Novel Sol–Gel Nano‐Glass–Ceramics Comprising Ln3+‐Doped YF3 Nanocrystals: Structure and High Efficient UV Up‐Conversion

Transparent glass‐ceramics containing Ln³⁺‐doped YF₃ nanocrystals are successfully obtained under adequate thermal treatment of precursor sol–gel glasses for the first time, to the best of our knowledge. Precipitation of YF₃ nanocrystals is confirmed by X‐ray diffraction and high‐resolution transmission electron microscopy images. An exhaustive structural analysis is carried out using Eu³⁺ and Sm³⁺ as probe ions of the final local environment in the nano‐structured glass–ceramic. Noticeable changes in luminescence spectra, related to relative intensity and Stark structure of band components, along with remarkably different lifetime values, allow us to discern between ions residing in precipitated YF₃ nanocrystals and those remaining in a glassy environment. A large fraction of optically active ions is efficiently partitioned into nanocrystals of small size, around 11 nm. Moreover, bright and efficient up‐conversion, including very intense high‐energy emissions in the UV range, due to 4‐ and 5‐infrared photon processes, are achieved in Yb³⁺–Tm³⁺ co‐doped samples. Up‐conversion mechanisms are analysed in depth by means of intensity dependence on sensitiser Yb³⁺ concentration and pump power.     

Embedding Perovskite Nanocrystals into a Polymer Matrix for Tunable Luminescence Probes in Cell Imaging

Lead halide perovskite nanocrystals (NCs) with bright luminescence and broad spectral tunability are good candidates as smart probes for bioimaging, but suffer from hydrolysis even when exposed to atmosphere moisture. In this paper, a strategy is demonstrated by embedding CsPbX₃ (X = Cl, Br, I) NCs into microhemispheres (MHSs) of polystyrene matrix to prepare “water‐resistant” NCs@MHSs hybrids as multicolor multiplexed optical coding agents. First, a facile room‐temperature solution self‐assembly approach to highly luminescent colloidal CsPbX₃ NCs is developed by injecting a stock solution of CsX?PbX₂ in N ,N ‐dimethylformamide into dichloromethane. Polyvinyl pyrrolidone (PVP) is chosen as the capping ligand, which is physically adsorbed and wrapped on the surface of perovskite NCs to form a protective layer. The PVP protective layer not only leads to composition‐tunable CsPbX₃ NCs with high quantum yields and narrow emission linewidths of 12–34 nm but also acts as an interfacial layer, making perovskite NCs compatible with polystyrene polymers and facilitating the next step to embed CsPbX₃ NCs into polymer MHSs. CsPbX₃ NCs@MHSs are demonstrated as multicolor luminescence probes in live cells with high stability and nontoxicity. Using ten intensity levels and seven‐color NCs@MHSs that show non‐overlapping spectra, it will be possible to individually tag about ten million cells.     

Improved external quantum efficiency of solution-processed P3HT:60PCBM photodetectors by the addition of Cu–In–Se nanocrystals

Photodetectors comprising a hybrid organic–inorganic photoconversion layer are prepared from solution under ambient conditions. Adding Cu–In–Se nanocrystals to a P3HT/60PCBM bulk heterojunction leads to a significant improvement of the maximum external quantum efficiency from 48% to 70% (at wavelength 520 nm) without impacting the temporal response or the linearity of the photodetector devices. This gain in efficiency with the addition of nanocrystals is attributed to the better light harvesting properties of the hybrid devices.     

Fully Chiral Light Emission from CsPbX3 Perovskite Nanocrystals Enabled by Cholesteric Superstructure Stacks

Halide perovskites have received tremendous attention due to their fantastic optical and electrical properties. Here, circularly polarized light emission is successfully demonstrated using a simple configuration consisting of inorganic perovskite nanocrystals embedded within a predefined handedness cholesteric superstructure stack. The helical structured cholesteric liquid crystal film acts as a selective filter to transform the unpolarized light emission from perovskite nanocrystals into circularly polarized luminescence. The transformation is accompanied by an extraordinary dissymmetry factor (|g_lum|) up to 1.6, well‐defined handedness, high photoluminescence quantum yield, and full‐color availability. Furthermore, the circularly polarized luminescence is angular dependent and can easily be modulated by shifting the overlap of the reflection band and the emission band. The proposed method is more straightforward and powerful than the previous approaches, offering new opportunities in optoelectronic and photonic devices.     

Centimeter‐Sized Cs4PbBr6 Crystals with Embedded CsPbBr3 Nanocrystals Showing Superior Photoluminescence: Nonstoichiometry Induced Transformation and Light‐Emitting Applications

An HBr‐assisted slow cooling method is developed for the growth of centimeter‐sized Cs₄PbBr₆ crystals. The obtained crystals show strong green photoluminescence with absolute photoluminescence quantum yields up to 97%. More importantly, the evolution process and structural characterizations support that the nonstoichiometry of initial Cs₄PbBr₆ crystals induce the formation of nanosized CsPbBr₃ nanocrystals in crystalline Cs₄PbBr₆ matrices. Furthermore, high efficiency and wide color gamut prototype white light‐emitting diode devices are also demonstrated by combining the highly luminescent Cs₄PbBr₆ crystals as green emitters and commercial K₂SiF₆:Mn⁴⁺ phosphor as red emitters with blue emitting GaN chips. The optimized devices generate high‐quality white light with luminous efficiency of ≈151 lm W⁻¹ and color gamut of 90.6% Rec. 2020 at 20 mA, which is much better than that based on conventional perovskite nanocrystals. The combination of improved efficiency and better stability with comparable color quality provides an alternative choice for liquid crystal display backlights.     

Improved performance of Ge‐alloyed CZTGeSSe thin‐film solar cells through control of elemental losses

Nanocrystal‐based Cu₂Zn(Sn_yGe_1‐y)(S_xSe_4‐x) (CZTGeSSe) thin‐film solar cell absorbers with tunable band gap have been prepared. Maximum solar‐conversion total area efficiencies of up to 9.4% are achieved with a Ge content of 30 at.%. Improved performance compared with similarly processed films of Cu₂ZnSn(S_xSe_4‐x) (CZTSSe, 8.4% efficiency) is achieved through controlling Ge loss from the bulk of the absorber film during the high‐temperature selenization treatment, although some Ge loss from the absorber surface is still observed following this step. Despite limitations imposed by elemental losses present at the absorber surface, we find that Ge alloying leads to enhanced performance due to increased minority charge carrier lifetimes as well as reduced voltage‐dependent charge carrier collection. Copyright © 2013 John Wiley & Sons, Ltd.     

Photocrosslinkable Zwitterionic Ligands for Perovskite Nanocrystals: Self-Assembly and High-Resolution Direct Patterning

Perovskite nanocrystals (PNCs) are attractive photoactive materials in various optoelectronic devices including light-emitting diodes, solar cells, and photodetectors. However, the weakly bound surface ligands on PNCs reduce colloidal stability and cause film formation and patterning difficulties, severely restricting their practical applications. Herein, a rationally designed photocrosslinkable zwitterionic (PZ) ligand is introduced to obtain directly patternable CsPbBr₃ PNCs with enhanced colloidal stability, optical properties, and self-assembly propensity. The PZ ligands strongly interact with the pre-synthesized PNCs in solution, substantially replacing the original capping ligands and effectively passivating surface defects. This surface engineering induces strong electrostatic interactions between the PNCs, enabling the fabrication of densely packed CsPbBr₃ PNC films. Furthermore, the methacrylate group of the PZ ligands serves as a bridge for active radical propagation in the ligand shells around the PNCs upon UV exposure. Accordingly, high-resolution direct photopatterning can be achieved through ligand crosslinking, and the resulting PNC patterns (minimum line spacing of 4 µm) maintain optical stability for over 2 weeks. Therefore, this study demonstrates that a tailored ligand design strategy enables the simultaneous achievement of high colloidal stability, optical properties, photopatternability, and self-assembly propensity and has considerable potential to be extended to other PNC materials.     

Metal Nanocrystal‐Embedded Hollow Mesoporous TiO2 and ZrO2 Microspheres Prepared with Polystyrene Nanospheres as Carriers and Templates

Noble metal nanocrystals with different shapes and compositions are embedded in hollow mesoporous metal oxide microspheres through an ultrasonic aerosol spray. Polystyrene (PS) nanospheres are employed simultaneously as a hard template to create hollow interiors inside the oxide microspheres and as the carrier to bring pregrown metal nanocrystals, including Pd nanocubes, Au nanorods, and Au core/Pd shell nanorods, into the oxide microspheres. Calcination removes the PS template and causes the metal nanocrystals to adsorb on the inner surface of the hollow oxide microspheres. The catalytic performances of the Pd nanocube‐embedded TiO₂ and ZrO₂ microspheres are investigated using the reduction of 4‐nitrophenol as a model reaction. The presence of the mesopores in the oxide microspheres allows the reactant molecules to diffuse into the hollow interiors and subsequently interact with the Pd nanocubes. The embedding of the metal nanocrystals in the hollow oxide microspheres prevents the aggregation of the metal nanocrystals and reduces the loss of the catalyst during recycling. The Pd nanocube‐embedded ZrO₂ microspheres are found to exhibit a much higher catalytic activity, a much larger catalytic reaction rate, and a superior recyclability in comparison with a commercial Pd/C catalyst. This preparation approach could potentially be utilized to incorporate various types of mono‐ and multimetallic nanocrystals with different sizes, shapes, and compositions into hollow mesoporous oxide microspheres. Such a capability can facilitate the studies of the catalytic properties of various combinations of metal nanocrystals and metal oxide supports and therefore guide the design and creation of high‐performance catalysts.     

321/Qd370qD爆炸焊接基板侧界面组织特征

利用透射电子显微镜研究了321/Qd370q D爆炸焊接界面附近基板内的组织和前漩涡组织。结果表明,界面附近存在大量的非晶相、纳米晶,在距界面一定距离基板内也存在大量的纳米晶,在基板内存在调幅分解组织。前漩涡内存在片状孪晶马氏体和面心立方的M23C6相。