Al2 O3 Research Articles

4D Additive-Subtractive Manufacturing of Shape Memory Ceramics.

The development of high-temperature structural materials, such as ceramics, is limited by their extremely high melting points and the difficulty in building complicated architectures. Four-dimensional (4D) printing helps enhance the geometrical flexibility of ceramics. However, ceramic 4D printing systems are limited by the separate processes for shape and material transformations, low accuracy of morphing systems, low resolution of ceramic structures, and their time-intensive nature. Here, a paradigm for a one-step shape/material transformation, high-2D/3D/4D-precision, high-efficiency, and scalable 4D additive-subtractive manufacturing of shape memory ceramics is developed. Original/reverse and global/local multimode shape memory capabilities are achieved using macroscale SiOC-based ceramic materials. The uniformly deposited Al2 O3 -rich layer on the printed SiOC-based ceramic lattice structures results in an unusually high flame ablation performance of the complex-shaped ceramics. The proposed framework is expected to broaden the applications of high-temperature structural materials in the aerospace, electronics, biomedical, and art fields.

Nucleation of equiaxed δ-ferrite by accelerating TiN formation controlled by oxide during welding of ferritic stainless steel

The accelerating effect of oxides on TiN formation to promote the nucleation of equiaxed ferrite was investigated under simulated gas tungsten arc (GTA) welding conditions. This revealed that the formation of oxides such as Ti2O3, (Ti, Al)2O3, and MgAl2O4 is essential for the solidification of equiaxed δ-ferrite. MgAl2O4 significantly accelerates the formation of TiN and produces a fine-grained equiaxed structure. Minor alloying with Ti, Al, and Mg significantly influenced the composition and crystal structure of the oxides. Ti2O3 and (Ti, Al)2O3 were identified as corundum structures with the same orientation relationship as TiN on the {0001} crystal plane. Ti2O3 and (Ti, Al)2O3 could act as heterogeneous nuclei for TiN because low lattice misfits of 0.6% and 0.6–8.1% could be reached for Ti2O3 and (Ti, Al)2O3 for {0001}oxide//{111}TiN and [10–10]oxide//[110]TiN, respectively. Spinel type MgAl2O4 was found to have a fully paralleled orientation relationship with TiN, resulting in a 4.8% misfit with TiN in each crystal plane. This indicates that all the crystal planes of MgAl2O4 could accelerate the formation of TiN. Baker-Nutting orientation relationship was confirmed for TiN and δ-ferrite. Therefore, the TiN formed by oxide acceleration could nucleate δ-ferrite. The multiple accelerating planes of MgAl2O4 and a high quantity of MgAl2O4-TiN as nucleation sites showed an optimal effect on equiaxed solidification under a high-temperature gradient.

Scalable, Patternable Glass-Infiltrated Ceramic Radiative Coolers for Energy-Saving Architectural Applications.

A huge concern on global climate/energy crises has triggered intense development of radiative coolers (RCs), which are promising green-cooling technologies. The continuous efforts on RCs have fast-tracked notable energy-savings by minimizing solar absorption and maximizing thermal emission. Recently, in addition to spectral optimization, ceramic-based thermally insulative RCs are reported to improve thermoregulation by suppressing heat gain from the surroundings. However, a high temperature co-firing process of ceramic-based thick film inevitably results in a large mismatch of structural parameters between designed and fabricated components, thereby breaking spectral optimization. Here, this article proposes a scalable, non-shrinkable, patternable, and thermally insulative ceramic RC (SNPT-RC) using a roll-to-roll process, which can fill a vital niche in the field of radiative cooling. A stand-alone SNPT-RC exhibits excellent thermal insulation (≈0.251Wm-1 K-1 ) with flame-resistivity and high solar reflectance/long-wave emissivity (≈96% and 92%, respectively). Alternate stacks of intermediate porous alumina/borosilicate (Al2 O3 -BS) layers not only result in outstanding thermal and spectral characteristics, causing excellent sub-ambient cooling (i.e., 7.05 °C cooling), but also non-shrinkable feature. Moreover, a perforated SNPT-RC demonstrates its versatility as a breathable radiative cooling shade and as a semi-transparent window, making it a highly promising technology for practical deployment in energy-saving architecture.

A Novel Al-Cu Composite with Ultra-High Strength at 350°C via Dual-Phase Particle Reinforced Submicron-Structure.

Thermal stability determines a material's ability to maintain its performance at desired service temperatures. This is especially important for aluminum (Al) alloys, which are widely used in the commercial sector. Herein, an ultra-strong and heat-resistant Al-Cu composite is fabricated with a structure of nano-AlN and submicron-Al2 O3 particles uniformly distributed in the matrix. At 350°C, the (8.2AlN+1Al2 O3 )p /Al-0.9Cu composite achieves a high strength of 187MPa along with a 4.6% ductility under tension. The high strength and good ductility benefit from strong pinning effect on dislocation motion and grain boundary sliding by uniform dispersion of nano-AlN particles, in conjunction with the precipitation of Guinier-Preston (GP) zones, enhancing strain hardening capacity during plastic deformation. This work can expand the selection of Al-Cu composites for potential applications at service temperatures as high as ≈350°C.

Metal-Driven Autoantifriction Function of Artificial Hip Joint.

The service life of an artificial hip joint is limited to 10-15years, which is not ideal for young patients. To extend the lifespan of these prostheses, the coefficient of friction and wear resistance of metallic femoral heads must be improved. In this study, a Cu-doped titanium nitride (TiNX -Cu) film with "autoantifriction" properties is deposited on a CoCrMo alloy via magnetron sputtering. When delivered in a protein-containing lubricating medium, the Cu in TiNX -Cu quickly and consistently binds to the protein molecules in the microenvironment, resulting in the formation of a stable protein layer. The proteins adsorbed on the TiNX -Cu surface decompose into hydrocarbon fragments owing to the shear stress between the Al2 O3 /TiNX -Cu tribopair. The synergistic effect of the catalysis of Cu and shear stress between the Al2 O3 /TiNX -Cu tribopair transforms these fragments into graphite-like carbon tribofilms with an antifriction property. These tribofilms can simultaneously reduce the friction coefficient of the Al2 O3 /TiNX -Cu tribopair and enhance the wear resistance of the TiNX -Cu film. Based on these findings, it is believed that the autoantifriction film can drive the generation of antifriction tribofilms for lubricating and increasing the wear resistance of prosthetic devices, thereby prolonging their lifespan.

Flexible Transparent Electrodes Formed from Template-Patterned Thin-Film Silver.

Template-patterned, flexible transparent electrodes (TEs) formed from an ultrathin silver film on top of a commercial optical adhesive - Norland Optical Adhesive 63 (NOA63) -are reported. NOA63 is shown to be an effective base-layer for ultrathin silver films that advantageously prevents coalescence of vapor-deposited silver atoms into large, isolated islands (Volmer-Weber growth), and so aids the formation of ultrasmooth continuous films. 12 nm silver films on top of free-standing NOA63 combine high, haze-free visible-light transparency (T ≈ 60% at 550nm) with low sheet-resistance ( ≈ 16 Ω sq-1), and exhibit excellent resilience to bending, making them attractive candidates for flexible TEs. Etching the NOA63 base-layer with an oxygen plasma before silver deposition causes the silver to laterally segregate into isolated pillars, resulting in a much higher sheet resistance ( > 8 × 106 Ω sq-1) than silver grown on pristine NOA63 . Hence, by selectively etching NOA63 before metal deposition, insulating regions may be defined within an otherwise conducting silver film, resulting in a differentially conductive film that can serve as a patterned TE for flexible devices. Transmittance may be increased (to 79% at 550nm) by depositing an antireflective layer of Al2O3 on the Ag layer at the cost of reduced flexibility.

PVA-Al sol film derived superior anti-oxidation layer on the surface of AISI304 steel

In this research, the polyvinyl alcohol (PVA) modified Al sol is coated on the AlSl304 steel to resist the oxidation etching by espousing to the air at 900℃. Compared with the substrate, the coated sample demonstrates the superior oxidation resistance indicated by the decreasing mass gain. Meanwhile, the generated oxide layer exhibits the features of dense, continuous and no flaking, which suppresses the inward diffusion of the O atoms. In the virtue of the PVA-Al sol film, the beneficial anti-oxidation (Cr, Al)2O3 and the Fe3O4 phase are derived and the general detrimental Fe-rich hematite phase is avoided.

Confined Synthesis of Amorphous Al2 O3 Framework Nanocomposites Based on the Oxygen-Potential Diagram as Sulfur Hosts for Catalytic Conversion.

Sulfur cathodes in Li-S batteries suffer significant volumetric expansion and lack of catalytic activity for polysulfide conversion. In this study, a confined self-reduction synthetic route is developed for preparing nanocomposites using diverse metal ions (Mn2+ , Co2+ , Ni2+ , and Zn2+ )-introduced Al-MIL-96 as precursors. The Ni2+ -introduced Al-MIL-96-derived nanocomposite contains a "hardness unit", amorphous aluminum oxide framework, to restrain the volumetric expansion, and a "softness unit", Ni nanocrystals, to improve the catalytic activity. The oxygen-potential diagram theoretically explains why Ni2+ is preferentially reduced. Postmortem microstructure characterization confirms the suppressive volume expansion. The in situ ultraviolet-visible measurements are performed to probe the catalytic activity of polysulfide conversion. This study provides a new perspective for designing nanocomposites with "hardness units" and "softness units" as sulfur or other catalyst hosts.

(Invited) NiO/ β-(Al x Ga1-x )2O3 /Ga2O3 Heterojunction Lateral Rectifiers with Reverse Breakdown Voltage > 7kV

NiO/ β-(Al x Ga1-x )2O3 /Ga2O3 heterojunction lateral geometry rectifiers with diameter 50-100 µm exhibited maximum reverse breakdown voltages >7kV, showing the advantage of increasing the bandgap using the β-(Al x Ga1-x )2O3 alloy. This Si-doped alloy layer was grown by Metal Organic Chemical Vapor Deposition with an Al composition of ~21 %. On state resistances were in the range 50-2180 Ω.cm2, leading to power figures-of-merit up to 0.72 MW.cm-2. The forward turn-on voltage was in the range 2.3-2.5 V, with maximum on/off ratios >700 when switching from 5V forward to reverse biases up to -100V. Transmission line measurements showed the specific contact resistance was 0.12 Ω.cm2. The breakdown voltage is among the highest reported for any lateral geometry Ga2O3-based rectifier.

A UV-Reflective Organic-Inorganic Tandem Structure for Efficient and Durable Daytime Radiative Cooling in Harsh Climates.

Radiative cooling shows great promise in eco-friendly space cooling due to its zero-energy consumption. For subambient cooling in hot humid subtropical/tropical climates, achieving ultrahigh solar reflectance (≥96%), durable ultraviolet (UV) resistance, and surface superhydrophobicity simultaneously is critical, which, however, is challenging for most state-of-the-art scalable polymer-based coolers. Here an organic-inorganic tandem structure is reported to address this challenge, which comprises a bottom high-refractive-index polyethersulfone (PES) cooling layer with bimodal honeycomb pores, an alumina (Al2 O3 ) nanoparticle UV reflecting layer with superhydrophobicity, and a middle UV absorption layer of titanium dioxide (TiO2 ) nanoparticles, thus providing thorough protection from UV and self-cleaning capability together with outstanding cooling performance. The PES-TiO2 -Al2 O3 cooler demonstrates a record-high solar reflectance of over 0.97 and high mid-infrared emissivity of 0.92, which can maintain their optical properties intact even after equivalent 280-day UV exposure despite the UV-sensitivity of PES. This cooler achieves a subambient cooling temperature up to 3 °C at summer noontime and 5 °C at autumn noontime without solar shading or convection cover in a subtropical coastal city, Hong Kong. This tandem structure can be extended to other polymer-based designs, offering a UV-resist but reliable radiative cooling solution in hot humid climates.

A Novel Anderson-Type POMs-Based Hybrids Flame Retardant for Reducing Smoke Release and Toxicity of Epoxy Resins.

Smoke emission and smoke toxicity have drawn more attention to improving the fire safety of polymers. In this work, a polyoxometalates (POMs)-based hybrids flame retardant (P-AlMo6 ) epoxy resin (EP) is prepared with toxicity-reduction and smoke-suppression properties via a peptide coupling reaction between POMs and organic molecules with double DOPO (bisDOPA). It combines the good compatibility of the organic molecule and the superior catalytic performance of POMs. Compared to pure EP, the glass transition temperature and flexural modulus of EP composite with 5 wt.% P-AlMo6 (EP/P-AlMo6 -5) are raised by 12.3°C and 57.75%, respectively. Notably, at low flame-retardant addition, the average CO to CO2 ratio (Av-COY/Av-CO2 Y) is reduced by 33.75%. Total heat release (THR) and total smoke production (TSP) are lowered by 44.4% and 53.7%, respectively. The Limited Oxygen Index (LOI) value achieved 31.7% and obtained UL-94V-0 rating. SEM, Raman, X-ray photoelectron spectroscopy, and TG-FTIR are applied to analyze the flame-retardant mechanism in condensed and gas phase. Outstanding flame retardant, low smoke toxicity properties are attained due to the catalytic carbonization ability of metal oxides Al2 O3 and MoO3 produced from the breakdown of POMs. This work advances the development of POMs-based hybrids flame retardants with low smoke toxicityproperties.

Buried Interface Dielectric Layer Engineering for Highly Efficient and Stable Inverted Perovskite Solar Cells and Modules.

Stability and scalability are essential and urgent requirements for the commercialization of perovskite solar cells (PSCs), which are retarded by the non-ideal interface leading to non-radiative recombination and degradation. Extensive efforts are devoted to reducing the defects at the perovskite surface. However, the effects of the buried interface on the degradation and non-radiative recombination need to be further investigated. Herein, an omnibearing strategy to modify buried and top surfaces of perovskite film to reduce interfacial defects, by incorporating aluminum oxide (Al2 O3 ) as a dielectric layer and growth scaffolds (buried surface) and phenethylammonium bromide as a passivation layer (buried and top surfaces), is demonstrated. Consequently, the open-circuit voltage is extensively boosted from 1.02 to 1.14V with the incorporation of Al2 O3 filling the voids between grains, resulting in dense morphology of buried interface and reduced recombination centers. Finally, the impressive efficiencies of 23.1% (0.1 cm2 ) and 22.4% (1 cm2 ) are achieved with superior stability, which remain 96% (0.1 cm2 ) and 89% (1 cm2 ) of its initial performance after 1200 (0.1 cm2 ) and 2500h (1 cm2 ) illumination, respectively. The dual modification provides a universal method to reduce interfacial defects, revealing a promising prospect in developing high-performance PSCs and modules.

A Highly Reliable Molybdenum Disulfide-Based Synaptic Memristor Using a Copper Migration-Controlled Structure.

Memristors are drawing attention as neuromorphic hardware components because of their non-volatility and analog programmability. In particular, electrochemical metallization (ECM) memristors are extensively researched because of their linear conductance controllability. Two-dimensional materials as switching medium of ECM memristors give advantages of fast speed, low power consumption, and high switching uniformity. However, the multistate retention in the switching conductance range for the long-term reliable neuromorphic system has not been achieved using two-dimensional materials-based ECM memristors. In this study, the copper migration-controlled ECM memristor showing excellent multistate retention characteristics in the switching conductance range using molybdenum disulfide (MoS2 ) and aluminum oxide (Al2 O3 ) is proposed. The fabricated device exhibits gradual resistive switching with low switching voltage (<0.5V), uniform switching (σ/µ∼ 0.07), and a wide switching range (>12). Importantly, excellent reliabilities with robustness to cycling stress and retention over 104 s for more than 5-bit states in the switching conductance range are achieved. Moreover, the contribution of the Al2 O3 layer to the retention characteristic is investigated through filament morphology observation using transmission electron microscopy (TEM) and copper migration component analysis. This study provides a practical approach to developing highly reliable memristors with exceptional switching performance.

Structural Electromagnetic Absorber Based on MoS2 /PyC-Al2 O3 Ceramic Metamaterials.

Limited by the types of suitable absorbents as well as the challenges in engineering the nanostructures (e.g., defects, dipoles, and hetero-interface) using state-of-the-art additive manufacturing (AM) techniques, the electromagnetic (EM) wave absorption performance of the current ceramic-based materials is still not satisfying. Moreover, because of the high residual porosity and the possible formation of cracks during sintering or pyrolysis, AM-formed ceramic components may in many cases exhibit low mechanical strength. In this work, semiconductive MoS2 and conductive PyC modified Al2 O3 (MoS2 /PyC-Al2 O3 ) ceramic-based structural EM metamaterials are developed by innovatively harnessing AM, precursor infiltration and pyrolysis (PIP), and hydrothermal methods. Three different meta-structures are successfully created, and the ceramic-based nanocomposite benefit from its optimization of EM parameters. Ultra-broad effective absorption bandwidth (EAB) of 35GHz is achieved by establishment of multi-loss mechanism via nanostructure engineering and fabrication of meta-structures via AM. Due to the strengthening by the PyC phase, the bending strength of the resulting ceramics can reach ≈327MPa, which is the highest value measured on 3D-printed ceramics of this type that has been reported so far. For the first time, the positive effect deriving from the engineering of the microscopic nano/microstructure and of the macroscopic meta-structure of the absorber on the permittivity and EM absorption performance is proposed. Integration of outstanding mechanical strength and ultra-broad EAB is innovatively realized through a multi-scale design route. This work provides new insights for the design of advanced ceramic-based metamaterials with outstanding performance under extreme environment.

Ultrahigh Energy Storage Density in Superparaelectric-Like Hf0.2 Zr0.8 O2 Electrostatic Supercapacitors.

Electrostatic capacitors attract great interest in energy storage fields due to their advantages of high power-density, fast charge/discharge speed, and great reliability. Intensive efforts have been placed on the development of high-energy-density of capacitors. Herein, a novel supercapacitor with Hf0.2 Zr0.8 O2 /xAl2 O3 /Hf0.2 Zr0.8 O2 (HAHx) is designed to improve the breakdown strength (Eb ) through optimizing Al2 O3 (AO) film thickness. Low-temperature annealing is first proposed to enhance the polarization difference (Pm -Pr ) due to the formation of dispersed polar nanoregions, which is called "superparaelectric-like" similar to previous super-paraelectric behavior of perovskite structures. As results, both large Eb and Pm -Pr values are obtained, leading to an ultrahigh energy storage density of 87.66 Jcm-3 with a high efficiency of 68.6%, as well as a reliable endurance of 107 cycles. This work provides a feasible pathway to improve both the polarization difference and breakdown strength of HfO2 -based films by the combination of insulation insertion layer and low-temperature annealing. The proposed strategy can contribute to the realization of high-performance electrostatic supercapacitors with excellent microsystem compatibility.

Examination of proper impurity doping and annealing conditions for solution processed Ga2O3 thin films

We investigated a method to improve the resistivity of Ga2O3 thin films using a wet-process and controlling the Sn-doping conditions. Undoped and Sn-doped single layer Ga2O3 thin films were prepared by changing the solution concentration, the annealing time, the rate of temperature rise, and the speed of the sample rotation in spin coating during deposition. As a result, the films were deposited uniformly with good crystallinity and transmittance and relatively small surface roughness. To improve the resistivity by another Sn-doping method, we prepared bilayer samples consisting of undoped Ga2O3 and SnO2 layers in which Sn atoms can diffuse into the Ga2O3 layer through annealing, i.e. the drive-in diffusion method. Although the changed resistivity, X-ray electron spectroscopy (XPS) and transmission electron microscope, energy dispersion X-ray spectroscopy measurements revealed that Al diffused from the sapphire substrate, indicating a mixed β-(Ga,Al)2O3 was prepared. By changing the annealing temperature to 800 °C, Al diffusion was suppressed and pure Ga2O3 thin films were prepared. After investigating various conditions of the annealing atmosphere, we found that samples annealed in a nitrogen atmosphere for both Ga2O3 and SnO2 showed the lowest resistivity.

Multifunctional Coatings on Sulfide-Based Solid Electrolyte Powders with Enhanced Processability, Stability, and Performance for Solid-State Batteries.

Sulfide-based solid-state electrolytes (SSEs) exhibit many tantalizing properties including high ionic conductivity and favorable mechanical properties for next-generation solid-state batteries. Widespread adoption of these materials is hindered by their intrinsic instability under ambient conditions, which makes them difficult to process at scale, and instability at the Li||SSE and cathode||SSE interfaces, which limits cell performance and lifetime. Atomic layer deposition is leveraged to grow thin Al2 O3 coatings on Li6 PS5 Cl powders to address both issues simultaneously. These coatings can be directly grown onto Li6 PS5 Cl particles with negligible chemical modification of the underlying material and enable exposure of powders to pure and H2 O-saturated oxygen environments for ≥4 h with minimal reactivity, compared with significant degradation of the uncoated powder. Pellets fabricated from coated powders exhibit ionic conductivities up to 2× higher than those made from uncoated material, with a simultaneous decrease in electronic conductivity and significant suppression of chemical reactivity at the Li-SSE interface. These benefits result in significantly improved room temperature cycle life at high capacity and current density. It is hypothesized that this enhanced performance derives from improved intergranular properties and improved Li metal adhesion. This work points to a completely new framework for designing active, stable, and scalable materials for next-generation solid-state batteries.

Two-dimensional Aluminum Oxide Nanosheets Decorated with Palladium Oxide Nanodots for Highly Stable and Selective Hydrogen Sensing.

Hydrogen (H2 ) sensing materials such as semiconductor metal oxides may suffer from poor long-term stability against humidity and unsatisfactory selectivity against other interfering gases. To address the above issues, highly stable and selective H2 sensing built with palladium oxide nanodots decorating aluminum oxide nanosheets (PdO NDs//Al2 O3 NSs) has been achieved via combined template synthesis, photochemical deposition, and oxidation. Typically, the PdO NDs//Al2 O3 NSs are observed with thin NSs (≈17nm thick) decorated with nanodots (≈3.3nm in diameter). Beneficially, the sensor prototypes built with PdO NDs//Al2 O3 NSs show excellent long-term stability for 278 days, high selectivity against interfering gases, and outstanding stability against humidity at 300°C. Remarkably, the sensor prototypes enable detection of a wide-range of 20ppm - 6V/V% H2 , and the response and recovery times are ≈5 and 16 s to 1V/V% H2 , respectively. Theoretically, the heterojunctions of PdO NDs-Al2 O3 NSs with a large specific surface ratio and Al2 O3 NSs as the support exhibit excellent stability and selective H2 sensing. Practically, a sensing device integrated with the PdO NDs//Al2 O3 NSs sensor prototype is simulated for detecting H2 with reliable sensing response.

Optimal Aluminum Doping Method in PEALD for Designing Outstandingly Stable InAlZnO TFT

AbstractOxide semiconductors are promising semiconducting materials for next‐generation thin‐film transistors (TFTs). The role of the cations should be considered in the design of oxide semiconductors suitable for various applications. Ga has been widely used as a carrier suppressor in oxide semiconductors; however, research has recently been conducted to replace it with Al, which is cheaper and forms a stronger bond with O. Deposition using plasma‐enhanced atomic layer deposition (PEALD) is very useful for controlling the composition of the cations in an oxide semiconductor. In this study, an InAlZnO (IAZO) semiconductor was deposited using super‐cycle PEALD for the first time. Al2O3 (AO), AlZnO (AZO), and InAlO (IAO) as Al doping layers in IAZO are evaluated. Considering its electrical characteristics and stability, AZO is selected as the optimal Al doping layer. The IAZO thin film and TFT characteristics according to the Al doping method are examined through the role of the cations and H concentration. In addition, the Al concentration is controlled by adjusting the number of cycles in super‐cycle PEALD. As the Al concentration decreased, the mobility increased; however, the stability degraded significantly, which is induced by the increase in oxygen vacancies. Finally, the high‐Al IAZO system using AZO successfully showed overall excellent properties including mobility over 10 cm2 V−1 s, and outstanding stability under 0.1 V, which are greatly improved compared to previously reported IAZO TFTs.

Synthesis of Visible Light Excitable Carbon Dot Phosphor-Al2 O3 Hybrids for Anti-Counterfeiting and Information Encryption.

The preparation of room temperature phosphorescent carbon dots still faces great challenges, especially in the case of carbon dots endowed of visible-light excitable room temperature phosphorescence (RTP). To date, a limited number of substrates have been exploited to synthesize room temperature phosphorescent carbon dots, and most of them can emit RTP only in solid state. Here, the synthesis of a composite obtained from the calcination of green carbon dots (g-CDs) blended with aluminum hydroxide (Al(OH)3 ) is reported. The resultant hybrid material g-CDs@Al2 O3 exhibits blue fluorescence and green RTP emissions in an on/off switch process at 365nm. Notably, this composite manifests strong resistance to extreme acid and basic conditions up to 30 days of treatment. The dense structure of Al2 O3 formed by calcination contributes to the phosphorescent emission of g-CDs. Surprisingly, g-CDs@Al2 O3 can also emit yellow RTP under irradiation with white light. The multicolor emissions can be employed for anti-counterfeiting and information encryption. This work provides a straightforward approach to produce room temperature phosphorescent carbon dots for a wide range of applications.