbit interaction strength. It is shown that the nonlinear Hall effect in the system originates from the broken inversion symmetry that plays an indispensable role in developing finite Berry curvature and its relevant dipole moment. It is found that at zero temperature, the nonlinear Hall response is maximal when the Fermi energy is twice the bandgap parameter and vanishes at large Fermi energies. Notably, the peak of nonlinear Hall response shifts to lower Fermi energies at finite temperature.

Dynamically Tunable Circularly Polarized Selectivity in Plasmon-Enhanced Halide Perovskite Nanocrystal Glasses.

Ultrafast spin manipulation for optical spin-logic applications requires material systems with strong spin-selective light-matter interactions. The optical Stark effect can realize spin-selective light-matter interactions by breaking the degeneracy of spin-selective transitions with an external electric field. Halide perovskites have large exciton binding energies, which enable a room-temperature optical Stark effect. However, halide perovskites are prone to degradation when interacting with light and polar solvents, limiting further integration with nanophotonic structures. We demonstrate a hybrid material system consisting of CsPbBr3 nanocrystal glass weakly coupled to resonant plasmonic silver nanoparticles, showing ultrafast tunable spin-based polarization selectivity at room temperature. We performed circularly polarized pump-probe characterizations to investigate the optical Stark effect in this material system, which resulted in a maximum energy shift of ∼3.67 meV (detuning energy of 0.11 eV and pump intensity of 0.62 GW/cm2). We show that halide perovskite nanocrystal glasses have excellent resistance to heat and moisture, which may be favorable for integration with nanophotonic structures for further engineering polarization states, energy tuning, and coherence time.

Two-Coordinate Dinuclear Donor-Gold(I)-Acceptor Complexes Exhibiting Multiple Excitation Wavelength Dependent Phosphorescence.

Two-coordinate Au(I) complexes with a donor-metal-acceptor (D-M-A) structure have shown rich luminescent properties. However, charge-neutral dinuclear donor-metal-acceptor type Au(I) complexes featuring aurophilic interactions have been seldom explored. Herein, we describe the structures and photoluminescence properties of two dinuclear Au(I) complexes, namely DiAu-Ph and DiAu-Me. Single crystal X-ray structural analysis of DiAu-Ph reveals a short intramolecular Au-Au distance of 3.224 Å. In dilute solution and doped films, excitation wavelength dependent multiple phosphorescence phenomena were observed for these dinuclear complexes. Theoretical calculations reveal that the aurophilic interaction causes increased contribution of the Au d orbital to the highest occupied molecular orbitals. Thus, the gap between singlet and triplet excited states (ΔEST) is enlarged, which disables the thermally activated delayed fluorescence (TADF). Moreover, the large energy separation (0.45-0.52 eV) and the different orbital configurations between the various excited states result in an inefficient internal conversion, accounting for their multiple phosphorescence properties.

Recent Developments in Fullerene‐Based Materials for Photocatalytic Applications in Wastewater Treatment and Water Splitting

AbstractThe use of semiconductor‐based photocatalytic methods has been widespread for a range of applications, including pollution control and energy generation. However, certain analytical concerns limit the effectiveness of these photocatalysts, such as their limited light absorption capacity, physicochemical instability, and large energy band gap. To address these issues, scientists have been exploring integrating carbonaceous materials into photocatalytic systems to enhance their activity. This review focuses specifically on fullerene photocatalysts, a type of carbonaceous photocatalyst that has shown great promise in recent research. Fullerenes, which include C60 and C70, have unique properties that make them ideal for use as photocatalyst amplifiers in combination with other semiconductors or non‐semiconductors. This review summarizes recent research into the use of fullerene‐based materials for a variety of photocatalytic applications, including pollutant degradation, and hydrogen energy production. The efficacy of fullerene‐based photocatalysts is also discussed in recent breakthroughs in photocatalytic mechanisms and synthesis methods, focusing on pollution removal and hydrogen generation. Finally, the review addresses ongoing challenges and opportunities for fullerene‐based photocatalysts. The goal is to contribute to advancements in environmental protection and energy generation.

Long-term memory induced correction to Arrhenius law

The Kramers escape problem is a paradigmatic model for the kinetics of rare events, which are usually characterized by Arrhenius law. So far, analytical approaches have failed to capture the kinetics of rare events in the important case of non-Markovian processes with long-term memory, as occurs in the context of reactions involving proteins, long polymers, or strongly viscoelastic fluids. Here, based on a minimal model of non-Markovian Gaussian process with long-term memory, we determine quantitatively the mean FPT to a rare configuration and provide its asymptotics in the limit of a large energy barrier E. Our analysis unveils a correction to Arrhenius law, induced by long-term memory, which we determine analytically. This correction, which we show can be quantitatively significant, takes the form of a second effective energy barrier E′<E\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$E^{\\prime} \\, < \\, E$$\\end{document} and captures the dependence of rare event kinetics on initial conditions, which is a hallmark of long-term memory. Altogether, our results quantify the impact of long-term memory on rare event kinetics, beyond Arrhenius law.

Oxygen-doped Carbon Nitrides with Visible Room-temperature Phosphorescence and Invisible Thermal-Stimuli-Responsive Ultraviolet Delayed Fluorescence for Security Applications.

Multi-mode emissive materials with stimuli-responsive producing invisible signals are very attractive for advanced security applications, but development of such materials remains highly challenging. In this work, oxygen-doped carbon nitrides (O-CNs) are prepared via microwave-assisted heating of urea, which exhibit ultraviolet (UV) solid-state fluorescence (SSFL), visible room temperature phosphorescence (RTP) and thermal-stimuli production of invisible UV delayed fluorescence (DF) properties. Further studies confirmed that the SSFL and RTP could be attributed to the introduction of oxygen functional group (e.g., C=O) in the skeleton of O-CNs, thus minimizing the aggregation caused quenching effect, facilitating intersystem crossing, and stabilizing the excited triplet states. The specific thermal-stimuli production of UV DF is deemed to be the relatively large energy gap between ground and excited singlet states as well as an effective triplet-triplet annihilation. Notably, the emission maximum of UV DF locates at ~310 nm with an ultra-narrow full width at half maximum (FWHM) down to 19 nm, so it is completely invisible to the naked eyes, but detectable by a UV camera. To employ the unique characteristics of O-CNs, security protection strategies with superior concealment by virtue of the thermal-stimuli quenching visible RTP and meanwhile producing invisible UV DF are demonstrated.

Oxygen‐doped Carbon Nitrides with Visible Room‐temperature Phosphorescence and Invisible Thermal‐Stimuli‐Responsive Ultraviolet Delayed Fluorescence for Security Applications

Multi‐mode emissive materials with stimuli‐responsive producing invisible signals are very attractive for advanced security applications, but development of such materials remains highly challenging. In this work, oxygen‐doped carbon nitrides (O‐CNs) are prepared via microwave‐assisted heating of urea, which exhibit ultraviolet (UV) solid‐state fluorescence (SSFL), visible room temperature phosphorescence (RTP) and thermal‐stimuli production of invisible UV delayed fluorescence (DF) properties. Further studies confirmed that the SSFL and RTP could be attributed to the introduction of oxygen functional group (e.g., C=O) in the skeleton of O‐CNs, thus minimizing the aggregation caused quenching effect, facilitating intersystem crossing, and stabilizing the excited triplet states. The specific thermal‐stimuli production of UV DF is deemed to be the relatively large energy gap between ground and excited singlet states as well as an effective triplet‐triplet annihilation. Notably, the emission maximum of UV DF locates at ~310 nm with an ultra‐narrow full width at half maximum (FWHM) down to 19 nm, so it is completely invisible to the naked eyes, but detectable by a UV camera. To employ the unique characteristics of O‐CNs, security protection strategies with superior concealment by virtue of the thermal‐stimuli quenching visible RTP and meanwhile producing invisible UV DF are demonstrated.