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This work introduces new methods to characterize dispersions of small-diameter or low-mass-fraction nanoparticles (NPs) by single-particle inductively coupled plasma-mass spectrometry (SP ICP-MS). The optimization of ion extraction, ion transport, and the operation of the quadrupole with increased mass bandwidth improved the signal-to-noise ratios significantly and decreased the size detection limits for all NP dispersions investigated. As a model system, 10.9 ± 1.0 nm Au NPs were analyzed to demonstrate the effects of increasing ion transmission. Specifically, increasing the mass bandwidth of the quadrupole improved the size detection limit to 4.2 nm and enabled the resolution of NP signals from ionic background and noise. Subsequently, the methods were applied to the characterization of lanthanide-doped upconversion nanoparticles (UCNPs) by SP ICP-MS. Three different types of UCNPs (90 nm NaYF4: 20% Yb, 2% Er; 20 nm NaGdF4: 20% Yb, 1% Er; 15 nm NaYF4: 20% Yb, 2% Er) were investigated. Y showed the best signal-to-noise ratios with optimized ion extraction and transport parameters only, whereas the signal-to-noise ratios of Gd, Er, and Yb were further improved by increasing the mass bandwidth of a quadrupole mass filter. The novel methods were suitable for detailed characterization of diluted UCNP dispersions including particle stoichiometries and size distributions. A Poisson model was further applied to assess particle–particle interactions in the aqueous dispersions. The methods have considerable potential for the characterization of small-diameter and/or low-mass-fraction nanoparticles.

Due to the crucial implication of oil risks for economic growth and policy making, the aim of this paper is to explore the heterogeneous interconnections of supply or demand in oil risks over time horizons and different countries. Specifically, we first examine the correlation of supply or demand in oil return risks and show the relationships in different countries based on wavelet coherence. Furthermore, we explore the time-varying interconnections between supply- or demand-side and oil return risks, as well as oil producers and demand countries. The empirical results show that the correlation between supply and oil return risks is relatively stable, whereas the linkage between demand and oil return risks shows greater volatility due to the impact of specific events. Further study indicates that there are heterogeneous interconnections between supply- or demand-side and oil return risks over sample periods. Specifically, the sign of response could be divided into four phases, i.e., 1997–2002, 2002–2010, 2010–2013 and 2014–2018. In addition, the interconnections of the demand side could be divided into three phases due to the sign of it. What is more, the dynamic interconnections of oil producers’ or countries’ demands behave quite heterogeneously in different countries. Thus policymakers should focus on the coordination level and space capacity in the global crude oil market.

Lanthanide ion doped upconversion nanoparticles (UCNPs) hold great promise as multimodal contrast agents for a range of medical imaging techniques, including optical bioimaging (OBI), magnetic resonance imaging (MRI), and computed tomography (CT). However, it is challenging to obtain UCNPs with both maximal contrast enhancement effects for both OBI and MRI simultaneously owing to the dilemma in the size of UCNPs. UCNPs in large dimensions contain more photonic Ln ions and less surface defects, which is favored for high luminescent emissions, while small UCNPs with high specific surface areas allow a higher proportion of paramagnetic Ln ions to be more accessible to water molecules, which offers enhanced contrast in MRI. In this work, we report the novel design of core−porous shell UCNPs with both high luminescent emissions and magnetic relaxivities as potential dual-modal contrast agents. The core–porous shell UCNPs were fabricated via the selective etching of the inert shell of NaYF4: 30%Gd at the active core of NaYF4: 20%Yb, 1%Er. Their morphology and composition were carefully characterized using transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy, X-ray diffraction, and high resolution TEM. Their photoluminescent and magnetic resonance properties were experimentally determined and compared for the core, core–dense shell, and core–porous shell UCNPs. Core–porous shell UCNPs were found to display bright luminescence and superior MRI contrast enhancement, thus showing great potential as bimodal OBI and MRI contrast agents.

Integrating fluorescent nanoparticles with high-Q, small mode volume cavities is indispensable for nanophotonics and quantum technologies. To date, nanoparticles have largely been coupled to evanescent fields of cavity modes, which limits the strength of the interaction. Here, we developed both a cavity design and a fabrication method that enable efficient coupling between a fluorescent nanoparticle and a cavity optical mode. The design consists of a fishbone-shaped, one-dimensional photonic crystal cavity with a nano-pocket located at the electric field maximum of the fundamental optical mode. Furthermore, the presence of a nanoparticle inside the pocket reduces the mode volume substantially and induces subwavelength light confinement. Our approach opens exciting pathways to achieve strong light confinement around fluorescent nanoparticles for applications in energy, sensing, lasing and quantum technologies.