Faculty Publications

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Yellow emissive and high fluorescence quantum yield carbon dots from perylene-3,4,9,10-tetracarboxylic dianhydride for anticounterfeiting applications
(Royal Society of Chemistry, 2024) Ullal, N.; Sahoo, B.; Dhanya, D.; Kulkarni, S.D.; Bhat K, U.; Anand, P.J.
Forged products are widespread in the market and there is an immediate need to counter this growing menace. Anti-counterfeit techniques using fluorescent materials with covert features that appear hidden under daylight and display characteristic fluorescence upon specific source irradiation have gained popularity. Carbon dots (CDs) that can be prepared through facile synthesis from various raw materials are a class of fluorescent materials that provide tremendous opportunities to combat counterfeiting. This work focuses on the fabrication of perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA) derived CDs via the solvothermal approach and their subsequent purification using column chromatography. The fifth fraction obtained exhibited remarkable yellow emission (λem = 540 nm) with a high fluorescence quantum yield of 53.22% and a lifetime of 4 ns. The CDs appeared quasi-spherical during TEM imaging with an average diameter of 1-3 nm and appeared polycrystalline from the SAED pattern. The XPS and TEM-EDS results suggested carbon as the major element along with oxygen and nitrogen as the other heteroatoms. The water-based ecofriendly ink formulated using the CDs was printed on UV dull paper using the flexography technique. The print-proof paper samples appeared pale pink under daylight and fluorescent yellow upon 365 nm UV illumination. Moreover, the stability of the print was confirmed upon exposure to strong UV radiation cycles and abrasion resistance. Besides, the fluorescence emission remained unaltered even after 5 months of storage under room temperature conditions. The ink was used to print on PVC sheets and FBB boards with good stability against scuffing, suggesting its applicability in the packaging industry. The CDs could also serve as fluorescent markers for identifying post-consumer plastic packaging for a circular economy. © 2024 The Royal Society of Chemistry.
Ink formulations using Eu3+ doped strontium aluminates for security printing
(Elsevier B.V., 2025) Ullal, N.; Sahoo, B.; Dhanya, D.; Kulkarni, S.D.; Bhat K, U.; P.j, A.; Rao, A.
Counterfeiting is a widespread menace that affects multiple sectors of society, which is increasing due to technological advancements and growing globalization of trade. It undermines economic growth, endangers public safety, damages brand integrity, and facilitates criminal activities. The present study focuses on the synthesis of thermally stable europium (Eu3+) doped orthorhombic Sr4All4O25 (SAO) system by solid state method for use as a colorant in the formulation of viz based and polyvinyl alcohol (PVA) based screen inks. The steady state spectrum of Eu3+ doped SAO depicts the charge transfer taking place between host (O2-) and half-filled f-orbital of Eu3+ ion. Mono-exponential decay with lifetime value recorded in milliseconds indicates substitution of single Sr host lattice. The screen prints obtained on UV dull paper using PVA based ink with Eu3+ doped SAO as pigment displayed better photostability and abrasion resistance. Both Viz and PVA based formulations could serve as invisible inks for security printing and information storage applications. The prints produced using the viz-based and PVA-based formulations appeared fluorescent blue under UV illumination, while they exhibited red and green fluorescence, respectively, when viewed through long-pass filters. A user familiar with these features can easily authenticate the prints, whereas replicating them is challenging for counterfeiters. © 2025 The Authors

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