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Upconversion core–shell nanoparticles have attracted a large amount of attention due to their multifunctionality and specific applications. In this work, based on a NaGdF4 sub-10 nm ultrasmall nanocore, a series of core–shell upconversion nanoparticles with uniform size doped with Yb3+, Er3+ and NaDyF4 shells with different thicknesses were synthesized by a facile sequential growth process. NaDyF4 coated upconversion luminescent nanoparticles showed an obvious fluorescence quenching under excitation at 980 nm as a result of energy resonance transfer between Yb3+, Er3+ and Dy3+. NaGdF4:Yb,Er@NaDyF4 core–shell nanoparticles with ultrathin layer shells exhibited a better T1-weighted MR contrast.

Ultrathin KMnF 3 nanowires with several nanometers in diameter have been synthesized successfully by a high temperature organic solution method for the first time. The morphologies and size of the as-prepared products were investigated by X-ray diffraction (XRD), transmission electron microscopy (TEM) and X-ray photoelectron spectra (XPS), respectively. Ultrathin KMnF 3 nanowires and nanoparticles can be selectively synthesized by adjusting the amount of oleylamine. Moreover, the magnetic properties have been investigated using a vibrating sample magnetometer (VSM). Magnetic hysteresis loops revealed that the as-prepared KMnF 3 nanowires exhibit stronger paramagnetic performance than that of as-prepared nanoparticles.

It is a significant challenge to develop nanoscale magnetic resonance imaging (MRI) contrast agents with high performance of relaxation. In this work, Gd3+-doped CaF2-based core–shell nanoparticles (CaF2:Yb,Er@CaF2:Gd) of sub-10 nm size were controllably synthesized by a facile sequential growth method. The as-prepared hydrophilic CaF2:Yb,Er@CaF2:Gd nanoparticles modified using PEG-PAA di-block copolymer benefited from the presence of Gd only in the outer CaF2 layer of the nanoparticles, which exhibited r1 as high as 21.86 mM−1 s−1 under 3.0 T, seven times as high as that of commercially used gadopentetate dimeglumine (Gd-DTPA). Low cytotoxicity, no hemolysis phenomenon and no potential gadolinium ion leakage phenomenon of the hydrophilic CaF2:Yb,Er@CaF2:Gd nanoparticles have been observed and confirmed. Clear vascular details can be observed in magnetic resonance angiography and obvious MR signal of 4T1 tumor area could be significantly improved by intravenous injection of the hydrophilic CaF2:Yb,Er@CaF2:Gd nanoparticles at a low dosage in mice. A series of in vivo biological safety evaluations confirmed the good biocompatibility of the hydrophilic CaF2:Yb,Er@CaF2:Gd nanoparticles, which might be employed in clinical blood pool imaging and tumor diagnosis as a safe and efficient MRI probe.

Monodisperse sub-10 nm core–shell nanocrystals have been extensively studied owing to their important applications in catalysis, bioimaging, nanomedicine, and so on. In this work, an amorphous shell component crystallization strategy has been proposed to prepare high quality sub-10 nm NaYF4:Yb/Er@NaGdF4 core–shell nanocrystals successfully via a sequential growth process. The dynamic light scattering technique has been used to investigate the secondary nucleation and growth process forming the core–shell nanocrystals. The size and morphology evolution of the core–shell nanocrystals reveals that the secondary nucleation of the shell component is unavoidable after hot-injecting the shell precursor at high temperatures, which was followed by dissolution and recrystallization (an Ostwald ripening process) to partially produce the core–shell nanocrystals. The present study demonstrates that the size of seed nanocrystals and the injection temperature of the shell component precursor play a vital role in the for...

Upconversion nanoparticles/semiconductor nanocomposites have received intense interest in the past two decades. In this work, we demonstrated a facile electrospinning technique and a hydrothermal-assisted crystallization process to fabricate upconversion nanoparticles (UCNPs)/CdS/TiO2 nanofibers successfully. Polyvinylpyrrolidone (PVP, Mw ≈ 1 300 000) has been selected as the polymer matrix and tetrabutyl titanate (TBT, 99.0%) was used as the titanium source. The morphologies and phase of the as-prepared samples have been studied using field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD). Experimental results revealed that the polymer matrix (PVP) can be dissolved and removed completely under hydrothermal conditions. In addition, the crystalline phase of TiO2 was also achieved under hydrothermal conditions. The as-prepared composite nanofibers are hundreds of micrometers in length and 650 nm in diameter and show weak upconversion fluorescence under the excitation of near-infrared light (980 nm), indicating the high energy transfer efficiency between upconversion nanoparticles and semiconductors. As expected, the UCNPs/CdS/TiO2 nanofibers may have enhanced photocatalytic performance as they make full use of solar energy using UCNPs as nanotransducers for infrared (IR) light.