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Photoluminescence (PL) spectroscopy of individual semiconductor nanocrystals (NCs) is a powerful method for understanding the intrinsic optical properties of these materials. Here, we report the temperature dependence of the PL spectra of single perovskite FAPbBr3 and CsPbBr3 NCs [FA = HC(NH2)2]. The temperature dependences of the PL linewidths were mainly determined by the Fröhlich interaction between excitons and longitudinal optical phonons. For FAPbBr3 NCs, a redshift in the PL peak energy appeared between 100 and 150 K, which was because of the orthorhombic-to-tetragonal phase transition. We found that the phase transition temperature of FAPbBr3 NCs decreases with decreasing NC size.

Solar-driven water-splitting has been considered as a promising technology for large-scale generation of sustainable energy for succeeding generations. Recent intensive efforts have led to the discovery of advanced multi-element-compound water-splitting electrocatalysts with very small overpotentials in anticipation of their application to solar cell-assisted water electrolysis. Although photocatalytic and photoelectrochemical water-splitting systems are more attractive approaches for scaling up without much technical complexity and high investment costs, improving their efficiencies remains a huge challenge. Hybridizing photocatalysts or photoelectrodes with cocatalysts has been an effective scheme to enhance their overall solar energy conversion efficiencies. However, direct integration of highly-active electrocatalysts as cocatalysts introduces critical factors that require careful consideration. These additional requirements limit the design principle for cocatalysts compared with electrocatalysts, decelerating development of cocatalyst materials. This perspective first summarizes the recent advances in electrocatalyst materials and the effective strategies to assemble cocatalyst/photoactive semiconductor composites, and further discusses the core principles and tools that hold the key in designing advanced cocatalysts and generating a deeper understanding on how to further push the limits of water-splitting efficiency.

Since the discovery of high-order harmonic generation (HHG) in solids, much effort has been devoted to understand its generation mechanism and both inter- and intraband transitions are known to be essential. However, intraband transitions are affected by the electronic structure of a solid, and how they contribute to nonlinear carrier generation and HHG remains an open question. Here we use mid-infrared laser pulses to study HHG in CdSe and CdS quantum dots, where quantum confinement can be used to control the intraband transitions. We find that both HHG intensity per excited volume and generated carrier density increase when the average quantum dot size is increased from about 2 to 3 nm. We show that the reduction in sub-bandgap energy in larger quantum dots enhances intraband transitions, and this—in turn—increases the rate of photocarrier injection by coupling with interband transitions, resulting in enhanced HHG., 半導体ナノ粒子からの高次高調波観測により物質中の新たな光学遷移過程を発見 --レーザー光で固体中の電流を超高速制御する次世代フォトニクス応用に期待--. 京都大学プレスリリース. 2022-06-24.

Shape and nanocrystal transformations Cation exchange reactions that change the composition of a nanocrystal (NC) under mild conditions usually preserve the sublattice of the larger anions. Li et al. found that the shape of roxbyite (Cu 1.8 S) nanocrystals, which have a distorted, hexagonal, close-packed sulfide anion sublattice, affected the outcome of exchange reactions with cobalt ions. Flat nanoplates retained the anion lattice and formed cobalt sulfide, but tall nanorods transformed into Co 9 S 8 nanocrystals with a cubic, close-packed structure. Facile crystal plane sliding in the taller nanocrystals appears to have driven the different layer stacking of sulfide anions. Science , abh2741, this issue p. 332

Optimizing the stability and improving photoluminescence quantum yields (PLQYs) of all-inorganic halide perovskite nanocrystals has become an urgent and challenging task to promote its application ...

Efficient, robust and environmentally friendly cocatalysts for photocatalysts are important for large-scale solar hydrogen production. Herein, we demonstrate that a Rh–Zr mixed oxide is an efficient cocatalyst for hydrogen evolution. Impregnation of Zr and Rh precursors (Zr/Rh = 5 wt/wt%) formed RhZrOx cocatalyst particles on Al-doped SrTiO3, which exhibited 31× higher photocatalytic water-splitting activity than a RhOx cocatalyst. X-ray photoelectron spectroscopy proved that the dissociation of Cl− ions from preformed Rh–Cl–Zr–O solid led to formation of the active phase of RhZrOx, in which the Zr/Rh ratio was critical to high catalytic activity. Additional CoOx loading as an oxygen evolution cocatalyst further improved the activity by 120%, resulting in an apparent quantum yield of 33 (±4)% at 365 nm and a long durability of 60 h. Our discovery could help scale up photocatalytic hydrogen production., An efficient, robust and environmentally friendly Rh–Zr mixed oxide formed though the activation of Rh–Cl–Zr–O solid efficiently functions as a HER cocatalyst on Al-doped SrTiO3.

Lead halide perovskite nanocrystals (NCs) are a class of promising light-emitting materials and have been considered as gain media in lasers. Strong exciton-exciton interactions in NCs cause an energy shift of the lowest optical transition and affect the optical gain threshold. Here, we clarify the dynamics of exciton-exciton interactions in highly photoexcited CsPbI3 NCs by double-pump transient absorption spectroscopy. This method provides control over the population of each excited state by varying the time interval between the two pump pulses. We find that the band-edge energy shift induced by the formation of asymmetric hot-biexcitons (comprising one ground-state exciton and one hot exciton) is smaller than that induced by hot excitons and hot biexcitons in the ensemble. We demonstrate that the generation of asymmetric hot-biexcitons reduces the optical gain threshold in the CsPbI3 NC ensemble.

Control over the composition and nanostructure of solid electrocatalysts is quite important for drastic improvement of their performance. The cation exchange reaction of nanocrystals (NCs) has been reported as the way to provide metastable crystal structures and complicated functional nanostructures that are not accessible by conventional synthetic methods. Herein we demonstrate the cation exchange-derived formation of metastable spinel Ni3Se4 NCs (sp-Ni3Se4) and phase segregated berzelianite Cu2−xSe (ber-Cu2−xSe)/sp-Ni3Se4 heterostructured NCs as active oxygen evolution reaction (OER) catalysts. A rare sp-Ni3Se4 phase was formed by cation exchange of ber-Cu2−xSe NCs with Ni2+ ions, because both phases have the face-centered cubic (fcc) Se anion sublattice. Tuning the Ni : Cu molar ratio leads to the formation of Janus-type ber-Cu2−xSe/sp-Ni3Se4 heterostructured NCs. The NCs of sp-Ni3Se4 and ber-Cu2−xSe/sp-Ni3Se4 heterostructures exhibited high catalytic activities in the OER with small overpotentials of 250 and 230 mV at 10 mA cm−2 in 0.1 M KOH, respectively. They were electrochemically oxidized during the OER to give hydroxides as the real active species. We anticipate that the cation exchange reaction could have enormous potential for the creation of novel heterostructured NCs showing superior catalytic performance.

Solar-driven water-splitting has been considered as a promising technology for large-scale generation of sustainable energy for succeeding generations. Recent intensive efforts have led to the discovery of advanced multi-element-compound water-splitting electrocatalysts with very small overpotentials in anticipation of their application to solar cell-assisted water electrolysis. Although photocatalytic and photoelectrochemical water-splitting systems are more attractive approaches for scaling up without much technical complexity and high investment costs, improving their efficiencies remains a huge challenge. Hybridizing photocatalysts or photoelectrodes with cocatalysts has been an effective scheme to enhance their overall solar energy conversion efficiencies. However, direct integration of highly-active electrocatalysts as cocatalysts introduces critical factors that require careful consideration. These additional requirements limit the design principle for cocatalysts compared with electrocatalysts, decelerating development of cocatalyst materials. This perspective first summarizes the recent advances in electrocatalyst materials and the effective strategies to assemble cocatalyst/photoactive semiconductor composites, and further discusses the core principles and tools that hold the key in designing advanced cocatalysts and generating a deeper understanding on how to further push the limits of water-splitting efficiency.

Lead halide perovskite nanocrystals (NCs) have superior photoluminescence (PL) properties, such as high PL quantum yields and wide PL wavelength tunability, for optoelectronic applications. Here, we report the PL spectra of single formamidinium lead halide perovskite FAPbX3 (X = Br, I) NCs examined by single-dot spectroscopy at low temperature. We found four PL peaks in the low-energy region below the strong exciton PL peak that originate from two longitudinal-optical (LO) phonon replicas of the exciton PL, biexcitons, and charged excitons (trions). The binding energies of the biexcitons and trions become larger as the NCs decrease in size. The LO phonon energies show no size dependence, but the Huang-Rhys factors, which reflect the strength of the exciton-phonon coupling, become larger for smaller NCs. Our findings provide important insights into the exciton properties of perovskite NCs.

Ionization of nanocrystals (NCs) causes both photoluminescence intermittency and a reduction in luminescence quantum efficiency and thus plays a critical role in the optoelectronic performance of NC-based devices. Here, we study the ionization and neutralization processes of CsPbBr3 perovskite NCs under strong photoexcitation by means of double-pump transient absorption spectroscopy. A strong initial pulse is used to generate ionized NCs, and their optical responses are investigated by varying the excitation intensity and delay time of the second pump pulse. We find that charging can occur either via nonradiative Auger recombination of biexcitons or via any possible recombination of trions. The presence of the extra charge inside of an ionized perovskite NC significantly reduces its absorption cross section. The experiments reveal that ionized NCs exhibit two types of neutralization processes with time constants on the order of nanoseconds and microseconds. These results are useful for the optimal design of NC-based photonic devices.

Control over the composition and nanostructure of solid electrocatalysts is quite important for drastic improvement of their performance. The cation exchange reaction of nanocrystals (NCs) has been reported as the way to provide metastable crystal structures and complicated functional nanostructures that are not accessible by conventional synthetic methods. Herein we demonstrate the cation exchange-derived formation of metastable spinel Ni3Se4 NCs (sp-Ni3Se4) and phase segregated berzelianite Cu2−xSe (ber-Cu2−xSe)/sp-Ni3Se4 heterostructured NCs as active oxygen evolution reaction (OER) catalysts. A rare sp-Ni3Se4 phase was formed by cation exchange of ber-Cu2−xSe NCs with Ni2+ ions, because both phases have the face-centered cubic (fcc) Se anion sublattice. Tuning the Ni : Cu molar ratio leads to the formation of Janus-type ber-Cu2−xSe/sp-Ni3Se4 heterostructured NCs. The NCs of sp-Ni3Se4 and ber-Cu2−xSe/sp-Ni3Se4 heterostructures exhibited high catalytic activities in the OER with small overpotentials of 250 and 230 mV at 10 mA cm−2 in 0.1 M KOH, respectively. They were electrochemically oxidized during the OER to give hydroxides as the real active species. We anticipate that the cation exchange reaction could have enormous potential for the creation of novel heterostructured NCs showing superior catalytic performance., Bimetallic selenide nanocrystals formed by cation exchange reaction work as a precursor of efficient water oxidation electrocatalyst.

Manipulation of excitons via coherent light-matter interaction is a promising approach for quantum state engineering and ultrafast optical modulation. Various excitation pathways in the excitonic multilevel systems provide controllability more efficient than that in the two-level system. However, these control schemes have been restricted to limited control-light wavelengths and cryogenic temperatures. Here, we report that lead halide perovskites can lift these restrictions owing to their multiband structure induced by strong spin-orbit coupling. Using CsPbBr₃ perovskite nanocrystals, we observe an anomalous enhancement of the exciton energy shift at room temperature with increasing control-light wavelength from the visible to near-infrared region. The enhancement occurs because the interconduction band transitions between spin-orbit split states have large dipole moments and induce a crossover from the two-level optical Stark effect to the three-level Autler-Townes effect. Our finding establishes a basis for efficient coherent optical manipulation of excitons utilizing energy states with large spin-orbit splitting., ペロブスカイトナノ粒子において近赤外光による大きな超高速光変調を室温で実現 --光通信帯における新たな超高速光スイッチング技術の開発に期待--. 京都大学プレスリリース. 2021-05-24.

ConspectusElaborate chemical synthesis methods allow the production of various types of inorganic nanocrystals (NCs) with uniform shape and size distributions. Many single-step synthesis approaches, such as the reduction of metal ions, the decomposition of metal complexes, double replacement reactions, and hydrolysis, have been adapted to promote the generation of monodisperse metal and ionic NCs. However, the question has become, how can we synthesize NCs with thermodynamically metastable phases or very complex structures? The transformation of already-synthesized NCs via elemental substitutions, such as ion exchange reactions for ionic NCs and galvanic replacement reactions for metal NCs, can overcome the difficulties facing conventional one-step syntheses. In particular, NC ion exchange reactions have been studied with numerous combinations of foreign ions and ionic NCs with various shapes. They have been investigated extensively because the reactions proceed under relatively mild conditions thanks to the large surface-to-volume ratio of the NCs relative to their bulk form. The functionality of the resulting ionic NCs, including semiconducting and plasmonic properties, can be easily tuned in a wide range, from the visible to near-infrared. Because anions generally have much larger ionic radii than cations within the frameworks of NCs, the cation exchange reactions proceed much faster than the anion exchange reactions. For ionic NCs above a critical size, the anion framework remains intact, and the original shape of the parent NCs is retained throughout the cation exchange reaction. In contrast, the anion exchange reaction often provides the new NCs with unique structures, such as hollow or anisotropically phase-segregated assemblies.This Account focuses on the full and partial ion exchange reactions involving ionic NCs, which have been thoroughly investigated by our group and others while highlighting important aspects such as the preservation of appearance and dimensions. First, we discuss how each type of ion exchange reaction progresses to understand the morphologies and crystal structures of their final products. This discussion is supported by emphasizing important examples, which help to explore the formation of NCs with thermodynamically metastable phases and complex structures, and other significant features of the ion exchange reactions leading to structure-specific functions. As a special case, we examine how the shape-dependent anionic framework (surface anion sublattice and stacking pattern) of polyhedral Cu2O NCs determines the crystalline structure of the anion-exchanged products of hollow CuxS NCs. In addition, we review the characteristic anion exchange behavior of metal halide perovskite NCs observed in our laboratory and other laboratories. Finally, a general outline of the transformation of NCs via ion exchange reactions and future prospects in this field are provided.

Halide perovskite nanocrystals are suitable materials for photonic devices because their highly efficient luminescence can be tuned over a wide wavelength range by changing the nanocrystal composition and size. Here, we report on the high-order harmonic generation in a solution-processed perovskite ${\mathrm{CsPbBr}}_{3}$ nanocrystal film that is excited by a strong midinfrared laser. We observe harmonics up to the 13th order, which is ultraviolet light well above the band-gap energy. By using elliptically polarized laser light, we analyze the influence of the sample structure on the intensity of the 5th harmonic. It is also found that the randomness in the orientation of the nanocrystals in the film induces a reduction in the harmonic intensities due to the interference among the harmonics emitted from nanocrystals with different phases. Our observation of high-order harmonics from nanocrystal films opens a way towards the development of an intensity modulator that can be tuned simply by changing the excitation ellipticity.

Lead halide perovskite nanocrystals (NCs) are a class of promising light-emitting materials and have been considered as gain media in lasers. Strong exciton-exciton interactions in NCs cause an energy shift of the lowest optical transition and affect the optical gain threshold. Here, we clarify the dynamics of exciton-exciton interactions in highly photoexcited CsPbI

Lead halide perovskite (APbX3) nanocrystals exhibit photoluminescence (PL) with both wide wavelength tunability and high quantum efficiency. While the Pb–X6 octahedra mainly determines the near-ban...

Lead halide perovskite nanocrystals (NCs) are one of the most anticipated and promising materials for light-emitting diodes and lasers because of their high photoluminescence quantum yields (PLQYs). However, the formation of trions (charged excitons) in the NCs reduces their PLQYs. Here, we clarify the trion formation mechanism in perovskite CsPbBr3 NCs by analyzing the excitation fluence dependence of transient absorption signals. Under weak photoexcitation, trions are formed by charge carrier trapping at surface states. In contrast, biexciton Auger recombination dominates the trion formation under strong photoexcitation. We found that the postsynthetic surface treatment suppresses the extrinsic surface-related formation of trions. The thorough understanding of the trion formation mechanisms is essential for the PLQY improvement of perovskite NCs and helps to reduce ionization of NCs in solid-state devices.

Combining the superior optical properties of their bulk counterparts with quantum confinement effects, lead halide perovskite nanocrystals are unique laser materials with low-threshold optical gain. In such nonlinear optical regimes, multiple excitons are generated in the nanocrystals and strongly affect the optical gain through many-body interactions. Here, we investigate the exciton–exciton interactions in CsPbI3 nanocrystals by femtosecond transient absorption spectroscopy. From the analysis of the induced absorption signal observed immediately after the pump excitation, we estimated the binding energy for the hot biexcitons that are composed of an exciton at the band edge and a hot exciton generated by the pump pulse. We found that the exciton–exciton interaction becomes stronger for hot excitons with greater excess energies and that the optical gain can be controlled by changing the excess energy of the hot excitons.

The high overpotential of the oxygen evolution reaction is a critical issue to be overcome to realize efficient overall water splitting and enable hydrogen generation powered by sunlight. Homogeneous and stable nanoparticles (NPs) dispersed in solvents are useful as both electrocatalysts and cocatalysts of photocatalysts for the electro- and photo-catalytic oxygen evolution reaction, respectively, through their adsorption on various electrode substrates. Here, phase-segregated NiPx@FePyOz core@shell NPs are selectively synthesized by the reaction of Fe(CO)5 with amorphous NiPx seed-NPs. The NiPx@FePyOz NPs on conductive substrates exhibit higher electrocatalytic activity in the oxygen evolution reaction than those of other metal phosphide-based catalysts. The NiPx@FePyOz NPs can also be used as a cocatalyst of an anodic BiVO4 photocatalyst to boost the photocatalytic water oxidation reaction. The excellent catalytic activity and high stability of the NiPx@FePyOz NPs without any post-treatments are derived from in situ activation through both the structural transformation of NiPx@FePyOz into mixed hydroxide species, (Ni, Fe)OxHy, and the spontaneous removal of the insulating organic ligands from NPs to form a smooth and robust (Ni, Fe)OxHy/substrate heterointerface during the oxygen evolution reaction.

The effect of cobalt doping into a manganese oxide (tetragonal spinel Mn3O4) nanoparticle cocatalyst up to Co/(Co + Mn) = 0.4 (mol/mol) on the activity of photocatalytic water oxidation was studied. Monodisperse ∼10 nm CoyMn1−yO (0 ≤ y ≤ 0.4) nanoparticles were uniformly loaded onto photocatalysts and converted to CoxMn3−xO4 nanoparticles through calcination. 40 mol% cobalt-doped Mn3O4 nanoparticle-loaded Rh@Cr2O3/SrTiO3 photocatalyst exhibited 1.8 times-higher overall water splitting activity than that with pure Mn3O4 nanoparticles. Investigation on the band structure and electrocatalytic water oxidation activity of CoxMn3−xO4 nanoparticles revealed that the Co doping mainly contributes to the improvement of water oxidation kinetics on the surface of the cocatalyst nanoparticles.

It remains challenging to develop alternatives, based on widely abundant elements, to highly active Pt catalysts for the hydrogen evolution reaction. Metal sulfide nanoparticles (NPs) are potential candidates for such catalysts because of their metallic features and intrinsic high surface area; however, their poor electrocatalytic activity, owing to the presence of surface ligands, is an obstacle to practical use. Here we report the selective synthesis of oleylamine (OAm)-stabilized Ni₃S₄ (Ni₃S₄/OAm) NPs. The insulating ligands were exchanged with S²¯ and loaded on electrodes by a layer-by-layer (LbL) assembly method with metal cation linkers. The enhanced catalytic properties were confirmed by electrochemical measurements. A LbL assembled film with Ni²+ as a linker (11 cycles) showed an overpotential of 555 mV@-4 mA/cm² at pH 6.8 and a stable current density for 12 h. In addition, when this LbL assembly method was applied to a CdS/Cu(In,Ga)Se₂ photocatalyst electrode, the resulting photoelectrode showed an enhanced photocurrent compared with that of the Ni₃S₄/OAm NPs-spin coated and bare photoelectrodes. These results indicate the versatility of LbL assembly for fabrication of ligand-free NP electrocatalyst films.

Giant-shell CdSe/CdS core/shell nanocrystals have attracted much attention due to their unique quasi-type-II band alignment, where a large valence band offset confines holes strongly to the core but electrons are delocalized due to a small conduction band offset. Here, we report the observation of the relative enhancement in the radiative recombination rate of a biexciton compared to that of an exciton in giant-shell CdSe/CdS nanocrystals. We found a clear correlation between the shell thickness of the CdSe/CdS nanocrystals and the ratio between the radiative recombination rates of the biexciton and exciton. Our finding can be explained by a picture in which the biexciton emission efficiency is enhanced through electron localization around the core due to the strong Coulomb potential of the two holes confined in the core.

Metal–halide perovskite nanocrystals (NCs) are promising photonic materials for use in solar cells, light-emitting diodes, and lasers. The optoelectronic properties of these devices are determined by the excitons and exciton complexes confined in their NCs. In this study, we determined the relaxation dynamics of charged excitons and biexcitons in CsPbBr3 NCs using femtosecond transient-absorption (TA), time-resolved photoluminescence (PL), and single-dot second-order photon correlation spectroscopy. Decay times of ∼40 and ∼200 ps were obtained from the TA and PL decay curves for biexcitons and charged excitons, respectively, in NCs with an average edge length of 7.7 nm. The existence of charged excitons even under weak photoexcitation was confirmed by the second-order photon correlation measurements. We found that charged excitons play a dominant role in luminescence processes of CsPbBr3 NCs. Combining different spectroscopic techniques enabled us to clarify the dynamical behaviors of excitons, charged ex...

Ionization of nanocrystals (NCs) causes both photoluminescence intermittency and a reduction in luminescence quantum efficiency and thus plays a critical role in the optoelectronic performance of NC-based devices. Here, we study the ionization and neutralization processes of CsPbBr

We synthesized a heterotetrapod composed of a chalcopyrite(ch)-CuInS2 core and wurtzite(w)-CdS arms and elucidated its optical properties and light-stimulated carrier dynamics using fs-laser flash photolysis. The CuInS2/CdS heterotetrapod possessed quasi-type II band alignment, which caused much longer-lived charge separation than that in the isolated CuInS2 nanocrystal.

Lead halide perovskite nanocrystals are promising light emitting materials with high photoluminescence quantum yields and widely tunable emission wavelengths. Their optical responses are significantly influenced by efficient nonradiative Auger recombination of trions (charged excitons) and biexcitons. Here, we report the observation of positive and negative trions in formamidinium lead bromide nanocrystals and discuss their role in the photoluminescence dynamics. It is found that the addition of copper thiocyanate causes an additional intermediate state by photochemical doping. We clarify that as-prepared nanocrystals show a two-state blinking between neutral excitons and positive trions, while the postsynthesis treated nanocrystals exhibit blinking between all three states, including negative trions. We confirmed that the biexciton Auger rate evaluated from femtosecond transient absorption measurements can be expressed as the sum of the Auger rates of positive and negative trions obtained by single-dot spectroscopy.

The effect of cobalt doping into a manganese oxide (tetragonal spinel Mn

The high overpotential of the oxygen evolution reaction is a critical issue to be overcome to realize efficient overall water splitting and enable hydrogen generation powered by sunlight. Homogeneous and stable nanoparticles (NPs) dispersed in solvents are useful as both electrocatalysts and cocatalysts of photocatalysts for the electro- and photo-catalytic oxygen evolution reaction, respectively, through their adsorption on various electrode substrates. Here, phase-segregated NiP

We study the origin of photoluminescence (PL) intermittency in formamidinium lead bromide (FAPbBr3, FA = HC(NH2)2) nanocrystals and the impact of postsynthetic surface treatments on the PL intermittency. Single-dot spectroscopy revealed the existence of different individual nanocrystals exhibiting either a blinking (binary on–off switching) or flickering (gradual undulation) behavior of the PL intermittency. Although the PL lifetimes of blinking nanocrystals clearly correlate with the individual absorption cross sections, those of flickering nanocrystals show no correlation with the absorption cross sections. This indicates that flickering has an extrinsic origin, which is in contrast to blinking. We demonstrate that the postsynthetic surface treatment with sodium thiocyanate improves the PL quantum yields and completely suppresses the flickering, while it has no significant effect on the blinking behavior. We conclude that the blinking is caused by Auger recombination of charged excitons, and the flicker...

Recently, metal-halide perovskite semiconductors have been extensively studied because of their potential use in solar-cell, photodetector, light-emitting-diode, and laser applications. In particular, perovskite nanocrystals (NCs) are gaining more and more attention because their optical spectra can be manipulated by changing the NC size and the halogen composition [1]. In contrast to the conventionally structured NCs such as colloidal CdSe NCs, high-quality perovskite NCs with unique cubic shapes and large sizes can be fabricated. However, their intrinsic photocarrier recombination dynamics have not yet been understood. Especially, the recombination dynamics of exciton complexes including biexcitons and charged excitons (trions) are complicated due to the fast Auger recombination [2]. Thus, a combination of different optical techniques for ensemble and single NC samples should be performed for a deep understanding of multiexciton dynamics in perovskites.

Metal-halide perovskite nanocrystals (NCs) are promising photonic materials for use in solar cells, light-emitting diodes, and lasers. The optoelectronic properties of these devices are determined by the excitons and exciton complexes confined in their NCs. In this study, we determined the relaxation dynamics of charged excitons and biexcitons in CsPbBr

CdS/CdTe nanopencils were synthesized via anion exchange. The effect of the geometry on the carrier dynamics was investigated. Transient absorption measurements indicated that these factors did not affect the charge separation rate in CdS/CdTe nanopencils. The results provide important insight for designing heterostructured nanocrystals with efficient charge separation and integrated structures.

Ion exchange of ionic semiconductor nanoparticles (NPs) is a facile method for the synthesis of type-II semiconductor heterostructured NPs with staggered alignment of band edges for photoelectric applications. Through consideration of the crystallographic orientation and strain at the heterointerface, well-designed heterostructures can be constructed through ion exchange reactions. Here we report the selective synthesis of anisotropically phase-segregated cadmium sulfide (CdS)/ cadmium telluride (CdTe) heterodimers via a novel anion exchange reaction of CdS NPs with an organic telluride precursor. The wurtzite-CdS/zinc blende-CdTe heterodimers in this study resulted from spontaneous phase segregation induced by the differences in the crystal structures of the two phases, accompanying a centrosymmetry breaking of the spherical CdS NPs. The CdS/CdTe heterodimers exhibited photoinduced spatial charge separation because of their staggered band-edge alignment.

Uniformly sized CdS nanoparticles exhibiting quantum size effect have been synthesized as a suspension in hexane solution containing oleic acid and 9-octadecenylamine as protective ligands. Our stu...

Anisotropically phase-segregated nanoparticles, so-called patchy nanoparticles, are promising materials, because the close coupling of different components on the nanoscale may significantly improv...

Seed-mediated growth synthesis has provided us with anisotropically phase-segregated CdPd sulfide heterostructured nanoparticles with seed-dependent morphologies and crystal structures.

High-quality CdS and Cu7S4 quantum dots are synthesized from cadmium or copper stearate in oleylamine and di-octyl ether using N,N-dibutylthiourea as an organic sulfur source.