While single thiolate-stabilized silver nanoclusters (NCs) are well studied, multiligand-protected analogues remain rare. Herein, we report a luminescent Ag24 nanocluster, co-stabilized by two distinct heterocyclic thiols, 2-mercapto-5-n-propylpyrimidine and 6-(dibutylamino)-1,3,5-triazine-2,4-dithiol, together with triphenylphosphine, whose composition was confirmed by high resolution electrospray ionization (HR-ESI) mass spectrometry. It shows aggregation-caused quenching as it self-assembles into nonemissive sheets, but the emission reappears after mechanical grinding, demonstrating mechanoresponsive luminescence. Interestingly, individual ligands form nonluminescent clusters exhibiting no aggregation behavior. Femtosecond transient absorption measurements indicate that aggregation alters the excited-state dynamics, reflecting the effect of multiligand stabilization on structural rigidity and photophysical behavior in the NCs.

Atomic migration is a key challenge in phase change (PC) materials. Although several techniques have been proposed to address phase segregation, the role of phase segregation in PC materials remains unclear. In this study, the local structural changes during phase segregation in the Ge15Sb85 PC material are investigated using Raman and X-ray photoelectron spectroscopy (XPS). We then propose two feasible solutions to address the phase segregation. First, in-situ depth profiling of the etched crystalline films probed by XPS reveals an enhancement in Ge-Sb bonds and a decline in Ge-Ge bonds, indicating the suppression of undesired phase segregation in the scaled-down crystalline films. Second, the 3-bit multilevel accumulative switching technique, realized using low-energy (12 mJ/cm(2)) nanosecond laser pulses in a 100 nm Ge15Sb85 thin film, reduces the Ge-Ge Raman vibration modes responsible for phase segregation. Additionally, the simulations predict a maximum growth velocity of 35 m/s with an optimized, scaled-down thickness of 19 nm. Hence, the results demonstrate that phase-segregation suppression can be achieved in scaled-down crystalline Ge15Sb85 films, and, together with accumulative switching, phase-segregation can be tackled to a greater extent, thereby improving the write endurance of highly-scalable binary PC material for future photonic memory applications.

We report the synthesis of [Ag17(o1-CBT)12]3- abbreviated as Ag17, a stable 8e⁻ anionic cluster with a unique Ag@Ag12@Ag4 core-shell structure, where o1-CBT is ortho-carborane-1-thiol. By substituting Ag atoms with Au and/or Cu at specific sites we created isostructural clusters [AuAg16(o1-CBT)12]3- (AuAg16), [Ag13Cu4(o1-CBT)12]3- (Ag13Cu4) and [AuAg12Cu4(o1-CBT)12]3- (AuAg12Cu4). These substitutions make systematic modulation of their structural and electronic properties. We show that Au preferentially occupies the core, while Cu localizes in the tetrahedral shell, influencing stability and structural diversity of the clusters. The band gap expands systematically (2.09 eV for Ag17 to 2.28 eV for AuAg12Cu4), altering optical absorption and emission. Ultrafast optical measurements reveal longer excited-state lifetimes for Cu-containing clusters, highlighting the effect of heteroatom incorporation. These results demonstrate a tunable platform for designing nanoclusters with tailored electronic properties, with implications for optoelectronics and catalysis. Tuning the structure and composition of atomically precise metal nanoclusters leads to property changes which, however, are still poorly understood. Here, the authors synthesize precisely substituted analogues of Ag17 clusters and study the changes in luminescence and electronic properties.

Investigating large metal nanoclusters decorated with three-dimensional molecular cages, with complete structural characterization, is challenging; however, their detailed understanding is important to study electronic confinement and associated properties. We have structurally resolved a nearly spherical 2.2 nm silver cluster with the molecular composition [Ag62S12(CBT)32]4+, altogether having 842 atoms, solely protected with meta-carborane-thiolates (CBTs). This is the largest nanocluster with carborane-based molecular cages reported so far. Abscission of the cluster reveals that it has a face-centered-cubic Ag14 inner core encapsulated with 12 sulfides, which is further surrounded by an outer scaffold of Ag48-S32 shell, protected with 32 meta-carboranes. The silver-sulfide skeleton of the nanocluster showed an assembly of multilayered polyhedra, having a mixture of Platonic and Archimedean solids. High-resolution mass spectrometric analyses and other spectroscopic studies further confirmed the molecular composition. This nanocluster exhibits characteristic molecular multiband optical absorption features along with a weak near-infrared (NIR) emission band. Ultrafast femtosecond transient absorption studies revealed stable photoexcited states linked to interlayer electron mobility between the neutral Ag14 core and the positively charged Ag48 shell, which are surrounded by negatively charged sulfide (S12 and S32) layers. Computational analysis shows that this cluster behaves as a two-electron superatom with a band gap of 1.77 eV, which is associated with the energy difference between the 1S symmetric and 1P nonsymmetric states. Successful structural characterization and associated optical properties of the nanocluster suggested that other larger metal nanoclusters encapsulated by three-dimensional molecular cages may be suitable for single-particle photonic and optoelectronic applications.

Cluster-assembled luminescent microstructures built with metal nanoclusters (NCs) represent a promising class of nanomaterials with diverse applications in photonics and sensing. In this work, we have designed a strategy to make a photoluminescent material by assembling atom-precise NCs of [Cu8(TFMPT)4(DPPE)4] (abbreviated as Cu8), where TFMPT is 4-hydroxy-6-(trifluoromethyl) pyrimidine-2-thiolate and DPPE is 1,2-bis(diphenylphosphino)ethane. Single-crystal X-ray diffraction (SC-XRD) reveals a unique tetracapped tetrahedral Cu8 core structure. Upon gradual addition of water (50-85 vol %) to the visibly nonluminescent dimethylformamide (DMF) solution of the clusters, a strong orange luminescence (emission at 625 nm under ultraviolet (UV) light) was observed. It is due to the formation of spheroidal assemblies of nanometer dimension. The cluster-assembled spheroids (CASs) are formed due to hydrophobic interactions among clusters as the concentration of water increases in the solution. Time-correlated single-photon counting reveals that the lifetime of luminescent aggregates is on a microsecond scale, which suggests phosphorescence. Such phosphorescent CASs show a fast response, high selectivity, and naked-eye detection of volatile amines (VAs). Spectroscopic studies and density functional theory (DFT) calculations provide an in-depth understanding of luminescence quenching of CASs and a mechanistic understanding of ammonia and trimethyl amine sensing. The limits of detection (LoD) of ammonia and trimethyl amine were measured to be 0.568 × 10-7 M (0.001 ppm) and 0.362 0.568 × 10-7 M (0.002 ppm), respectively. Overall, apart from enriching the family of copper clusters, this work additionally introduces a new photoluminescent material for volatile organic amine (VOA) compound sensing of environmental relevance.

The interaction of nonresonant intense periodic optical field shifts the ground state excitonic position which can be understood by Floquet manipulation in Jaynes-Cummings model. The induced shift can be manifested by the optical Stark effect (OSE) and Bloch-Siegert effect (BSE) via controlling the light helicity. It is noteworthy that the energy shift is proportional to field intensity and inversely to the detuning at nearly resonant excitation which understood by rotating wave approximation. Recently, OSE and BSE have observed simultaneously with very large detuning (infrared excitation) for CsPbI3 quantum dots. However, observing the BSE at near resonance with small detuning is difficult due to the dominance shift by OSE. Here, we have chosen Cu-doped CsPbI3 nanocrystals and incorporated a helicity-resolved transient absorption spectroscopic technique. Moreover, the dynamical excitonic effect in a small percentage of Cu-doping reduced the binding energy and blueshifted the continuum band without changing the excitonic position. Interestingly we observe blueshift in excitonic position for co (sigma(+)sigma(+))-and cross(sigma(+)sigma(-))-polarization of pump and probe at small detuning. We observed a huge BSE shift similar to 122 meV with the ratios of shifts (i.e., Delta(BSE)/Delta(OSE)) are 0.74 at the lowest detuning, 193 meV Cu-doped CsPbI3, respectively. Thus, our study advances high-field Floquet engineering with a doping mechanism and can be potentially exploited in strong-field device applications as well as a quantum information process.

Transition metal dichalcogenides exhibit remarkable optical properties due to the diverse number of strongly bound excitons, which can be fine-tuned by alloying. Despite a flurry of research activity in characterizing these excitons, a comprehensive and profound understanding of their behavior with temperature is lacking. Here, we report the rich spectrum of excitonic features within bulk van der Waals alloy Mo0.5W0.5S2 and Mo0.5W0.5Se2 single crystals through temperature-dependent reflectance spectroscopy and first-principles calculations. We observed Rydberg excitons and interlayer excitons in both the single crystals. Notably, we provide the first experimental evidence of highly energetic A' and B' excitons in Mo0.5W0.5S2 at room temperature. The strong carrier-phonon scattering significantly broadens the A', B', and interlayer excitons at room temperature in bulk Mo0.5W0.5S2 single crystal compared to its selenide. Our findings, supported by density functional theory and Bethe-Salpeter equation calculations, signify the crucial role of carrier-phonon interactions. These results open pathways for next-generation optoelectronic devices and quantum technologies operating at high temperature.

Metal-halide perovskites (MHPs) with unique electronic and optical properties have emerged as promising materials with a broad spectrum of applications in photovoltaics, optoelectronic, and photonic devices. The distinct properties and tremendous potential of MHPs are intricately defined by excitons and collective quantum states. This article reviews the excitonic states and coordinated interplay of charge, spin, and lattice. We discuss the recent experimental and theoretical discoveries of excitonic phenomena, as well as correlated states involving condensation and cooperative emission. Additionally, our exploration extends to the structural properties of MHPs that facilitate the emergence of robust quantum states, even at room temperatures. Finally, an overview of the remaining challenges and potential applications of MHPs in quantum optics, coherent light sources, electrically driven amplified spontaneous emission, and superfluorescent lasing is provided.

Lead halide perovskite nanocrystals have been extensively studied in recent years as efficient optical materials for their bright and color-tunable emissions. However, these are mostly confined to their 3D nanocrystals and limited to the anisotropic nanostructures. By exploring the Cs-sublattice-induced metal(II) ion exchange with Pb(II), crack CsPbBr3 perovskite platelet nanocrystals having polar surfaces in all three directions are reported here, which remained different than reported standard square platelets. The crack platelets are also passivated with halides to enhance their brightness. Further, as these crack and passivated crack platelets have defects and polar surfaces, the exciton and biexciton generation in these platelets is investigated using femtosecond photoluminescence and transient absorption measurement at ambient as well as cryogenic temperatures, correlated with time-resolved single-particle photoluminescence spectroscopy, and compared with standard square platelets having nonpolar facets. These investigations revealed that the crack platelets and passivated crack platelets possess enhanced biexciton emission compared to square platelets due to the presence of polar surfaces in all three directions. These results provide insights into not only the design of the anisotropic nanostructures of ionic nanocrystals but also the possibility of tuning the single exciton to biexciton generation efficiency, which has potential applications in optoelectronic systems.

Hot carrier extraction is crucial for efficient solar energy harvesting, and lead halide perovskite nanocrystals (NCs) are potential candidates for photovoltaic and light-emitting applications. Therefore, swift extraction of hot carriers is an immediate requirement to improve the energy conversion efficiency, which need longer thermalization time. To address this issue, we synthesized nominally Cu-doped CsPbI3 NCs with enhanced structural and optical characteristics compared to undoped CsPbI3 NCs. We investigated the hot carrier dynamics in both the NCs at different fluences using ultrafast transient absorption spectroscopy. Interestingly, we observed very fast thermalization at higher fluences that indicated breaking of the phonon bottleneck. On the contrary, doped NCs preserved the effects and decayed over a longer period of time possibly due to increase in size and introduction of shallow trap states of Cu 3d and Cu 4s electrons in the conduction band, as computed using density functional theory. Notably, as the carrier–carrier interaction increased, we observed a dominating bandgap renormalization in the doped system compared to the undoped system. Overall, our studies improve the understanding of Cu doping in enhancing the hot carrier dynamics in perovskites and open possibilities for further investigation in the quantum phenomenon of these materials.

Transformation chemistry of atomically precise metal nanoclusters has emerged as a novel strategy for fundamental research on the structure-property correlations of nanomaterials. However, a thorough understanding of the transformation mechanism is indeed necessary to understand the structural growth patterns and corresponding property evolutions in nanoclusters. Herein, we present the ligand-exchange-induced transformation of the [Au-23(SR)(16)](-) (8e(-)) nanocluster to the [Au-25(SR ')(18)](-) (8e(-)) nanocluster, through the Au-23(SR)(17) (6e(-)) intermediate species. Identification of this key intermediate through a partially reversible transformation helped in a detailed investigation into the transformation mechanism with atomic precision. Moreover, photophysical studies carried out on this Au-23(SR)(17) species, which only differs by a single ligand from that of the [Au-23(SR)(16)](-) nanocluster reveal the property evolutions at the slightest change in the nanocluster structure.

Atomically precise, quantum-sized gold nanoclusters (NCs) exhibit interesting photoluminescence (PL) properties because of their quantized electronic energy levels and semiconductor nature. Among several parameters, the surface motifs play a crucial role in controlling the PL properties of the gold NCs. Here, a series of Au36(SR)24 NCs with varying ligand bulkiness at the para-position of benzenethiolates are synthesized and their PL properties are explored. Detailed photophysical studies revealed that the PL quantum yield (QY) of these NCs can be tailored by tuning the ligand bulkiness. Moreover, the single-crystal X-ray diffraction (SCXRD) comparison of the structural patterns and interligand interactions in these Au36(SR)24 NCs helped in the comprehension of the photophysical properties in a superior way. Overall, this work provides interesting insights into custom tailoring the structure of atomically precise NCs to find applications in these potential fields.

Photocatalytic processes are among the prime means for mitigating the pollution caused by toxic effluents. In this context, photocatalysis presents a promising path and is undergoing rapid evolution. Halide perovskite‐nanocrystals (HP‐NCs) are excellent candidates due to their negative conduction band minimum and low work function, essential for photocatalysis. Yet, HP‐NCs face limitations within this domain because they are prone to chemical degradation when exposed to external factors like high temperature, polar solvents, oxygen, and light. A practical approach toward stabilizing HP‐NCs involves hybridizing them with a chemically inert material that can provide steric stabilization and act as a cocatalyst. Transition‐metal dichalcogenides emerge as outstanding candidates to sterically stabilize the HPs as they are stable, chemically inert, and can serve as co‐catalysts, enabling suppressed charge recombination. Herein, the photocatalytic performance of Cs4PbBr6/WS2‐nanocomposites towards organic dye degradation in polar solvents under visible light illumination is investigated. We found that the presence of WS2 nanostructures significantly stabilizes the HP‐NCs and promotes dye degradation rate compared to pristine Cs4PbBr6‐NCs. Using transient absorption measurements, we found that the WS2‐nanostructures act as an electron transport channel, effectively reducing charge recombination in the NCs. These findings pave the way for implementing Cs4PbBr6/WS2‐nanocomposites as stable and superior photocatalysts.

Atomically precise copper nanoclusters (NCs) attract research interest due to their intense photoluminescence, which enables their applications in photonics, optoelectronics, and sensing. Exploring these properties requires carefully designed clusters with atomic precision and a detailed understanding of their atom-specific luminescence properties. Here, we report two copper NCs, [Cu-4(MNA)(2)(DPPE)(2)] and [Cu-6(MNA-H)(6)], shortly Cu-4 and Cu-6, protected by 2-mercaptonicotinic acid (MNA-H-2) and 1,2-bis(diphenylphosphino)ethane (DPPE), showing "turn-off" mechanoresponsive luminescence. Single-crystal X-ray diffraction reveals that in the Cu-4 cluster, two Cu-2 units are appended with two thiols, forming a flattened boat-shaped Cu4S2 kernel, while in the Cu6 cluster, two Cu-3 units form an adamantane-like Cu6S6 kernel. High-resolution electrospray ionization mass spectrometry studies reveal the molecular nature of these clusters. Lifetime decay profiles of the two clusters show the average lifetimes of 0.84 and 1.64 mu s, respectively. These thermally stable Cu NCs become nonluminescent upon mechanical milling but regain their emission upon exposure to solvent vapors. Spectroscopic data of the clusters match well with their computed electronic structures. This work expands the collection of thermally stable and mechanoresponsive luminescent coinage metal NCs, enriching the diversity and applications of such materials.

Metal halide perovskites nanocrystals(MHPN), owing to their unique and outstanding photophysical properties, have recently envisioned as promising active materials for wide range of photovoltaic and optoelectronic nanoscale device applications. Several degrees of freedom have been utilized to improve their photophysical properties with increased devise efficiency. Herein, we report the design strategy of shape engineering of CsPbBr3 nanocrystals (NCs) as a new degree of freedom for the first time to tune their photophysical properties. We demonstrate a remarkably contrasting behavior of dynamic Burstein-Moss effect (BME) and reduced many-particle Auger recombination when the shape of CsPbBr3 NCs optimized from usual 6 faceted cube to 12 faceted rhombic dodecahedron and 26 faceted rhombicuboctahedron. The BME is observed in the cubic and rhombic-dodecahedrons NCs with shift 26 and 20 meV respectively, and no shift in rhombicuboctahedron. It is observed that second-order decay is the major channel for carrier recombination with the rate of 3.68×10−10, 3.65×10−10 and 2.03×10−10 cm3 s−1 in cubic, rhombicdodecahedrons and rhombicuboctahedron. Furthermore, we reveal a manyfold reduction in gain threshold of amplified spontaneous emission (ASE) in the shape engineered NCs. These results offer critical insights into intrinsic photophysics in MHPN with direct implications for photovoltaic and optoelectronic applications by engineering shape of NCs.

Herein, the emission characteristics of diammonium N,N,N ',N '-tetramethyl-1,4-phenylenediammonium (TMPDA) are investigated based on lead iodide (TMPDA)PbI4 perovskite single crystals correlated with the localized lattice vibrations. Dual emission characteristics are ascribed to the existence of free exciton and bound exciton. The photoluminescence spectra as a function of excitation power and temperature show that structural distortion and exciton-phonon coupling impact emission characteristics substantially. The coupling strength between excitons and phonons in (TMPDA)PbI4 is estimated as gamma ac = 308.96 mu eV and gamma LO = 62.3 meV, which is much higher than inorganic semiconductors. Further, bound exciton band recombination is significantly suppressed at lower temperatures due to increased localization of carriers. Specific heat deviation from the Dulong-Petit law indicates strong coupling in the lattice. The Debye-Einstein model reveals multiple low-energy localized independent vibrations, leading to phonon coupling with bound excitons. This interplay, along with Bosonic features, significantly influences emission properties. Further, it is observed that photocurrent as a function of the incident intensity follows a law proportional to I0 alpha with alpha = 0.54, attributed to substantial bimolecular recombination of carriers. The findings of the study provide an in-depth understanding of emission characteristics, lattice distortion, and interplay of electron-phonon coupling in DJ phase 2D perovskite system.

The electrocatalytic activity of hematite (alpha-Fe2O3) in photoelectrochemical (PEC) water splitting is hindered mainly by its slow water oxidation kinetics and low absorption coefficient. In this report, we have demonstrated a facile, one-step growth of highly porous alpha-Fe2O3/Fe3O4/Fe heterojunction via controlled annealing of the Fe substrate in the presence of a moist atmosphere. This effectively improves the PEC water-splitting performance by enhancing bulk carrier density and charge transfer at the interface. The bulk transport of photogenerated electrons in this n-type catalyst is improved due to the conducting Fe3O4 underlayer through metallic Fe at the back contact. By comparing performances of nonporous mesocrystals (n-PMC) and porous mesocrystals (PMC), the latter being oxidized in water vapor, it is seen that the PMC photoanode exhibits higher PEC activity toward the PEC water splitting than n-PMC by means of a twofold improved photocurrent density, anodically shifted flat band potential from 0.16 VRHE to 0.37 VRHE, and better charge carrier transfer ability. While the presence of both the oxide phases as well as metallic Fe, their growth sequence, surface chemistry, and electronic structure were characterized using X-ray diffraction (XRD), grazing incidence XRD, Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS), the measurements do not show much changes in n-PMC and PMC; their morphology, investigated with SEM/TEM (scanning/tunneling electron microscopy), shows major differences. Interestingly, neither the core nor the valence band XPS of n-PMC and PMC samples show much differences, clearly hinting at sole morphological contributions toward improved catalytic performances in PMC. The oxide layer thicknesses are further determined to be similar to 6 mu m from interference fringes of Fourier transform infrared spectra. Thus, it is concluded that our cost-effective yet effortlessly grown PMCs of the alpha-Fe2O3/Fe3O4/Fe heterojunction are superior photoelectrocatalysts for water splitting and outperform the widely studied thin films of alpha-Fe2O3 due to their unique porous morphology. The present study thus offers new facile avenues to grow nanostructured oxide on the surface of metal substrates, which can easily be extended for other low-cost substrates, viz., zinc and copper, for realizing their potential as the electrode material for application in PEC water splitting.

Superfluorescence, a cooperative coherent spontaneous emission, is of great importance to the understanding of many-body correlation in optical processes. Even though superfluorescence has been demonstrated in many diverse systems, it is hard to observe in electron-hole plasma (EHP) due to its rapid dephasing and hence needs strong magnetic fields or complex microcavities. Herein, we report the first experimental observation of superfluorescence from EHP up to a moderate temperature of 175 K without external stimuli in a coupled metal halide perovskite quantum dots film. The EHP exhibits macroscopic quantum coherence through spontaneous synchronization. The coherence of the excited state decays by superfluorescence, which is redshifted 40 meV from the spontaneous emission with a ∼1700 times faster decay rate and exhibits quadratic fluence dependence. Notably, the excited state population's delayed growth and abrupt decay, which are strongly influenced by the pump fluence and the Burnham-Chiao ringing, are the characteristics of the superfluorescence. Our findings will open up a new frontier for cooperative emission and light beam-based technologies.

Catalytic conversion of CO2 into value-added chemicals is necessary to mitigate the increasing global warming and energy-related issues. The selective production of C2 or C2+ products by photoreduction of CO2 is a challenging task due to the sluggish kinetics of C & horbar;C coupling. Herein, the potential of a silver nanoparticle (Ag NP) incorporated metal-organic framework (MOF), NU-1000 is introduced, to harvest light and ease the uphill electron transfer. The growth of silver nanoparticles on thiol-functionalized NU-1000 is studied using the atomic pair distribution function (PDF) analysis. The C2 product formed using Ag@NU-1000-SH without any sacrificial agents is acetic acid, which is confirmed by 1H-NMR and HRMS data. The catalyst displays a high acetate output of 293.58 mu molg-1h-1 with a selectivity of 79.4%. The XPS and DFT calculations evidence that the presence of the charge-polarised states in the as-synthesized catalyst act as asymmetric centers that favor the C & horbar;C coupling reaction. The combined experimental (in situ DRIFT spectroscopic studies) and theoretical calculations reveal that the C & horbar;C coupling takes place via the coupling of COOH*intermediates.

Nonlinear optical phenomena play a critical role in understanding microscopic light-matter interactions and have far-reaching applications across various fields, such as biosensing, quantum information, optical switching, and all-optical data processing. Most of these applications require materials with high third-order absorptive and refractive optical nonlinearities. However, most materials show weak nonlinear optical responses due to their perturbative nature and often need to be improved for practical applications. Here, we demonstrate that the charge donor-acceptor hybrid of VSe2-reduced graphene oxide (rGO) hybrid exhibits enhanced ultrafast third-order absorptive and refractive nonlinearities compared to the pristine systems, at least by one order of magnitude. Through density functional theory and Bader charge analysis, we elucidate the strong electronic coupling in the VSe2-rGO hybrid, involving the transfer of electrons from VSe2 to rGO. Steady-state and time-resolved photoluminescence (PL) measurements confirm the electronic coupling and charge transfer. Furthermore, we fabricate an ultrafast optical limiter device with better performance parameters, such as an onset threshold of 2.5 mJ cm-2 and differential transmittance of 0.42.