Yb³⁺/Er³⁺co-doped cubic-(α-) phase NaYF₄ nanocrystals were prepared through a microwave- assisted hydrothermal method. Temperature-dependent upconversion luminescence (UCL) and sensing properties were systematically studied. It is interesting that anomalous temperature- dependent UCL behavior is observed. With increasing temperature (303-573 K), the UCL intensity of Er³⁺ does not quench monotonously but reaches a minimum around 483 K and then increases. However, it was found that the UCL spectra change in a different way with decreasing temperature (573-303 K) from the one measured with increasing temperature. The fluorescence intensity ratio of ²H₁₁/₂ --> ⁴I₁₅/₂ to ⁴S₃/₂ --> ⁴I₁₅/₂ at any measured temperature point remains almost constant in all measurement processes, indicating the consistency of temperature in each spectrum measurement at all temperature points regardless of the heating or the cooling process in our experiments. The results demonstrate that NaYF₄:Yb³⁺/Er³⁺ UC nanocrystal has good sensing stability and may have potential application in the nanoscale thermal sensor.
Tm³⁺/Yb³⁺ codoped NaY(WO₄)₂ microstructures with various Tm³⁺ concentrations and 10 mol% Yb³⁺ concentration were prepared by a microwave-assisted hydrothermal method, and their upconversion luminescence (UCL) was investigated. Under excitation at 980 nm, Tm³⁺/Yb³⁺ codoped NaY(WO₄)₂ exhibited strong blue and near infrared (NIR) emissions, respectively, corresponding to ¹G₄ --> ³H₆ and ³H₄ --> ³H₆ transitions, with weak red emission due to the ¹G₄ --> ³H₄ transition. The optimum doping concentrations of Tm³⁺ for the highest blue and NIR UCL were investigated, and it was found that the optimal concentrations for blue and NIR emissions were 0.5 mol% and 1.5 mol%, respectively. In addition, an analysis of temperature dependent blue and NIR UCL in both the samples with low and high Tm³⁺ concentrations, respectively, was undertaken. The results implied that the sample with low Tm³⁺ concentration displayed more obvious effect on the thermal quenching of ¹G₄ level.
Graphene‐based electromagnetic absorbing materials have attracted growing attention, due to their great absorption efficiency and light weight. One common design principle is to load magnetic particles onto graphene. However, the agglomeration of magnetic nanoparticles on the graphene sheets limits further improvement in their electromagnetic absorption performances. In this work, polyaniline/nano‐Fe3O4/graphene ternary hybrids with regulated multi‐interfaces are designed by simply adjusting the adding order of graphene. The dispersion of nano‐Fe3O4 on graphene and the interactions among the ternary interfaces are synchronously controlled, which are considered to be the key factors restricting the hybrids’ performances. The polyaniline/nano‐Fe3O4/graphene ternary composites show ultra‐broadband electromagnetic absorption, with the optimal reflection loss peak reaching −57.2 dB at 11.4 GHz, and the effective bandwidth achieves 13.2 GHz, covering 4.8–18 GHz. It is found that the well dispersion of nano‐Fe3O4 can enhance the overall ferromagnetism and magnetic losses, while the modulation of the multi‐interfaces can further ameliorate the interfacial and dipole polarization, synergistically making the ultra‐broadband electromagnetic absorption. This work provides areferencing path for the design of subsequent multi‐interfacing electromagnetic absorbing materials.
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