Development of strontium aluminate embedded photochromic cellulose hydrogel for mapping of fingermarks

Simple and efficient fluorescent identification of fingerprints without background interferences has been a challenge. Dual-mode security encoding using fluorescence photochromism has been utilized to create very reliable authenticating materials. Herein, lanthanide-doped strontium aluminate phosphor (LSAP) nanoparticles (NPs) were synthesized and immobilized into carboxymethyl cellulose (CMC) hydrogel, which has the potential for low costs, low environmental impact, self-healing and high scale production. We report the development of smart photochromic anticounterfeiting LSAP@CMC hydrogel toward mapping of fingermarks. The photochromic hydrogel was prepared and fingerprinted onto paper surface, displaying a colorless film (365 nm) with green emission (518 nm) under ultraviolet light as verified by CIE Lab and luminescence analyses. The fluorescence security inks were tested for their security features and printability. Both excitation and emission analyses were used to evaluate the optical performance of fingermarks printed onto paper documents. Highly reversible photochromism was detected without fatigue. LSAP nanoparticles were inspected by transmission electron microscope (TEM) to designate diameters of 25-34 nm, whereas the fingermark-printed paper sheets were analyzed by energy-dispersive X-ray (EDX) and scanning electron microscope (SEM). The durability and printability of the LSAP@CMC hydrogel ink were also tested. The rheological behavior of hydrogel and mechanical properties of fingerprints were investigated.