Optical anti-counterfeiting and information storage based on rare-earth-doped luminescent materials

Unleashing the Potential of Defect Engineered Persistent Pr3+-Activated Phosphors for Multi-Dimensional Anti-Counterfeiting and X-Ray Imaging Applications

Persistent luminescence (PersL) in inorganic phosphors offers great potential for anti-counterfeiting and optical storage, with optimization of PersL, multicolor tuning, and defect engineering. This study presents a Ca3Ga2Ge3O12:Pr3+ (CGGO:Pr) phosphor with long-lasting PersL and multicolor emissions. Aliovalent codoping with Er3+ and Yb3+ ions optimizes deep/shallow trap redistribution, controlling trap depths from 0.98 to optimal 0.73 eV through the creation of new shallow electron traps (YbCa •, ErCa •) alongside existing VO levels. The smart Pr3+/Er3+/Yb3+:CGGO phosphor exhibits three-dimensional visible emissions under 275  and 380 nm excitation, as well as upconversion emissions under 980 nm laser irradiation. Hybrid density functional calculations, thermoluminescence, and positron annihilation lifetime spectroscopy revealed the nature and density of different traps controlling the PersL. Together, a single system featuring multicolor luminescence has been developed, exhibiting improved PersL and regulated trap depths (≈0.73 eV) suitable for robust and multimodal anti-counterfeiting of documents, pharmaceuticals, and industrial products. Furthermore, the composite PMMA-CGGO:Pr phosphor films have shown remarkable capability for X-ray imaging, achieving a resolution of 4 lp/mm, which exceeds that of commercial Gd2O2S:Tb screens. These findings highlight the potential of this work for advanced anti-counterfeiting and X-ray imaging applications, offering enhanced PersL with controlled trap depths.

Crystal Structures, Phase Transition, and Optical Properties of Two Rare Earth Borate Fluorides: α- and β-BaGdBO3F2

Borate materials possess diverse crystal structures and exhibit outstanding physical properties, making them highly suitable for optical applications. In this work, two new compounds, α-BaGdBO3F2 and β-BaGdBO3F2, were synthesized by the high-temperature solid solution method and a temperature-controlled phase transition from α-BaGdBO3F2 to β-BaGdBO3F2 was observed. In the crystal structures of α-BaGdBO3F2 and β-BaGdBO3F2, the [BO3] basic building unit and the [GdO6F2] polyhedra are interconnected to form a complex three-dimensional network. The title compounds exhibit good thermal stability, a short ultraviolet cutoff of 274 nm, and a moderately large birefringence (0.072 and 0.059@ 546 nm). The DFT calculations also reveal that β-BaGdBO3F2 could be a potential nonlinear optical (NLO) material. The results indicate that α-BaGdBO3F2 and β-BaGdBO3F2 are promising candidates for UV birefringent and NLO crystal materials.

Luminescent nanomaterials based covert tags for anti-counterfeiting applications: A review

Counterfeiting has emerged as a new global threat that challenges companies, securities, governments, and customers. Because of the banal advancements in technology, it is extremely prevalent. Ultimately have a more concerning effect than terrorism in terms of the standard of goods, organizations, banks' financial standing, people's health, the nation's financial situation, etc. Thus, it requires an urgent high-tech solution to combat counterfeiting. The present review surveys the anti-counterfeiting technologies that have been applied to combat and discourage counterfeiting. It presents the photoluminescence properties of quantum dots, metal-organic-framework, and lanthanide-doped nanomaterials and their applications in anti-counterfeiting. Recently, lanthanide-doped nanomaterials have emerged as potential candidates that provide strong security for the products due to their excellent color tunable luminescence properties under the wide range (UV to NIR) of excitation. Therefore, the present review mainly focused on the strategies of luminescence features of lanthanide-doped downconversion/downshifting and upconversion nanomaterials and their potential uses in fighting counterfeiting. Moreover, the key barriers and opportunities to combat counterfeiting advances are discussed. In addition, the crucial factors, such as the fabrication of luminescent ink, various printing techniques employed for printing different kinds of fluorescent security labels, patterns, and codes, etc., have been highlighted. This review will provide detailed information to the readers to design the security labels based on the lanthanide-doped luminescent nanomaterials for high-tech security against counterfeiting.

Multi-Emitting Ratiometric Temperature Sensing and Tunable White Light Emitting Based on Effective Energy Transfer in a Lanthanide-Brønsted Acidic Ionic Liquid Coordination Polymer

Isostructured lanthanide-Brønsted acidic ionic liquid coordination polymers, {[Ln(C7H7N2O4)(H2O)4]Cl2}n (LnIMDC(H2O)4, Ln = Eu3+, Gd3+, or Tb3+, C7H7N2O4 = [IMDC]-) and {[Eu0.5Tb0.5(C7H7N2O4)(H2O)4]Cl2}n (Eu0.5Tb0.5IMDC(H2O)4)), have been synthesized using 1,3-bis(carboxymethyl) imidazolium chloride ([H2IMDC]Cl) as linkers. LnIMDC(H2O)4 (Ln = Eu3+ or Tb3+) and Eu0.5Tb0.5IMDC(H2O)4 exhibit good temperature sensing performance over a wide temperature range with maximum sensitivities Sr of 2.73%·K-1 (392 K) and 2.74%·K-1 (362 K), and 2.21% K-1 (383 K), respectively. Meanwhile, the white light emission of Eu0.5Tb0.5IMDC(H2O)4 was achieved with Commission Internationale de l'Eclairage coordinates of (0.323, 0.328), a correlated color temperature of 5942 K, and a color rendering index (CRI) of 90. Moreover, the temperature response of the as-synthesized Eu0.5Tb0.5IMDC(H2O)4@PDMS film was monitored. The energy transfer efficiency and phosphorescence lifetime in the abovementioned coordination polymers were investigated to explore the energy transfer efficiency between [IMDC]- and Ln3+ as well as between Tb3+ and Eu3+.

Photonic Inks with Dual-Layer Security Features by Encapsulation of Color Tunable Fluorescent Dyes in PMMA Colloidal Microspheres

To counter economic terrorism by preventing counterfeit currency, documents and high-value commercial products, new-generation security inks with multiple safety features are required. Herein, color-tunable pyrylium and pyridinium dye-encapsulated polymethyl methacrylate (PMMA) colloidal microspheres are reported to exhibiting brilliant emission and photonic properties. A combination of the PMMA colloidal photonic ink having structural color variation and the dye-encapsulated colloidal photonic ink with fluorescence modulation is used for security labeling. The angle-dependent structural color variations, a remarkable 250-fold fluorescence enhancement, non-toxicity, and the rare earth-free formulation have made the ink novel and suitable for dual-layer high-security printing. Covert security patterns and labels are made overt under 365 nm UV light, while also exhibiting angle-dependent structural color. The increased level of security with developed photonic colloidal inks is demonstrated with dual-layer screen-printed images and patterns on flexible substrates.

AIE Active Imidazole-Stilbene Conjugated Fluorescent Probes: Illuminating Latent Fingerprints and Advancing Anticounterfeiting Technologies

Aggregation-induced emission luminogens (AIEgens) are widely used in the realm of latent fingerprint visualization owing to their luminosity and resistance to photobleaching. However, challenges such as significant background interference and limited resolution hinder their rapid advancement. Consequently, there is a pressing need to improve the detailed visualization of latent fingerprint (LFP) imaging, particularly for analyzing level 3 details. To address this, we have designed donor-acceptor (D-A) type AIEgens named MMIMV, DMIMV, and TMIMV. These compounds exhibit robust emissions ranging from 481 to 552 nm and signify positive fluorosolvatochromism. When applied as powder dusting, these derivatives enable the fluorescence imaging of LFPs on various material substrates. The analysis of these imaged LFPs yields intricate details regarding fingerprint ridge patterns. Our results underscore the potential of highly emissive AIEgens MMIMV, DMIMV, and TMIMV as promising candidates for fingerprint visualization, thus offering significant implications for forensic investigations. Furthermore, these derivatives serve as effective fluorescent security inks for writing and drawing, presenting a novel avenue for robust anticounterfeiting applications.

IR Hidden Patterns for Security Labels

Authentication of a product's originality by anticounterfeiting labels represents a crucial point toward protection against forgery. Fast and scalable fabrication methods of original labels with a high degree of protection are in high demand for the protection of valuable goods. Here, we propose a simple strategy for fabrication of hidden security tags with IR luminescent readout by the direct femtosecond laser patterning of silicon-erbium-silicon sandwiched thin films. The choice of laser processing parameters makes possible the creation of random or quasi-regular self-organized surface nanotextures. The controlled laser-driven oxidation accompanying this process provides simultaneous regulation of the film's optical properties and spontaneous emission yield of the embedded Er atoms. The regimes are detected when optically similar patterned areas demonstrate different Er emission intensities, allowing us to create hidden security tags with facile readout at the C-band telecommunication wavelengths. The obtained results take another step toward the application of IR-luminescent erbium-based anticounterfeiting labels for covert and/or forensic security levels.

Synthesis and fluorescence properties of europium complex functionalized fiberglass paper

The development of novel rare earth fluorescent materials and the exploration of their applications have consistently been focal points of research in the fields of materials science and chemistry. In this work, a novel rare earth composite material with good photo-fluorescence properties and self-supporting has been prepared via a simple ultrasonic solvent reaction method. Initially, the Phen moieties is immobilized onto the surface of a self-supporting fiberglass paper using ICPTES, followed by the coordination of Eu(TTA)3 moieties with Phen moieties through a convenient ultrasonic solvent reaction. The resulting GF-Phen-Eu(TTA)3 has been characterized using FTIR, UV-Vis DRS, fluorescence measurements, and so on. The results indicate that the composite material exhibits strong fluorescent emission and presents a vivid red color under ultraviolet light. Further research has shown that the fluorescence of GF-Phen-Eu(TTA)3 strips demonstrated a pronounced quenching effect in response to some transition metal ions (1 mM). Hence, the rare earth composite materials presented here can be utilized not only for the production of optical materials, but also for the development of fluorescence sensing strips.

Dramatic Impact of Materials Combinations on the Chemical Organization of Core-Shell Nanocrystals: Boosting the Tm3+ Emission above 1600 nm

This article represents the first foray into investigating the consequences of various material combinations on the short-wave infrared (SWIR, 1000-2000 nm) performance of Tm-based core-shell nanocrystals (NCs) above 1600 nm. In total, six different material combinations involving two different types of SWIR-emitting core NCs (α-NaTmF4 and LiTmF4) combined with three different protecting shell materials (α-NaYF4, CaF2, and LiYF4) have been synthesized. All corresponding homo- and heterostructured NCs have been meticulously characterized by powder X-ray diffraction and electron microscopy techniques. The latter revealed that out of the six investigated combinations, only one led to the formation of a true core-shell structure with well-segregated core and shell domains. The direct correlation between the downshifting performance and the spatial localization of Tm3+ ions within the final homo- and heterostructured NCs is established. Interestingly, to achieve the best SWIR performance, the formation of an abrupt interface is not a prerequisite, while the existence of a pure (even thin) protective shell is vital. Remarkably, although all homo- and heterostructured NCs have been synthesized under the exact same experimental conditions, Tm3+ SWIR emission is either fully quenched or highly efficient depending on the type of material combination. The most efficient combination (LiTmF4/LiYF4) achieved a high photoluminescence quantum yield of 39% for SWIR emission above 1600 nm (excitation power density in the range 0.5-3 W/cm2) despite significant intermixing. From now on, highly efficient SWIR-emitting probes with an emission above 1600 nm are within reach to unlock the full potential of in vivo SWIR imaging.

Study on the Luminescence Performance and Anti-Counterfeiting Application of Eu2+, Nd3+ Co-Doped SrAl2O4 Phosphor

This manuscript describes the synthesis of green long afterglow nanophosphors SrAl2O4:Eu2+, Nd3+ using the combustion process. The study encompassed the photoluminescence behavior, elemental composition, chemical valence, morphology, and phase purity of SrAl2O4:Eu2+, Nd3+ nanoparticles. The results demonstrate that after introducing Eu2+ into the matrix lattice, it exhibits an emission band centered at 508 nm when excited by 365 nm ultraviolet light, which is induced by the 4f65d1→4f7 transition of Eu2+ ions. The optimal doping concentrations of Eu2+ and Nd3+ were determined to be 2% and 1%, respectively. Based on X-ray diffraction (XRD) analysis, we have found that the physical phase was not altered by the doping of Eu2+ and Nd3+. Then, we analyzed and compared the quantum yield, fluorescence lifetime, and afterglow decay time of the samples; the co-doped ion Nd3+ itself does not emit light, but it can serve as an electron trap center to collect a portion of the electrons produced by the excitation of Eu2+, which gradually returns to the ground state after the excitation stops, generating an afterglow luminescence of about 15 s. The quantum yields of SrAl2O4:Eu2+ and SrAl2O4:Eu2+, Nd3+ phosphors were 41.59% and 10.10% and the fluorescence lifetimes were 404 ns and 76 ns, respectively. In addition, the Eg value of 4.98 eV was determined based on the diffuse reflectance spectra of the material, which closely matches the calculated bandgap value of SrAl2O4. The material can be combined with polyacrylic acid to create optical anti-counterfeiting ink, and the butterfly and ladybug patterns were effectively printed through screen printing; this demonstrates the potential use of phosphor in the realm of anti-counterfeiting printing.