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Long‐lived room‐temperature phosphorescence (RTP) materials have been widely applied in various fields. However, achieving high‐performance carbon dots (CDs) RTP remains a great challenge. Here, a facile synthetic strategy is rationally designed for the synthesis of high‐performance dual‐mode emitting CDs by constructing rigid structures through the synergistic effect of the matrices. The obtained CD RTP powder possesses an ultrahigh photoluminescence quantum yield (PLQY) of 70.7%, a phosphorescence lifetime of about 0.45 s, and an afterglow that lasts for 15 s to the naked eyes. Most importantly, the prepared CD RTP powder can be utilized as a commercial phosphor powder for the fabrication of a high‐performance white lighting‐emitting diode (WLED) with a CIE coordinate of (0.39, 0.39), a high color rendering index of 93.6, and a color temperature of 3805 K for warm WLED. Especially the luminous efficiency of the fabricated WLED can reach up to 66.89 lm W−1, which is much higher than the values reported for most CDs‐based WLED devices. Additionally, CD RTP can be applied to advanced invisible inks for information encryption due to its excellent water solubility and can also be exploited for advanced information anti‐counterfeiting by utilizing phosphorescent properties. [ABSTRACT FROM AUTHOR]

Counterfeiting has turned out to be a major area of concern these days and is becoming a serious problem worldwide. Modern technological advances have made counterfeiting of sophisticated products easy. Therefore, it is essential to search new luminescent materials to combat counterfeiting. Herein, we report that a highly luminescent YBO3:Eu3+ phosphor was synthesized by the sol-gel technique, which can be scaled up to 1 kg in a single batch at the laboratory level. This highly luminescent boron based YBO3:Eu3+ phosphor is optically active and is structurally and chemically stable. It has a particle size of ∼110 ± 10 nm, which provides a strong orange-red emission at 591 nm upon 245 nm excitation wavelength and is also excitable in the range of 280-480 nm excitation wavelengths. The structural/microstructural and photoluminescence (PL) behaviors were characterized by scanning electron microscopy, transmission electron microscopy/high-resolution transmission electron microscopy, and fluorescent spectroscopy. Furthermore, this phosphor was used to design luminescent security ink with a commercially available polyvinyl chloride gold medium for printing of security codes as investigated by photoluminescence (PL) mapping instruments. Thus, this facile method to synthesize a low-cost YBO3:Eu3+ phosphor based security ink offers a non-replicable security code for printing that can be easy to detect but is difficult to counterfeit. [ABSTRACT FROM AUTHOR]

Secret writing is the art of covered or hidden writing. The art of secret writing is meant to create a message unreadable by a third party however doesn’t hide the existence of the secret communication. This paper is meant as a technical introduction to secret writing for those unacquainted with the field. Invisible inks are generally used for secret writing. These are fluids used to write hidden messages that do not appear unless exposed by a revealing process. Invisible inks can be classified into three main categories: those that are revealed by heat, those revealed by chemical reactions and those that are visible under ultraviolet light. Some common household invisible inks are diluted fruit juices, vinegar and laundry detergent, all which can be applied by a paintbrush, special invisible ink pen or even a toothpick, Historically, used in times of war by governments and insurgents alike. The chemical processes of invisible inks are well known, so a variety of detection methods exist. The simplest invisible ink experiment consists of dipping a brush in vegetable juice, biological fluids and different chemicals and writing on a piece of blank varieties of paper. When the “ink” dries, it will be invisible to the naked eye, but if the paper is held up to a moderate heat source such as a light bulb, a radiator or an iron using UV lamp to deciphering invisible writing. Many other mild chemicals also used for restoration of secret writing. [ABSTRACT FROM AUTHOR]

Known today as "invisible ink," nineteenth-century writers called the chemical concoction that concealed writing by another name—"sympathetic ink." Readers encountered descriptions of sympathetic ink throughout American magazines, newspapers, and books. Capitalizing on the widespread interest in sympathetic ink, Edgar Allan Poe incorporated the device into his popular 1843 story, "The Gold-Bug," but not for sociable ends. Poe instead uses invisible ink to puncture fantasies of democratic conviviality by emphasizing the way secrecy (vis-à-vis invisible ink) allows for the formation of control over black bodies. Evoking the longue durée of American political history, "The Gold-Bug" presents a seventeenth-century treasure map written in invisible ink that brings together murder, transatlantic slavery, and white antebellum control over black labor. In Poe's hands, the fire that makes invisible ink visible simultaneously brings forth recurring temporalities of violence. [ABSTRACT FROM AUTHOR]

N-Protected 4-(anilinomethyl)thiophene-2-carbaldehydes were prepared by the reaction of easily available 4-chloromethylthiophene-2-carbaldehyde with N-(2-halogenophenyl) substituted acetamides, 4-methylbenzenesulfonamides and carbamates in the presence of K 2 CO 3 or Cs 2 CO 3 . The compounds obtained were converted to 4,5-dihydrothieno [3,2- c ]quinoline-2-carbaldehydes by palladium catalyzed intramolecular cyclization in homogenous or heterogenous (Pd/C) conditions with good yields and subsequently used for preparing of 2-functionally substituted thieno [3,2- c ]quinoline derivatives (nitriles, carboxamides, carboxylic acids, esters). The optical properties of 2-functionally substituted thieno[3,2- c ]quinolines and 4H-thieno[3,2- c ]chromenes have been studied. Moderate to high fluorescence quantum yields are observed for these compounds ranging from 0.15 to 0.87. Structure - optical properties relationships have been established for the compounds synthesized, and their prospective application as invisible ink dyes was practically demonstrated. [ABSTRACT FROM AUTHOR]

High capacity, secure, reversible watermarking scheme using a color image for image authentication and tampered detection is still an important area of research. In this investigation, we have proposed a weighted matrix based reversible watermarking scheme using the color image which provides image authentication and tampered detection. Here, we decomposed the original image into R, G, B color components and partitioned into (3 × 3) pixel blocks then we performed the sum of entry-wise-multiplication operations using a modified weighted matrix to embed the watermark. The watermark embedding locations are stored within an index file to enhance security, increase data hiding capacity, gain good visual quality, achieve reversibility and confirm authenticity. The proposed watermarking scheme not only perform authentication and tampered detection but also improved both data embedding capacity up to 8.00 (bpp) as well as increase visual quality measured by PSNR, 50.03 (dB). Finally, the scheme is compared with other existing state-of-the-art methods and gives a reasonably better performance in terms of visual quality and hiding capacity. Our scheme has been evaluated through various steganographic analysis and observed that the scheme is secure and robust against various attacks. [ABSTRACT FROM AUTHOR]

Polymeric carbon nitride quantum dots (CNQDs) with an average size of approximately 2.5 nm were prepared directly from melamine via a one-step molten salt method. The formation mechanism and photoluminescence (PL) properties of the resulting CNQDs were investigated by means of TEM, XRD and PL spectroscopy. The CNQDs can be dispersed in water to form a transparent colloidal solution and emit blue PL with excellent photostability. Interestingly, upon addition of CuCl2 and NaHCO3 in turn, the PL of CNQDs can be turned off and on accordingly. Taking advantage of the on–off–on PL response, the CNQDs can be used as a fluorescent security ink for information coding, encryption and decryption, indicating their promising application in data security and high-level anti-counterfeiting fields. [ABSTRACT FROM AUTHOR]

The curing characteristics of an ultraviolet (UV) ink layer are of utmost importance for the development of UV inks. Measuring either bulk or bottom cure in itself is not new and has been the subject of many articles. In this article, two methods are described based on Fourier transform infrared (FT-IR) spectrometry to measure in real time and simultaneously the bulk and bottom cure of a thin UV ink layer. The procedure consists of applying a thin (10–12 µm) layer of UV-curing ink on an attenuated total reflection (ATR) crystal. The bottom cure is measured with ATR. The bulk cure is measured simultaneously with a reflection analysis (method 1) or a transmission analysis (method 2). With both methods, the bulk and bottom cure can be determined. To overcome problems with the interference in the ATR reflection setup, it is recommended to use the ATR transmission setup. [ABSTRACT FROM AUTHOR]

Facile solution combustion route was used to prepare the optimized composite core shell SiO 2 @Y 2 O 3 :Eu 3+ , Li + fluorescent nanopowders (NPs) with superior fluorescence intensity under UV light. Powder dusting technique was used for the visualization of latent fingerprints (LFPs) on different porous and non-porous surfaces. The results display that the amorphous SiO 2 microspheres were covered by crystalline Y 2 O 3 :Eu 3+ , Li + NPs, resulting in spherical core-shell structure. The phosphors exhibit intense pure strong red emission corresponding to characteristic Eu 3+ ions 5 D 0 → 7 F 2 transitions under NUV excitation. The CIE co-ordinates were found to be (x = 0.63, y = 0.36) which is very close to standard NTSC values (x = 0.67, y = 0.33). Judd-Ofelt theory was used to estimate the intensity parameters (Ω 2 and Ω 4 ) as well as radiative properties. The CCT value was ∼ 3475 K which was less than 5000 K, as a result the phosphor was highly useful in warm light emitting diodes. Thus, results presented confirms that the developed method was simple, fast and optimized phosphor was effectively used for multifunctional applications namely luminescent sensor for visualization of LFPs, solid state lightning and security ink applications. [ABSTRACT FROM AUTHOR]

The proof of the security of quantum key distribution is a rather complex problem. Security is defined in terms different from the requirements imposed on keys in classical cryptography. In quantum cryptography, the security of keys is expressed in terms of the closeness of the quantum state of an eavesdropper after key distribution to an ideal quantum state that is uncorrelated to the key of legitimate users. A metric of closeness between two quantum states is given by the trace metric. In classical cryptography, the security of keys is understood in terms of, say, the complexity of key search in the presence of side information. In quantum cryptography, side information for the eavesdropper is given by the whole volume of information on keys obtained from both quantum and classical channels. The fact that the mathematical apparatuses used in the proof of key security in classical and quantum cryptography are essentially different leads to misunderstanding and emotional discussions [1]. Therefore, one should be able to answer the question of how different cryptographic robustness criteria are related to each other. In the present study, it is shown that there is a direct relationship between the security criterion in quantum cryptography, which is based on the trace distance determining the distinguishability of quantum states, and the criterion in classical cryptography, which uses guesswork on the determination of a key in the presence of side information. [ABSTRACT FROM AUTHOR]

Two aza-boron-diquinomethene (aza-BODIQU) complexes bearing phenyl and carbazyl substituents were synthesized and characterized. Their photophysical properties were investigated systematically via spectroscopic and theoretical methods. Both complexes exhibit strong π-π* transition absorptions ( λ = 400-540 nm) and intense fluorescent emissions ( λ = 440-600 nm, Φ = 0.93 and 0.78) in CHCl solution and in solid state at room temperature. Compared to the complex with phenyl groups, the complex bearing carbazyl groups shows significant bathochromic shift in both absorption and emission. This could be attributed to the larger π-electron conjugation of the carbazole unit and intramolecular charge transfer feature from carbazole to aza-BODIQU component. In addition, the complexes exhibit intense photoluminescence and good stability on antacid, anti-alkali and stability in printing ink samples, which makes them potential dopants for the application of fluorescent security inks. [ABSTRACT FROM AUTHOR]

Stimuli-responsive photoluminescent (PL) materials have been widely used as fluorescent ink for data security applications. However, traditional fluorescent inks are limited in maintaining the secrecy of information because the inks are usually visible by naked eyes either under ambient light or UV-light illumination. Here, we introduced metal-free water-soluble graphitic carbon nitride quantum dots (g-CNQDs) as invisible security ink for information coding, encryption, and decryption. The information written by the g-CNQDs is invisible in ambient light and UV light, but it can be readable by a fluorescence microplate reader. Moreover, the information can be encrypted and decrypted by using oxalic acid and sodium bicarbonate as encryption reagent and decryption reagent, respectively. Our findings provide new opportunities for high-level information coding and protection by using water-soluble g-CNQDs as invisible security ink. [ABSTRACT FROM AUTHOR]

Organic fluorophores with reversibleemission switching behaviorare promising materials for applications in sensors, optical recording,security inks, and optoelectronics. A variety of aggregation-inducedemission (AIE) luminogens with mechanochromic luminescence has beenprepared, and the transformation of efficient bluer-emitting crystalsto amorphous powders with redder and weaker emission is proposed tobe the cause for such behavior. However, detailed mechanistic understandingfrom experimental to theoretical is lacking. In this work, we presentthe design and synthesis of a group of bis(diarylmethylene)dihydroanthraceneswith butterfly-like shapes. These molecules exhibit aggregation-inducedemission characteristics due to the restriction of intramolecularmotion in the aggregated state. They show mechanochromism, becauseof the transformation between crystal and amorphous states with differentcolors and efficiencies aided by grinding/heating or solvent fumingprocesses. By investigation of their single-crystal structures andtheoretical calculations, the loose molecular packing with noncovalentintermolecular interactions, the extent of conformational twisting,and the packing density of the luminogens, as well as freedom of intermolecularmotion in the excited state, are stemmed for their reversible polymorphism-dependentemission behaviors. [ABSTRACT FROM AUTHOR]

Europium and terbium trisdipicolinate complexes are inkjet printed onto paper with commercially available desktop inkjet printers. Together with a commercial blue luminescent ink, the red-emitting luminescent ink containing europium and the green-emitting luminescent ink containing terbium are used to reproduce accurate full color images that are invisible under white light and appear under a 254 nm UV light. Such invisible luminescent images are attractive anti-counterfeiting security features. The luminescent prints have a color range (gamut) nearly as wide as the gamut of a standard sRGB display. The gamut of the luminescent prints is determined by relying on a simple model predicting the relative spectral radiant emittances of any printed luminescent color halftone. The model is also used to establish the correspondence between the surface coverages of the printed luminescent inks and the emitted color of these luminescent halftones. The accuracy of the spectral prediction model is very good and can be rationalized by the absence of quenching when the luminescent lanthanide complexes are printed in superposition with the other luminescent materials. [ABSTRACT FROM AUTHOR]

Cryptography is always taken as the secure way while transforming the confidential information over the network. But over the time, the traditional cryptography approaches are been replaced with more effective cryptographic systems such as quantum cryptography, biometric cryptography, geographical cryptography and DNA cryptography. The presented work is about to defined a DNA cryptography scheme in which DNA concept will be implemented at two stages. At the initial stage, the DNA sequence will be used as the key to perform the cryptography and later on the cryptography itself will be done using the DNA coded approach. The presented work will be implemented on text cryptography. At the earlier stage, the system will accept the DNA sequence as the input to generate the key. The DNA sequence will be identify the maximum frequency DNA pattern. This sequence pattern will be used as the key to the cryptography system. At the later stage, the DNA encoded dictionary will be defined for cryptography. Now the input text will be coded using this DNA coded dictionary. The presented work will also optimize the process of DNA sequence search mechanism so that the effectiveness of the cryptographic algorithm will be improved. [ABSTRACT FROM AUTHOR]

One of popular techniques in gambling fraud involves the use of invisible ink marks printed on the back surface of playing cards. Such covert patterns are transparent in the visible spectrum and therefore invisible to unaided human eyes. Invisible patterns can be made visible with ultraviolet (UV) illumination or a CCD camera installed with an infrared (IR) filter depending on the type of ink materials used. Cheating gamers often wear contact lenses or eyeglasses made of IR or UV filters to recognize the secret marks on the playing cards. This paper presents an image processing technique to reveal invisible ink patterns in the visible spectrum without the aid of special equipment such as UV lighting or IR filters. A printed invisible ink pattern leaves a thin coating on the surface with different refractive index for different wavelengths of light, which results in color dispersion or absorption difference. The proposed method finds the differences of color components caused by absorption difference to detect invisible ink patterns on the surface. Experiment results show that the proposed scheme is effective for both UVactive and IR-active invisible ink materials. [ABSTRACT FROM AUTHOR]

Secret information recorded by traditional single-encrypted invisible inks is easily cracked because the inks can switch only between "NONE" and "TRUTH". Developing double-encrypted systems makes the information reversibly switchable between "FALSE" and "TRUTH", which is helpful to ensure the safety of the secret information during transport. Here, we prepared heat-developed invisible inks by hydrochromic molecules donor-acceptor Stenhouse adducts (DASAs) and oxazolidines (OXs) and promoted the invisible inks from single to double encryption. DASAs coordinate with water molecules and form stable colorless cyclic DASA· x H 2 O molecules, which lose coordinated water molecules after heating and switch to colored linear DASAs. In contrast, OXs are colored with water and are colorless after heating. Single-encrypted secrecy was realized by DASA invisible inks. The information is invisible under the encrypted state and becomes bright purple after heating. Vapor treating re-encrypted the information in ∼5 min. Furthermore, the single-encryption was promoted to double-encryption by a DASA/OX invisible inks system. Heating and vapor treating switch the information between the "FALSE" and "TRUTH" reversibly. The DASA/OX invisible ink system is applied for secrecy of texts, graphic images, and quick response (QR) codes.

The article focuses on the pros and cons of mobile data management (MDM) software and networking services. Topics include the feature of MDM to be applied to multiple device architectures and mobile technology vendors like Apple, the combination of relatively strong cryptographic controls on local devices in MDM solutions, and the issue of significant threat to mobile connectivity caused by MDM solutions.

Highly photoluminescent gel-like carbon dots (G-CDs) were successfully synthesized for the first time by a rapid one-step solvothermal synthesis approach with citric acid and 1,2-ethylenediamine as the precursors. Their gel-like nature was revealed by the Tyndall and coagulation effects, which were elucidated by a negative ζ potential value. The influences of temperature on the properties and sizes of these G-CDs were analyzed, and the best method for a maximum quantum yield was identified. The resulting products emitted blue photoluminescence under UV light (λ=365 nm) and a gradient of color under regular light. In addition, the UV/Vis absorption and fluorescence emission spectra of the G-CDs indicated that those synthesized at 160 °C exhibited the highest fluorescence quantum yield (33 %). Atomic force microscopy and transmission electron microscopy measurements were performed, and a higher temperature of formation resulted in smaller G-CDs. Furthermore, band shifts in the UV/Vis and fluorescence spectra and sequential changes in the quantum yield values and ζ potentials in addition to elemental compositional changes as determined by X-ray photoelectron spectroscopy were monitored throughout the formation process of the G-CDs. As to applications, G-CDs were prepared as an invisible ink for printers, which exhibited the applicability of G-CDs in daily life and military activities., (© 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

A.‐S. Chauvin and co‐workers print lanthanide complexes on paper and, by controlling and calibrating an inkjet printer, obtain accurately reproduced luminescent images that are invisible under daylight but appear to glow under UV light. On page 5029, this shining application demonstrates the potential of luminescent lanthanide complexes to build unique anti‐counterfeit features that are both beautiful and difficult to reproduce. The frontispiece picture is a simple illustration of the material workflow involved in the production of such prints. [ABSTRACT FROM AUTHOR]

Counterfeiting costs governments and private industries billions of dollars annually due to loss of value in currency and other printed items. This research involves using lanthanide doped β-NaYF4 nanoparticles for security printing applications. Inks comprised of Yb3+/Er3+ and Yb3+/Tm3+ doped β-NaYF4 nanoparticles with oleic acid as the capping agent in toluene and methyl benzoate with poly(methyl methacrylate) (PMMA) as the binding agent were used to print quick response (QR) codes. The QR codes were made using an AutoCAD file and printed with Optomec direct-write aerosol jetting®. The printed QR codes are invisible under ambient lighting conditions, but are readable using a near-IR laser, and were successfully scanned using a smart phone. This research demonstrates that QR codes, which have been used primarily for information sharing applications, can also be used for security purposes. Higher levels of security were achieved by printing both green and blue upconverting inks, based on combinations of Er3+/Yb3+ and Tm3+/Yb3+, respectively, in a single QR code. The near-infrared (NIR)-to-visible upconversion luminescence properties of the two-ink QR codes were analyzed, including the influence of NIR excitation power density on perceived color, in term of the CIE 1931 chromaticity index. It was also shown that this security ink can be optimized for line width, thickness and stability on different substrates. [ABSTRACT FROM AUTHOR]