Department of Materials Engineering and Science Program, South Dakota School of Mines and Technology, 501 East St Joseph Street, Rapid City, SD 57701, USA.
Nanotechnology. 2012 Oct 5;23(39):395201. doi: 10.1088/0957-4484/23/39/395201. Epub 2012 Sep 11.
Counterfeiting costs governments and private industries billions of dollars annually due to loss of value in currency and other printed items. This research involves using lanthanide doped β-NaYF(4) nanoparticles for security printing applications. Inks comprised of Yb(3+)/Er(3+) and Yb(3+)/Tm(3+) doped β-NaYF(4) nanoparticles with oleic acid as the capping agent in toluene and methyl benzoate with poly(methyl methacrylate) (PMMA) as the binding agent were used to print quick response (QR) codes. The QR codes were made using an AutoCAD file and printed with Optomec direct-write aerosol jetting(®). The printed QR codes are invisible under ambient lighting conditions, but are readable using a near-IR laser, and were successfully scanned using a smart phone. This research demonstrates that QR codes, which have been used primarily for information sharing applications, can also be used for security purposes. Higher levels of security were achieved by printing both green and blue upconverting inks, based on combinations of Er(3+)/Yb(3+) and Tm(3+)/Yb(3+), respectively, in a single QR code. The near-infrared (NIR)-to-visible upconversion luminescence properties of the two-ink QR codes were analyzed, including the influence of NIR excitation power density on perceived color, in term of the CIE 1931 chromaticity index. It was also shown that this security ink can be optimized for line width, thickness and stability on different substrates.
由于货币和其他印刷品的价值损失，每年假冒伪劣产品给政府和私营企业造成数十亿美元的损失。本研究涉及使用镧系掺杂的 β-NaYF(4)纳米粒子进行安全印刷应用。以油酸作为配体，在甲苯和苯甲酸甲酯中制备了 Yb(3+)/Er(3+)和 Yb(3+)/Tm(3+)掺杂的β-NaYF(4)纳米粒子油墨，并与聚甲基丙烯酸甲酯（PMMA）作为结合剂，用于打印快速响应（QR）码。QR 码使用 AutoCAD 文件制作，并使用 Optomec 直接写入气溶胶喷射（®）打印。在环境光照条件下，这些 QR 码是不可见的，但可以使用近红外激光读取，并且可以成功地用智能手机扫描。本研究表明，QR 码主要用于信息共享应用，也可以用于安全目的。通过在单个 QR 码中分别打印基于 Er(3+)/Yb(3+)和 Tm(3+)/Yb(3+)组合的绿色和蓝色上转换油墨，可以实现更高水平的安全性。分析了双墨 QR 码的近红外（NIR）到可见上转换发光性能，包括近红外激发功率密度对感知颜色的影响，以 CIE 1931 色度指数表示。还表明，这种安全油墨可以针对不同基底的线宽、厚度和稳定性进行优化。
