Tuning multicolour emission of Zn2GeO4:Mn phosphors by Li+ doping for information encryption and anti-counterfeiting applications

Deep-trap persistent materials for future rewriteable optical information storage

Deep-trap persistent luminescent (PersL) materials with enriched traps, which allow signals to quickly write-in and read-out with low-energy consumption, are one of the most promising materials for information storage. In this review, considering the demand for optical information storage, we provide comprehensive insights into the data storage mechanism of PersL materials. Particularly, we focus on various "trap-state tuning" strategies involving doping to design new deep-trap persistent phosphors with controlled carrier trapping-de-trapping for non-volatile and high-capacity information storage. Subsequently, various recent significant strategies, including wavelength-multiplexing, intensity-multiplexing, mechanical-multiplexing, and three-dimensional and multidimensional trap-multiplexing technologies for improving the information storage capacity of PersL phosphors are highlighted. Finally, the challenges and opportunities regarding optical information storage by PersL materials are discussed. We hope that this review will provide new insights for the future development of PersL materials in the field of optical data storage.

Recent advances in photoresponsive printing inks for security encoding applications

Counterfeiting of banknotes, important documents, and branded goods continues to be a major worldwide problem for governments, businesses, and consumers. This problem has serious financial, security, and health implications. Due to their stability for printing on various substrates, the photochromic anticounterfeiting inks have received important interest. There have been various photochromic agents, such as polymer nanoparticles, quantum and carbon dots, and organic and inorganic fluorophores and luminophores, which have been broadly used for antiforging applications. In comparison to organic agents, inorganic photochromic materials have better stability under reversible/long-term light illumination. Recently, the remarkable optical characteristics and chemical stability of photoluminescent and photochromic agents have led to their extensive usage anticounterfeiting products. There have been also several strategies to tackle the rising problem of counterfeiting. Both of solvent-based and water-based inks have been developed for security encoding purposes. Additionally, the printing methods, including screen printing, labeling, stamping, inkjet printing, and handwriting, that have been used to apply anticounterfeiting inks onto various surfaces are discussed. The limitations of photoluminescent and photochromic agents and the potential for their future preparation to combat counterfeiting were discussed. This review would benefit academic researchers and industrial developers who are interested in the area of security printing.

Dynamic Luminescence of Lead-Doped Calcium Zinc Germanate Clinopyroxene for Multimode Anticounterfeiting

Anticounterfeiting plays an essential role in authenticating genuine documents and combating forged products. To further advance the anticounterfeiting technology, there is a strong demand to design new functional materials with unique properties that will be appropriate for making multimode complex security labels. Recently, dynamic security labels have emerged as a new type of advanced anticounterfeiting method as they can hold a much higher security level than the traditional static ones. In this work, we report that calcium zinc germanate (CZGO) clinopyroxenes doped with lead ions have several interesting optical properties, such as dynamic fluorescence, long persistent luminescence, and photochromism. We find that the concentration of lead dopants can significantly impact the reaction kinetics as well as the crystallinity and luminescence properties of CZGO phosphors. By fully utilizing these unique properties, we have successfully fabricated several security labels with multilevel information encoding and dynamic optical performance. The combination of multimode and dynamic luminescence makes these labels extremely challenging to illegally duplicate. With further optimization, this lead-doped CZGO clinopyroxene can be well-integrated into modern anticounterfeiting techniques that will generate highly secure anticounterfeiting labels to combat fake products.

Multicolor-emitting Er3+ and Er3+/Yb3+ doped Zn2GeO4 phosphors combining static and dynamic identifications for advanced anti-counterfeiting application

Anti-counterfeiting labels based on luminescence materials are a newly emerging technique for protecting legal goods and intellectual property. In the anti-counterfeiting field to prevent forgery and cloning, luminescence materials with properties different from the commercialized and traditional ones are in urgent need. In this work, multicolor-emitting Er3+ single-doped and Er3+/Yb3+ co-doped Zn2GeO4 phosphors combining static and dynamic identifications were developed in order to achieve advanced anti-counterfeiting application. The variation of trap content with increasing the doping content of rare earth ions was analyzed through X - ray photoelectron spectroscopy, thermoluminescence analysis. It was found that there are two types of traps with different depth in Zn2GeO4 phosphors. The depths of the traps were experimentally confirmed to be 0.68 and 0.79 eV, respectively. The transient photocurrent response measurement confirmed the existence of charge carriers, and the mechanism for long persistent luminescence was deduced. The multicolor upconversion mechanisms under 980 and 1550 nm excitation were also discovered. Based on the multicolor steady and transient emission features, an anti-counterfeiting pattern was designed using the phosphors. Static and dynamic identification was demonstrated and presented in detail. Finally, it is indicated that the studied phosphors are excellent candidates for potential applications in luminescence anti-counterfeiting labels.

Recent advances in the anti-counterfeiting applications of long persistent phosphors

Counterfeit products have infiltrated numerous regions worldwide, causing substantial damage to the financial interests of individuals, businesses, and countries. Moreover, counterfeit goods can pose a severe risk to human health. Therefore, it is crucial to develop effective anti-counterfeiting methods and authentication technologies. Persistent luminescence (PersL) materials show great potential for anti-counterfeiting applications due to their distinctive spatial and temporal dynamic spectrum performance. The unique luminescence properties of PersL materials enable the creation of optical codes with high capacity. In this perspective, we provide a summary of the latest advancements in anti-counterfeiting technology using long persistent phosphors. We discuss the various construction strategies of optical codes for anti-counterfeiting, which include multicolor luminescence, orthogonal luminescence, dynamic luminescence, and stimulus-response luminescence. In addition, we explore the mechanisms of PersL-based anti-counterfeiting materials and consider potential areas for future development to expand the applications of persistent phosphors.

Tuning Multicolor Emission of Manganese-Activated Gallogermanate Nanophosphors by Regulating Mn Ions Occupying Sites for Multiple Anti-Counterfeiting Application

The ability to manipulate the luminescent color, intensity and long lifetime of nanophosphors is important for anti-counterfeiting applications. Unfortunately, persistent luminescence materials with multimode luminescent features have rarely been reported, even though they are expected to be highly desirable in sophisticated anti-counterfeiting. Here, the luminescence properties of Zn₃Ga₂GeO₈:Mn phosphors were tuned by using different preparation approaches, including a hydrothermal method and solid-state reaction approach combining with non-equivalent ion doping strategy. As a result, Mn-activated Zn₃Ga₂GeO₈ phosphors synthesized by a hydrothermal method demonstrate an enhanced red photoluminescence at 701 nm and a strong green luminescence with persistent luminescence and photostimulated luminescence at 540 nm. While Mn-activated Zn₃Ga₂GeO₈ phosphors synthesized by solid-state reactions combined with a hetero-valent doping approach only exhibit an enhanced single-band red emission. Keeping the synthetic method unchanged, the substitution of hetero-valent dopant ion Li⁺ into different sites is valid for spectral fine-tuning. A spectral tuning mechanism is also proposed. Mn-activated Zn₃Ga₂GeO₈ phosphors synthesized by a hydrothermal approach with multimodal luminescence is especially suitable for multiple anti-counterfeiting, multicolor display and other potential applications.

Multimodal dynamic color-tunable persistent luminescent phosphor Ca3Al2Ge3O12:Mn2+,Cr3+ for anti-counterfeiting and industrial inspection

Ca3Al2Ge3O12:Mn2+,Cr3+ may be used in anti-counterfeiting and industrial inspection.

Reversible luminescence tuning behavior in a thermal-stimuli-responsive anthracene-based coordination polymer

A new coordination complex presented a series of structural changes accompanied by photo-fluorescence (PL) changes under different temperature stimuli.