Location-selective immobilisation of single-atom catalysts on the surface or within the interior of ionic nanocrystals using coordination chemistry

白金単原子触媒を担体表面/内部に選択的に担持する方法を開発 --錯体化学を用いた新しい合成戦略および触媒性能への効果--. 京都大学プレスリリース. 2023-07-20.Single-atom catalysts dispersed on support materials show excellent heterogeneous catalytic properties that can be tuned using the interactions between the single atoms and the support. Such interactions depend on whether the single atoms are located on the surface or within the interior of the support. However, little is known about immobilising single atoms on the surface or within the interior of supports deliberately and selectively. Herein, such location-selective placement of single atoms is achieved through the choice of metal complex precursor, solvent, and workup procedure. Using CdSe nanoplatelets as a support, a cis-[PtCl₂(SO(CH₃)₂)₂] precursor in an aprotic solvent exclusively attaches single Pt atoms on the surface of the support. In contrast, a [PtCl₄]²⁻ precursor in a protic solvent followed by amine treatment places 60% of the single Pt atoms inside the support by cation substitution. The surface-adsorbed single Pt atoms show higher stability in photocatalytic hydrogen evolution than the substituted ones, and the preclusion of substitution as internal Pt maximises the activity. Thus, this study provides a viable strategy for the structurally precise synthesis and design of single-atom catalysts

Collective enhancement of quantum coherence in coupled quantum dot films

協力し合えば強くなる、半導体量子ドットの集団増強効果の観測に成功 --量子センサーやエネルギー変換に新たな道--. 京都大学プレスリリース. 2021-12-21.Colloidal semiconductor quantum dots (QDs) are attractive materials that provide unique photophysics of multiple electron-hole pairs (multiexcitons) in strongly quantum confined systems. Multiexciton phenomena such as efficient Auger recombination have been intensively investigated with respect to individual QDs. However, the cooperative nature of QDs, especially in terms of multiexciton coherence, has not been elucidated thus far. Here, we report the observation of the collective enhancement of quantum coherence in coupled QD films. Using a photocurrent quantum interference technique, we find that the multiexciton quantum coherence in coupled QDs is significantly increased compared to the case of isolated QDs. This cooperative effect is induced by the coherent electronic coupling between QDs. Our results clarify the enhancement mechanism in coupled quantum systems and open the door to advanced optoelectronic applications such as coherent amplifiers and frequency upconverters

Harmonic Quantum Coherence of Multiple Excitons in PbS/CdS Core-Shell Nanocrystals

半導体ナノ粒子が光を電子へ変換する過程を解明 --高効率な太陽電池や光検出器への基礎メカニズム--. 京都大学プレスリリース. 2017-12-14.The generation and recombination dynamics of multiple excitons in nanocrystals (NCs) have attracted much attention from the viewpoints of fundamental physics and device applications. However, the quantum coherence of multiple exciton states in NCs still remains unclear due to a lack of experimental support. Here, we report the first observation of harmonic dipole oscillations in PbS/CdS core-shell NCs using a phase-locked interference detection method for transient absorption. From the ultrafast coherent dynamics and excitation-photon-fluence dependence of the oscillations, we found that multiple excitons cause the harmonic dipole oscillations with ω, 2ω, and 3ω oscillations, even though the excitation pulse energy is set to the exciton resonance frequency, ω. This observation is closely related to the quantum coherence of multiple exciton states in NCs, providing important insights into multiple exciton generation mechanisms

CdPd sulfide heterostructured nanoparticles with metal sulfide seed-dependent morphologies

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

Gold(0) Porphyrins on Gold Nanoparticles

No Abstrac

Strong spin-orbit coupling inducing Autler-Townes effect in lead halide perovskite nanocrystals

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.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

Interference effects in high-order harmonics from colloidal perovskite nanocrystals excited by an elliptically polarized laser

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 CsPbBr₃ 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

Intrinsic Visible Plasmonic Properties of Colloidal PtIn₂ Intermetallic Nanoparticles

コロイド状C1-PtIn2ナノ粒子による可視プラズモン特性の発現 --新規可視プラズモン材料としての金属間化合物ナノ粒子の設計指針--. 京都大学プレスリリース. 2024-01-12.Materials that intrinsically exhibit localized surface plasmon resonance (LSPR) in the visible region have been predominantly researched on nanoparticles (NPs) composed of coinage metals, namely Au, Ag, and Cu. Here, as a coinage metal-free intermetallic NPs, colloidal PtIn₂ NPs with a C1 (CaF₂-type) crystal structure are synthesized by the liquid phase method, which evidently exhibit LSPR at wavelengths similar to face-centered cubic (fcc)-Au NPs. Computational simulations pointed out differences in the electronic structure and photo-excited electron dynamics between C1-PtIn₂ and fcc-Au NPs; reduces interband transition and stronger screening with smaller number of bound d-electrons compare with fcc-Au are unique origins of the visible plasmonic nature of C1-PtIn₂ NPs. These results strongly indicate that the intermetallic NPs are expected to address the development of alternative plasmonic materials by tuning their crystal structure and composition

Phase segregated Cu₂₋ₓSe/Ni₃Se₄ bimetallic selenide nanocrystals formed through the cation exchange reaction for active water oxidation precatalysts

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 Ni₃Se₄NCs (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