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Surface ligation stage revealed through polarity-dependent fluorescence during perovskite nanocrystal growth
摘要： Methylammonium lead iodide perovskite (MAPbI3) nanocrystals (NCs) exhibit favorable photophysics for a range of light emitting applications. A comprehensive mechanistic understanding of the nucleation and growth processes for these NCs is still elusive. Absorbance and fluorescence spectra were measured during a NC synthesis with kinetics limited by precursor solvation using a rapid sampling technique wherein syringe filters quench NC growth. The signal from well-capped NCs in the reaction mixture was isolated by the use of polar syringe filters, enabling spectroscopic observation of the surface ligation process. Our results indicate that the formation of these NCs involves a single stage of nucleation and growth, followed by a terminal surface ligation stage.
关键词： perovskite nanocrystals,growth,nucleation,fluorescence,absorbance,surface ligation
更新于2025-09-23 15:19:57
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AMORPHOUS/NANOCRYSTALLIZATION OF TiN-TiB <sub/>2</sub> REINFORCED LASER CLAD COMPOSITES
摘要： Laser cladding (LC) of the Stellite6-BN-Cu-Y2O3 pre-placed powders on the Ti-6Al-4V alloy substrate formed the bulk TiN and needle-like Ti-B compounds reinforced composites, which improved the wear resistance of the substrate surface. The results showed that lots of the amorphous-nanocrystalline phases were produced in such composites; the proper content of Cu was used to reˉne microstructures, also a large number of the nanocrystals can be formed; the elements such as Co, Ni and Fe in Stellite6 favored the amorphous phase to be formed. The addition of Y2O3 improved the °uidity of the liquid metal, also retarding the growth of the dendrite, leading the ˉne microstructures to be formed, improving the property of the LC composites.
关键词： nanocrystals,amorphous phase,surface modiˉcation,Laser cladding
更新于2025-09-23 15:19:57
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Boosting the photocatalytic performances of covalent organic frameworks enabled by spatial modulation of plasmonic nanocrystals
摘要： Plasmonic Au nanocrystals (NCs) are incorporated into covalent organic frameworks (COFs) with precisely modulated distributions to improve the efficiency of electron-hole separation covalent reactions and assembly of NCs, sparsely dispersed Au NCs (AuSP/COFs) or the close packed ones (AuCP/COFs) in COFs are fabricated, in which the contributions of electron acceptors/cocatalysts on the catalytic properties of Au/COFs composites are addressed by EPR, PL, phenacyl bromide (conversion >99%, selectivity of acetophenone ~92.8%) under visible light irradiation, which are associated with accelerated electron transfer, increased available Au/COFs and optimize the charge-carrier utilization. Specifically, through balancing the rate of dynamic Schottky junctions and boosted interfacial reaction kinetics. Overall, this work contributes to the fundamental understanding of the how spatial distributions of NCs in COFs affect the photocatalytic performances.
关键词： metallic nanocrystals,heterojunctions,covalent organic frameworks,photocatalysis,inorganic/organic hybrids
更新于2025-09-23 15:19:57
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Integrated Raman Laser: A Review of the Last Two Decades
摘要： Important accomplishments concerning an integrated laser source based on stimulated Raman scattering (SRS) have been achieved in the last two decades in the fields of photonics, microphotonics and nanophotonics. In 2005, the first integrated silicon laser based upon SRS was realized in the nonlinear waveguide. This breakthrough promoted an intense research activity addressed to the realization of integrated Raman sources in photonics microstructures, like microcavities and photonics crystals. In 2012, a giant Raman gain in silicon nanocrystals was measured for the first time. Starting from this impressive result, some promising devices have recently been realized combining nanocrystals and microphotonics structures. Of course, the development of integrated Raman sources has been influenced by the trend of photonics towards the nano-world, which started from the nonlinear waveguide, going through microphotonics structures, and finally coming to nanophotonics. Therefore, in this review, the challenges, achievements and perspectives of an integrated laser source based on SRS in the last two decades are reviewed, side by side with the trend towards nanophotonics. The reported results point out promising perspectives for integrated micro- and/or nano-Raman lasers.
关键词： nonlinear waveguide,lasers,microphotonics,nanophotonics,stimulated Raman scattering,optical microcavity,photonics crystals,nonlinear optics,nanocrystals
更新于2025-09-23 15:19:57
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Editors' Choice—Optical Emission from Germanium Nanocrystals
摘要： We analyze the intense photoluminescence (PL) observed at energies from 600 to 1100 meV for a large number of Si1-xGex epitaxial layers grown by molecular beam epitaxy. In the present work we show that this previously unexplained broad PL peak can be assigned to Ge nanocrystals (NCs) self-assembled within the SiGe layers. These NCs are assumed to be lattice matched to the SiGe in the vertical, growth direction. A consequence of this assignment is that as the Ge-fraction in the SiGe layer increases the vertical strain in the NCs changes from compressive to tensile at x ～ 0.36, lowering the NC bandgap (BG) below that of bulk Ge. We examine the PL results for more than 60 samples exhibiting this broad PL peak by examining how it follows the strained Ge BG for x from 0.05 to 0.53. The PL is resolvable as two narrower peaks separated by the momentum conserving phonon energy for Ge. Strain and con?nement shifted NC bound exciton energies calculated numerically agree well with the measured ones. When Raman scattering results were examined for some of the same samples, the phonon mode frequencies obtained provided valuable corroborative evidence for the presence of the Ge NCs.
关键词： molecular beam epitaxy,SiGe epitaxial layers,Raman spectroscopy,Germanium nanocrystals,photoluminescence
更新于2025-09-23 15:19:57
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Biexciton Auger recombination in mono-dispersed, quantum-confined CsPbBr3 perovskite nanocrystals obeys universal volume-scaling
摘要： Auger recombination has been a long-standing obstacle to many prospective applications of colloidal quantum dots (QDs) ranging from lasing, light-emitting diodes to bio-labeling. As such, understanding the physical underpinnings and scaling laws for Auger recombination is essential to these applications. Previous studies of biexciton Auger recombination in various QDs established a universal scaling of biexciton lifetime (τXX) with QD volume (V ): τXX = γV. However, recent measurements on perovskite nanocrystals (NCs), an emerging class of enablers for light harvesting and emitting applications, showed significant deviations from this universal scaling law, likely because the measured NCs are weakly-confined and also have relatively broad size-distributions. Here we study biexciton Auger recombination in mono-dispersed (size distributions within 1.7%–9.0%), quantum-confined CsPbBr3 NCs (with confinement energy up to 410 meV) synthesized using a latest approach based on thermodynamic equilibrium control. Our measurements clearly reproduce the volume-scaling of τXX in confined CsPbBr3 QDs. However, the scaling factor γ (0.085 ± 0.001 ps/nm3) is one order of magnitude lower than that reported for CdSe and PbSe QDs (1.00 ± 0.05 ps/nm3), suggesting unique mechanisms enhancing Auger recombination rate in perovskite NCs.
关键词： biexciton,Auger recombination,perovskite nanocrystals,ultrafast spectroscopy,volume-scaling
更新于2025-09-23 15:19:57
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Robust Polymer Matrix Based on Isobutylene (Co)Polymers for Efficient Encapsulation of Colloidal Semiconductor Nanocrystals
摘要： We introduce new oxygen- and moisture-proof polymer matrices based on polyisobutylene (PIB) and its block copolymer with styrene (poly(styrene-block-isobutylene-block-styrene), PSt-b-PIB-b-PSt) for encapsulation of colloidal semiconductor nanocrystals. In order to prepare transparent and processable composites, we developed a special procedure of the nanocrystal surface engineering including ligand exchange of parental organic ligands to inorganic species followed by attachment of specially designed short-chain PIB functionalized with amino-group (PIB-NH2). The latter provides excellent compatibility of the particles with the polymer matrices. As colloidal nanocrystals, we chose CdSe nanoplatelets (NPLs), since they possess a large surface and thus are very sensitive to the environment, in particular in terms of their limited photostability. The encapsulation strategy is quite general and can be applied to a wide variety of semiconductor nanocrystals, as demonstrated on the example of PbS quantum dots. All obtained composites exhibited excellent photostability being tested in a focus of a powerful white-light source, as well as exceptional chemical stability in a strongly acidic media. We compared these properties of the new composites with those of widely used polyacrylate based materials, demonstrating the superiority of the former. The developed composites are of particular interest for application in optoelectronic devices, such as color-conversion light emitting diodes (LEDs), laser diodes, luminescent solar concentrators, etc.
关键词： photoluminescence,nanocrystals-in-polymer composites,lead sulfide quantum dots,semiconductor nanocrystals,isobutylene (co)polymers,cadmium selenide nanoplatelets,photostability,chemical stability
更新于2025-09-19 17:15:36
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Anion Exchange and the Quantum-Cutting Energy Threshold in Ytterbium-Doped CsPb(Cl1-xBrx)3 Perovskite Nanocrystals
摘要： Colloidal halide perovskite nanocrystals of CsPbCl3 doped with Yb3+ have demonstrated remarkably high sensitized photoluminescence quantum yields (PLQYs), approaching 200%, attributed to a picosecond quantum-cutting process in which one photon absorbed by the nanocrystal generates two photons emitted by the Yb3+ dopants. This quantum-cutting process is thought to involve a charge-neutral defect cluster within the nanocrystal's internal volume. Here, we demonstrate that Yb3+-doped CsPbCl3 nanocrystals can be converted post-synthetically to Yb3+-doped CsPb(Cl1-xBrx)3 nanocrystals without compromising the desired high PLQYs. Nanocrystal energy gaps can be tuned continuously from Eg ~ 3.06 eV (405 nm) in CsPbCl3 down to Eg ~ 2.53 eV (~490 nm) in CsPb(Cl0.25Br0.75)3 while retaining a constant PLQY above 100%. Reducing Eg further causes a rapid drop in PLQY, interpreted as reflecting an energy threshold for quantum cutting at approximately twice the energy of the Yb3+ 2F7/2 → 2F5/2 absorption threshold. These data demonstrate that very high quantum-cutting energy efficiencies can be achieved in Yb3+-doped CsPb(Cl1-xBrx)3 nanocrystals, offering the possibility to circumvent thermalization losses in conventional solar technologies. The presence of water during anion exchange is found to have a deleterious effect on the Yb3+ PLQYs but does not affect the nanocrystal shapes, morphologies, or even reduce the excitonic PLQYs of analogous undoped CsPb(Cl1-xBrx)3 nanocrystals. These results provide valuable information relevant to development and application of these unique materials for spectral-shifting solar energy conversion technologies.
关键词： ytterbium doping,quantum cutting,anion exchange,Perovskite nanocrystals
更新于2025-09-19 17:15:36
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Broadband ultrafast nonlinear optical studies revealing exciting multi-photon absorption coefficients in phase pure zero-dimensional Cs <sub/>4</sub> PbBr <sub/>6</sub> perovskite films
摘要： Lead halide perovskite nanocrystals (NCs) apart from their overwhelming optoelectronic applications have recently demonstrated promising nonlinear optical (NLO) properties such as strong two-photon absorption cross-sections (～105 GM), two-photon fluorescence, and saturable absorption even at very high peak intensity. Zero-dimensional perovskite-related materials (0-D PRMs) are a new class of materials offering a high exciton binding energy (Eg ≥ 180 meV) with a strong photoluminescence (PL) quantum yield in few cases. Herein, we report the broadband third-order NLO properties of phase pure Cs4PbBr6 0-D PRM achieved using the Z-scan and degenerate four-wave mixing techniques in the femtosecond regime. Considering the growing content of the fluorescent and non-fluorescent forms of this material, we have performed our studies on both of them. These perovskite NCs exhibited strong multi-photon absorption properties in the near-infrared region with two-photon absorption (2PA) (cross-section, σ2 = 10?43–10?44 cm4 s equivalent to ～106 GM) in the 500–800 nm region, three-photon absorption (3PA) (cross-section, σ3 ～10?73 cm6 s2) in the 900–1200 nm region and four-photon absorption (4PA) (cross-section, σ4 ～10?100 cm8 s3) in the 1300–1500 nm spectral region. These multi-photon absorption processes are explained using a simple band diagram. The measured NLO coefficients and cross-sections are fairly large when compared to some of the earlier reports on perovskite-based NCs. Cs4PbBr6 0-D PRM also demonstrated a large third-order NLO susceptibility χ(3) (～10?7 esu), which can be attributed to the strong quantum confinement arising from spatially isolated, exciton containing individual [PbBr6]4? octahedron. These results clearly suggest the potential of 0D-PRMs in applications such as photonics and ultrafast all-optical switching devices.
关键词： Z-scan,perovskite nanocrystals,ultrafast optics,degenerate four-wave mixing,multi-photon absorption,nonlinear optical properties
更新于2025-09-19 17:15:36
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Ethanol-Precipitable Silica-Passivated Perovskite Nanocrystals Incorporated into Polystyrene Microspheres for Long-Term Storage and Re-Usage
摘要： Perovskite nanocrystals (PNCs) are emerging luminescent materials due to their fascinating physic-optical properties. However, their sensitive surface chemistry with organic polar solvents, oxygen and moisture greatly hinders their developments towards practical applications. Herein we promote silica-passivated PNCs (SP-PNCs) by in situ hydrolyzing the surface ligands of (3-aminopropyl) triethoxysilane. The resultant SP-PNCs possesses a high quantum yield (QY) of 80% and are precipitable by polar solvents, such as ethanol and acetone, without destroying their surface chemistry or losing QY, which offers an eco-friendly and efficient method for separation, purification and phase transfer of PNCs compared with the traditional solvent evaporation technique. Moreover, we further promoted a swelling-deswelling encapsulation process to incorporate the as-made SP-PNCs into polystyrene microspheres (PMs), which can largely increase the stability of the SP-PNCs against moisture for long-term storage. Besides, the embedded SP-PNCs can also be reused and mono-dispersed by totally dissolving the PMs in suitable solvents for making all-solution-processed devices. We thereby believe this work should open new avenues for greener synthesis, scalable production, and long-term storage of PNCs towards the emerging practical applications.
关键词： surface engineering,polar environment,perovskite nanocrystals,encapsulation,stability
更新于2025-09-19 17:15:36