Nonlinear Optical Activity of a Chiral Organic-Inorganic ([(NH3CH2CH2)3NH])2[MnBr5]Br5 Photoluminescent and Piezoelectric Crystal

The family of Mn-based organic-inorganic hybrids has greatly expanded due to their advantages in applications. They also show superior bright and size-tunable photoluminescence and can be considered a perfect alternative to toxic lead-based compounds. In this work, we present the detailed structural, optical, and electrical characterization of ([(NH3CH2CH2)3NH])2[MnBr5]Br5. The title compound exhibits a unique type of inorganic arrangement created by the trigonal bipyramids. It crystallizes in noncentrosymmetric space group R32, indicating its optical activity, piezoelectricity, and second-order optical nonlinearity proven by the second harmonic of light measurements. The studied crystals exhibit intense photoluminescence originating from the Mn(II) ion 4T1(G) → 6A1 transition. The measured lifetime of the photoluminescence emission is ≤1.5 ms, while the measured quantum yield for both powder and crystal samples reaches ∼70%.

The halogen substitution strategy of inorganic skeletons triggers dielectric and band gap regulation of hybrid perovskites

Organic-inorganic hybrid perovskites (OIHPs) with dielectric switching functions have aroused comprehensive scientific interest, benefitting from their promising applications in sensors and information storage. However, to date, most of these materials discovered thus far possess a single function and are limited in their applicability, failing to meet the requirements of diverse applications. Moreover, the discovery of these materials has been largely serendipitous. Building multifunctional OIHPs with dielectric switching and semiconductors remains a daunting task. In this context, by introducing [C7H16N]+ as cations and in combination with lead halide with semiconducting properties, two OIHPs [C7H16N]PbI3 (1) and [C7H16N]PbBr3 (2) ([C7H16N]+ = (cyclopropylmethyl) trimethylammonium) have been successfully designed. They have dielectric switching properties close to 253 and 279 K and semiconducting behavior with band gaps of 2.67 and 3.22 eV. The phase transition temperature increased by 26 K through halogen substitution. In summary, our findings in this study provide insights into the application of the halogen substitution regulation strategy and open up new possibilities for designing perovskite semiconductors with dielectric switching functionality.

Halogen-regulating induced reversible high-temperature dielectric and thermal transitions in novel layered organic-inorganic hybrid semiconducting crystals

Organic-inorganic hybrid metal halides for high-temperature phase transition have become increasingly popular owing to their wide operating temperature range in practical applications, e.g., energy storage, permittivity switches and opto-electronic devices. This paper describes the subtle assembly of two new hybrid perovskite crystals, [Cl-C6H4-(CH2)2NH3]2CdX4 (X = Br 1; Cl 2), undergoing high-T reversible phase transformations around 335 K/356 K. Differential scanning calorimetry (DSC), differential thermal analysis (DTA) and VT PXRD tests uncover their reversible first-order phase transition behaviors. Furthermore, the compounds exhibit switchable dielectricity near T, making them potential dielectric switching materials. Hirshfeld surface analysis well discloses a distinct difference in hydrogen-bonding interaction between 1 and 2. UV spectra and computational analysis demonstrate that the compounds are a type of direct-band-gap semiconductor. This research will contribute an effective approach to the structure and development of multifunctional molecular hybrid crystals.

Sn(II)-doped one-dimensional hybrid metal halide [C5H14NO]CdCl3 single crystals with broadband greenish-yellow light emission

Low-dimensional organic-inorganic hybrid halides, as an important branch of metal halide materials, have attracted much attention due to their excellent photoelectric properties. Herein, we designed one new hybrid cadmium chloride [C₅H₁₄NO]CdCl₃ based on combinations of the d¹⁰ metal cation (Cd²⁺) and choline chloride molecules. [C₅H₁₄NO]CdCl₃ single crystals belong to the orthorhombic Pna2₁ space group and show a one-dimensional (1D) structure with distorted [CdCl₅O]^5- octahedra. The second harmonic generation (SHG) response of [C₅H₁₄NO]CdCl₃ exhibits an intensity of approximately 0.4 × KDP. Moreover, the photoluminescence properties of the [C₅H₁₄NO]CdCl₃ crystal are activated by doping with Sn²⁺ ions having stereochemically active lone pair 5s² electrons. Under UV excitation conditions, bright greenish-yellow light emission can be observed, and the quantum efficiency (PLQY) is as high as 91.27%. The luminescence mechanism is revealed by combining the results of temperature dependent luminescence and density functional theory (DFT) calculation. This work can serve as a guide for the design and synthesis of emerging optical materials.

[SMe3]2[Bi2Ag2I10], a silver iodido bismuthate with an unusually small band gap

Iodido metalates of heavy main group elements have seen much research interest in the last years due to their possible application as absorbers in photovoltaics. However, for materials based on the non-toxic element bismuth one challenge lies in narrowing the optical band gap for sufficient solar absorption. Here, we present a new iodido silver bismuthate, [SMe₃]₂[Bi₂Ag₂I₁₀] (1), which is prepared from solution and characterized regarding its structure, thermal stability and optical absorption. While compounds with similar anion compositions are known, the band gap of 1.82 eV is the smallest in chain-like Bi/Ag/I-compounds that has been reported to date. To support our experimental findings we carried out computational investigations and were able to reproduce the surprisingly narrow band gap, highlighting the subtle influence of the connectivity of different building units in multinary bismuthates. We also prepared and characterized the simple iodido pentelates [SMe]₃[E₂I₉] (E = Bi, Sb; 2, 3) to provide a point of comparison.

Ferroelectric properties, narrow band gap and ultra-large reversible entropy change in a novel nonlinear ionic chromium(VI) compound

A novel chromium(VI)-based compound, [(CH₃CH₂)₃N(CH₂Cl)][CrO₃Cl] (1), undergoes a high-temperature phase transition at around 340.9 K, accompanied by an ultra-large entropy change of 63.49 J mol^-1 K^-1. Compound 1 exhibits a moderate ferroelectric polarization of 0.48 μC cm^-2 and a remarkable CD signal. Strikingly, 1 occupies a narrow band gap of 2.22 eV, which is chiefly attributed to the inorganic [CrO₃Cl]^- tetrahedron. It is believed that these findings will contribute to an alternative pathway for the design of multifunctional ferroelectric materials, whose potential applications will be in semiconductors, energy storage, etc.

A multifunctional molecular ferroelectric with chiral features, a high Curie temperature, large spontaneous polarization and photoluminescence: (C9H14N)2CdBr4

Low-dimensional chiral organic-inorganic hybrid metal halides have attracted a lot of attention in recent years due to their unique intrinsic properties, including having potential applications in optoelectronic and spintronic devices. However, low-dimensional chiral molecular ferroelectrics are very rare. In this paper, we report a novel zero-dimensional molecular ferroelectric (C9H14N)2CdBr4 (C9H14N+ = protonated 3-phenylpropylamine), which has obvious dielectric and thermal anomalies and shows a high Curie temperature at 395 K. It crystallizes in the P21 space group at room temperature, showing a strong CD signal, large spontaneous polarization (P s = 13.5 μC cm-2), and a clear ferroelectric domain. In addition, it also exhibits a flexible SHG response. The photoluminescence spectrum shows that 1 has broadband luminescence. At the same time, compound 1 has a wide band gap, which is mainly contributed to by the inorganic CdBr4 tetrahedron. The high tunability of low-dimensional chiral molecular ferroelectrics also opens up a way to explore multifunctional chiral materials.

High-Temperature and Large-Polarization Ferroelectric with Second Harmonic Generation Response in a Novel Crown Ether Clathrate

Molecular ferroelectrics of high-temperature reversible phase transitions are very rare and have attracted increasing attention in recent years. In this paper is described the successful synthesis of a novel high-temperature host-guest inclusion ferroelectric: [(C₆ H₅ NF₃ )(18-crown-6)][BF₄ ] (1) that shows a pair of reversible peaks at 348 K (heating) and 331 K (cooling) with a heat hysteresis about 17 K by differential scanning calorimetry measurements, thus indicating that 1 undergoes a reversible structural phase transition. Variable-temperature PXRD and temperature-dependent dielectric measurements further prove the phase-transition behavior of 1. The second harmonic response demonstrates that 1 belongs to a non-centrosymmetric space group at room temperature and is a good nonlinear optical material. In its semiconducting properties, 1 shows a wide optical band gap of about 4.43 eV that comes chiefly from the C, H and O atoms of the crystals. In particular, the ferroelectric measurements of 1 exhibit a typical polarization-electric hysteresis loop with a large spontaneous polarization (P_s ) of about 4.06 μC/cm² . This finding offers an alternative pathway for designing new ferroelectric-dielectric and nonlinear optical materials and related physical properties in organic-inorganic and other hybrid crystals.

Para–ferroelectric phase transition induces an excellent second harmonic generation response and a prominent switchable dielectric constant change based on a metal-free ionic crystal

A novel metal-free compound, [H₂(bpyp)][ClO₄]₂, undergoes a ferroelectric to paraelectric reversible phase transition at T_c, with excellent NLO response, prominent dielectric constant change, moderate ferroelectric polarization, and wide bandgap.