1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 z Materials Science inc. Nanomaterials & Polymers Triluminescent Functional Composite Pigment for Non-Replicable Security Codes to Combat Counterfeiting Amit K. Gangwar, [a, b] Kanika Nagpal, [a] and Bipin K. Gupta* [a] Herein, a novel strategy to design of unclonable triluminescent pigment derived security ink is formulated to protect valuable merchandise, bank notes, pharmaceuticals, confidential docu- ments etc. against counterfeiting, by embedding luminescent security codes/images. This triluminescent security ink is designed with combinatory chemistry that involves the strate- gically admixing of the triluminescent functional composite pigments in commercially available polyvinyl chloride gold medium. The triluminescent functional composite pigment is composed of NaYF 4 : Yb 3 + , Er 3 + (Sodium Yttrium Fluoride doped with Ytterbium and Erbium ions), NaYF 4 : Eu 3 + (Sodium Yttrium Fluoride doped with Europium ion) and ZnO (Zinc Oxide) materials which have multifunctional features as it looks white in ambient light and shows strong green (NaYF 4 : Yb 3 + , Er 3 + ), red (NaYF 4 : Eu 3 + ) and green (ZnO) colors at three different excitations of 980 nm, 254 nm and 379 nm wavelengths, respectively. The structural/microstructural and photolumines- cence properties of triluminescent functional composite are confirmed by XRD (X-ray diffraction), SEM (Scanning electron microscope), TEM (Transmission electron microscope) and photoluminescence spectroscopic techniques, respectively. The quality and spatially distributed PL intensity of printed images/ code from triluminescent ink was investigated by photo- luminescence confocal mapping microscopy technique. Hence, the obtained results suggest that the security code/images printed by using ink formulated from triluminescent functional composite pigment provides one step ahead novel security features which could be easy to detect but extremely difficult to replicate. Introduction Counterfeiting and piracy are terms used to describe imitation activities linked to intellectual property rights infringement, [1] has become a real threat to global economy. Illicit activities of all such items that affect the consumer’s health and wealth have become the serious concern all over the world. Further, a report illustrates around 10% of global business and costs an approximately 40,000 jobs per year in France and 2.5 million in G20 countries got affected by such type of crimes. [2] Another, survey by U.S. Department of Commerce estimates that the size of global fake drug market has upto $75 to $200 billion and can occupy half of all trade in developing countries. [3] All these reports poses serious wealth and health threat to consumers globally. [4–6] Many efforts have been done to secure the official documents, banknotes, pharmaceuticals and high value merchandise from counterfeiting on global level, but the easily availed high-tech equipment and advanced technologies have made counterfeit easier. [2,7] Therefore, counterfeiting has become a big trouble for researcher worldwide to come up with highly reliable anti-counterfeiting technologies to combat the illegal activities. In the past few years, some technologies; metal threads as well as electronic tracking using radio frequency identification (RFID), simple watermarks, plasmonic security tags, holograms, luminescent security inks etc. were introduced to combat counterfeiting. [8–10] Although, the luminescent materials pre- ferred more due to their superb opto-physical properties. [11] Different kinds of luminescent materials; lanthanide based luminescent conventional organic dyes, nanomaterials, metal- organic-frameworks (MOFs), plasmonic nanomaterials, carbon based quantum dots, semiconductor quantum dots etc. have been explored up to now for the fabrication of security ink to solve the counterfeiting problems. [4,12–14] Most of the above stated materials have their own pros and cons, which is well investigated in our earlier studies. [2,12,15–18] Among all, semi- conductor and lanthanide based luminescent materials are preferred more due to their unique qualities; highly stable, easy to produce in bulk, cost-effective and have sharp emission with high intensity. [19,20] Generally, single color emissive luminescent materials at single excitable wavelength are being developed for the anti-counterfeiting purpose, [12] but duplicity is easy of these kind of luminescent materials. Our group as well as some other groups have done many efforts to make the luminescent security ink which can excite by single and dual mode excitation wavelengths (UV and NIR) to develop strong anti- counterfeiting features of security codes/patterns/ images. [2,14–18,21] Currently, we have added one more feature for the further advancement of luminescent security ink to combat counterfeiting. The aim of present investigations is centered on making a new strategy to develop the multi-mode trilumines- [a] A. K. Gangwar, K. Nagpal, Dr. B. K. Gupta CSIR - National Physical Laboratory, Dr. K S Krishnan Road, New Delhi, 110012, India E-mail: bipinbhu@yahoo.com [b] A. K. Gangwar Academy of Scientific and Innovative Research (AcSIR), CSIR – National Physical Laboratory Campus, Dr. K. S. Krishnan Road, New Delhi 110012, India Supporting information for this article is available on the WWW under https://doi.org/10.1002/slct.201801938 Communications DOI: 10.1002/slct.201801938 9627 ChemistrySelect 2018, 3, 9627–9633 © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim