Upconverted persistent luminescent Zn3Ga2SnO8: Cr3+, Yb3+, Er3+ phosphor for composite anti-counterfeiting ink

Herein, a novel colorless anti-counterfeiting luminous ink composite material, to the best of our knowledge, was prepared by incorporating upconverted persistent luminescent Zn₃Ga₂SnO₈:1%Cr³⁺, 5%Yb³⁺, 0.5%Er³⁺ (ZGSO: Cr,Yb,Er) phosphors into a resin solution, followed by stirring. Owing to its small particle size and uniform distribution, ZGSO: Cr, Yb, Er exhibits long-lasting, persistent near-infrared emission at 696 nm following the stoppage of excitation by a 274 nm ultraviolet light and a 980 nm excitation. ZGSO: Cr, Yb, Er composites were prepared and exhibited characteristic peaks corresponding to upconversion and an afterglow curve following excitation at 980 nm. With various special luminescent modes, sharp emission peaks, and emission intensity varying over time, the emission light of composite ink is easy to detect and not easily confused. Furthermore, the prepared composite ink can be calligraphic, visualized, and observable, and has good light-emitting performance following UV excitation. Our work provides a meaningful way to fabricate multifunctional anti-counterfeiting luminous ink composites with an intense persistent luminescence for use in anti-counterfeiting signs, inspection imaging, and other complex industrial applications.

Molecules for charge-based information storage

The inexorable drive to miniaturize information storage and processing devices has fueled the dreams of scientists pursuing molecular electronics: researchers in the field envisage exquisitely tailored molecular materials fulfilling the functions now carried out by semiconductors. A bottom-up assembly of such all-molecular devices would complement, if not supplant, the present top-down lithographic procedures of modern semiconductor fabrication. Short of these grand aspirations, a more near-term objective is to construct hybrid architectures wherein molecules are incorporated in semiconductor-based devices. Such a combined approach exploits the advantages of molecules for selected device functions while retaining the well-developed lithographic approaches for fabrication of the overall chip. In this Account, we survey more than a decade of results from our research programs to employ porphyrin molecules as charge-storage elements in hybrid semiconductor-molecular dynamic random access memory. Porphyrins are attractive for a variety of reasons: they meet the stability criteria for use in real-world applications, they are readily prepared and tailored synthetically, they undergo read-write processes at low potential, and they store charge for extended periods (up to minutes) in the absence of applied potential. Porphyrins typically exhibit two cationic redox states. Molecular architectures with greater than two cationic redox states are achieved by combinations of porphyrins in a variety of structures (for example, dyads, wherein the porphyrins have distinct potentials, triple deckers, and dyads of triple deckers). The incorporation of porphyrins in hybrid architectures has also required diverse tethers (alkyl, alkenyl, alkynyl, aryl, and combinations thereof) and attachment groups (alcohol, thiol, selenol, phosphonate, and hydrocarbon) for linkage to a variety of surfaces (Au, Si, SiO(2), TiN, Ge, and so forth). The porphyrins as monolayers exhibit high charge density and are robust to high-temperature excursions (400 °C for 30 min) under inert atmosphere conditions. Even higher charge densities, which are invaluable for device applications, were achieved by in situ formation of porphyrin polymers or by stepwise growth of porphyrin-imide oligomers. The various molecular architectures have been investigated by diverse surface characterization methods, including ellipsometry, atomic force microscopy, FTIR spectroscopy, and X-ray photoelectron spectroscopy, as well as a variety of electrochemical methods. These studies have further revealed that the porphyrin layers are robust under conditions of deposition of a top metal contact. The results to date indicate the superior features of selected molecular architectures for molecular electronics applications. The near-term utilization of such materials depends on further work for appropriate integration in semiconductor-based devices, whereas ultimate adoption may depend on advances that remain far afield, such as the development of fully bottom-up assembly processes.