Spatially confined luminescence process in tip-modified heterogeneous-structured microrods for high-level anti-counterfeiting

Excitation-Controlled Host-Guest Multicolor Luminescence in Lanthanide-Doped Calcium Zirconate for Information Encryption

Efficient control over lanthanide luminescence by regulating excitations offers a real-time and reversible luminescence-managing strategy, which is of great importance and highly desirable for various applications, including multicolor display and information encryption. Herein, we studied the crystal structure, luminescence properties, and mechanisms of undoped and Tb3+/Eu3+-doped CaZrO3 in detail. The intrinsic purple-blue luminescence from host CaZrO3 and the introduced green/red luminescence from guest dopants Tb3+/Eu3+ were found to have different excitation mechanisms and, therefore, different excitation wavelength ranges. This enables the regulation of luminescent color through controlling the excitation wavelengths of Tb3+/Eu3+-doped CaZrO3. Furthermore, preliminary applications for information encryption with these materials were demonstrated using portable UV lamps of 254 and 302 nm. This study not only promotes the development of multicolor luminescence regulation in fixed-composition materials, but also advances the practical applications of lanthanide luminescent materials in visually readable, high-level anti-counterfeiting and information encryption.

Modulating luminescence and assembled shapes of ultrasmall Au nanoparticles towards hierarchical information encryption

Because of their intriguing luminescence performances, ultrasmall Au nanoparticles (AuNPs) and their assemblies hold great potential in diverse applications, including information security. However, modulating luminescence and assembled shapes of ultrasmall AuNPs to achieve a high-security level of stored information is an enduring and significant challenge. Herein, we report a facile strategy using Pluronic F127 as an adaptive template for preparing Au nanoassemblies (AuNAs) with controllable structures and tunable luminescence to realize hierarchical information encryption through modulating excitation light. The template guided ultrasmall AuNP in situ growth in the inner core and assembled these ultrasmall AuNPs into intriguing necklace-like or spherical nanoarchitectures. By regulating the type of ligand and reductant, their emission was also tunable, ranging from green to the second near-infrared (NIR-II) region. The excitation-dependent emission could be shifted from red to NIR-II, and this significant shift was considerably distinct from the small range variation of conventional nanomaterials in the visible region. In virtue of tunable luminescence and controllable structures, we expanded their potential utility to hierarchical information encryption, and the true information could be decrypted in a two-step sequential manner by regulating excitation light. These findings provided a novel pathway for creating uniform nanomaterials with desired functions for potential applications in information security.

Achieving Multicolor Upconversion Emissions without Changing Compositions

It is widely recognized that a proper way of adjusting fluorescence color is meaningful for pushing forward upconversion materials to be utilized in anti-counterfeiting, display and solid-state lightning applications. Traditional routes that apply different host materials and/or doping categories to adjust fluorescence color have shown large color region tunability yet have to rely on complex synthesis process accompanied with time and raw material consumption. In this work, in order to get a wide luminous color gamut without depending on reciprocating synthesis, we desinged and provided a high-sensitizer-concentration upconversion crystals, hexagonal NaLuF₄:Yb³⁺/Er³⁺ (50/2 mol%), whose red-to-green emission intensity ratio can be conveniently tuned from 2.69 to 4.96 by simply modulating excitation power densities. The promoted three-photon-population progress of red emission achieved by using an intensive excitation laser is considered to be responsible for the facile upconversion modulation. The results may provide new ideas for emission color control that based on external parameters in identical host and the greatly amplified excitation power-sensitivity of NaLuF₄:Yb³⁺/Er³⁺ (50/2 mol%) is highly potential for fluorescence anti-fake and colorful display applications.

Rare-Earth Doping in Nanostructured Inorganic Materials

Impurity doping is a promising method to impart new properties to various materials. Due to their unique optical, magnetic, and electrical properties, rare-earth ions have been extensively explored as active dopants in inorganic crystal lattices since the 18th century. Rare-earth doping can alter the crystallographic phase, morphology, and size, leading to tunable optical responses of doped nanomaterials. Moreover, rare-earth doping can control the ultimate electronic and catalytic performance of doped nanomaterials in a tunable and scalable manner, enabling significant improvements in energy harvesting and conversion. A better understanding of the critical role of rare-earth doping is a prerequisite for the development of an extensive repertoire of functional nanomaterials for practical applications. In this review, we highlight recent advances in rare-earth doping in inorganic nanomaterials and the associated applications in many fields. This review covers the key criteria for rare-earth doping, including basic electronic structures, lattice environments, and doping strategies, as well as fundamental design principles that enhance the electrical, optical, catalytic, and magnetic properties of the material. We also discuss future research directions and challenges in controlling rare-earth doping for new applications.

Multidimensional Information Encryption and Storage: When the Input Is Light

The issue of information security is closely related to every aspect of daily life. For pursuing a higher level of security, much effort has been continuously invested in the development of information security technologies based on encryption and storage. Current approaches using single-dimension information can be easily cracked and imitated due to the lack of sufficient security. Multidimensional information encryption and storage are an effective way to increase the security level and can protect it from counterfeiting and illegal decryption. Since light has rich dimensions (wavelength, duration, phase, polarization, depth, and power) and synergy between different dimensions, light as the input is one of the promising candidates for improving the level of information security. In this review, based on six different dimensional features of the input light, we mainly summarize the implementation methods of multidimensional information encryption and storage including material preparation and response mechanisms. In addition, the challenges and future prospects of these information security systems are discussed.

Structural colour QR codes for multichannel information storage with enhanced optical security and life expectancy

Current schemes for encoding and decoding anticounterfeiting optical quick response (QR) codes involve miscellaneous challenges. The need for using multiple light sources to read out the wavelength-multiplexed data from optically encoded organic dyes, photoblinking from quantum dots, and autofluorescence from carbon dots are some typical examples. In order to address these restrictions, we exploited our previously devised nanoimprinting-exposure-thermal-treatment (NETT) data storage approach to present a new structural-colour-based regime for optical encoding of high-security QR codes. The angle-dependent readability of our diffraction-based nanostructures poses an enhanced optical security feature that can substitute the existing inefficient encoding strategies by eliminating the constraints associated with them. Additionally, in comparison with conventional optical encoding media, using the long-lasting photocrosslinked SU-8 in the NETT method considerably enhances the life expectancy of the proposed QR codes. Also, considering the rapid NETT-based Ni stamp origination method, which was previously introduced by our group, mass-generation of the proposed codes is feasible. Owing to the special optically variable effects provided by the nanostructures, duplication of our QR codes is very difficult. The colour code design, which embeds 766 characters in 2907 modules in red, green and blue channels, was generated and fabricated onto generic nanostructure arrays using the NETT process. The encoded information was successfully read out from the pattern using a broadband light source and a digital camera. Higher capacities are also deemed to be reachable by implementing image processing and machine learning algorithms to overcome in-channel module recognition and cross-channel interferences.

Simultaneous Dual-mode Emission and Tunable Multicolor in the Time Domain from Lanthanide-doped Core-shell Microcrystals

The dual-mode emission and multicolor outputs in the time domain from core-shell microcrystals are presented. The core-shell microcrystals, with NaYF₄:Yb/Er as the core and NaYF₄:Ce/Tb/Eu as the shell, were successfully fabricated by employing the hydrothermal method, which confines the activator ions into a separate region and minimizes the effect of surface quenching. The material is capable of both upconversion and downshifting emission, and their multicolor outputs in response to 980 nm near-infrared (NIR) excitation laser and 252 nm, and 395 nm ultraviolet (UV) excitation light have been investigated. Furthermore, the tunable color emissions by controlling the Tb³⁺- Eu³⁺ ratio in shells and the energy transfer of Ce³⁺→Tb³⁺→ Eu³⁺ were discussed in details. In addition, color tuning of core-shell-structured microrods from green to red region in the time domain could be obtained by setting suitable delay time. Due to downshifting multicolor outputs (time-resolved and pump-wavelength-induced downshifting) coupled with the upconversion mode, the core-shell microrods can be potentially applied to displays and high-level security.

Facile preparation of N-doped graphene quantum dots as quick-dry fluorescent ink for anti-counterfeiting

N-GQDs are synthesized using a simple and fast one-step protocol and applied for preparing quick-dry fluorescent ink for both writing and printing.