Preparation of persistently luminescent polyacrylic acid-based nanocomposite ink for secure encoding

Security encoding that use photochromism has been an appealing method for fabricating efficient authentication substrates. In order to overcome counterfeiting, a unique photochromic ink was created to be utilized as a stamped film, that persistently emits light under both ultraviolet rays and darkness. Nanoparticles of lanthanide-doped aluminate (NLDA) dispersed in a polymer binder was utilized to produce a smart composite ink. In order to develop a transparent film, NLDA must be evenly distributed throughout the polyacrylic acid ink solution. Cellulosic paper sheets were stamped with the fluorescent and color-tunable nanocomposite ink. As proved by CIE (Commission Internationale de ĺEclairage) Lab parameters, a transparent appearance was achieved by stamping a homogeneous ink layer onto paper surface. Using photoluminescence spectroscopy, the stamped surfaces exhibited an absorbance peak at 365 nm and a fluorescent band at 519 nm. The stamped pattern is invisible under daylight; however, a change in color was detected from colorless to green under UV rays. X-ray diffraction (XRD) and transmission electron microscopy (TEM) were employed to explore the structure of NLDA. Infrared spectroscopy (FTIR), energy-dispersive X-ray (EDS), scanning electron microscopy (SEM), and X-ray fluorescence (XRF) were all employed to determine the morphological features of the stamped papers. The imprinted paper sheets exhibited photochromism that could be switched back and forth between visible (colorless) and ultraviolet (green) lights without fatigue. Persistent greenish-yellow emission was detectable in the dark after exposure to smartphone light for a few seconds. Stamped sheets were analyzed for their mechanical properties, and the rheology of the photoluminescent ink was studied.