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Monolayer indium selenide (InSe), a two-dimensional material, exhibits exceptional electronic and optical properties that can be significantly modulated via strain engineering. This study employed density functional theory to examine the structural and vibrational properties of monolayer InSe under varying biaxial strains. Phonon dispersion analysis confirmed the stability of monolayer InSe, as indicated by the absence of imaginary frequencies. The study extensively detailed how Raman and infrared spectra adjust under strain, showing shifts in peak positions and variations in intensity that reflect changes in lattice symmetry and electronic structures. Specific findings include the stiffening of the A′1 mode and the increased intensity of E″ and E′ modes under strain, suggesting enhanced polarizability and asymmetric vibrations. Moreover, the Raman intensity for the E′ mode at 167.3 cm−1 increased under both tensile and compressive strain due to enhanced polarizability and symmetry disruption, while the IR intensity for the A″2 mode at 192.1 cm−1 decreased, likely from diminished dipole moment changes. In contrast, the low-frequency modes, such as E″ at 36.8 cm−1, demonstrated insensitivity to strain, implying a minimal impact on heavier atoms within these modes. Overall, this study highlights the sensitivity of vibrational modes to strain-induced changes, providing valuable insights into the behavior of monolayer InSe under mechanical stress. [ABSTRACT FROM AUTHOR]

Single‐component white‐light emitters are ideal for solid‐state lighting applications. Here, the dual‐emission white light in the 3D Cs2NaInCl6:0.1 Sb3+ crystal is successfully achieved by the high‐pressure treatment strategy. Upon compression, the remarkable self‐trapped exciton (STE) emission enhancement is observed at 20.6 GPa due to the tilting and twisting of inorganic octahedron caused by the phase transition of Cs2NaInCl6:0.1 Sb3+ crystal. Intriguingly, after undergoing the high‐pressure treatment, in addition to the blue high‐energy emission from the STEs, [SbCl6]3− exhibits the orange low‐energy emission from STEs, which is ascribed to the remaining local distortion of inorganic octahedron resulting from the presence of residual amorphous phase in the local region upon decompression. Furthermore, coherent phonon generation and density functional theory calculations indicate that the electrons exhibit a strong coupling to A1g stretch mode and T2gIn bending mode in Cs2NaInCl6:0.1 Sb3+. After high‐pressure treatment, the coupling between the electrons and the T2gIn bending mode disappears, suggesting local octahedral symmetry disruption due to residual amorphous structures induced by high‐pressure treatment. This work unveils the relationship between the electron‐phonon coupling and the STE emission and offers a new strategy to design and synthesize the new single‐component white‐light metal halide perovskites. [ABSTRACT FROM AUTHOR]

I–III–VI2 semiconductor nanocrystals (NCs), such as typical AgInS2 NCs, are promising candidates for fluorescent materials because of their lower toxicity and tunable optical properties. However, a long‐standing conventional dispute over the origin of defect emission of AgInS2 NCs restricts the material design and applications. Here, high pressure is introduced to distinguish the photophysical behavior of a core@shell structure of AgInS2@InSx NCs that exhibit both band‐edge (BE) emission and defect emission. Compared with the well‐established dopant mechanism of Ag+:CdS NCs, the decreasing relative shift of defect/BE emissions for AgInS2@InSx NCs excludes the Ag‐related emission associated with radiative free‐to‐bound recombination that contributes to the defect emission of AgInS2 NCs. Identification by the in situ high‐pressure transient spectra and comparative experiments passivated with different ligands, the donor−acceptor pair (DAP) recombination is responsible for the observed defect emission. Likewise, a narrow and strong BE emission with 5.3‐fold enhancement is achieved in AgInS2@InSx NCs by pressure processing. This in turn further confirms the DAP‐related origin of the defect emission. Overall, this study enables high pressure as a tool to resolve the traditional debate under ambient conditions, which facilitates the fundamental photophysical understanding for materials by design applied in solid‐state lighting. [ABSTRACT FROM AUTHOR]

The striking change in the emission color/intensity of piezochromic luminescent materials in response to external mechanical stimuli (e.g., pressure, grinding, and stretching) has attracted attention due to potential applications in optical data storage devices, pressure sensors, and optoelectronic devices. The majority of organic materials show redshifted and quenched emission with increasing pressure. Herein, covalently linked donor/acceptor (D/A) o‐carborane dyads that exhibit dual luminescence peaks due to the occurrence of photoinduced electron transfer (PET) are reported. Interestingly, an anomalous phenomenon of pressure‐induced blueshifted and enhanced luminescence is clearly observed. From 1 atm to 1.09 GPa, the restriction of intramolecular motion increases the luminescence of o‐carborane dyads. At high pressures, the compressed o‐carborane unit suppresses PET and decreases the energy gap between the upper excited states. Since the rate of the internal conversion (IC) process is higher than that of PET, the charge transfer (CT) emission gradually disappears, causing the o‐carborane dyads to exhibit blueshifted luminescence. Therefore, a novel strategy for achieving the pressure‐induced enhanced and blueshifted luminescence characteristics of organic materials is reported in this work. [ABSTRACT FROM AUTHOR]

The excellent luminescence properties and structural dynamics driven by the stereoactivity of the lone pair in a variety of low‐dimensional ns2 metal halides have attracted growing investigations for optoelectronic applications. However, the structural and photophysical aspects of the excited state associated with the lone pair expression are currently open questions. Herein, zero‐dimensional Sn‐based halides with static stereoactive 5 s2 lone pairs are selected as a model system to understand the correlations between the distinctive lone pair expression and the excited‐state structural relaxation and charge carrier dynamics by continuous lattice manipulation. Lattice compression drives 5 s2 lone pair active switching and self‐trapped exciton (STE) redistribution by suppressing excited‐state structural deformation of the isolated SnBr42− units. Our results demonstrate that the static expression of the 5 s2 lone pair results in a red broadband triplet STE emission with a large Stokes shift, while its dynamic expression creates a sky‐blue narrowband emission dominated by the radiative recombination of singlet STEs. Our findings and the photophysical mechanism proposed highlight the stereochemical effects of lone pair expression in controlling light emission properties and offer constructive guidelines for tuning the optoelectronic properties in diverse ns2 metal halides. [ABSTRACT FROM AUTHOR]

It is challenging to realize ultra‐pH‐responsive fluorescent carbon dots (CDs), especially reversibly adjustable multichromatic emission covering a broad wavelength range including deep‐red lasing. This study reports a one‐step solvothermal treatment of pyrogallol to obtain brilliant CDs with a substantial bathochromic shift (from blue to dark red emission) induced by pH changes. The CDs show an excellent reversible pH response: simple acid treatment instantaneously shifts their initial green emission by 140 nm to a deep‐red emission with high‐color‐purity and enhances brightness, subsequent alkali addition returned the green emission, suggesting smooth and reversible regulation of fluorescence. Detailed components analyses, morphology tracking, and photodynamic studies demonstrate the discrete, reversible shift of emission derived from structural transformations, which include protonation of the CDs and their subsequent assembly and partial aggregation triggered by hydrogen bonding. The abundant H‐bonds crosslink the network of CDs, ultimately raising the quantum yield from 11.3% to 16.0%. Furthermore, the aggregated CDs crystallized into sheet‐like structures that acted as a resonant cavity for lasing show excellent gain ability and lead to strong deep‐red lasing. This study draws together pH regulation, the effects of CD's assembly, and their lasing emission to demonstrate significant potential for the development of versatile CDs. [ABSTRACT FROM AUTHOR]

Carbon quantum dots (CQDs) feature bright and tunable photoluminescence, solution processability, and low toxicity, showing great potential in optoelectronics. However, the large‐scale synthesis of CQDs with near‐unity photoluminescence quantum yield (PLQY) has not been achieved so far. In this study, we perform radical‐assisted synthesis of hexagon‐shaped CQDs (H‐CQDs) delivering near‐unity PLQY (96 %). Experimental and theoretical analyses revealed that the large vertically oriented transition dipole moment of H‐CQDs originating from high symmetry results in nearly 100 % PLQY. The H‐CQDs also exhibited a high electron mobility of up to 0.07 cm2 V−1 s−1. These properties enable the H‐CQD‐based light‐emitting diodes with a high external quantum efficiency of 4.6 % and a record maximum brightness of over 11 000 cd m−2. This study represents a significant advance that CQDs‐based electroluminescent device can be utilized for potential display and lighting applications. [ABSTRACT FROM AUTHOR]

The wide application of excimer materials in the OLED field is mainly based on the regulation of their stacking structure. Therefore, based on whether anthracene groups can form excimers, three anthracene derivative molecules with sterically hindered substituents were designed and their crystals with different aggregating structures were prepared to study the relationship between their structures and properties. Under high pressures, these anthracene groups exhibit enhanced fluorescence during the formation of excimers (in the pressure range of 2.3 to 4.2 GPa) while the anthracene groups that have already formed excimers under ambient conditions exhibit a wider red-shift range. Their abundant piezochromic fluorescence behavior indicate that regulating the aggregation mode of anthracene groups can meet different application requirements and provide guidance for the expansion of the application of excimer materials. [ABSTRACT FROM AUTHOR]

Pressure‐induced emission (PIE) associated with self‐trapping excitons (STEs) in low‐dimensional halide perovskites has attracted great attention for better materials‐by‐design. Here, using 2D layered double perovskite (C6H5CH2CH2NH3+)4AgBiBr8 as a model system, we advance a fundamental physicochemical mechanism of the PIE from the perspective of carrier dynamics and excited‐state behaviors of local lattice distortion. We observed a pressure‐driven STE transformation from dark to bright states, corresponding a strong broadband Stokes‐shifted emission. Further theoretical analysis demonstrated that the suppressed lattice distortion and enhanced electronic dimensionality in the excited‐state play an important role in the formation of stabilized bright STEs, which could manipulate the self‐trapping energy and lattice deformation energy to form an energy barrier between the potential energy curves of ground‐ and excited‐state, and enhance the electron‐hole orbital overlap, respectively. [ABSTRACT FROM AUTHOR]

Multiphoton absorption (MPA) effects are suitable for biophotonic applications due to the long penetration depth and high spatial confinement. Compared with lead halide perovskites, relevant studies on MPA effects of lead‐free perovskites are still scarce, especially for the high‐order MPA effects. Herein, an all‐inorganic lead‐free Cs2TeCl6 perovskite crystal is reported that exhibits three‐ to six‐photon absorption (3PA to 6PA) effects over a wavelength range of 800–2200 nm. The results of steady and transient optical experiments indicate that the single‐ and multiphoton excited broadband orange emission in Cs2TeCl6 crystals is attributed to the self‐trapped excitons (STEs) recombination. What is more, the 6PA cross‐section (δ6) has been determined to be 1.87 × 10−174 cm12 s5 photon−5 (at 1980 nm). As far as it is known, the high‐order 6PA effect is unprecedented in lead‐free perovskites, which paves the way for the future development of lead‐free perovskite high‐order multiphoton application. [ABSTRACT FROM AUTHOR]

Reactive oxygen species (ROS) play important roles in cell signaling, immunity, and tissue homeostasis. The overproduction of ROS can induce the pathogenesis of various diseases. Carbon dots (CDs) are promising fluorescence materials for sensing and imaging ROS in cells, and they have great therapeutic potential for scavenging ROS. Herein, a kind of red emissive carbon dots (R-CDs) was synthesized by the hydrothermal treatment of o-phenylenediamine (OPD) and catechol in the presence of phosphoric acid (H3PO4). With the strong traction effect of H3PO4 in the hydrothermal process, these precursors undergo orientated polymerization and carbonization to form R-CDs with a uniformly conjugated structure. More significantly, the resultant R-CDs have a high yield (87.0 wt%), narrow full width at half maxima (FWHM) emission band of 21 nm, and sensitive colorimetric and fluorescence response to hydroxyl radical (˙OH), superoxide radical anion (˙O2−), and singlet oxygen (1O2) without interference from H2O2. Femtosecond transient absorption (fs-TA) spectra confirmed that the excited states of oxidized R-CDs (Ox-R-CDs) have a significantly increased absorbance in the range of 600–700 nm, and the absorbed photons are deactivated in a non-radiation form, which is responsible for the decrease in fluorescence upon reaction with ROS. Experimental characterizations and density functional theory (DFT) calculations revealed that R-CDs comprised two five-membered aromatic rings linked by pyrophosphate groups. The amino terminals of the aromatic ring are protected by phosphate groups, which should be responsible for the inactivity of R-CDs to H2O2. This study provides a new strategy for the synthesis of R-CDs with narrow FWHM and also provides a new metal-free nanoprobe with high sensitivity for ROS detection and imaging. [ABSTRACT FROM AUTHOR]

Mechanoresponsive luminescent (MRL) materials have become a high-profile research system in the fields of force sensing, anti-counterfeiting, and optical information storage because of their obvious variety on luminescence intensity or luminescence color under mechanical force. In this work, nitro-triphenylamine (TPA-NO2) crystal was selected to conduct in situ high pressure experiments based on diamond anvil cell combined with theory calculation, and the piezochromism of TPA-NO2 crystal was discussed in detail. During the compression process, the TPA-NO2 crystal showed the piezochromic behavior and a redshift of the emission peak. The mechanical response behavior of TPA-NO2 provides insight into the study of multicolor properties from a structural perspective, offering a clean means of using pressure to modulate different colors and contributing to the exploration of high-potency MRL materials. [ABSTRACT FROM AUTHOR]

Turn-on thermosensitive carbon dots (CDs) with dual functions of imaging and sensing are desirable for biological research and clinical diagnosis at the cellular level. Herein, we synthesized eight types of novel CDs by solvothermal treatment of selected carbon sources and chromatographic purification for turn-on fluorescence measurement of temperature and cell imaging. Comprehensive experimental characterization and theoretical calculations were conducted to reveal the structure and photoluminescence (PL) of the as-prepared CDs. The results elucidate that the co-planarization and electron cloud density distribution of the fluorophores can be regulated by the intramolecular hydrogen bonds, resulting in the temperature turn-on fluorescence response of the CDs by the effective suppression of nonradiative decay and enhancement of the radiative decay process during heating. The fluorescence responses are reversible to temperature variations in the tested range from 15 to 85 °C. The highest temperature sensitivity up to 5.3%/°C with a resolution of 0.09 °C is observed among all the prepared CDs, which is probably the most sensitive fluorescence thermometer reported so far. Moreover, the CDs exhibit excellent water solubility, minimal toxicity and superb photostability. Thus they have been successfully used as a dual functional turn-on nanothermometer with intracellular imaging probing features, demonstrating a promising prospect in the study of cellular states and functions with respect to temperature changes. [ABSTRACT FROM AUTHOR]

Pressure engineering can access novel optoelectronic properties and crystal structures in halide perovskite materials with soft lattice. However, such pressure‐induced phenomena are commonly realized under large pressure or difficult to retain at atmospheric pressure, thus severely hindering their prospects in practical applications. Herein, the pressure‐treated Mn‐doped/undoped Cs2NaBiCl6 exhibits a largely retained bandgap narrowing of 12.2% relative to its initial state via compression–decompression cycles, along with durable stability at ambient conditions. This abnormal behavior is attributed to the disordered arrangement of inorganic [NaCl6]5−/[BiCl6]3− octahedra, which occurs in the metastable state of double perovskites from structural reconstruction during decompression processes, and is accompanied by a characteristic of long‐range order and short‐range disorder. A remarkable pressure‐induced emission enhancement from Mn2+ ions is discovered upon modest compression, especially at <0.5 GPa, which results from the increased energy transfer efficiency from Bi3+ to Mn2+ ions owing to more overlapped electronic wave functions from each other. This work can be extended to the design and synthesis of new semiconductor materials with enhanced optoelectronic properties. [ABSTRACT FROM AUTHOR]

Light‐emitting chiral carbonized polymer dots (Ch‐CPDs) are attracting great interest because of their extraordinary photonic properties, but modulating their band‐gap emission, especially at long wavelength, and maintaining their chiral structure to achieve multicolor, high‐emission Ch‐CPDs remains challenging. Reported here for the first time is the synthesis of red‐ and multicolor‐emitting Ch‐CPDs using the common precursors L‐/D‐tryptophan and o‐phenylenediamine, and a solvothermal approach at one temperature. The quantum yield of the Ch‐CPDs was between 31 % and 54 %. Supramolecular self‐assembly provided multicolor‐emitting Ch‐CPDs showing novel circularly polarized luminescence, with the highest dissymmetric factor (glum) of 1×10−2. Importantly, circularly polarized white‐emitting CPDs were fabricated for the first time by tuning the mixing ratio of the three colored Ch‐CPDs in a gel. This strategy affords exciting opportunities for designing functional chiroptical materials. [ABSTRACT FROM AUTHOR]

As an emerging building unit, carbon dots (CDs) have been igniting the revolutionaries in the fields of optoelectronics, biomedicine, and bioimaging. However, the difficulty of synthesizing CDs in aqueous solution with full‐spectrum emission severely hinders further investigation of their emission mechanism and their extensive applications in white light emitting diodes (LEDs). Here, the full‐color‐emission CDs with a unique structure consisting of sp3‐hybridized carbon cores with small domains of partially sp2‐hybridized carbon atoms are reported. First‐principle calculations are initially used to predict that the transformation from sp3 to sp2 hybridization redshifts the emission of CDs. Guided by the theoretical predictions, a simple, convenient, and controllable route to hydrothermally prepare CDs in a single reaction system is developed. The prepared CDs have full‐spectrum emission with an unprecedented two‐photon emission across the whole visible color range. These full‐color‐emission CDs can be further nurtured by slight modifications of the reaction conditions (e.g., temperature, pH) to generate the emission color from blue to red. Finally a flexible LEDs with full‐color emission by using epoxy CDs films is developed, indicating that the strategy affords an industry translational potential over traditional fluorophores. [ABSTRACT FROM AUTHOR]

Designing low‐dimensional halide perovskites (LDHPs) for broadband emissions with enhanced emission and preferred chromaticity coordinator or color temperature remains a pressing challenge. Herein, a comprehensive study is conducted about the relationship between the crystal structure and broadband emission properties of 1D halide perovskite C4N2H14PbBr4, one of promising white‐emission LDHPs. It is found that the zigzag distortion degree tuned by pressure not only suppresses the general photoluminescence quenching, but also effectively adjusts the chromaticity coordinator and color temperature of C4N2H14PbBr4 nanocrystals (NCs). The initially broad white emissive C4N2H14PbBr4 NCs can be continuously modulated to a very bright bluish‐white emission with high color‐rendering index of 86, accompanied by a significant emission enhancement. The underlying mechanism of thus pressure‐induced emission enhancement (PIEE) can be attributed to the strengthening of electron–phonon interactions of compressed C4N2H14PbBr4 NCs. Furthermore, the zigzag distortion of [PbBr42−]∞ octahedral chains is able to rearrange the depths of multiple self‐trapped states, which is also corroborated by the wavelength‐dependent decay times under pressure, ultimately giving rise to adjustable emission chromaticity. This study offers a deep insight into the relationship between PIEE and distortion degree of LDHPs at extremes and facilitates the design of new materials with the desired emission properties. [ABSTRACT FROM AUTHOR]

Lithium-ion batteries are an attractive power source for a wide variety of applications. Expanding the performance limit of current Li-ion batteries requires ion–solvent interaction, which governs the ion transport behavior of electrolytes, to be fully understood. We herein examine the coordination number of the Li+ ion in LiPF6–PC solutions using femtosecond vibrational spectroscopy. Surprisingly, we found that the coordination number of PC in the first solvation shell of Li+ decreases from 4 to 2 as the salt concentration increases. At dilute salt concentrations, the Li(PC)4+ complex with a tetrahedral geometry is dominant, while at high salt concentrations, the presence of anions in the first solvation shell modifies the solvation structure, leading only 2 PC molecules to coordinate to Li+ directly. The variety of the solvation structure provides a rational explanation for the ionic conductivity changing as the salt concentration increases. [ABSTRACT FROM AUTHOR]