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Conventional photocatalysts must be activated by ultraviolet or visible light to meet the energy requirement of populating an initial excited state, while infrared light has a high penetration depth to reaction media but does not have enough photon energy to activate conventional photocatalysts. Here, we report the activation of Ag nanoparticles by upconversion nanoparticles (UCNPs) in UCNPs@SiO2@Ag with manipulated energy transfer for infrared photocatalysis. UCNPs can efficiently convert infrared light to visible and ultraviolet light and are very ideal candidates for bridging the advantage of infrared light and the activation energy requirement of conventional photocatalysts. In the UCNPs@SiO2@Ag nanosystem, we employ the UCNPs to activate conventional Ag nanoparticles under infrared light irradiation. The evanescent field of UCNPs is confined for enhancing the near-field energy-transfer efficiency using a designed core/shell heterostructure, while a SiO2 layer is used for blocking the phonon exchange of thermal vibration between photon upconverters and Ag nanoparticles. Based on the manipulated energy transfer, UCNPs@SiO2@Ag nanoparticles exhibit efficient photocatalytic activity under the irradiation of 980 nm infrared light, while single Ag nanoparticles have negligible catalytic activity under infrared irradiation.

Mesoporous materials have found a great number of important utilities due to their well-defined pore structure and high internal surface area, which are routinely synthesized with the assistance of block copolymers or templates. So far, a key challenge is how to assemble directly ligand-free inorganic nanocrystals into mesoporous structures, so that the high surface activity of ligand-free nanocrystals is not destroyed by further treatment to remove organic species or templates. In this paper, we report the direct assembly of highly uniform ZnO mesoporous ellipsoids from ligand-free ZnO nanocrystals of ∼5 nm. The size of the synthesized uniform ZnO mesoporous ellipsoids can be efficiently tuned from 132 × 75 to 190 × 111 nm (length × width), by varying the size and concentration of primary ZnO nanocrystal building blocks and the composition of the designed assembling solvent. The BET detection indicates that these ZnO mesoporous ellipsoids have high specific surface areas reaching to 136.57 m(2)/g, while their average BJH pore diameters are located at 8.8 nm. Especially, the high-resolution TEM images and XRD analysis revealed the occurrence of an oriented attachment mechanism in the assembly of uniform ZnO mesoporous ellipsoids, which supplied an important proof for the possibility of constructing stable three-dimensional structures by oriented attachment. The benefits of these ZnO mesoporous ellipsoids were demonstrated by their excellent photocatalytic activity under weak UV irradiation.

Here, we report upconversion nanoparticles with a core/porous-shell structure in which bulk emission and nanoemission are simultaneously observed. The activated porous shell can efficiently tune the bulk emission but has negligible influence on the nanoemission.