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Localized electric filed enhancement by surface plasmon resonance (SPR) of noble metal nanoparticles is an effective method to amplify the upconversion luminescence (UCL) strength of upconversion nanoparticles (UCNPs), whereas the highly effective UCL enhancement of UCNPs in colloids has not been realized until now. Here, we designed and fabricated the colloidal Au-Ag nanocage@NaYF4@NaYF4:Yb,Er core-shell hybrid with different intermediate thickness (NaYF4) and tunable SPR peaks from visible wavelength region to NIR region. After the optimization of the intermediate spacer thickness (~7.5 nm) of NaYF4 NPs and the SPR peak (~950 nm) of noble metal nanoparticles, an optimum enhancement as high as ~25 folds was obtained. Systematic investigation indicates that UCL enhancement mainly originates from the influence of the intermediate spacer and the coupling of Au-Ag nanocages with the excitation electromagnetic field of the UCNPs. Our findings may provide a new thinking on designing highly effective metal@UCNPs core-shell hybrid in colloids. [ABSTRACT FROM AUTHOR]

The corrosion behaviors of 13Cr martensitic steel under different CO 2 partial pressures (4-28 MPa) were investigated by weight loss tests and surface characterizations. The results show that the corrosion rate of 13Cr steel shows a sharp increase under higher CO 2 pressure (28 MPa), which reached approximately 20-180 times as large as those under lower CO 2 pressures (4-12 MPa). Under the lower CO 2 pressures, a single-layered Cr(OH) 3 passive film forms and completely covers the steel surface. However, when the CO 2 pressure reaches 28 MPa, a very different corrosion film which contains an inner Cr(OH) 3 passive layer and an outer FeCO 3 layer forms, and the inner passive layer shows local damage. This phenomenon can be explained by the lower pH (∼2.75) and the higher H 2 CO 3 concentration in the solution under the higher CO 2 pressure., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)