By utilizing opposite luminescence temperature-dependences between lanthanide-doped microrods and nanocrystals, upconversion hybrids with color-tunable emissions are developed for more secure anticounterfeiting applications.
terfeiting nanomaterials with highlevel security features have attracted increasing interest in recent years, taking advantages of diverse luminescence characteristics of UCNCs, such as multicolor emission, [2a,3] excitation power dependence, [4] dual-mode fluorescence, [5] tunable luminescence lifetime, [6] and plasmonic coupling effects. [7] These novel UCNCs can produce color-coded or color-tunable anticounterfeiting patterns, authenticated by changing the excitation wavelength/power or utilizing the timeresolved scanning method. Although the extra anticounterfeiting features make these novel UC nanomaterials or nanocomposites very hard to duplicate, they typically require complex fabrication processes and costly reading instruments, such as ultrahigh power lasers and time-gated decoding instrumentation. Hence, the exploration of novel UC nanomaterials with high-level security, simple fabrication procedures, and convenient authentication methods is highly desired.Luminescent materials generally suffer emission loss at higher temperatures, which is well known as the thermal quenching. However, Yb-sensitized core-only UCNCs have been found to show the dramatic upconversion luminescence (UCL) increase at elevated temperatures by our group [8] and also by Zhou et al. very recently. [9] This thermally induced UCL increase phenomenon has been ascribed to temperaturedependent surface effects of UCNCs. Zhou et al. proposed a surface phonon-assisted UCL model and suggested that the heat-favorable phonons existing at the NC surface increased the energy transfer from Yb 3+ to emitting ions and induced the UCL increase at elevated temperatures. [9] Nevertheless, deep spectral analysis at various temperatures and circumstances indicated that the UCL increase should be due to the gradually attenuated quenching effect of surface-adsorbed water molecules with increasing temperature. [10] The exact mechanism behind this totally different light-heat interplay behavior at the nanoscale need to be further elucidated. [11] On the other hand, this thermally induced UCL increase phenomenon provides a novel strategy to design UC anticounterfeiting nanomaterials with strengthened security features. In the present work, based on quite different UCL temperature-dependences of active-core@inert-shell NCs (thermal quenching) and active-core@active-shell ones (thermally induced increase), This work presents a novel and highly secure anticounterfeiting strategy based on core/shell upconversion nanocrystal (UCNC) hybrids with temperature-responsive multicolor emissions. Opposite luminescent temperaturedependences are found for active-core@inert-shell (thermal quenching) and active-core@active-shell (thermally induced enhancement) UCNCs. Accordingly, their hybrids are designed to show obvious color changes with increasing temperature under 975 nm excitation. Various color-shifting pathways (from white to green, blue to green, etc.) are achieved by adjusting the core/shell NC combinations in the hybrids. Moreover, color changes of the prin...
AbstractThis study presents a novel and high-level anticounterfeiting strategy based on Ce/Yb/Ho triply-doped NaGdF4 nanocrystals with temperature-responsive multicolor emission. A critical factor leading to the multicolor emission is confirmed by comparing the luminescence thermal behaviors of nanocrystals in various atmospheres. Through analyzing the temperature-dependent lifetimes of Yb3+ ions in air, we demonstrate that thermally-induced multicolor emission mainly originates from the gradually-attenuated H2O quenching effect. Because the cross-relaxations between Ce3+ and Ho3+ ions and the nonradiative transitions of Yb3+ ions create plenty of phonon heat, the multicolor emission of nanocrystals can be achieved under 975 nm excitation at a relatively low power density. This recognition method is efficient and convenient for security authentication. The as-synthesized core nanocrystals can be directly used to fabricate anticounterfeiting ink without further processing (e.g. core/shell or hybrid). Therefore, the small-sized β-NaGdF4:Yb/Ce/Ho nanocrystals are promising candidate for security application.
According to the thickening principle and molecular structure of thickeners, supercritical carbon dioxide (sc-CO2) thickeners were summarized and introduced by dividing into polymers, small molecular compounds, and surfactants. The properties...
In this study, three oligomeric cationic Gemini surfactants (Ⅲ1, Ⅲ2, and Ⅲ3) were prepared from different major raw materials, including long-chain alkyl amine (dodecyl amine, tetradecyl amine or cetyl amine), formic acid, formaldehyde, diethyl amine hydrochloride and epichlorohydrin. The synthesis conditions for one of the three surfactants, bis-[2-hydroxy-3-(N,N-dimethyl-N-dodecyl)propyl]dipropylammonium chloride (Ⅲ1), were optimised by orthogonal experiments. The optimum synthesis conditions were: molar ratio of intermediate Ⅱ to intermediate Ⅰ1 = 1.0:2.2, reaction temperature = 85 °C and reaction time = 16 h. The structures of the three prepared compounds were characterised by FTIR and 1H NMR. Their thermal properties were evaluated by thermal gravimetric analysis (TGA). The Geminisurfactants prepared exhibited better surface active properties than conventional single chain cationic surfactants. With increasing carbon chain length from C12 to C16, both CMC and surface tension γ
CMC decreased, while the viscosity of the thickening solution prepared with the synthesised oligomeric cationic Gemini surfactants as the main component increased. The optimum thickening formula was: 2.0 wt% Ⅲ3 + 0.8 wt% sodium salicylate (NaSal) + 0.6 wt% KCl. The viscosity of the optimum thickening formulation was 190.4 mPa s. Gemini oligomeric cationic surfactants could be used as thickeners in the production of fracturing fluids, flooding agents and drilling fluids for oil and gas production in oil fields.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.