Xi Li,Junlu Sun,Wentao Huang,Fuhang Jiao,Yuan Deng,Wei Zhang,Ying Xiao,Chong-Xin Shan,Lin Dong
As the Internet of Things (IoT) continues its pervasive influence and digital technologies increasingly weave into the fabric of daily lives, the imperative for robust security measures becomes paramount to mitigate the escalating risks to the digital landscape. Traditional anti-counterfeiting technologies, while capable to some extent, are constrained by factors such as material toxicity, low-security efficacy, and intricate fabrication process. Mechanoluminescent materials have shown great potential in the areas of anti-counterfeiting and security. Here, a multicolor mechanoluminescent (ML) material (lanthanide doped Ca 2 B 2 O 5 ) synthesized by solid-phase reaction is reported for the first time at a relatively lower temperature of 750 °C. The ML devices are obtained by embedding ML materials into polydimethylsiloxane elastomer, allowing for stress visualization with colors ranging from blue and green to orange and red. Through elaborate co-doping, successive and accurate stress visualizations are realized. Finally, security labels based on the lanthanide ions doped Ca 2 B 2 O 5 are prepared and also demonstrated to safeguard valuable packages. This work provides a novel multicolor ML material and pioneers its use in security labels, offering a universal solution for multicolor display, information security, dynamic anti-counterfeiting, and other potential applications within the realm of IoT.
The synthesis of whiskers is an important means of high-value utilization of calcium resources. Calcium borate (Ca 2 B 2 O 5 ·H 2 O) whiskers were synthesized by microwave hydrothermal method using CaCl 2 , Na 2 B 4 O 7 ·10H 2 O and NaOH as raw materials at 140 °C for 2 h. A series of characterizations were conducted on the obtained calcium borate whiskers, including phase identification (XRD and FT-IR), crystal morphology (SEM), crystal structure (TEM and SAED), and thermal stability (TG). Through batch experiments under the control of influencing factors, the effects on product phase and morphology were systematically studied, such as raw material concentration (Ca 2+ concentration and the molar ratio of boron/calcium), reaction temperature, holding time and pH value. For the prepared calcium borate whiskers, SAED demonstrated that the whiskers have a single crystal structure, characterized by a sarciniform shape with diameter ranging from 1.2 to 3.1 μm and a length of 50 to 120 μm. And thermal analysis revealed that the calcium borate whiskers remained stable without losing crystalline water at a synthesis temperature of 140 °C, while releasing crystalline water at a temperature range of 383.6 °C to 430.9 °C. The optimal conditions for Microwave-Hydrothermal synthesis were identified based on experimental phenomena, and the solution-liquid–solid (SLS) process of whisker formation was proposed and analyzed. The possible chemical reactions and growth mechanisms of calcium borate whiskers under microwave hydrothermal synthesis were briefly proposed by adjusting the reaction conditions and observing the process of morphological changes.
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