Switchable up and down-conversion luminescent properties of Nd(III)-nanopaper for visible and near-infrared anti-counterfeiting

A series of lanthanide-based nanopaper (Nd-nanopaper) was synthesized via a neodymium organic framework (Nd-MOFs)-grafted TEMPO-oxidized cellulose nanofibrils (tCNF) using a solvothermal reaction. Not using the traditional down-conversion visible emissions of anti-counterfeiting techniques, this Nd-nanopaper achieved down-conversion near-infrared (NIR) and up-conversion visible emissions. The down-conversion luminescent property of these Nd-nanopapers exhibited characteristic NIR luminescence (λEm = 1080 nm) of Nd3+ ions with 311 nm excitation, undergoing an "antenna" effect. In contrast, the up-conversion visible light emission (λEm =450 nm) of Nd-nanopaper was detected under 580 nm excitation. The mechanism of up-conversion fluorescence was ascribed to excited-state absorption and energy transfer up-conversion. Interestingly, Nd-nanopaper induced both up and down-conversions for visible and NIR emissions that were completely devoid of the interference from fluorescent brighteners and background fluorescence. These switchable up and down-conversion fluorescent Nd-nanopapers with visible and NIR dual emissions or dual channels could be applied in high level anti-counterfeiting applications.