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Yb 3+ and Er 3+ /Tm 3+ co-doped NaLuF 4 upconversion nanoparticles (UCNPs) with strong visible luminescence under the excitation of infrared light are successfully synthesized. The synthesized NaLuF 4 upconversion nanorystals have acidic ligand and can quickly capture the basic dyes to form UCNPs@dye nanosystem, in which the efficient luminescence resonance energy transfer (LRET) can be observed from UCNPs to dyes. We select NaLuF 4 :Yb 3+ /Er 3+ UCNPs as a model to detect Rhodamine B (RB) in plant cells. NaLuF 4 :Yb 3+ /Er 3+ UCNPs can emit green light at the wavelength of ∼545 nm while RB can efficiently absorb the green light of ∼545 nm to emit red light of 610 nm. As a result, the LRET process can occur in NaLuF 4 :Yb 3+ /Er 3+ @RB system. Based on the LRET process, an excitation power limit of 60 μW can be achieved in detecting traces of RB in plant cells. This LRET process is also used for detecting sodium fluorescein with the excitation power limit of 65 μW. [ABSTRACT FROM AUTHOR]

The objective of this paper was to assess the coupling effect of vacuum, pressure and temperature on microstructure and mechanical properties of PM aluminum alloy. The results showed that the densification of PM aluminum alloy mainly depended on the powder plastic deformation caused by hot pressing, but the state of particle boundary (PB) was affected by vacuum besides temperature and pressure. When the powder was sintered under high vacuum of 10−3 Pa, the oxide film at PB could be disrupted by pressure, resulting in the formation of narrow regions of metal/metal contact. While under low vacuum of 10−1 Pa, the oxide film coarsened by secondary oxidation was unable to be broken by powder compressing, resulting in residual microcracks and segregation of second phases at the PB. This seriously weakened mechanical properties of PM aluminum alloy. The eutectic liquid formed by increased temperature would make the above process more complex. • Vacuum affects microcrack and precipitates in hot-pressing sintered aluminum. • The low vacuum makes the oxide film unable to be disrupted by powder compressing. • Hot pressing and high vacuum are necessities for the metal/metal contact of aluminum. [ABSTRACT FROM AUTHOR]