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The unique intermolecular van der Waals force in emerging two-dimensional inorganic molecular crystals (2DIMCs) endows them with highly tunable structures and properties upon applying external stimuli. Using high pressure to modulate the intermolecular bonding, here we reveal the highly tunable charge transport behavior in 2DIMCs for the first time, from an insulator to a semiconductor. As pressure increases, 2D α-Sb2O3 molecular crystal undergoes three isostructural transitions, and the intermolecular bonding enhances gradually, which results in a considerably decreased bandgap by 25% and a greatly enhanced charge transport. Impressively, the in-situ resistivity measurement of the α-Sb2O3 flake shows a sharp drop by 5 orders of magnitude in 0 - 3.2 GPa. This work sheds new light on the manipulation of charge transport in 2DIMCs and is of great significance for promoting the fundamental understanding and potential applications of 2DIMCs in advanced modern technologies.

Two rare earth oxysulfides Ln 5V3O7S6 (Ln = La, Ce) have been synthesized and their structures determined. The two isostructural compounds crystallize in the orthorhombic space group Pmmn (no. 59). The structure features one-dimensional edge-sharing VS4O2 octahedron chains parallel to the b axis. The bonding between V and S/O is covalent, and between Ln 3+ and the rest of the matrix ionic. Magnetic susceptibility measurement revealed that V is in a mixed valence state of V3+ and V4+. Its magnetic behavior follows the Curie-Weiss law.

Two-dimensional (2D) semiconductor heterostructures are key building blocks for many electronic and optoelectronic devices. Reconfiguring the band-edge states and modulating their interplay with charge carriers at the interface in a continuous manner have long been sought yet are challenging. Here, using organic semiconductor–incorporated 2D halide perovskites as the model system, we realize the manipulation of band-edge states and charge distribution via mechanical—rather than chemical or thermal—regulation. Compression induces band-alignment switching and charge redistribution due to the different pressure responses of organic and inorganic building blocks, giving controllable emission properties of 2D perovskites. We propose and demonstrate a “pressure gating” strategy that enables the control of multiple emission states within a single material. We also reveal that band-alignment transition at the organic-inorganic interface is intrinsically not well resolved at room temperature owing to the thermally activated transfer and shuffling of band-edge carriers. This work provides important fundamental insights into the energetics and carrier dynamics of hybrid semiconductor heterostructures.

Organic-inorganic hybrid semiconducting (OIHS) materials, which can detect broader spectral regions, are highly desired in several applications including biomedical imaging, night vision, and optical communications. Although lead (Pb)-halide perovskites have reached a mature research stage, high toxicity of Pb hinders their large-scale viability. Tin (Sn)-based perovskites are the most common OIHS broadband light absorbers that replace toxic Pb; however, they are extremely unstable due to the notorious Sn

Pressure processing is efficient to regulate the structural and physical properties of two-dimensional (2D) halide perovskites which have been emerging for advanced photovoltaic and light-emitting applications. Increasing numbers of studies have reported pressure-induced and/or enhanced emission properties in the 2D halide perovskites. However, no research has focused on their photoresponse properties under pressure tuning. It is also unclear how structural change affects their excitonic features, which govern the optoelectronic properties of the halide perovskites. Herein, we report significantly enhanced photocurrents in the all-inorganic 2D perovskite Cs2PbI2Cl2, achieving over 3 orders of magnitude increase at the industrially achievable level of 2 GPa in comparison with its initial photocurrent. Lattice compression effectively regulates the excitonic features of Cs2PbI2Cl2, reducing the exciton binding energy considerably from 133 meV at ambient conditions to 78 meV at 2.1 GPa. Impressively, such a reduced exciton binding energy of 2D Cs2PbI2Cl2 is comparable to the values of typical 3D perovskites (MAPbBr3 and MAPbI3), facilitating the dissociating of excitons into free carriers and enhancing the photocurrent. Further pressurization leads to a layer-sliding-induced phase transition and an anomalous negative linear compression, which has not been observed so far in other halide perovskites. Our findings reveal the dramatically enhanced photocurrents in the 2D halide perovskite by regulating its excitonic features and, more broadly, provide new insights into materials design toward extraordinary properties.

Lone-pair electrons (LPEs) ns2 in subvalent 14 and 15 groups lead to highly anharmonic lattice and strong distortion polarization, which are responsible for the groups' outstanding thermoelectric and optoelectronic properties. However, their dynamic stereochemical role in structural and physical properties is still unclear. Here, by introducing pressure to tune the behavior of LPEs, we systematically investigate the lone-pair stereochemical role in a Bi2O2S. The gradually suppressed LPEs during compression show a nonlinear repulsive electrostatic force, resulting in two anisotropic structural transitions. An orthorhombic-to-tetragonal phase transition happens at 6.4 GPa, caused by the dynamic cation centering. This structural transformation effectively modulates the optoelectronic properties. Further compression beyond 13.2 GPa induces a 2D-to-3D structural transition due to the disappearance of the Bi-6s2 LPEs. Therefore, the pressure-induced LPE reconfiguration dominates these anomalous variations of lattice, electronic, and optical properties. Our findings provide new insights into the materials optimization by regulating the characters of LPEs.

A remarkable PL enhancement by 12 fold is achieved using pressure to modulate the structure of a recently developed 2D perovskite (HA)2 (GA)Pb2 I7 (HA=n-hexylammonium, GA=guanidinium). This structure features a previously unattainable, extremely large cage. In situ structural, spectroscopic, and theoretical analyses reveal that lattice compression under a mild pressure within 1.6 GPa considerably suppresses the carrier trapping, leading to significantly enhanced emission. Further pressurization induces a non-luminescent amorphous yellow phase, which is retained and exhibits a continuously increasing band gap during decompression. When the pressure is released to 1.5 GPa, emission can be triggered by above-band gap laser irradiation, accompanied by a color change from yellow to orange. The obtained orange phase could be retained at ambient conditions and exhibits two-fold higher PL emission compared with the pristine (HA)2 (GA)Pb2 I7 .

A novel two-dimensional (2D) oxysulfide, Sr3.5Pb2.5Sb6O5S10, with a band gap of 1.34 eV was successfully synthesized. The device exhibits notable current density enhancement under irradiation (Jlight/Jdark = 38.7 at 10 V) as well as a steady and reversible on/off switching mode.

Designing new semiconductors with an extremely low thermal conductivity is of considerable significance. In this study, we successfully synthesized a new semiconductor SrOCuBiSe2 with an intrinsically low thermal conductivity via the molten salt method. It possesses a typical multicomponent layered structure which is composed of alternatively stacked [CuBiSe2] (electronic conduction unit, ECU) and [SrO] (electronic insulation unit, EIU) layers. Its intrinsically low thermal conductivity (κ = 0.45 W m-1 K-1 at 700 K) is attributed to the dual effects of high atomic displacement parameter and extremely large Gruneisen parameter, which are caused by rattling vibration of Cu atoms and lone-pair electrons of Bi atoms, respectively. Such knowledge highlights the importance of lone-pair electrons in impelling the phonon anharmonicity and multicomponent structure design concept, providing a stepping stone to the design of new semiconductors with a low thermal conductivity.

Molecular crystals of dicoronylene (C48H20), a member of very large polycyclic aromatic hydrocarbons (PAHs), exhibits strong red fluorescence under ambient conditions. This strong fluorescence induced by visible light excitation obscures entire Raman spectrum of dicoronylene. We employed in-situ high-pressure photoluminescence spectroscopy to observe a reversible piezochromic effect, in which the fluorescence exhibits a drastic red-shift with a rapid quenching of intensity. Above 4 GPa, under red-shifted and reduced fluorescence, hidden Raman modes are observed with 532 nm green laser up to 20 GPa. In this work, we show that the application of pressure can finely tune the fluorescence of dicoronylene, allowing the observation of the Raman spectrum with an appropriate laser wavelength and we discovered that dicoronylene has high chemical stability among PAH molecules with multiple aromatic rings.

Solids can be generally categorized by their structures into crystalline and amorphous states with different interactions among atoms dictating their properties. Crystalline-amorphous hybrid structures, combining the advantages of both ordered and disordered components, present a promising opportunity to design materials with emergent collective properties. Hybridization of crystalline and amorphous structures at the sublattice level with long-range periodicity has been rarely observed. Here, we report a nested order-disorder framework (NOF) constructed by a crystalline matrix with self-filled amorphous-like innards that is obtained by using pressure to regulate the bonding hierarchy of Cu12Sb4S13. Combined in situ experimental and computational methods demonstrate the formation of disordered Cu sublattice which is embedded in the retained crystalline Cu framework. Such a NOF structure gives a low thermal conductivity (~0.24 W·m−1·K−1) and a metallic electrical conductivity (8 × 10−6 Ω·m), realizing the collaborative improvement of two competing physical properties. These findings demonstrate a category of solid-state materials to link the crystalline and amorphous forms in the sublattice-scale, which will exhibit extraordinary properties.

Earth-abundant antimony trisulfide (Sb2S3), or simply antimonite, is a promising material for capturing natural energies like solar power and heat flux. The layered structure, held up by weak van-der Waals forces, induces anisotropic behaviors in carrier transportation and thermal expansion. Here, we used stress as mechanical stimuli to destabilize the layered structure and observed the structural phase transition to a three-dimensional (3D) structure. We combined in situ x-ray diffraction (XRD), Raman spectroscopy, ultraviolet-visible spectroscopy, and first-principles calculations to study the evolution of structure and bandgap width up to 20.1 GPa. The optical band gap energy of Sb2S3 followed a two-step hierarchical sequence at approximately 4 and 11 GPa. We also revealed that the first step of change is mainly caused by the redistribution of band states near the conduction band maximum. The second transition is controlled by an isostructural phase transition, with collapsed layers and the formation of a higher coordinated bulky structure. The band gap reduced from 1.73 eV at ambient to 0.68 eV at 15 GPa, making it a promising thermoelectric material under high pressure. Antimonite (Sb2S3) has potential applications for solar energy, but how its layered structure changes under pressure is incompletely understood. Here diamond anvil cell experiments supported by first principles calculations offer a structural explanation for experimentally observed phase transitions.

Low‐dimensional hybrid metal halides are emerging as a highly promising class of single‐component white‐emitting materials for their unique broadband emission from self‐trapped excitons (STEs). Despite substantial progress in the development of these metal halides, many challenges remain to be addressed to obtain a better fundamental understanding of the structure–property relationship and realize the full potentials of this class of materials. Here, via pressure regulation, a near 100% photoluminescence quantum yield (PLQY) of broadband emission is achieved in a corrugated 1D hybrid metal halide C5N2H16Pb2Br6, which possesses a highly distorted structure with an initial PLQY of 10%. Compression reduces the overlap between STE states and ground state, leading to a suppressed phonon‐assisted non‐radiative decay. The PL evolution is systematically demonstrated to be controlled by the pressure‐regulated exciton–phonon coupling which can be quantified using Huang–Rhys factor S. Detailed studies of the S‐PLQY relation for a series of 1D hybrid metal halides (C5N2H16Pb2Br6, C4N2H14PbBr4, C6N2H16PbBr4, and (C6N2H16)3Pb2Br10) reveal a quantitative structure–property relationship that regulating S factor toward 28 leads to the maximum emission., This work demonstrates a quantitative relationship between photoluminescence quantum yield (PLQY) and exciton–phonon coupling in a series of 1D hybrid metal halides. Using pressure to regulate the exciton–phonon interaction, a near 100% PLQY of broadband emission from self‐trapped excitons is achieved in a corrugated 1D compound C5N2H16Pb2Br6 whose initial PLQY is 10%.

Layered sulfides with high selectivity for binding heavy metal ions and radionuclide ions are promising materials in effluent treatment and water purification. Here we present a rationally designed layered sulfide Kx[Bi4-xMnxS6] (x = 1.28) deriving from the Bi2Se3-structure type by targeted substitution to generate quintuple [Bi4-xMnxS6]x- layers and K+ cations between them. The material has dual functionality: it is an attractive semiconductor with a bandgap of 1.40 eV and also an environmental remediation ion-exchange material. The compound is paramagnetic, and optical adsorption spectroscopy and DFT electronic structure calculations reveal that it possesses a direct band gap and a work function of 5.26 eV. The K+ ions exchange readily with alkali or alkaline-earth ions (Rb+, Cs+, and Sr2+) or soft ions (Pb2+, Cd2+, Cr3+, and Zn2+). Furthermore, when the K+ ions are depleted the Mn2+ ions in the Bi2Se3-type slabs can also be replaced by soft ions, achieving large adsorption capacities. The ion exchange reactions of Kx[Bi4-xMnxS6] can be used to create new materials of the type Mx[Bi4-xMnxS6] in a low temperature kinetically controlled manner with significantly different electronic structures. The Kx[Bi4-xMnxS6] (x = 1.28) exhibits efficient capture of Cd2+ and Pb2+ ions with high distribution coefficient, Kd (107 mL/g), and exchange capacities of 221.2 and 342.4 mg/g, respectively. The material exhibits excellent capacities even in high concentration of competitive ions and over a broad pH range (2.5-11.0). The results highlight the promise of the Kx[Bi4-xMnxS6] (x = 1.28) phase to serve not only as a highly selective adsorbent for industrial and nuclear wastewater but also as a magnetic 2D semiconductor for optoelectronic applications.

The layered oxyselenides with the formula LnCrSe2O (Ln = Ce-Nd) were synthesized via molten salt methods. The isostructural compounds crystallize in the monoclinic space group of C2/m. The crystal structures feature ∞2[CrSe2O]3- motifs stacked along the a axis, which are separated by Ln3+ ions. The ∞2[CrSe2O]3- layers are composed of [Cr1Se6]9- and [Cr2Se4O2]9- octahedra via corner and edge sharing. Powder X-ray diffraction results confirm the phase purities of the as-synthesized compounds. LnCrSe2O (Ln = Ce-Nd) show typical antiferromagnetic ordering with TN = 125, 120, and 118 K, respectively. Heat capacity measurement for NdCrSe2O indicates that the Debye temperature is 278.4 K. Similar metal-to-semiconductor phase transitions were observed for LnCrSe2O (Ln = Ce-Nd) plates with transition temperatures of 115, 109, and 95 K, respectively. NdCrSe2O also possesses a magnetoresistance effect at low temperature (

Determination of the crystal structure of Rb0.21(H2O)yWS2 is beneficial to understanding the topotactic reaction process to form metastable WS2. The temperature dependence of the electrical resistance indicates that Rb0.21(H2O)yWS2 is semiconducting at 80-300 K., Rb0.21(H2O)yWS2, rubidium hydrate di­thio­tungstate, is a new quasi two-dimensional sulfide. Its crystal structure consists of ordered WS2 layers, separated by disordered Rb+ ions and water mol­ecules. All atomic sites are located on mirror planes. The WS2 layers are composed of edge-sharing [WS6] octa­hedra and extend parallel to (001). The presence of structural water was revealed by thermogravimetry, but the position and exact amount could not be determined in the present study. The temperature dependence of the electrical resistance indicates that Rb0.21(H2O)yWS2 is semiconducting between 80–300 K.

A new nonlinear optical (NLO) oxysulfide, Sr6 Cd2 Sb6 O7 S10 , which contains the functional groups [SbOx S5-x ]7- (x=0, 1) with a 5s2 electron configuration, is synthesized by a solid-state reaction. This compound displays a phase-matchable second harmonic generation (SHG) response four times stronger than AgGaS2 (AGS) under laser irradiation at 2.09 μm. Single-crystal-based optical measurements reveal a SHG intensity that can be tuned by temperature and novel photoluminescence properties. Theoretical analyses demonstrate that tetragonal [SbOS4 ]7- and [SbS5 ]7- pyramids make the predominant contribution to the enhanced SHG effect. Among those, the [SbOS4 ]7- units with mixed anions make a larger contribution. This work proposes that oxysulfide groups with an ns2 electron configuration can serve as new functional building units in NLO materials and opens a new avenue for the design of other optoelectronic materials.

Exploring novel electrocatalysts with prominent performance is highly demanded for electrochemical hydrogen evolution. As one family member of layered transition-metal dichalcogenides (TMDs), metal...

Noncentrosymmetric MoS2 semiconductors (1H, 3R) possess not only novel electronic structures of spin-orbit coupling (SOC) and valley polarization but also remarkable nonlinear optical effects. A more interesting noncentrosymmetric structure, the so-called 1T‴-MoS2 layers, was predicted to be built up from [MoS6] octahedral motifs by theoreticians, but the bulk 1T‴ MoS2 or its single crystal structure has not been reported yet. Here, we have successfully harvested 1T‴ MoS2 single crystals by a topochemical method. The new layered structure is determined from single-crystal X-ray diffraction. The crystal crystallizes in space group P31m with a cell of a = b = 5.580(2) A and c = 5.957(2) A, which is a √3 a × √3 a superstructure of 1T MoS2 with corner-sharing Mo3 triangular trimers observed by the STEM. 1T‴ MoS2 is verified to be semiconducting and possesses a band gap of 0.65 eV, different from metallic nature of 1T or 1T' MoS2. More surprisingly, the 1T‴ MoS2 does show strong optical second-harmonic generation signals. This work provides the first layered noncentrosymmetric semiconductor of edge-sharing MoS6 octahedra for the research of nonlinear optics.

Multiband materials have received increasing attention due to their superior solar absorption properties. Here we design a new multiband compound, namely Ba5Bi2Co2S10, which crystallizes in the space group C22h-P21/m (No. 11) of the monoclinic system. Ba5Bi2Co2S10 is composed of one-dimensional 1∞[Bi2Co2S10]10- chains along the a axis. The adjacent chains are separated by Ba2+ ions. The optical band gap of the compound is 1.05 eV and 0.74 eV, presenting typical multi-absorption characteristics. First-principles calculations, which are perfectly consistent with the experimental results, show that the hybrid coupling effect between Co and S gives rise to multiband characteristics. Evident optoelectronic conversion properties were observed under visible light illumination with a photocurrent density of 4.0 mA cm-2 at 1 V.

The extraordinary oxygen evolution reaction (OER) in alkaline fuel cells and water-splitting systems demands a high electron transfer rate and catalysts with numerous active sites and massive hydroxyl groups. Herein, we proposed a new heterostructure of nanosheets 〈electron depletion|interfacial reaction center|hydroxyl captor〉, demonstrated as 〈nickel nitride (Ni3N)|nickel phosphide (Ni2P)|black phosphorus (BP)〉. Compared with other catalysts reported for the OER, the 〈Ni3N|Ni2P|BP〉 heterostructure shows superior electrocatalytic performance with an ultralow overpotential of 247 mV at 10 mA cm−2 and high durability in alkaline electrolytes. The high performance of the catalyst results from (i) the superior capability of the hydroxyl groups captured by ultrathin oxide layers on the catalyst surface; (ii) the stable connection between Ni3N and BP via the formation of the Ni2P interface; and (iii) the excellent electron transfer rate due to the metallic nature of Ni3N.

Pressure processing is efficient to regulate the structural and physical properties of two-dimensional (2D) halide perovskites which have been emerging for advanced photovoltaic and light-emitting applications. Increasing numbers of studies have reported pressure-induced and/or enhanced emission properties in the 2D halide perovskites. However, no research has focused on their photoresponse properties under pressure tuning. It is also unclear how structural change affects their excitonic features, which govern the optoelectronic properties of the halide perovskites. Herein, we report significantly enhanced photocurrents in the all-inorganic 2D perovskite Cs

Metal halide perovskites possess unique atomic and electronic configurations that endow them with high defect tolerance and enable high-performance photovoltaics and optoelectronics. Perovskite light-emitting diodes have achieved an external quantum efficiency of over 20%. Despite tremendous progress, fundamental questions remain, such as how structural distortion affects the optical properties. Addressing their relationships is considerably challenging due to the scarcity of effective diagnostic tools during structural and property tuning as well as the limited tunability achievable by conventional methods. Here, using pressure and chemical methods to regulate the metal off-centering distortion, we demonstrate the giant tunability of photoluminescence (PL) in both the intensity (>20 times) and wavelength (>180 nm/GPa) in the highly distorted halide perovskites [CH3NH3GeI3, HC(NH2)2GeI3, and CsGeI3]. Using advanced in situ high-pressure probes and first-principles calculations, we quantitatively reveal a universal relationship whereby regulating the level of off-centering distortion towards 0.2 leads to the best PL performance in the halide perovskites. By applying this principle, intense PL can still be induced by substituting CH3NH3+ with Cs+ to control the distortion in (CH3NH3)1-xCsxGeI3, where the chemical substitution plays a similar role as external pressure. The compression of a fully substituted sample of CsGeI3 further tunes the distortion to the optimal value at 0.7 GPa, which maximizes the emission with a 10-fold enhancement. This work not only demonstrates a quantitative relationship between structural distortion and PL property of the halide perovskites but also illustrates the use of knowledge gained from high-pressure research to achieve the desired properties by ambient methods., By regulating the highly distorted halide perovskites using pressure, a quantitative relationship between structural distortion and emission property is demonstrated. The extracted principle is applied to materials design and the results give further support to the revealed relationship.

A remarkable PL enhancement by 12 fold is achieved using pressure to modulate the structure of a recently developed 2D perovskite (HA)

We report two new chromium chalcogenides Cr(en)(3)SbSe4 and Cr(en)(2)AsSe3 which were obtained by solvothermal reactions at 170 degrees C. Cr(en)(3)SbSe4 adopts the tetragonal space group P4(2)bc with isolated [Cr(en)(3)](3+) ions and [SbSe4](3-) tetrahedrons. Cr(en)(2)AsSe3 is a molecular crystal with the monoclinic space group P2(1)/n. It has [Cr(en)(2)Se-2](-) octahedrons and [AsSe3](3-) triangle cones which are edge shared by Se atoms. Cr(en)(3)SbSe4 has a band gap of 2.3 eV, whereas Cr(en)(2)AsSe3 displays multiple-absorption characters with two absorption edges at 1.7 and 2.2 eV, respectively. Remarkably, Cr(en)(3)SbSe4 is a Curie-Weiss paramagnet between 2 and 300 K with an effective magnetic moment of 3.98 mu B, and is a potential magneto-caloric material with -Delta S-m = 16.3 J (kg K)(-1) at 4 K and Delta H = 8 T. Cr(en)(2)AsSe3 shows antiferromagnetism below 9 K. (c) 2018 Published by Elsevier B.V.

The 2H molybdenum disulfide (MoS2 ), as a stable hexagonal phase, has been one of the most studied transition metal dichalcogenides over the past decades. In the last five years, the metastable phases of MoS2 (1T, 1T', 1T'', and 1T''') have seen a revival of interests. Different from the edge-sharing [MoS6 ] trigonal prisms in the 2H MoS2 phase, these metastable phases are composed of the edge-sharing [MoS6 ] octahedra, in which the neighboring Mo-Mo distances differ. Due to the various crystal structures and different electronic configurations of the building [MoS6 ] motifs, these metastable polytypes are endowed with intriguing physical properties and potential applications in diverse fields. In this Review, the recent research progress on metastable MoS2 is summarized, especially with an emphasis on the diverse synthetic approaches and the newly uncovered physical properties. The phase structures and electronic band structures are also outlined. In the end, a perspective of the future investigation on metastable MoS2 is discussed.

We report the use of 2H-NbS2 film as a novel counter electrode in perovskite solar cells fabricated with a cold isostatic pressing method. The 2H-NbS2 film, which was prepared through an exfoliation method followed by restacking from LixNbS2 powder, shows high electrical conductivity of 8.7 × 103 S cm−1 and work function of 5.20 eV. The two-dimensional transition metal dichalcogenide was used for the first time as a counter electrode in meso-structured perovskite solar cells. Through this process, we demonstrated a new alternative to noble metals. The perovskite solar cell base on the 2H-NbS2 counter electrode showed an open-circuit voltage of 1.046 V, comparable to that of gold, and a power conversion efficiency of 8.3%.

TiO2 mesoporous crystal has been prepared by one-step corroding process via an oriented attachment (OA) mechanism with SrTiO3 as precursor. High resolution transmission electron microscopy (HRTEM) and nitrogen adsorption–desorption isotherms confirm its mesoporous crystal structure. Well-dispersed ruthenium (Ru) in the mesoporous nanocrystal TiO2 can be attained by the same process using Ru-doped precursor SrTi1–xRuxO3. Ru is doped into lattice of TiO2, which is identified by HRTEM and super energy dispersive spectrometer (super-EDS) elemental mapping. X-ray photoelectron spectroscopy (XPS) and electron paramagnetic resonance spectroscopy (EPR) suggest the pentavalent Ru but not tetravalent, while partial Ti in TiO2 accept an electron from Ru and become Ti3+, which is observed for the first time. This Ru-doped TiO2 performs high activity for electrocatalytic hydrogen evolution reaction (HER) in alkaline solution. First-principles calculations simulate the HER process and prove TiO2:Ru with Ru5+ and Ti3+ h...

Six isostructural antiperovskite-derived chalcohalides, Ba2MQ3X (M = As, Sb; Q = S, Se; X = Cl, Br, I), crystallizing in the space group Pnma, have been synthesized by solid-state reactions. The crystal structure features a 3D framework with the [XBa5]9+ disordered square pyramids as building blocks and [MQ3]3- units filling the interspace. [XBa5]9+ disordered square pyramids are edge-sharing along [010], derived from the fusing of the two pyramids in octahedral [XBa6]11+. Surprisingly, Ba2AsS3X (X = Cl, Br, I) show almost the same optical band gap of 2.80 eV, and Ba2AsSe3X (X = Br, I) also have a similar band gap of 2.28 eV. The optical band gap of Ba2SbS3I is 2.64 eV. First-principles calculations reveal that the optical absorption is attributed to the transitions between Q np at the valence band maximum (VBM) and M np-Q np at the conduction band minimum (CBM). These compounds also possess interesting photoluminescence properties with splitting emission peaks on excitation at 200 nm.