In situ confinement of perovskite nanocrystals for efficient blue light-emitting LEDs

 

Metal halide perovskites have emerged as promising semiconductor materials for the fabrication of next-generation light-emitting diodes (LEDs) owing to their outstanding luminescent properties, tunable band gaps, high color purity, and low-cost fabrication processes. Perovskite LEDs (PeLEDs) have undergone rapid development, achieving external quantum efficiencies exceeding 30% for green and red emissions. 

However, for blue light emitters, the performance of PeLEDs has not yet matched that of organic LEDs (OLEDs) or metal chalcogenide quantum-dot LEDs (QD-LEDs). Blue PeLEDs still lag behind in terms of efficiency, operational lifetime, or both. Improving the performance of blue PeLEDs requires perovskite materials with both high crystallinity and nanoscale grain sizes.

High crystallinity with a low defect density suppresses non-radiative recombination losses and material degradation, whereas small grains enhance radiative efficiency through charge confinement and limited carrier diffusion. However, simultaneously achieving highly crystalline and nanoscale-confined perovskite nanocrystals via in situ synthesis on substrates remains a major challenge.

Researchers from China and the Netherlands have developed a simple in situ polymerization strategy to produce highly crystalline and size-confined Cs₀.₇EA₀.₃PbBr₃ perovskite nanocrystals (EA = ethylamine). The polymer network formed in situ from oligo(ethylene glycol) methyl ether acrylate (OEGA) dynamically restricts the excessive growth of nanocrystals during crystallization, reducing their size from more than 250 nm to 11 nm while achieving a high photoluminescence quantum yield of 83%.

Owing to its strong coordination affinity, OEGA interacts effectively with the perovskite precursors, moderating the rapid initial growth of perovskite seeds and thereby improving crystallinity. The fully confined nanocrystals exhibit a cubic phase at room temperature with reduced octahedral distortions, substantially mitigating non-radiative losses caused by electron-phonon coupling. Consequently, the resulting blue PeLEDs achieve an external quantum efficiency of 21.8% at 491 nm, placing them among the best-performing blue PeLEDs reported to date.

This work demonstrates a viable in situ nanocrystal confinement strategy that provides deeper insight into the role of ligand engineering in perovskite nanocrystal synthesis, thereby advancing the development of efficient blue PeLEDs and related optoelectronic technologies.

For further information go to Nature 

Synthesis of 2D diamonds

 

Diamond is renowned for its exceptional hardness, high thermal conductivity, and low chemical reactivity. However, it exhibits low fracture toughness and poor electrical conductivity compared with many metallic materials and nonmetallic inorganic solids. For decades, it has been theorized that two-dimensional (2D) diamond may exhibit enhanced properties relative to bulk diamond because of its two-dimensional nature, including greater mechanical strength, extraordinary carrier mobility, and a tunable band gap.

Researchers from institutions in China successfully synthesized high-quality two-dimensional diamonds by heating graphene layers with a near-infrared (NIR) laser. They employed a high-pressure, high-temperature (HPHT) process to irreversibly transform graphene layers into 2D diamond. A polished rhenium (Re) metal foil was used as both the substrate and the laser-energy absorber to facilitate the heating process. The researchers succeeded in synthesizing 2D diamonds with thicknesses ranging from the equivalent of a graphene bilayer (~1 nm) to several hundred nanometers.

The 2D diamonds were characterized by Raman spectroscopy, whose spectra exhibited a well-defined characteristic peak at 1332 cm⁻¹ with a full width at half maximum (FWHM) of approximately 3.6 cm⁻¹, indicating their high crystalline quality. Photoluminescence measurements demonstrated that these diamonds are excellent candidates for quantum computing and sensing applications. 

Furthermore, the researchers found that the band gap can be tuned within the range of 1.4 to 1.9 eV, depending on the proportion of sp³ species in the sample, which varied from 71.3% to 89.9%. Finally, they found that the diamonds remain stable at temperatures above 1000 °C.

This study demonstrates the successful synthesis of 2D diamond and reveals properties that differ from those of bulk (3D) diamond. The results indicate that 2D diamonds possess significant potential for applications in nanoelectronics and optoelectronics.

For further information go to nature communications

Competitive reactivities determine the size and composition of multimetallic nanocrystals

 

Multimetallic nanocrystals (NCs) have attracted considerable attention due to their physical, chemical, and catalytic properties, which often surpass those of their monometallic counterparts. The distinctive properties of NCs are determined by the synergistic interactions among their constituent metals.

Synthesizing these materials with precise control over size and composition remains a major challenge because of the differences in the reactivities of the metal precursors. Owing to these differences, one would expect that increasing the number of metal precursors would enhance the formation of heterogeneous products (mixtures of particles with different sizes and compositions).

However, a multinational team of researchers demonstrated a counterintuitive effect in the synthesis of multimetallic nanocrystals: differences in the reactivities of metal precursors can actually promote the formation of highly uniform multimetallic nanocrystals.

Ru nanoparticles (≈ 4.5 nm) and precursor solutions of Fe, Co, Ni, and Cu were used as seeds. Upon introducing five metals (RuFeCoNiCu), a uniform product was obtained: pentametallic nanocrystals of ≈ 14.1 ± 1.4 nm with a narrow size distribution. This effect persisted even when the seed size, precursor ratios, and additional metals (Cr, In) were varied.

The mechanism underlying this remarkable process was elucidated through time-lapse analysis of intermediate products and tomography. As shown in the Figure, the formation of pentametallic nanocrystals proceeded through three distinct stages: (i) predominant reduction of Cu on previously formed Ru seeds, (ii) onset of Co, Ni, and Fe reduction accompanied by partial surface-layer formation, and (iii) complete reduction and integration of all constituent metals into fully formed RuFeCoNiCu nanocrystals.

When the pentametallic nanocrystals supported on Al2O3 were used as catalysts, they exhibited a reaction rate more than four times higher than that of monometallic Ru in ammonia decomposition (NH3 → N2 + 3H2), while maintaining comparable activation energy and thermal stability.

This work proposes a new principle for the design of complex multimetallic nanocrystals: rather than suppressing the competition among metal precursor reactivities, it can be harnessed. This finding leads the way toward libraries of nanomaterials with unique synergistic properties for applications such as catalysis and sustainable energy technologies.

For further information go to: Science

Self-assembled DNA micelles with Gold Nanoparticles for the Detection of miRNAs Associated with Alzheimer’s Disease

 

Alzheimer’s disease is a progressive neurodegenerative disorder that represents one of the greatest challenges in modern medicine. The disease is characterized by the abnormal accumulation of beta-amyloid (Aβ) plaques and tau protein in the brain, leading to inflammation, neuronal damage, and cognitive decline. One of the major challenges is that clinical symptoms typically emerge only after the brain is substantially damaged, thereby limiting the effectiveness of current treatments. Consequently, early detection has become a primary objective.

A research group in China developed an innovative strategy based on lateral flow assays (LFAs), a diagnostic tool for the sensitive, specific, and accessible detection of biomarkers, with the aim of identifying microRNA (miRNA) strands associated with the early stages of Alzheimer’s disease. miRNAs are small non-coding RNA molecules that regulate gene expression by binding to specific messenger RNAs and inhibiting their translation or promoting their degradation.

The proposed method employs DNA micelles functionalized with

gold nanoparticles (AuNPs) and equipped with miRNA strands.

A key feature of this approach is the use of self-assembled DNA micelles, namely nanostructures that spontaneously organize into spherical aggregates in aqueous solution. The DNA micelles were functionalized with gold nanoparticles (AuNPs) and mixed with strands of the target miRNA. When the sample is applied to the LFA test strip, the DNA–AuNP–miRNA complex migrates by capillary action toward the test line, where it is captured by a second probe containing a sequence complementary to the target miRNA and immobilized by a biotin/streptavidin interaction. The accumulation of AuNPs on the test strip produces a visible red band due to their plasmonic properties, with an intensity proportional to the concentration of miRNA present in the sample.

Since target miRNAs coexist with other miRNA species in real samples, it is essential for the system to exhibit high specificity toward the targets of interest. To evaluate this, the authors assessed cross-reactivity against other miRNAs and observed that no signal was produced at the test lines in the presence of interfering species. Red bands appeared only when the corresponding target miRNA (miR-34a, miR-125b, or miR-15a) was present.

Overall, the results demonstrate that the LFA enables the simultaneous detection of multiple miRNAs in serum with greater sensitivity and selectivity than conventional assays. This performance is attributed to the use of nanostructures that function as highly efficient recognition platforms capable of amplifying signals that would otherwise remain undetectable.

For further details, consult: Biosensors and bioelectronics

An ultra-sound scanning in vivo light source

 

Advances concerning the interaction of technological devices with biological tissues still face significant limitations. In many cases, researchers must choose between achieving high spatiotemporal imaging resolution and using flexible systems capable of investigating multiple regions of the body. While implantable devices provide cellular-level precision, they are invasive and restricted to highly localized sites, making them ill-suited for investigation of dynamic or spatially distributed biological processes.

In this work, researchers at Stanford University developed a material capable of emitting light within tissues using focused ultrasound. To achieve this, they synthesized biocompatible mechanoluminescent nanotransducers (MLNTs), composed of Sr₄Al₁₄O₂₅:Eu,Dy, derived from bulk material. The surface of the nanoparticles was functionalized with polyethylene glycol (PEG), forming a stable colloidal dispersion in an aqueous medium. These particles exhibited sizes ranging from 30 to 110 nm and stability of up to one week, retaining the same diffraction patterns and emission spectra as the bulk material.

Experimental validation was carried out in mice injected with MLNTs and stimulated with focused ultrasound. As a demonstration, the researchers were able to observe the three-dimensional distribution of different regions in the brains of living animals. Ultrasound, which can penetrate tissues and can be precisely focused, is thus confirmed as a powerful non-invasive tool for studying biological processes.

The authors propose that light emission originates when ultrasound induces mechanical deformations that activate energy traps in the material. This process involves electric fields generated by the movement of dislocations associated with intergranular sliding. The hypothesis is consistent with the observed proportional relationship between the intensity of emitted light and ultrasonic pressure. They additionally observed that by increasing the ultrasound frequency, the luminous spot decreased in size, allowing the light emission to be tuned in a manner analogous to optical focusing with lenses.

The ability to generate light within biological tissues in a controlled spatiotemporal manner opens applications in gene editing, photodynamic therapy, deep-tissue imaging, and drug delivery, laying the groundwork for new reconfigurable light-based biotechnologies.

For further information, consult: Nature Materials

Grain boundary stabilization of ultrathin ferroelectric ZrO₂ films

 

Grain boundaries (GBs) are ubiquitous topological defects in polycrystalline materials that play a crucial role in determining their macroscopic properties, such as mechanical strength, radiation tolerance, and thermal conductivity. For example, dense networks of GBs hinder dislocation motion, thereby hardening and strengthening nanostructured metals and superhard materials.

Defect engineering and microstructural modification have traditionally treated GBs simply as auxiliary elements for tuning material properties. However, recent studies suggest that GBs not only act as secondary regulators but also as independent heterointerfaces capable of stabilizing grain phase structures and inducing emergent functionalities.

The possibility of controlling crystalline phases through GB manipulation gained relevance with the discovery of ferroelectricity in nanocrystalline fluorite-based films of HfO₂ and ZrO₂, where ferroelectricity arises in a metastable, non-centrosymmetric orthorhombic (O) phase. However, the role of GBs in stabilizing the O-phase at the nanoscale has been scarcely explored, partly due to the difficulty of accurately determining their atomic-scale structure and chemical composition.

A group of researchers in China succeeded in growing, by chemical methods, an ordered La(Sr)–Mn–O superstructure exclusively at the GBs of ultrathin polycrystalline ZrO₂ films (with thicknesses below 5 nm), which stabilizes the metastable ferroelectric O-phase. The atomic configurations of the La(Sr)–Mn–O superstructure and its ordered growth were identified using atomic-resolution imaging and electron energy loss spectroscopy (EELS). Charge distribution and Mn–O electronic interactions were confirmed using four-dimensional scanning transmission electron microscopy (4D-STEM). First-principles calculations demonstrate an ordered arrangement of the eg/t2g orbitals of Mn³⁺/Mn⁴⁺ ions along the GBs. This arrangement induces alternating interactions with oxygen ions, periodically modulating the strength of Zr–O bonds and ultimately stabilizing the ferroelectric state on both sides of the GBs.

These findings propose a stabilization mechanism for metastable polar phases through a novel grain boundary chemistry, opening pathways toward ultra-stable nanoelectronics.

For further information go to: Nature Materials

Practical lithium–organic batteries enabled by an n-type conducting polymer

 

Currently, the widespread use of portable electronic devices demands batteries with higher storage capacities and longer lifetimes. Among the various options available on the market, lithium-ion batteries (LIBs) stand out due to their high energy storage capacity and long service life. However, these devices are typically composed of inorganic materials derived from limited mineral resources, which leads to negative environmental impacts. For this reason, research efforts have been directed toward finding more sustainable and environmentally friendly alternatives.

Scientists from several Chinese universities have developed organic lithium batteries using an n-type conductive polymer, poly(benzodifurandione) (PBFDO). PBFDO exhibits excellent ionic and electronic transport properties, high electrical conductivity (>2000 S/cm), low solubility in liquid electrolytes, and thermal structural stability up to 200 °C. The researchers constructed polymer cathodes with an ultrahigh mass loading of up to 206 mg/cm², achieving a specific capacity of 42 mAh/cm². In addition, 2.5 Ah lithium-organic pouch cells were fabricated with an energy density of 255 Wh/kg, comparable to that of commercial lithium-ion batteries.

The results reveal π–π stacking of the (010) planes with interplanar distances of 0.34 nm and lamellar stacking of the (100) planes with interplanar distances of 1.04 nm. Within these stacked structures, channels containing a large number of carbonyl groups are formed, which are attributed to enabling efficient lithium transport. These cells demonstrated strong cycling stability, resistance to nail penetration without explosion or fire, and efficient performance across an extreme temperature range (−70 °C to 80 °C). The flexibility of the PBFDO cathodes was also highlighted, making them suitable for applications in portable electronics. Furthermore, the energy storage mechanism of PBFDO was investigated, showing that carbonyl groups act as active sites for lithium-ion storage.

This work opens the door to the use of n-type conductive polymers as electrodes in LIBs, since the type of charge carriers (electrons) helps maintain charge balance when Li⁺ is inserted into the electrode, in contrast to p-type conductive polymers whose charge carriers (holes) make charge balance more difficult.

More information at: NATURE