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Each person's latent fingerprints (LFP) are unique and hardly change, so LFP detection provides essential clues in forensic science. Currently, the powder dusting method is being promoted for viewing LFP due to its environmental safety; however, its low efficiency, low sensitivity, and toxicity are drawbacks, restricting its applications. To overcome these points, we proposed a NaYF 4 :Eu3+ downshifting microparticle (DSMPs) phosphor synthesized by a hydrothermal method with intense emission of ∼590–620 nm under excitation of 395 nm. We systematically studied the effect of synthesis conditions such as chelator, reaction time, temperatures, and doping concentrations on the structural, luminescent properties, and decay curves. The obtained results reveal that the crystal phase and particle morphology strongly depend on the reaction temperature. The emission properties of NaYF 4 :Eu3+ DSMPs can be significantly improved by changing the reaction temperatures and Eu doping contents. The optimized DSMPs with the most intense luminescent intensity were achieved when the phosphors were prepared at 180 οC for 24 hours, the rare earth stearate/oleic acid ratio of 1:24, and Eu doping amount of 10 mol%. This finding contributes to the suppression of substrate interference in LFP detection. The prepared NaYF 4 :Eu3+ DSMPs address the earlier limitations and show good potential for LFP detection. [ABSTRACT FROM AUTHOR]

Rare-earth-doped NaYF 4 nanoparticles are considered crucial upconversion luminescent materials with many applications, including anti-counterfeiting printing, biological imaging, and optical information storage. This work presents progress in obtaining hydrophilic pigments based on NaYF 4 :Er,Yb@SiO 2 nanoparticles, and their utilization in water-based ink printing for anti-counterfeiting applications. Coating NaYF 4 :Yb/Er microparticles with SiO 2 shells can provide several benefits for printing purposes, such as improved stability, dispersion, and ease of printing. The hydrophilic core-shell structured β-NaYF 4 :Er, Yb@SiO 2 microparticles were successfully prepared using the hydrothermal synthesis and sol-gel Stober method. The obtained microparticles were characterized by Scanning Electron Microscopy, X-ray diffraction, and Energy-dispersive X-ray spectroscopy. Such characterizations confirm that the Er3+ and Yb3+ ions are incorporated in NaYF 4 cores, the NaYF 4 :Er, Yb cores are in hundreds of nanometer sizes, and the NaYF 4 :Er, Yb microparticles are coated by a silica layer of 50 nm thick. Both NaYF 4 :Er, Yb and NaYF 4 :Er, Yb@SiO 2 behave as up-conversion luminescent microparticles for both green and red emissions. The CIE chromaticity coordinates indicate that both the nanoparticles have their greenish color under excitation at 980 nm. Although decorating the NaYF 4 :Er, Yb nanoparticles with the SiO 2 shell decreases luminescent intensity (by a factor of 2), this step is still necessary to achieve hydrophilic surfaces for preparing water-based printing inks. Using the synthesized NaYF 4 :Er, Yb@SiO 2 as a pigment, a new water-based ink formula was created based on Polyamide as a polymer matrix. The obtained ink is printable on paper and on transparent and flexible Polyethylene substrate. The printed patterns with a height of 2 cm and a width of 2.5 cm were observed clearly under the irradiation of a 980 nm LED. Their durability in terms of sharpness and color was also assessed after six months. [ABSTRACT FROM AUTHOR]

The relative humidity (RH) and temperature dependence of the conductance and mechanical properties of poly(styrenesulfonic acid) (PSSA)-grafted poly(ethylene-co-tetrafluoroethylene) polymer electrolyte membrane (ETFE-PEM) at a grafting degree (GD) of 36%, corresponding to an ion exchange capacity (IEC) of 2.03 mmol/g with Nafion-212 as a reference, were investigated. The activation energy of ETFE-PEM was 8.2 kJ/mol, which is lower than that of Nafion-212 (13.2 kJ/mol). The tensile strength of ETFE-PEM (12 − 34 MPa) is higher than that of Nafion-212 (10 − 25 MPa) under dry, wet, or humidified conditions (at 0% and 98% RH at 80 °C). The excellent mechanical properties of ETFE-PEM under humidified conditions can be explained by partial or total compensation effects between PSSA grafts containing water and the ETFE backbone and hierarchical crystalline structures of the membrane. The pristine ETFE, grafted-ETFE, and ETFE-PEM exhibited crystallinities of 30.3%, 22.4%, and 14.6% according to X-ray diffraction results. Thus, sulfonation strongly altered the natural crystalline structures of the pristine ETFE film. Additionally, the 112 XRD reflections played an essential role in the crystalline properties, which determined the mechanical strength of the membrane. The results indicate that ETFE-PEM with an IEC of 2.03 mmol/g exhibited promising electrochemical and mechanical properties under moderately severe operating conditions for fuel cell applications. [ABSTRACT FROM AUTHOR]