Conventional optical security devices provide authentication by manipulating a specific property of light to produce a distinctive optical signature. For instance, microscopic colour prints modulate ...the amplitude, whereas holograms typically modulate the phase of light. However, their relatively simple structure and behaviour is easily imitated. We designed a pixel that overlays a structural colour element onto a phase plate to control both the phase and amplitude of light, and arrayed these pixels into monolithic prints that exhibit complex behaviour. Our fabricated prints appear as colour images under white light, while projecting up to three different holograms under red, green, or blue laser illumination. These holographic colour prints are readily verified but challenging to emulate, and can provide enhanced security in anti-counterfeiting applications. As the prints encode information only in the surface relief of a single polymeric material, nanoscale 3D printing of customised masters may enable their mass-manufacture by nanoimprint lithography.
0D lead‐free metal halide nanocrystals (NCs) are an emerging class of materials with intriguing optical properties. Herein, colloidal synthetic routes are presented for the production of 0D Cs3Cu2X5 ...(X = I, Br, and Cl) NCs with orthorhombic structure and well‐defined morphologies. All these Cs3Cu2X5 NCs exhibit broadband blue‐green photoluminescence (PL) emissions in the range of 445–527 nm with large Stokes shifts, which are attributed to their intrinsic self‐trapped exciton (STE) emission characteristics. The high PL quantum yield of 48.7% is obtained from Cs3Cu2Cl5 NCs, while Cs3Cu2I5 NCs exhibit considerable air stability over 45 days. Intriguingly, as X is changed from I to Br and Cl, Cs3Cu2X5 NCs exhibit a continuous redshift of emission peaks, which is contrary to the blueshift in CsPbX3 perovskite NCs.
0D all‐inorganic Cs3Cu2X5 (X = I, Br, and Cl) nanocrystals (NCs) with orthorhombic structure and well‐defined morphologies are produced. The NCs exhibit a continuous redshift of broadband blue‐green photoluminescence emissions in the range of 445–527 nm as X is changed from I to Br and Cl, which are attributed to their intrinsic self‐trapped exciton emission characteristics.
Lanthanide‐doped nanophosphors are promising in anti‐counterfeiting and security printing applications. These nanophosphors can be incorporated as transparent inks that fluoresce by upconverting ...near‐infrared illumination into visible light to allow easy verification of documents. However, these inks typically exhibit a single luminescent color, low emission efficiency, and low print resolutions. Tunable resonator‐upconverted emission (TRUE) is achieved by placing upconversion nanoparticles (UCNPs) within plasmonic nanoresonators. A range of TRUE colors are obtained from a single‐UCNP species self‐assembled within size‐tuned gap‐plasmon resonances in Al nanodisk arrays. The luminescence intensities are enhanced by two orders of magnitude through emission and absorption enhancements. The enhanced emissive and plasmonic colors are simultaneously employed to generate TRUE color prints that exhibit one appearance under ambient white light, and a multicolored luminescence appearance that is revealed under near‐infrared excitation. The printed color and luminescent images are of ultrahigh resolutions (≈50 000 dpi), and enable multiple colors from a single excitation source for increased level of security.
Tunable resonator‐upconverted emission is demonstrated with embedding monolayer NaGdF4:Yb,Er nanocrystals within gap‐plasmon resonators. Plasmonic enhanced absorption and radiative decay underpin the greatly enhanced luminescence. Multiple luminescent and plasmonic colors are simultaneously utilized to incorporate different covert luminescent information underneath an ultrahigh resolution plasmonic color print.
The coloration of some butterflies, Pachyrhynchus weevils, and many chameleons are notable examples of natural organisms employing photonic crystals to produce colorful patterns. Despite advances in ...nanotechnology, we still lack the ability to print arbitrary colors and shapes in all three dimensions at this microscopic length scale. Here, we introduce a heat-shrinking method to produce 3D-printed photonic crystals with a 5x reduction in lattice constants, achieving sub-100-nm features with a full range of colors. With these lattice structures as 3D color volumetric elements, we printed 3D microscopic scale objects, including the first multi-color microscopic model of the Eiffel Tower measuring only 39 µm tall with a color pixel size of 1.45 µm. The technology to print 3D structures in color at the microscopic scale promises the direct patterning and integration of spectrally selective devices, such as photonic crystal-based color filters, onto free-form optical elements and curved surfaces.
We demonstrate a molecular-level observation of driving CO2 molecules into a quasi-condensed phase on the solid surface of metal nanoparticles (NP) under ambient conditions of 1 bar and 298 K. This ...is achieved via a CO2 accumulation in the interface between a metal–organic framework (MOF) and a metal NP surface formed by coating NPs with a MOF. Using real-time surface-enhanced Raman scattering spectroscopy, a >18-fold enhancement of surface coverage of CO2 is observed at the interface. The high surface concentration leads CO2 molecules to be in close proximity with the probe molecules on the metal surface (4-methylbenzenethiol), and transforms CO2 molecules into a bent conformation without the formation of chemical bonds. Such linear-to-bent transition of CO2 is unprecedented at ambient conditions in the absence of chemical bond formation, and is commonly observed only in pressurized systems (>105 bar). The molecular-level observation of a quasi-condensed phase induced by MOF coating could impact the future design of hybrid materials in diverse applications, including catalytic CO2 conversion and ambient solid–gas operation.
Here we design an interface between a metal nanoparticle (NP) and a metal–organic framework (MOF) to activate an inert CO2 carboxylation reaction and in situ monitor its unconventional ...regioselectivity at the molecular level. Using a Kolbe–Schmitt reaction as model, our strategy exploits the NP@MOF interface to create a pseudo high-pressure CO2 microenvironment over the phenolic substrate to drive its direct C–H carboxylation at ambient conditions. Conversely, Kolbe–Schmitt reactions usually demand high reaction temperature (>125 °C) and pressure (>80 atm). Notably, we observe an unprecedented CO2 meta-carboxylation of an arene that was previously deemed impossible in traditional Kolbe–Schmitt reactions. While the phenolic substrate in this study is fixed at the NP@MOF interface to facilitate spectroscopic investigations, free reactants could be activated the same way by the local pressurized CO2 microenvironment. These valuable insights create enormous opportunities in diverse applications including synthetic chemistry, gas valorization, and greenhouse gas remediation.
Current surface-enhanced Raman scattering (SERS)-based anticounterfeiting strategies primarily encode molecular information in single two-dimensional (2D) planes and under-utilize the ...three-dimensionality (3D) of plasmonic hot spots. Here, we demonstrate a 3D SERS anticounterfeiting platform, extending “layered security” capabilities from 2D to 3D. We achieve this capability by combining 3D candlestick microstructures with 3D hyperspectral SERS imaging to fully resolve at least three layers of encoded information within the same 2D area along the z-axis, notably using only a single probe molecule. Specific predesigned covert images can only be fully recovered via SERS imaging at predetermined z values. Furthermore, our 3D SERS anticounterfeiting security labels can be fabricated on both rigid and flexible substrates, widening their potential usages to curved product surfaces and banknotes.
Current microscale tracking of chemical kinetics is limited to destructive ex situ methods. Here we utilize Ag nanocube-based plasmonic liquid marble (PLM) microreactor for in situ molecular-level ...identification of reaction dynamics. We exploit the ultrasensitive surface-enhanced Raman scattering (SERS) capability imparted by the plasmonic shell to unravel the mechanism and kinetics of aryl-diazonium surface grafting reaction in situ, using just a 2-μL reaction droplet. This reaction is a robust approach to generate covalently functionalized metallic surfaces, yet its kinetics remain unknown to date. Experiments and simulations jointly uncover a two-step sequential grafting process. An initial Langmuir chemisorption of sulfonicbenzene diazonium (dSB) salt onto Ag surfaces forms an intermediate sulfonicbenzene monolayer (Ag–SB), followed by subsequent autocatalytic multilayer growth of Ag–SB3. Kinetic rate constants reveal 19-fold faster chemisorption than multilayer growth. Our ability to precisely decipher molecular-level reaction dynamics creates opportunities to develop more efficient processes in synthetic chemistry and nanotechnology.
0D hybrid metal halides (0D HMHs) are considered to be promising luminescent emitters. 0D HMHs commonly exhibit self‐trapped exciton (STE) emissions originating from the inorganic metal halide anion ...units. Exploring and utilizing the emission features of the organic cation units in 0D HMHs is highly desired to enrich their optical properties as multifunctional luminescent materials. Here, tunable emissions from organic and inorganic units are successfully achieved in triphenylsulfonium (Ph3S+)‐based 0D HMHs. Notably, integrated afterglow and STE emissions with adjustable intensities are obtained in (Ph3S)2Sn1−xTexCl6 (x = 0–1) via the delicate combination of SnCl62− and TeCl62−. Moreover, such a strategy can be readily extended to develop other HMH materials with intriguing optical properties. As a demonstration, 0D (Ph3S)2Zn1−xMnxCl4 (x = 0–1) are constructed to achieve integrated afterglow and Mn2+ d–d emissions with high efficiency. Consequently, these novel 0D HMHs with colorful afterglow and STE emissions are applied in multiple anti‐counterfeiting applications.
A novel strategy is developed to modulate the afterglow and self‐trapped exciton (STE) emissions in 0D (Ph3S)2Sn1−xTexCl6 (x = 0–1) single crystals. Moreover, the integration of afterglow and STE emissions is realized in (Ph3S)2Sn0.92Te0.08Cl6. These as‐prepared 0D hybrid metal halides with colorful emissions are demonstrated for multiple anti‐counterfeiting and information storage applications.
Colloidal gold nanocups are synthesized through single‐vertex‐initiated gold deposition on PbS nanooctahedrons and subsequent selective dissolution of the PbS component. They possess strong magnetic ...plasmon resonance and exhibit remarkable orientation‐dependent plasmonic properties when deposited on flat substrates. They can also effectively couple s‐polarized light into the interfacial region between the nanocup and substrate.
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