Efficient Visible-to-UV Photon Upconversion Systems Based on CdS Nanocrystals Modified with Triplet Energy Mediators

Developing high-performance visible-to-UV photon upconversion systems based on triplet–triplet annihilation photon upconversion (TTA-UC) is highly desired, as it provides a potential approach for UV light-induced photosynthesis and photocatalysis. However, the quantum yield and spectral range of visible-to-UV TTA-UC based on nanocrystals (NCs) are still far from satisfactory. Here, three different sized CdS NCs are systematically investigated with triplet energy transfer to four mediators and four annihilators, thus substantially expanding the available materials for visible-to-UV TTA-UC. By improving the quality of CdS NCs, introducing the mediator via a direct mixing fashion, and matching the energy levels, a high TTA-UC quantum yield of 10.4% (out of a 50% maximum) is achieved in one case, which represents a record performance in TTA-UC based on NCs without doping. In another case, TTA-UC photons approaching 4 eV are observed, which is on par with the highest energies observed in optimized organic systems. Importantly, the in-depth investigation reveals that the direct mixing approach to introduce the mediator is a key factor that leads to close to unity efficiencies of triplet energy transfer, which ultimately governs the performance of NC-based TTA-UC systems. These findings provide guidelines for the design of high-performance TTA-UC systems toward solar energy harvesting.     

正电子湮没研究Al、Nb共掺CaCu3Ti4O12陶瓷高介电常数机理

关于CaCu₃Ti₄O₁₂陶瓷的高介电常数机理，目前广泛接受的是非本征的内阻挡层电容模型。该模型认为在多晶中元素变价、缺陷和非化学计量比等导致的半导化晶粒被绝缘晶界层，即内阻挡层所包围。其中内阻挡层的厚度对材料的介电性能影响较大，而扫描电子显微镜（SEM）测试表明样品晶界呈稀烂的果酱状，SEM难以测量晶界区域绝缘内阻挡层厚度。本文采用正电子湮没技术表征其厚度，通过对CaCu₃Ti₄O₁₂陶瓷共掺不同浓度的Al、Nb（CaCu₃Ti_4-xAl_0.5xNb_0.5xO₁₂，x=0.2%、0.5%、5.0%）改变其晶粒和晶界的微观结构，研究CaCu₃Ti₄O₁₂陶瓷高介电常数机理。正电子湮没结果显示，掺杂样品符合多普勒展宽谱S参数的变化趋势与平均寿命的变化趋势一致。x=0.5%掺杂样品的介电常数最高，其平均寿命、S参数和湮没长寿命成分均最小，阻挡层最薄。实验结果验证了描述CaCu₃Ti₄O₁₂陶瓷高介电常数机理的内阻挡层电容模型的预测。     

The microstructure and magnetic properties of Ca2+ ion doped GdCrO3

In this paper, the crystal structure, vacancy defect, local electron density and magnetic properties of Gd_1-xCa_xCrO₃ (0 ≤ x ≤ 0.3) polycrystalline samples were investigated systematically. The crystal structural analyses show that all the samples are orthorhombic phase and a structural distortion happens around x = 0.3. Due to the formation of Cr⁴⁺ ions, both the lattice constant and the Cr–O bond length decrease. The results of positron annihilation spectrum reveals that the vacancy defect concentration increases and the local electron structure changes with the introduction of Ca²⁺ ions. The field-cooled (FC) and zero-field cooled (ZFC) curves of Gd_1-xCa_xCrO₃ samples measured under H = 100 Oe exhibits negative magnetization characteristics due to the interaction between Gd³⁺ and Cr³⁺ ions, and the magnetism can be affected by the structural distortion.     

Photon Upconversion Hydrogels for 3D Optogenetics

The ability to optically induce biological responses in 3D has been dwarfed by the physical limitations of visible light penetration to trigger photochemical processes. However, many biological systems are relatively transparent to low-energy light, which does not provide sufficient energy to induce photochemistry in 3D. To overcome this challenge, hydrogels that are capable of converting red or near-IR (NIR) light into blue light within the cell-laden 3D scaffolds are developed. The upconverted light can then excite optically active proteins in cells to trigger a photochemical response. The hydrogels operate by triplet–triplet annihilation upconversion. As proof-of-principle, it is found that the hydrogels trigger an optogenetic response by red/NIR irradiation of HeLa cells that have been engineered to express the blue-light sensitive protein Cry2olig. While it is remarkable to photoinduce the clustering of Cry2olig with blanket NIR irradiation in 3D, it is also demonstrated how the hydrogels trigger clustering within a single cell with great specificity and spatiotemporal control. In principle, these hydrogels may allow for photochemical control of cell function within 3D scaffolds, which can lead to a wealth of fundamental studies and biochemical applications.     

Investigation of the interaction between hydrogen and irradiation defects in titanium by using positron annihilation spectroscopy

The formation of mono-vacancy, vacancy clusters and hydrogen-vacancy complexes with 30 keV H ion-irradiated pure titanium at different doses and temperatures was measured using by Positron annihilation spectroscopy (PAS). Results show a large number of H_mV_n clusters and vacancy-like defects in the samples irradiated at for room temperature, and that the formation of H_mV_n (m > n) at the sample irradiated at a high dose inhibits the increase of the S parameter. At increased irradiation temperature, the shrinkage of vacancy clusters and the effective open volume of defects decrease the S parameters. The high-temperature irradiation results in decreased vacancy-type defect concentration, and some hydrogen atoms diffuse from the cascade region to the track region, forming a large number of hydrogen-vacancy complexes in the track region. The coincidence Doppler broadening spectroscopy, an element analysis method, used to detect hydrogen in the ion-irradiated pure titanium sample, and results show hydrogen-related peaks in the high-momentum region, which may be due to the information of positron annihilation in the covalent bond formed by the H and the Ti elements. The increased radiation dose and temperature contribute to the formation of the hydrogen vacancy-complex, and the positron annihilation in high-momentum regions easily obtain hydrogen-related information.     

Sensitivity of positrons at hydrogen storage sites in FeCr alloy containing vacancy and helium atom

Here, the storage sites of hydrogen in FeCr alloy, namely (H, He)–V nano-clusters with open volume, have been investigated by first-principles calculations and positron annihilation spectroscopy. The positron lifetimes in the nano-clusters obtained by theoretical calculations and experiments were compared. These results suggest that positron is sensitive to the relative position of the gas atoms decorating the open volume; and a helium atom forms a more repulsive ion core than a hydrogen atom when it occupies the vacancy, resulting in a decrease in positron lifetime. Interpretation of the PAS data was successfully combined with theoretical calculations, and allowed us to determine the defect status in specimens after H/He irradiation with different implantation patterns. The speculated kinds of hydrogen storage sites formed after irradiation are summarized. For the He-ions pre-implanted situation, the helium-vacancy clusters or bubbles forming in advance may recombine with H atoms to form stable He–H–V complex.     

Structure and defects evolution at temperature and activation treatments of the TiCr2 intermetallic compound of Laves phase C36-type

In this work, microstructure and defect evolution at a temperature and activation treatment of the TiCr₂ intermetallic compound of Laves phase C36-type synthesized in the abnormal glow discharge plasma were investigated. The crystalline structure of the C36TiCr₂ powder crushed by hydrogenation-dehydrogenation (HD) method is characterized by the following lattice parameters: a = 4.932 Å and c = 16.059 Å. The dilatation of the crystal lattice under the hydrogenation at the HD crushing process leads to the formation of partial dislocations. For the first time ever the experimental value of the positron lifetime of the synthesized compound of the C36TiCr₂ Laves phase, this amounted to (141 ± 2) ps, established by the positron spectroscopy. The optimal activation parameters of the HD-crushing C36TiCr₂ powder were established: the temperature should be in the range from 450 to 500 °C, the exposure time in a hydrogen atmosphere at a pressure of (1–8) atm. must be at least 10 min.     

O/W型微乳液应用于三线态湮灭上转换介质研究

光子上转换是吸收低能量（长波长）的光发射高能量（短波长）光的过程,在太阳能光伏、光催化等领域具有潜在应用价值而受到广泛研究,然而通常介质采用有机溶剂及绝氧处理都大大限制了上转换的实际应用.本文报道了可用于三线态湮灭上转换过程的新介质-O/W型微乳液,该体系制备简单、无毒环保,无需除氧脱气条件下,上转化发光稳定,具有未来实际应用的潜力.     

A study on the characteristics and pervaporation performance of polyamide thin‐film composite membranes with modified polyacrylonitrile as substrate for bioethanol dehydration

To improve the pervaporation performance in separating an aqueous ethanol solution, polyamide thin‐film composite (TFC) membranes (m‐tolidine‐H‐TMC/mPAN) were prepared through the interfacial polymerization reaction between trimesoyl chloride (TMC) and 2,2'‐dimethylbenzidine hydrochloride (m‐tolidine‐H) on the surface of a modified polyacrylonitrile (mPAN) membrane. The effects of the feed ethanol concentration on the pervaporation performance and the durability of m‐tolidine‐H‐TMC/mPAN TFC membranes were investigated. To choose the optimal mPAN membrane as the TFC substrate, the effect of hydrolysis time on the chemical properties and separation performance of an mPAN substrate was also studied. An appropriate hydrolysis time of 15 min was chosen to obtain the mPAN substrate due to the corresponding high permeation flux. The m‐tolidine‐H‐TMC/mPAN TFC membrane exhibited a high pervaporation performance for ethanol dehydration. A positron annihilation lifetime spectroscopy experiment was used to estimate the mean free‐volume radius of the m‐tolidine‐H‐TMC polyamide selective layer, which lay between the radii of the water and ethanol molecules. © 2013 Society of Chemical Industry     

Realization of triplet–triplet annihilation in planar heterojunction exciplex-based organic light-emitting diodes

Triplet–triplet annihilation (TTA) for enhancement of luminous efficiency occurs with difficulty in exciplex-based organic light-emitting devices (OLEDs) because it is an interaction among several neighboring donor and acceptor molecules. However, TTA has been realized in our planar-heterojunction (PHJ) exciplex-based OLEDs by using a thin recombination zone to enhance the interfacial density of the triplet states. The TTA process, which is characterized by a high-field decrease (HFD) in the magneto-electroluminescence from the PHJ OLEDs, appears at approximately 150 K and becomes stronger with decreasing temperature. At a given temperature, the higher the injected current is, the stronger HFD is observed. Additionally, we find that TTA could even happens at room temperature with appropriate selection of the donor molecule, which may be attributed to the favorable electron-donating ability of the methoxy group (–OCH₃) in the donor molecule and the matched overlaps of the intermolecular conformation of the donor and the acceptor.