Encryption and optical authentication of confidential cellulosic papers by ecofriendly multi-color photoluminescent inks.

Photodetection of originality and authentication of security documents such as money, passport, bank note, and national card have been a significant challenge in recent decade. Using of advanced optical systems could remarkably reduce copy and counterfeiting of such national and international documents. Novel ecofriendly multi-color photoluminescent inks were developed for information encryption on cellulosic papers and optical authentication of confidential/original documents by synthesis of water-based latex nanoparticles modified with photoluminescent coumarin (blue emission) and two photochromic spiropyran derivatives (red and orange emissions). Some of the latexes with higher fluorescence emission were formulated to water-based inks, and then loaded to stamps with different marks for printing of quick response code, barcode, finger print, and other marks on cellulosic documents. All of the printed marks display ultra-bright blue, red, and orange fluorescence emissions upon UV irradiation, which have potential applications in encryption, security marking and optical authentication of confidential cellulose substrates.