Two Noncentrosymmetric Bismuth Phosphates: Rational Design Synthesis and Optical Properties.

Developing strategies to rational design noncentrosymmetric structure still attract much interest for their applications in nonlinear optical and piezoelectric materials. Two noncentrosymmetric (NCS) alkaline earth metal bismuth phosphates have been successfully achieved via partial replacement of Bi3+ with Ca2+ or Sr2+ ions. BiCa(H0.5PO4)2 (designated as CaBiPO) and BiSr(H0.5PO4)2 (designated as SrBiPO), together with their solid solution Bi(Sr1-xCax)(H0.5PO4)2 (0 < x ≤ 0.5), crystallize in the NCS space group C2. Both CaBiPO and SrBiPO exhibit ultraviolet nonlinear optical (NLO) properties, and their second-harmonic generation effects belong to type-II phase matching. Meanwhile, they could also act as photoluminescence hosts in which the Eu3+-doping samples SrBiPO:xEu3+ (x = 0.02-0.2) emit orange light. The effect of different radius ions on the derivative structures and the structure-NLO property relationship has also been discussed in detail.

Strategy for a Rational Design of Deep-Ultraviolet Nonlinear Optical Materials from Zeolites.

Deep-ultraviolet (DUV) nonlinear optical (NLO) materials play a crucial role in cutting-edge laser technology. In order to solve the serious layered growth tendency of the sole commercial DUV NLO crystal KBe2BO3F2 (KBBF), developing alternative systems of compounds with bulk crystal habits has become an urgent task for practical applications. Herein, a novel strategy was developed by applying non-centrosymmetric (NCS) cancrinite (CAN)-type zincophosphates {Na6(OH)2(H2O)2}Cs2[ZnPO4]6 with bulk-crystal habits as the prototype to design new DUV NLO crystals. Two new anhydrous alkali zincophosphates, namely, {(Li6 -xNaxO)A2}[(ZnPO4)6] (A = Cs, Rb; x = 2-3) crystallizing in the NCS hexagonal space group P63 (no. 173) with a CAN-type framework, were successfully synthesized via a modified fluoro-solvo-hydrothermal method by applying triethylamine (TEA) and concentrated NaF solution as a co-solvent. Interestingly, the rigidity of the NCS CAN-type framework acting as the host ensures the non-centrosymmetry of the resulting new compounds. Meanwhile, the replacement of water molecules by guest cationic species in the channels or cages can greatly improve the thermal stability of the resultant crystal and tune its NLO properties. The synergetic effect of the host framework and the guest species makes the two compounds transparent down to the DUV region (<200 nm) and exhibit SHG effects. Therefore, the proposed rational design strategy of applying the known zeotype NCS frameworks as prototypes together with the modified fluoro-solvo-hydrothermal method opens a great avenue for highly effectively exploring new DUV NLO materials.

Environmental regulation effect on green total factor productivity in the Yangtze River Economic Belt.

As a typical watershed ecological economy in China, the Yangtze River Economic Belt has two equally important objectives, namely ecological protection and economic development. Improving green total factor productivity is an essential approach to achieve these two objectives and promote sustainable growth in this area as well as the whole country. Therefore, this study explores the impact of environmental regulation on green total factor productivity with a panel data of 108 cities in the Yangtze River Economic Belt between 2003 and 2019. We first adopt the super slacks-based measure model to estimate city-level green total factor productivity. With kernel density curve, we find that green total factor productivity shows a downward pressure, and its absolute difference among cities shows a narrowing trend. Trend surface analysis displays an inverted U-shaped as well as a U-shaped spatial structures of green total factor productivity in the north-south as well as east-west directions, respectively. By using Spatial Durbin Model, we find a U-shaped direct impact of environmental regulation on green total factor productivity for the entire sample and three subsamples. For an indirect effect, environmental regulation has a positive spatial spill-over impact in the entire area; an insignificant effect in upstream and midstream areas; and an inverted U-shaped spatial spill-over in downstream area. Besides, we utilize threshold effect analysis to explore the impacts of technology innovation. The results show a single-threshold effect of technology innovation and the promotion effect decreases when technology innovation expenditure exceeds the threshold value. Based on our research findings, we suggest that the authorities should adhere to implementing and increasing the intensity of environmental regulation, so as to achieve better policy results. Moreover, local governments should keep technological innovation expenditure at a reasonable level to maximize the promoting effect of environmental regulation on green total factor productivity.

Cerium Doping Double Perovskite Scintillator for Sensitive X-ray Detection and Imaging.

Scintillators are widely used for nondestructive testing, nuclear medicine imaging, space exploration and security inspection. Recently, lead halide perovskite scintillation crystals have been brought into focus due to their effective atomic number, fast scintillation decay time, strong luminous efficiency, and tunable band gap. However, their application is limited by lead toxicity. Here we report that Ce-doping can increase sensitivity in lead-free double perovskite crystals (Cs2 NaTbCl6 ) for X-ray detection and imaging. The introduction of Ce ions as sensitizer can be used to improve the radioluminescence of the crystals. The light output of Ce : Cs2 NaTbCl6 crystals is about 52153 ph/MeV, which is 25 % higher than that of un-doped crystal. The X-ray sensitivity is significantly enhanced. Based on our scintillation film X-ray detector the detection limit is 30 nGy ⋅ s-1 , which is about 1/183 of the typical medical imaging dose. Our scintillating film has excellent imaging ability with spatial resolution of up to 10 lp/mm. This research shows that Ce : Cs2 NaTbCl6 perovskite crystal scintillators are promising materials for X-ray imaging application.

Rational Design and Synthesis of a Deep-Ultraviolet Nonlinear Optical Fluorinated Orthophosphate: BaZn(PO4)F.

Rational design and tailored synthesis of noncentrosymmetric compounds with nonlinear optical (NLO) properties, especially in the deep-ultraviolet (deep-UV) region, remains a great challenge. Herein, we report on the development of a modified fluoro-solvo-hydrothermal method with two additive reagents (trimethylamine and NaF solution) as the solvents, using BaFe(PO4)(OH) ( P212121) as the prototype, for the rational design and tailored synthesis of the first deep-UV fluorinated orthophosphate, BaZn(PO4)F. It crystallizes in the polar space group Pna21 and exhibits transparency down to deep-UV region (<190 nm) with SHG effect at 0.26 × KH2(PO4). Its structure is built from strictly alternating ZnO4F trigonal bipyramids and PO4 tetrahedra, resulting in a four-connected ABW-type zeolite framework. First-principles calculations confirm the deep-UV absorption edge and reveal that ZnO4F plays an essential role in the NLO properties. The synergetic effect of Zn and F atoms leads to its more polar crystal structure, much deeper absorption edge, and better SHG effect than the prototype.

Layered Chalcogenide Scintillators Enabled by Reversible Hydrous-Induced Phase Transformation for High-Resolution X-ray Imaging.

Scintillation materials have been widely used in various fields, such as medical diagnosis and industrial detection. Chalcogenides have the potential to become a new generation of high-performance scintillation materials due to their high effective atomic number and good resistance to radiation damage. However, research on their application in radiation detection is currently very scarce. Herein, single crystals of rare earth ion-doped ternary chalcogenides NaGaS2/Eu were grown by a high-temperature solid-phase method. It exhibits unique characteristics of structure transformation by absorbing water molecules from the air. To maintain the anhydrous phase of the material, we have used a strategy of organic-inorganic composites of epoxy resin and NaGaS2/Eu to prepare devices for radiation detection and discuss the irradiation luminescence properties of the two phases. The anhydrous phase of NaGaS2/Eu demonstrates excellent sensitivity to X-rays, with a low detection limit of 250 nGy s-1, which is approximately 1/22 of the medical imaging dose. Additionally, composite flexible films were prepared, which exhibited excellent performance in X-ray imaging. These films enable clear observation of a wide range of objects with a high spatial resolution of up to 13.2 line pairs per millimeter (lp mm-1), indicating that chalcogenide holds promising prospects in the realm of X-ray imaging applications.

Tetraphenylene-based semiconductive metal-organic framework crystals for direct X-ray detection and imaging.

MOFs have good potential for X-ray detection, but direct X-ray detection in single crystal form is rarely reported. In this work, we successfully synthesized Pb-TCPE, and the single crystal achieves a low detection limit and high detection sensitivity of 4812.6 µC Gyair-1 cm-2, which exhibits great potential for X-ray detection and imaging.

Methylammonium-Based Quasi-Two-Dimensional Perovskite Single Crystals for Highly Sensitive X-ray Detection and Imaging.

The strategy of introducing large organic cations into three-dimensional perovskites could reduce the dimensionality of perovskites to form quasi-two-dimensional (quasi-2D) perovskites, resulting in increased stability and reduced detection limits due to less ion migration. Herein, a quasi-2D perovskite single crystal (BDA)(MA)2Pb3Br10 (BDA = NH3C4H8NH3, MA = CH3NH3) with a layered structure was grown by the temperature-cooling solution method. The X-ray detector based on the (BDA)(MA)2Pb3Br10 single crystal has a sensitivity as high as 1984 µC Gy-1 cm-2 at 55.6 V/mm, and it could detect X-rays as low as 28.12 nGy s-1 at 22.2 V/mm. In addition, the X-ray imaging system based on the single-crystal device easily distinguishes between metals and plastics and exhibits a spatial resolution estimated as 250 µm, indicating the feasibility of (BDA)(MA)2Pb3Br10 crystals for X-ray imaging. This research offers a method for the design of quasi-2D layered perovskites and enhances photoelectronic applications in X-ray inspection and imaging.

Wide-Bandgap Rare-Earth Iodate Single Crystals for Superior X-Ray Detection and Imaging.

Semiconductor-based X-ray detectors with low detectable thresholds become critical in medical radiography applications. However, their performance is generally limited by intrinsic defects or unresolved issues of materials, and developing a novel scintillation semiconductor for low-dose X-ray detection is a highly urgent objective. Herein, a high-quality rare-earth iodate Tm(IO3 )3 single crystal grown through low-cost solution processing is reported with a wide bandgap of 4.1 eV and a large atomic number of 53.2. The roles of IO and TmO groups for charge transport in the Tm(IO3 )3 are revealed with the structural difference between the [101] and [ 1 ¯ 01 ] $[{\bar{1}}01]$ crystal orientations. Based on anisotropic responses of material properties and detection performances, it is found that the [ 1 ¯ 01 ${\bar{1}}01$ ] orientation, the path with fewer IO groups, achieves a high resistivity of 1.02 × 1011 Ω cm. Consequently, a single-crystal detector exhibits a low dark current and small baseline drifting due to the wide bandgap, high resistivity and less ion migration of Tm(IO3 )3 , resulting in a low detection limit of 85.2 nGyair s-1 . An excellent X-ray imaging performance with a high sensitivity of 4406.6 µC Gyair -1 cm-2 is also shown in the Tm(IO3 )3 device. These findings provide a new material design perspective for high-performance X-ray imaging applications.

5d → 4f transition of a lanthanide-activated MGa2S4 (M = Ca, Sr) semiconductor for mechanical-to-light energy conversion mediated by structural distortion.

Materials exhibiting mechanoluminescence (ML) are a class of smart materials capable of mechanical-to-light energy conversion. Thus, ML materials have been widely used in various electronic applications such as smart sensors, security systems, human-machine interfaces, and energy harvesting systems. Herein, we report a centrosymmetric ML semiconductor host material family MGa2S4 (M = Ca, Sr), which features in-layered structures constructed with unique distorted bi-tetrahedral [Ga2S2S4/2] lattice units. It exhibited similar structural characteristics to the well-known ML semiconductor host ZnS. Remarkably, the lanthanide ions of 5d → 4f transition-activated hosts showed sensitive and high ML luminance under natural lighting upon mechanical stimulation; thus, an efficient mechanical-to-light energy conversion of a self-powered display was achieved. Moreover, because of structural distortion and strain-gradient-induced electrical polarization in the ML host material upon mechanical stimulation, a ML mechanism based on the synergy effect between local electronic polarization and flexoelectricity was proposed. This study facilitates a deeper understanding of the relationship between the structure and underlying ML, and promotes further development of ML-material-based products and technologies.

Terbium doped LiLuF4 nanocrystal scintillator-based flexible composite film for high resolution X-ray imaging.

Radiographic screens are widely used in high energy physics, national defense, aviation, radiodynamic therapy and medical imaging due to their scintillation materials that can transform high-energy particles or rays into ultraviolet (UV) visible light or other signals. In recent years, lanthanide doped fluoride nanocrystals (NCs) have attracted much attention due to their excellent optical properties and stability. In this work, multiple lanthanide-doped LiLuF4 nanocrystal scintillation materials were synthesized by thermal decomposition. Among them, Tb-doped LiLuF4 nanocrystals have high X-ray sensitivity and low detection limit (36.31 nGy s-1), which is much lower than the requirement of medical imaging dose rate. After the irradiation of 42.29 mGy s-1 X-ray for 1 hour, the intensity of radioluminescence basically remained unchanged. Based on the good properties of our nanocrystals, we further prepared the flexible film of nanocomposites with epoxy resin. This kind of uniform, large area, high loaded flexible film exhibits excellent performance in X-ray imaging with a spatial resolution greater than 20 line pairs per millimeter (LP/mm).

Multiple Light Source-Excited Organic Manganese Halides for Water-Jet Rewritable Luminescent Paper and Anti-Counterfeiting.

Rewritable luminescent paper is particularly crucial, considering the ultrahigh paper consumption and confidential information security, but a highly desirable stimuli-responsive smart luminescent material with excellent water solubility has rarely been studied. Herein, a new type of rewritable paper made by highly efficient green light emissive zero-dimensional (0D) organic manganese halides is rationally designed by virtue of the reversible photoluminescence (PL) off-on switching. Specifically, the green emission can be linearly quenched by water vapor in a wide humidity range and again recovered in a dry atmosphere, which make it a smart hydrochromic PL off-on switching and humidity sensor. Benefiting from the reversible luminescence off-on switch and excellent water solubility, rewritable luminescent paper is realized through water-jet security printing technology on 0D halide-coated commercial paper with high resolution. The printed/written information can be easily cleaned by slight heating with outstanding "write-erase-write" cycle capabilities. In addition, multiple light source-induced coincident green light emissions further provide convenience to realize anti-counterfeiting, encryption and decryption of confidential information, and so forth. This work highlights the superiority of dynamic ionic-bonded 0D organic manganese halides as reversible PL switching materials in rewritable luminescent paper, high-security-level information printing, storage and protection technologies, and so forth.

Integration of negative, zero and positive linear thermal expansion makes borate optical crystals light transmission temperature-independent.

Negative and zero thermal expansion (NTE and ZTE) materials are widely adopted to eliminate the harmful effect from the "heat expansion and cool contraction" effect and frequently embrace novel fundamental physicochemical mechanisms. To date, the manipulation of NTE and ZTE materials has mainly been realized by chemical component regulation. Here, we propose another method by making use of the anisotropy of thermal expansion in noncubic single crystals, with maximal tunability from the integration of linear NTE, ZTE and positive thermal expansion (PTE). We demonstrate this concept in borate optical crystals of AEB2O4 (AE = Ca or Sr) to make the light transmission temperature-independent by counterbalancing the thermal expansion and thermo-optics coefficient. We further reveal that such a unique thermal expansion behavior in AEB2O4 arises from the synergetic thermal excitation of bond stretching in ionic [AEO8] and rotation between covalent [BO3] groups. This work has significant implications for understanding the thermal excitation of lattice vibrations in crystals and promoting the functionalization of anomalous thermal expansion materials.

Isotypic lanthanide-organic frameworks and scintillating films with colour-tunable X-ray radioluminescence for imaging applications.

Lanthanide-organic frameworks (LnOFs) have been brought into focus due to their unique structure-function relevance, and have shown good application prospects in many fields. According to the characteristics of scintillating materials, we synthesized two isomorphic LnOFs with the lanthanides terbium and europium as emission centers: Tb(bmb)3·H2O (LnOF-1) and Eu(bmb)3·H2O (LnOF-2). Tb3+ and Eu3+ were used as X-ray absorption centers, and large conjugated organic ligands were used as energy transfer bridges, which can effectively convert X-rays into visible light. LnOF-1 and LnOF-2 show good X-ray scintillation performance and anti-radiation stability. At the same time, we prepared a LnOF-1 mixed matrix scintillating film by the physical deposition method for X-ray imaging experiments, and its spatial resolution can reach 9.5 lp mm-1@MTF20%. The excellent imaging application effect prospect makes the lanthanide-organic frameworks show development potential in the field of scintillating materials.

Polymer Composites Entrapped Ce-Doped LiYF4 Microcrystals for High-Sensitivity X-ray Scintillation and Imaging.

Scintillators are widely used for radiation detection. The ability of converting ionizing radiation into visible photons is critical for application in X-ray security, computed tomography, and nuclear cameras. Conventional scintillators involve a high-temperature preparation and pose challenges for device integration and processability. Here, we report a facile hydrothermal synthesis of Ce-doped LiYF4 microcrystals (MCs) and their polymer composites for high-sensitivity X-ray detection and imaging application. These MC scintillators exhibit strong X-ray radioluminescence (RL) at ultraviolet wavelengths and show a high sensitivity to X-rays. Scintillating bulks based on these MCs display both strong RL and tunable emission across the visible spectrum. Further, these MC scintillators can be readily spun into a uniform film with a suitable MC content for X-ray imaging. Scintillating films can generate a strong X-ray-induced emission and long-term stability under X-ray illumination. Dose dependence of the RL intensity of our scintillating film indicates a high sensitivity to X-rays. Importantly, we exhibit an archetype application of scintillating films as X-ray radiography for a printed circuit board (PCB). Such an archetype can provide a decent spatial resolution as high as 0.54 mm. Our finding manifests MC composites of steady and efficient RL as a promising approach for X-ray radiography application.

2-(4-Pyridinio)benzimidazolium tetra-chloridopalladium(II).

The asymmetric unit of the title compound, (C(12)H(11)N(3))[PdCl(4)], consists of a 2-(4-pyridinio)benzimidazolium cation and two half [PdCl(4)](2-) anions, which are located on inversion centres. The cations lie in sheets parallel to (1). The cations and anions are connected by N-H⋯Cl and C-H⋯Cl contacts.

Zero Linear Compressibility in Nondense Borates with a "Lu-Ban Stool"-Like Structure.

Discovering materials that exhibit zero linear compressibility (ZLC) behavior under hydrostatic pressure is extremely difficult. To date, only a handful of ZLC materials have been found, and almost all of them are ultrahard materials with densified structures. Here, to explore ZLC in nondense materials, a structural model analogous to the structure of the "Lu-Ban stool," a product of traditional Chinese woodworking invented 2500 years ago, is proposed. The application of this model to borates leads to the discovery of ZLC in AEB2 O4 (AE = Ca and Sr) with the unique "Lu-Ban stool"-like structure, which can obtain a subtle mechanical balance between pressure-induced expansion and contraction effects. Coupled with the very wide ultraviolet transparent windows, the ZLC behavior of AEB2 O4 may result in some unique but important applications. The applications of the "Lu-Ban stool" model open a new route for pursuing ZLC materials in nondense structural systems.

Structural diversities induced by cation sizes in a series of fluorogermanophosphates: A2[GeF2(HPO4)2] (A = Na, K, Rb, NH4, and Cs).

Germanophosphates, in comparison with other metal phosphates, have been less studied but potentially exhibit more diverse structural chemistry with wide applications. Herein we applied a hydro-/solvo-fluorothermal route to make use of both the "tailor effect" of fluoride for the formation of low dimensional anionic clusters and the presence of alkali cations of different sizes to align the anionic clusters to control the overall crystal symmetries of germanophosphates. The synergetic effects of fluoride and alkali cations led to structural changes from chain-like structures to layered structures in a series of five novel fluorogermanophosphates: A2[GeF2(HPO4)2] (A = Na, K, Rb, NH4, and Cs, denoted as Na, K, Rb, NH4, and Cs). Although these fluorogermanophosphates have stoichiometrically equivalent formulas, they feature different anionic clusters, diverse structural dimensionalities, and contrasting crystal symmetries. Chain-like structures were observed for the compounds with the smaller sized alkali ions (Na+, K+, and Rb+), whereas layered structures were found for those containing the larger sized cations ((NH4)+ and Cs+). Specifically, monoclinic space groups were observed for the Na, K, Rb, and NH4 compounds, whereas a tetragonal space group P4/mbm was found for the Cs compound. These compounds provide new insights into the effects of cation sizes on the anionic clusters built from GeO4F2 octahedra and HPO4 tetrahedra as well as their influences on the overall structural symmetries in germanophosphates. Further characterization including IR spectroscopy and thermal analyses for all five compounds is also presented.

Near-Zero Thermal Expansion and High Ultraviolet Transparency in a Borate Crystal of Zn4 B6 O13.

Intrinsic isotropic near-zero thermal expansion is discovered in borate crystal Zn4 B6 O13 with high transparency in the ultraviolet region. First-principles calculations demonstrate that the very low thermal expansion originates mainly from the invariability of the solid [B24 O48 ] truncated octahedra that are fixed by the [Zn4 O13 ] clusters in the ZBO structure.