Search Results (7)

This work describes the synthesis, crystal structure, and hydrophobicity tests of four bismuth(III)– and silver(I)–bromide complexes using the triammonium cations diethylenetriaminonium (H₃DETA³⁺) and N,N,N′,N″,N‴-pentamethyldiethylenetriammonium (H₃PMDTA³⁺). The prepared compounds are the 0D perovskites (H₃DETA)[BiBr₆] (1), (H₃DETA)₂[AgBr₄]Br₃ (2), and (H₃PMDTA)[BiBr₆] (3), as well as the 1D/2D mixed perovskite with minimum formula (H₃PMDTA)[Ag₃Br₆] (4), being the last three novel materials. Compounds 1 and 3 crystallize in the orthorhombic P2₁2₁2₁ space group and are discrete [BiBr₆]³⁻ units with the cation surrounding them. In both compounds, the bismuth(III) metal ion is found in a distorted octahedral coordination geometry. Compound 2 crystallizes in the monoclinic P2₁/c space group, and it is a mixed salt consisting of (H₃DETA)[AgBr₄] and (H₃DETA)Br₃, whereas the silver(I) complexes are also isolated. Finally, compound 4, which crystallizes in the orthorhombic space group Pbcn, is a combination of a 2D and 1D silver–bromide perovskite, with the cations filling the voids. The 2D structure has the minimal formula [Ag₄Br₇]³⁻, with the 1D coordination polymer [Ag₂Br₅]³⁻ being both built up by a combination of bromide ions acting as tetrahedra corner and edge-sharing bridging ligands. The silver(I) in 2 and 4 is found in a tetrahedral coordination geometry. All compounds were deposited on pristine FTO glass, resulting in an increase in the contact angle from 22° to 44°, 36°, 62°, and 54° for films of 1, 2, 3, and 4, respectively. Compounds 1 and 3 were also deposited onto Cs₂AgBiBr₆ film, and the contact angles were observed to be the same as when deposited directly onto the FTO cover glass. Full article

Compounds of the general composition A₂B^IB^IIIX₆ with a double perovskite (elpasolite) structure are currently considered as an alternative to lead halide perovskites APbX₃ in electronics and photovoltaics due to their greater compositional flexibility and low toxicity. One such alternative is the recently synthesized double perovskite Cs₂AgNaBiBr₆ and a number of various substituted compounds. The close values of the radii of silver and sodium cations make tuning the optoelectronic properties of the double perovskite via the substitution of Ag⁺ by Na⁺ promising if the formation of the substitution solid solution Cs₂Ag_1−xNa_xBiBr₆ takes place. We explored different possible routes for the synthesis of this class of materials, including solid-phase or melt crystallization ampoule syntheses. Varying heating temperature and duration and using standard cooling processing or a quenching-like process, we demonstrate the instability of Cs₂NaBiBr₆ and Na-substituted compounds Cs_2−xNa_xAgBiBr₆ in the temperature range of 300–650 °C. It is worth noting that the formation of Cs₂Ag_1−xNa_xBiBr₆ solid solutions by a solid-phase method is more favorable. Full article

The lead-free halide perovskite Cs₃Bi₂Br₉ is a promising semiconductor material for room-temperature X-ray detection due to its excellent properties. However, material purity and crystal quality still limit the use of Cs₃Bi₂Br₉ crystals as detectors. In this work, we present a highly efficient purification method using continuous vacuum extraction to sublimate BiBr₃ precursors for Cs₃Bi₂Br₉. Impurity analysis via inductively coupled plasma mass spectroscopy showed that the purification method successfully removed most of the impurities in BiBr₃ precursors and improved the purity by at least one order of magnitude. Centimeter-sized Cs₃Bi₂Br₉ single crystals were grown by the vertical Bridgman method. The improved properties after purification were confirmed by UV-Vis-NIR spectra, infrared transmittance, and current–voltage (I–V) measurements. The results showed that the average transmittance of Cs₃Bi₂Br₉ crystals significantly increased from 62% to 75% in the 0.5–20 μm spectral range. Additionally, the resistivity increased by nearly three orders of magnitude from 5.0 × 10⁹ Ω·cm to 2.2 × 10¹² Ω·cm, meaning the material will have low leakage currents and be suitable for developing applications for room temperature radiation detection. Full article

Perovskite-type lead halides exhibit promising performances in optoelectronic applications, for which lasers are one of the most promising applications. Although the bulk structure has some advantages, perovskite has additional advantages at the nanoscale owing to its high crystallinity given by a lower trap density. Although the nanoscale can produce efficient light emission, its comparatively poor chemical and colloidal stability limits further development of devices based on this material. Nevertheless, bulk perovskites are promising as optical amplifiers. There has been some developmental progress in the study of optical response and amplified spontaneous emission (ASE) as a benchmark for perovskite bulk phase laser applications. Therefore, to achieve high photoluminescence quantum yields (PLQYs) and large optical gains, material development is essential. One of the aspects in which these goals can be achieved is the incorporation of a bulk structure of high-quality crystallization films based on inorganic perovskite, such as cesium lead halide (CsPb(Br/Cl)₃), in polymethyl methacrylate (PMMA) polymer and encapsulation with the optimal thickness of the polymer to achieve complete surface coverage, prevent degradation, surface states, and surface defects, and suppress emission at depth. Sequential evaporation of the perovskite precursors using a single-source thermal evaporation technique (TET) effectively deposited two layers. The PL and ASEs of the bare and modified films with a thickness of 400 nm PMMA were demonstrated. The encapsulation layer maintained the quantum yield of the perovskite layer in the air for more than two years while providing added optical gain compared to the bare film. Under a picosecond pulse laser, the PL wavelength of single excitons and ASE wavelength associated with the stimulated decay of bi-excitons were achieved. The two ASE bands were highly correlated and competed with each other; they were classified as exciton and bi-exciton recombination, respectively. According to the ASE results, bi-exciton emission could be observed in an ultrastable CsPb(Br/Cl)₃ film modified by PMMA with a very low excitation energy density of 110 µJ/cm². Compared with the bare film, the ASE threshold was lowered by approximately 5%. A bi-exciton has a binding energy (26.78 meV) smaller than the binding energy of the exciton (70.20 meV). Full article

A recent publication on single crystals of two-dimensional, layered organic–inorganic (BA)₂CsAgBiBr₇ double perovskite (BA⁺ = $C{H}_3{\left(C{H}_2\right)}_{3}N{H}_3^{+}$) suggested the great potential of this semiconductor material in the detection of X-ray radiation. Our powder XRD measurement confirms the crystallinity and purity of all samples that crystallise in the monoclinic space group $P{2}_1/m$, while the single crystal XRD measurements reveal the dominant {001} lattice planes. The structure–property relationship is reflected in the lower resistivity values determined from the van der Pauw measurements (1.65–9.16 × 10¹⁰ Ωcm) compared to those determined from the IV measurements (4.19 × 10¹¹–2.67 × 10¹² Ωcm). The density of trap states and charge-carrier mobilities, which are determined from the IV measurements, are 1.12–1.76 × 10¹¹ cm^–3 and 10⁻⁵–10⁻⁴ cm²V^–1s^–1, respectively. The X-ray photoresponse measurements indicate that the (BA)₂CsAgBiBr₇ samples synthesised in this study satisfy the requirements for radiation sensors. Further advances in crystal growth are required to reduce the density of defects and improve the performance of single crystals. Full article

A three-dimensional cellular automata-lattice Boltzmann (CA-LBM) coupling model is established to simulate the facet growth process and the controlled cooling growth process of Cs₂AgBiBr₆ perovskite single crystals. In this model, the LBM method is used to calculate the real-time solute field, the CA method is used to simulate the crystal growth process driven by supersaturation of solute, and the geometric parameter g related to the adjacent grid is introduced to reduce the influence of grid anisotropy. The verification of the model is achieved by comparing the simulation results with the experimental results. The comparison results show that a smaller cooling rate is helpful for the growth of large-size single crystals, which verifies the rationality and correctness of the model. Full article

Borates have been regarded as a rich source of functional materials due to their diverse structures and wide applications. Therein, zincobrates have aroused intensive interest owing to the effective structural and functional regulation effects of the strong-bonded zinc cations. In recent decades, numerous zincoborates with special crystal structures were obtained, such as Cs₃Zn₆B₉O₂₁ and AZn₂BO₃X₂ (A = Na, K, Rb, NH₄; X = Cl, Br) series with KBe₂BO₃F₂-type layered structures were designed via substituting Be with Zn atoms, providing a feasible strategy to design promising non-linear optical materials; KZnB₃O₆ and Ba₄Na₂Zn₄(B₃O₆)₂(B₁₂O₂₄) with novel edge-sharing [BO₄]⁵⁻ tetrahedra were obtained under atmospheric pressure conditions, indicating that extreme conditions such as high pressure are not essential to obtain edge-sharing [BO₄]⁵⁻-containing borates; Ba₄K₂Zn₅(B₃O₆)₃(B₉O₁₉) and Ba₂KZn₃(B₃O₆)(B₆O₁₃) comprise two kinds of isolated polyborate anionic groups in one borate structure, which is rarely found in borates. Besides, many zincoborates emerged with particular physicochemical properties; for instance, Bi₂ZnOB₂O₆ and BaZnBO₃F are promising non-linear optical (NLO) materials; Zn₄B₆O₁₃ and KZnB₃O₆ possess anomalous thermal expansion properties, etc. In this review, the synthesis, crystal structure features and properties of representative zincoborates are summarized, which could provide significant guidance for the exploration and design of new zincoborates with special structures and excellent performance. Full article