A multi-color persistent luminescent phosphor β-NaYF4:RE3+ (RE = Sm, Tb, Dy, Pr) for dynamic anti-counterfeiting

Current Developments in Emerging Lanthanide-Doped Persistent Luminescent Scintillators and Their Applications

Lanthanide-doped scintillators have the ability to convert the absorbed X-ray irradiation into ultraviolet (UV), visible (Vis), or near-infrared (NIR) light. Lanthanide-doped scintillators with excellent persistent luminescence (PersL) are emerging as a new class of PersL materials recently. They have attracted great attention due to their unique "self-luminescence" characteristic and potential applications. In this review, we comb through and focus on current developments of lanthanide-doped persistent luminescent scintillators (PersLSs), including their PersL mechanism, synthetic methods, tuning of PersL properties (e. g. emission wavelength, intensity, and duration time), as well as their promising applications (e. g. information storage, encryption, anti-counterfeiting, bio-imaging, and photodynamic therapy). We hope this review will provide valuable guidance for the future development of PersLSs.

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.

Multi-Layered Composites of Natural Rubber (NR) and Bismuth Oxide (Bi2O3) with Enhanced X-ray Shielding and Mechanical Properties

Due to rapid increases in the utilization of radiation and nuclear technologies, effective and suitable radiation-shielding materials have become one of the most sought-after options to protect users and the public from excessive exposure to the radiation. However, most radiation-shielding materials have greatly reduced mechanical properties after the addition of fillers, resulting in their limited useability and shortened lifetime. Therefore, this work aimed to alleviate such drawbacks/limitations by exploring a possible method to simultaneously enhance both the X-ray shielding and mechanical properties of bismuth oxide (Bi₂O₃)/natural rubber (NR) composites through multi-layered structures, with varying (1-5) layers and a total combined thickness of 10 mm. To correctly determine the effects of the multi-layered structures on the properties of NR composites, the formulation and layer configuration for all multi-layered samples were tailored such that their theoretical X-ray shielding properties were equal to those of a single-layered sample that contained 200 phr Bi₂O₃. The results indicated that the multi-layered Bi₂O₃/NR composites with neat NR sheets on both outer layers (sample-D, sample-F, sample-H, and sample-I) had noticeably higher tensile strength and elongation at break than those of the other designs. Furthermore, all multi-layered samples (sample-B to sample-I), regardless of the layer structure, had enhanced X-ray shielding properties compared to those with a single layer (sample-A), as shown by their higher values of the linear attenuation coefficient (µ) and lead equivalence (Pb_eq) and the lower value of the half-value layer (HVL) in the former. This work also determined the effects of thermal aging on relevant properties for all samples, with the results revealing that all the thermal-aged composites had higher values for the tensile modulus but lower values for the swelling percentage, tensile strength, and elongation at break, compared with the non-aged composites. Hence, based on the overall outcomes from this work, it could be concluded that the worrisome decreases in mechanical properties of the common single-layered NR composites after the addition of Bi₂O₃ could be prevented/reduced by introducing appropriate multi-layered structures, which would not only widen potential applications but also prolong the lifetime of the composites.

Multi-color luminescence and anticounterfeiting application of upconversion nanoparticle†

Multi-color luminescence materials are important in the illumination, solid-state three-dimensional display, information storage, biological labelling and anticounterfeiting fields. Herein, we designed a novel core–shell structure upconversion nanoparticle (UCNP) material (NaYF₄) with lanthanide ion doping to achieve multi-color luminescence under a single NIR excitation laser. Different from the typical single-sensitizer materials, the core–shell structure utilizes Nd³⁺, Yb³⁺, Tm³⁺ and Er³⁺ ions to obtain tuning of the color and brightness. The doping of Nd³⁺ ions enhances the weak color (red) light source to maintain the light color balance. Benefiting from the color adjustment of the sensitizers and the change of the core–shell coating, bright-white emission and flexible color emission from red to green, cyan and blue can be achieved via the diverse doped rare earth ions in a single UCNP under continuous-wave laser excitation (980 nm). Simultaneously, the emission color of the UCNPs can change with the intensity of the excitation light source and the wavelength. The bright-white emission can be used for lighting displays, and the flexible full-color emission can be applied in the anticounterfeiting and information storage fields.

Quadruply doped (Nd³⁺, Tm³⁺, Er³⁺ and Yb³⁺) core–shell structure NaYF₄ UCNPs achieve multi-color luminescence based on a single material under 980 nm excitation. Their applicability to anticounterfeiting and information storage has been verified.

Modulating A site compositions of europium(iii)-doped double-perovskite niobate phosphors

Eu3+-activated double-perovskite niobates of A2InNbO6 were synthesized with the modulation of their A site and the polydimethylsiloxane flexible light-emitting films based on the optimized phosphors were implemented for versatile applications.