Weijing Yao

Large-scale synthesis and screen printing of upconversion hexagonal-phase NaYF4:Yb3+,Tm3+/Er3+/Eu3+ plates for security applications

Up-conversion materials can be applied in anti-counterfeit fields because of their high concealment and high up-conversion fluorescence efficiency. Herein, different lanthanide ions-doped β-NaYF4 up-conversion micro-particles (UCMPs) with uniform hexagonal morphology were synthesized on a large-scale (more than 0.5 g) via a facile hydrothermal method. It is very interesting to find out the fluorescence intensity and the eventual morphology of the UCMPs were highly dependent on the reaction conditions. Then, the optimal UCMPs with uniform morphology and strong fluorescence intensity were selected as promising candidates for preparing ink. Eventually, we successfully printed designable and multicolor fluorescent patterns on flexible substrates (common paper and polyethylene terephthalate, PET) using the as-prepared β-NaYF4:Yb3+,Tm3+/Er3+/Eu3+ UCMPs inks. Under ambient conditions, the printed patterns on conventional paper are invisible, while such printed patterns on PET are white. However, all the patterns could display blue, yellow-green and green fluorescence patterns under the irradiation of a 980 nm laser when using the β-NaYF4:Yb3+,Tm3+/Er3+/Eu3+ UCMPs inks. We envision that the UCMPs fluorescent inks-based flexible and rapid screen printing patterns have enormous potential for anti-counterfeit and security applications.

Facile synthesis and screen printing of dual-mode luminescent NaYF4:Er,Yb (Tm)/carbon dots for anti-counterfeiting applications

Rare-earth ion (RE3+) doped up-conversion (UC) fluorescent materials and novel fluorescent carbon quantum dots (CDs) have been widely used as traditional anti-counterfeiting materials owing to their excellent optical properties. The drawbacks of these materials are being exposed gradually with the widespread occurrence of counterfeit products in the market because of their single fluorescence mode and easy replication. In this work, we propose a novel strategy to combine both luminescent materials with different modes via a facile solvothermal method. Interesting, the composite materials show unalterable down-conversion (DC) blue light under a 365 nm ultraviolet (UV) analyzer, except for adjustable UC luminescence properties. The UC and DC optical properties are measured and the probable mechanism is proposed, indicating that the dual-mode fluorescence processes are separate and do not interference with each other. Moreover, we use a mixture containing a small number of UCMPs/CDs and poly(acrylic acid) (PAA) aqueous solution as a colorless anti-counterfeiting ink, and successfully print a variety of dual-mode fluorescence patterns through the screen printing technique, including QR codes, the logo of Wuhan University, and clover patterns. The composite materials show good dispersion and outstanding dual-mode fluorescence properties, suggesting that they are promising luminescent materials in the anti-counterfeiting field.

Zinc Oxide Coating Effect for the Dye Removal and Photocatalytic Mechanisms of Flower-Like MoS2 Nanoparticles

Flower-like MoS2 nanoparticles (NPs) consist of ultra-thin MoS2 nanosheets are synthesized via a facile one-pot hydrothermal method. The MoS2/ZnO p-n heterostructure is formed by coating n-type ZnO on the surface of flower-like MoS2 NPs through the seed-mediate route and post-annealing treatment. The effects for the dye removal and photocatalytic performances after ZnO coating are systematically investigated. The results demonstrated that the coating of ZnO nanoparticles has a positive promotion to the photodegrading properties while negative effect on the adsorption capacity of the MoS2/ZnO heterostructures. The related mechanisms on the relationship of adsorption capacity and photocatalysis are discussed in detail.

Full-spectrum-activated Z-scheme photocatalysts based on NaYF4:Yb3+/Er3+, TiO2 and Ag6Si2O7

The development of efficient full-spectrum-activated photocatalysts has become a research topic of intense interest in environmental remediation or solar energy conversion applications. Herein, newly Z-scheme UV-vis-NIR-activated photocatalysts consisting of β-NaYF4:18% Yb3+, 2% Er3+@TiO2–Ag6Si2O7 (denoted as NaYF4@T–ASO) were designed and used as full-spectrum response photocatalysts. For tailoring NaYF4@T–ASO, the size of in situ deposited ASO nanoparticles on the surface of NaYF4@T microplates was determined by the pumping rate of the AgNO3 precursor, which played indirect roles in the photocatalytic activity with different carrier migration distances. Especially, NaYF4@T–ASO (S10) with the smallest and well distributed ASO nanoparticles showed superior photocatalytic activity than the commercial P25 TiO2 by 15 fold under the stimulated solar light irradiation. The enhanced photocatalytic performance of NaYF4@T–ASO could be ascribed to the synergic effect of the upconversion material and the direct Z-scheme heterojunction formed between TiO2/ASO, where the Z-scheme heterojunction induced efficient separation of photogenerated carriers and highly oxidative species (h+ and ˙O2−). Alternative mechanisms of carriers and energy transfer under various light sources have been proposed and discussed in detail.

Dual upconversion nanophotoswitch for security encoding

Light-harvesting lanthanide ions (Ln3+) doped NaYF4 inks could provide polychromatic patterns for opposing counterfeiting commodity infestation because of their distinctive upconversion photoluminescence (UPL) properties. Herein, three kinds of core-triple-shell Ln3+ ions doped NaYF4 upconversion nanocrystals (UCNCs) are synthesized through modified high-temperature coprecipitation, which demonstrate excellent UPL properties of independent emitting colors under 808 or 980 nm laser excitation. Additive mixing three kinds of 808 nm emitted red-green-blue (RGB) UCNCs colloid solution can precisely regulate the emissions of the suspension for achieving full-color display. The as-obtained RGB three-primary colors induced by 808 nm laser accomplish broader color gamut than traditional standard RGB (sRGB) model and printing cyan-magenta-yellow (CMY) model. In addition, various China zodiac patterns and complex multicolor images are printed by the as-formulated UCNCs inks through screen printing technology. The printed patterns present colorful and polychromatic sequential toning visualization patterns under 808 nm excitation, while present another succession of gradually changed versatile patterns under 980 nm excitation. As a proof of concept, transparent polyvinyl chloride (PVC) self-adhesive anti-counterfeiting label is attached to the bottle of wine package for practical application. The demonstration of multiple model patterns of Chinese zodiac and poetry images based on these core-tripleshell UCNCs can be selected as a conceivable substitute of traditional single model patterns, underlining the full-color anti-counterfeiting level.摘要镧系离子掺杂的NaYF4油墨由于其独特的上转换光致发光特性可以被应用到防伪领域. 本文首先通过高温共沉淀法合成了三种核-壳结构的镧系离子掺杂的NaYF4上转换纳米材料, 它们在808和980 nm激光激发下均可以表现出差异性的上转换荧光性能. 其次, 通过物理混合808 nm激发的不同颜色的悬溶液红绿蓝, 可以调节混合液的发光颜色, 实现全彩色显示. 808 nm激发产生的颜色可以实现比sRGB和印刷CMY颜色空间模型更宽的色域. 最后, 我们使用传统丝网印刷技术印刷出中国十二生肖图案和其他大面积的复杂图像, 印刷图案在808 nm激发下可以呈现出一组多色连续的图案, 同时在980 nm激发下也可呈现出另一组逐渐改变的多色图案, 而且,印刷在透明聚氯乙烯PVC标签的图案可以附在酒瓶包装上, 实现酒瓶包装的防伪. 基于NaYF4的双模式荧光图案可以替代传统单模式荧光图案, 实现高水平的全色防伪及安全编码.

NIR light-activated upconversion semiconductor photocatalysts

Harvesting of near infrared (NIR) light in the abundant and environmentally friendly solar spectrum is particularly significant to enhance the utilization rate of the cleanest energy on earth. Appreciating the unique nonlinear optical properties of upconversion materials for converting low-energy incident light into high-energy radiation, they become the most promising candidates for fabricating NIR light-active photocatalytic systems by integrating with semiconductors. The present review summarizes recent NIR light-active photocatalytic systems based on a sequence of NaYF4-based, fluoride-based, oxide-based and Ln3+ ion-doped semiconductor-based photocatalysts for degradation of organic molecules. In addition, we provide an in-depth analysis of various photocatalytic mechanisms and enhancement effects for efficient photo-redox performance of different upconversion semiconductor photocatalysts. We envision that this review can inspire multidisciplinary research interest in rational design and fabrication of efficient full-spectrum active (UV-visible-NIR) photocatalytic systems and their wider applications in solar energy conversion.

Highly conductive, flexible and stretchable conductors based on fractal silver nanostructures

The emergence of flexible and stretchable conductors provides a direction for future development of wearable electronics, because they play a fundamental role in flexible and stretchable electronic devices. Herein, we fabricated a flexible and stretchable conductor by embedding fractal-structured silver particles in a PDMS substrate. The flexible and stretchable conductor can stretch up to 100% and bend and twist up to 180°, and it also possesses a good mechanical stability. Interestingly, the resistance of this conductor decreases under bending and twisting conditions. The change trend of resistance of the conductor can be negligible under 100 cycles of stretching at a strain of 30% and 100 tape test cycles. In addition, a flexible and stretchable LED circuit consisting of the conductor and a light emitting diode (LED) demonstrated that the conductor can be applied to flexible and stretchable electronic devices.