Yuansheng Wang

Hydrothermal Synthesis, Structural Characteristics, and Enhanced Photocatalysis of SnO2/α-Fe2O3 Semiconductor Nanoheterostructures

Branched SnO(2)/alpha-Fe(2)O(3) semiconductor nanoheterostructures (SNHs) of high purity were synthesized by a low-cost and environmentally friendly hydrothermal strategy, through crystallographic-oriented epitaxial growth of the SnO(2) nanorods onto the alpha-Fe(2)O(3) nanospindles and nanocubes, respectively. It was demonstrated that the SnO(2) nanorods would change their preferential growth direction on the varied alpha-Fe(2)O(3) precursors with distinct crystallographic surface, driven by decrease in the distortion energy induced by lattice mismatch at the interfaces. All of the prepared SNHs were of high purity, ascribing to the successful preinhibition of the SnO(2) homonucleation in the reaction system. Significantly, some of the SnO(2)/alpha-Fe(2)O(3) SNHs exhibited excellent visible light or UV photocatalytic abilities, remarkably superior to their alpha-Fe(2)O(3) precursors, mainly owing to the effective electron-hole separation at the SnO(2)/alpha-Fe(2)O(3) interfaces.

Modifying the size and shape of monodisperse bifunctional alkaline-earth fluoride nanocrystals through lanthanide doping.

In this communication, a simple route for modifying the uneven size and shape of alkaline-earth fluoride nanophases to monodisperse ultrasmall nanospheres through lanthanide doping is offered. These nanospheres are found to exhibit bifunctionality, i.e., tunable upconversion emissions as well as proper paramagnetism, making them potentially applicable in the biological field. The synthesis strategy, which involves doping of an impurity with a different valence than the cation in the nanophase, might be useful for controlling the solution growth of some technologically important nanomaterials.

Bright upconversion white light emission in transparent glass ceramic embedding Tm3+∕Er3+∕Yb3+:β-YF3 nanocrystals

Intense red (Er3+:F9∕24→I15∕24, Tm3+:G41→F43), green (Er3+:H11∕22, S3∕24→I15∕24), and blue (Tm3+:D21→F43, G41→H63) upconversion emissions were simultaneously generated in the transparent glass ceramics containing Tm3+∕Er3+∕Yb3+:β-YF3 nanocrystals under single 976nm laser excitation. It was demonstrated that Tm3+ behaves as the sensitizer for red luminescence of Er3+ and Er3+ as the quenching center for blue, red, and near-infrared upconversion emissions of Tm3+. Various colors of the luminescence, including perfect and bright white light with CIE-X=0.310 and CIE-Y=0.358, can be easily tuned by adjusting the concentrations of the rare earth ions in the material.

Near-infrared quantum cutting in transparent nanostructured glass ceramics

Quantum cutting downconversion involving the emission of two near-infrared photons for each blue photon absorbed is realized in transparent glass ceramics with embedded Pr3+/Yb3+: beta-YF3 nanocrystals. On excitation of Pr3+ ions with a visible photon at 482 nm, Yb3+ ions emit two near-infrared photons at 976 nm through an efficient cooperative energy transfer from Pr3+ to Yb3+, with optimal quantum efficiency close to 200%. The development of the near-infrared quantum cutting transparent glass ceramic could open a route to enhance the energy efficiency of the silicon solar cell by converting one blue solar photon to two near-infrared ones.

Quantum cutting downconversion by cooperative energy transfer from Ce3+ to Yb3+ in borate glasses

Quantum cutting downconversion (DC) involving the emission of two near-infrared (NIR) photons for each ultraviolet (UV) photon absorbed is realized in the Ce3+/Yb3+ codoped borated glasses. Upon excitation of Ce3+ ion with an UV photon at 330 nm, Yb3+ ions emit two NIR photons at 976 nm through an efficient excitation of Ce3+:5d and subsequent cooperative energy transfer (ET) from Ce3+:5d to Yb3+:F25/2. The maximum ET efficiency and the corresponding DC quantum efficiency were estimated to be 74% and 174%, respectively.

Intense ultraviolet upconversion luminescence from Tm3+/Yb3+: β-YF3 nanocrystals embedded glass ceramic

The infrared to ultraviolet upconversion emissions of Tm3+ I61→F43 (346nm) and D21→H63 (362nm) transitions, originating from the five- and four-photon upconversion processes, respectively, were observed in the Tm3+∕Yb3+ codoped precursor glass and glass ceramic containing β-YF3 nanocrystals. The ultraviolet luminescence of the glass ceramic is 30 times stronger than that of the precursor glass, which could be attributed to the decreased probability of the F23→F43 transition and the increased cross relaxation of F23+H43→H63+D21 resulted from the partition of rare earth ions into nanocrystals.

Ultra-broadband near-infrared excitable upconversion core/shell nanocrystals

Monodisperse Er(3+):NaGdF(4)@Ho(3+):NaGdF(4)@NaGdF(4) active-core/active-shell/inert-shell nanocrystals, which can extend the near-infrared wavelength excitable range for upconversion (UC) emissions, were successfully fabricated for the first time. Importantly, doping of Er(3+) and Ho(3+) into the core and shell respectively suppresses adverse energy transfers between them, resulting in intense UC emissions for both Er(3+) and Ho(3+) dopants.

Ultraviolet-blue to near-infrared downconversion of Nd(3+)-Yb(3+) couple.

To reduce energy losses by thermalization of charge carriers in a silicon solar cell, quantum-cutting luminescent materials are desired for the efficient downconversion of UV-visible radiation into near-IR radiation. In this Letter, quantum cutting involving emission of two near-IR photons for each UV-blue photon absorbed is demonstrated in Nd(3+)/Yb(3+):beta-YF(3) nanocrystals embedded in transparent bulk-glass ceramics. Upon excitation of an Nd(3+) ion with a UV-blue photon, Yb(3+) ions emit two near-IR photons through an efficient two-step energy transfer from Nd(3+) to Yb(3+) with Nd(3+):(4)F(3/2) acting as the intermediate state.

Near-infrared quantum cutting in Ho 3+ /Yb 3+ codoped nanostructured glass ceramic

A first-order quantum cutting luminescence of Ho3+/Yb3+ couples, which are incorporated in the YF3 nanocrystals embedded in transparent glass ceramic, is reported for the first time, to our knowledge. When Ho3+ is excited with one blue photon, it was experimentally demonstrated that the resonant energy transfer from Ho3+ to Yb3+ occurs, leading to the near-infrared quantum cutting with one Ho3+ photon emitting at 1180 nm and one Yb3+ photon at 980 nm. The theoretical quantum efficiency is evaluated to be 159%.

Lanthanide dopant-induced formation of uniform sub-10 nm active-core/active-shell nanocrystals with near-infrared to near-infrared dual-modal luminescence

We present a novel strategy involving the lanthanide dopant-induced formation of ultrasmall (sub-10 nm) uniform Ln3+:BaF2/Ln3+:SrF2 active-core/active-shell architectures. The lanthanide ions doped in the shell are demonstrated to play a key role to retard the growth of the core/shell nanocrystals. Particularly, adopting ∼3 nm Tm3+,Yb3+:BaF2 nanocrystals as cores prepared by a solvothermal reaction, growth of Gd3+,Nd3+:SrF2 shells is successfully induced on the surfaces of these cores through a thermal decomposition process, forming ∼7 nm highly uniform and monodisperse Tm3+,Yb3+:BaF2/Gd3+,Nd3+:SrF2 active-core/active-shell nanocubes. In this architecture, the Gd3+,Nd3+:SrF2 shell not only benefits the enhancement of the near-infrared to near-infrared upconversion luminescence of the Tm3+,Yb3+:BaF2 core, but also acts as the host to realize the near-infrared to near-infrared downconversion luminescence of Nd3+ dopants and the paramagnetism of Gd3+ ones. Importantly, the doping of Tm3+/Yb3+ and Nd3+ into the core and shell respectively effectively suppresses the adverse energy transfer from Tm3+ to Nd3+ as well as from Nd3+ to Yb3+, resulting in lessening of the quenching for both Tm3+ upconversion and Nd3+,Yb3+ downconversion emissions. These hydrophobic core/shell nanocrystals are further converted into hydrophilic ones using thioglycolic acid as the surface ligand. The sub-10 nm water-soluble active-core/active-shell architectures with near-infrared to near-infrared dual-modal luminescence and proper paramagnetism may find potential applications in biomedical imaging and detection.