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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]

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]