Shi Zhenxu, Zhao Weiwei, Zhang Yue, Yang Dimei, Gan Lin, Huang Jin
State Key Laboratory of Silkworm Genome Biology, and Chongqing, Key Laboratory of Soft-Matter Material Chemistry and Function Manufacturing, School of Chemistry and Chemical Engineering, Southwest University, Chongqing, 400715, China.
School of Chemistry and Chemical Engineering, Engineering Research Center of Materials-Oriented Chemical Engineering of Xinjiang Bintuan, Shihezi University, Shihezi, 832003, China.
Small. 2023 Jan;19(3):e2205697. doi: 10.1002/smll.202205697. Epub 2022 Nov 21.
Optical encryption technologies are widely used in information security, whereas the technology with one single optical secret key can be easily cracked. Here, a triple encryption is reported, which hides patterned information in excitation-dependent allochroic materials with long afterglow, enhancing the security level. The allochroic materials are based on a uniaxial co-assembly structure of cellulose nanocrystals (CNCs) and silica. The assembled CNCs present blue emission with quantum yield of 19.8% under 367 nm UV radiation. The blue emission is maintained in the inverse structure when CNCs are calcinated and converted to carbon dots (CDs). The inverse uniaxial-assembly structure improves the CD emission by 6.7 times. The assembly structure can even improve the phosphorescence of CDs, leading to excellent excitation-dependent allochroic properties. Specifically, the materials maintain a cyan long afterglow luminescence at 480 nm after removing 365 nm UV light, whose lifetime is 0.492 s. Changing the excitation wavelength to 254 nm, a UV emission at 343 nm can be obtained, alongside a blue long afterglow luminescence of 420 nm, whose lifetime is 1.574 s. Combining with blue afterglow materials, optical encryption labels are prepared, which hide different patterned information in three scenarios: natural light, UV light, and afterglow luminescence.
光学加密技术在信息安全领域得到了广泛应用，然而，单一光学密钥的技术很容易被破解。在此，报道了一种三重加密方法，该方法将图案信息隐藏在具有长余辉的激发依赖变色材料中，从而提高了安全级别。这种变色材料基于纤维素纳米晶体（CNC）和二氧化硅的单轴共组装结构。组装后的CNC在367nm紫外辐射下呈现量子产率为19.8%的蓝色发射。当CNC被煅烧并转化为碳点（CD）时，蓝色发射在反结构中得以保持。反单轴组装结构使CD发射提高了6.7倍。这种组装结构甚至可以改善CD的磷光，从而产生优异的激发依赖变色特性。具体而言，在去除365nm紫外光后，材料在480nm处保持蓝绿色长余辉发光，其寿命为0.492s。将激发波长改为254nm，可以获得343nm处的紫外发射，同时还有420nm处的蓝色长余辉发光，其寿命为1.574s。结合蓝色余辉材料，制备了光学加密标签，其在三种场景下隐藏不同的图案信息：自然光、紫外光和余辉发光。
