Search

Lead-free double perovskite materials have attracted much interest for optoelectronic applications due to their nontoxicity and high stability. In this work, centimetre-sized Cs2AgBiBr6 single crystals were successfully grown using methylammonium bromide (MABr) as the flux by a top-seeded solution growth (TSSG) method. The low-temperature crystal structure of Cs2AgBiBr6 single crystals was determined and refined. To investigate the interface problems between Cs2AgBiBr6 single crystals and electrodes, the optical band gap, X-ray photoelectron spectroscopy (XPS), and ultraviolet photoemission spectroscopy (UPS) measurements were performed on Cs2AgBiBr6 single crystals. More importantly, we investigated the photodetectors based on Cs2AgBiBr6 single crystals with different contact electrodes (Au, Ag, and Al). It is found that a good Ohmic contact with Ag electrodes enables excellent photo-response behaviors. Furthermore, we studied the photodetectors based on Cs2AgBiBr6 single crystals using Ag electrodes under room and low temperature conditions, which underwent phase transition. Cs2AgBiBr6 single crystal photodetectors show clear differences at room and low temperatures, which is caused by the work function changes of Cs2AgBiBr6 single crystals induced by the reversible phase transition. These attractive properties may enable opportunities to apply emerging double perovskite single-crystalline materials for high-performance optoelectronic devices. [ABSTRACT FROM AUTHOR]

This paper describes the crystal growth, structure and properties of a new semi-organic hybrid crystal with an accurate molecular formula of ZnMnCl4(TPPO)4 by a guest–host combination of ZnCl2(TPPO)2 and MnCl2(TPPO)2 for the first time and its formation is bidirectional. It crystallizes in the acentric space group Fdd2. The 3D framework of the crystal structure is formed by triphenylphosphine oxide (TPPO), linked with a mixture of zinc(ii) chloride and manganese(ii) chloride. A mixed occupancy of zinc and manganese atoms was designed to form a noncentrosymmetric coordination compound, which exhibits relatively strong second-order nonlinear properties. The powder of this crystal shows a phase-matchable SHG effect that is twice that of KH2PO4 (KDP). The crystal has a broad optical transmission range, relatively good stability and a wide band gap. It is also magnetic and luminescent. The properties of this new crystal make it a potential candidate for improved or even novel devices. [ABSTRACT FROM AUTHOR]

The growth, ion concentrations, powder X‐ray diffraction, thermal properties, and optical spectroscopy of Nd3⁺‐doped Ca₃(BO₃)₂ single crystals are investigated. The Nd3+‐doped Ca₃(BO₃)₂ single crystals with 1.97 at.% Nd3⁺ are successfully grown using the Czochralski (Cz) technique. To address the chemical valence imbalance between Nd3⁺ and Ca2⁺ in the Ca₃(BO₃)₂ crystals, the Na⁺ ions are introduced. The concentrations of Nd3⁺ and Na⁺ ions in the as‐grown crystals are measured using inductively coupled plasma atomic emission spectroscopy (ICP‐AES), yielding concentrations of 1.97 at% (N0 = 1.55 × 1020 cm−3), 1.94 at% (N0 = 1.52 × 1020 cm−3), respectively. The thermal behavior of the Nd3⁺‐doped Ca3(BO3)2 crystals, including thermal expansion coefficients, specific heat, and thermogravimetric and differential thermal analysis (TG‐DTA), is systematically investigated. At room temperature, the polarized absorption spectra, polarized fluorescence spectra, and fluorescence decay lifetimes are measured. Spectral parameters, including polarized absorption and stimulated emission cross‐sections, intensity parameters, transition probabilities, radiative lifetime, and branching ratios are determined using the Judd‐Ofelt (J‐O) theory. The results indicate that Nd3+‐doped Ca3(BO3)2 crystals are promising materials for near‐infrared lasers, offering advantages such as rapid growth, large size, high specific heat, strong emission, and environmental stability. [ABSTRACT FROM AUTHOR]

Organic-inorganic hybrid metal halides have unique optical and electronic properties, which are advantageous in the study of nonlinear optical materials. To investigate the effect of stereoactive lone pair electrons and the induction of organic cations on the structure of hybrid antimony(III) halides on nonlinear optics, we synthesize two noncentrosymmetric hybrid antimony(III)-based halide single crystals (TMA) 3 Sb 2 X 9 (TMA = NH(CH 3 ) 3 + , X = Cl, Br) by a room-temperature slow evaporation method, and their single-crystal structures, phase transition, X-ray photoelectron spectroscopy, and energy-band structure calculations are studied. More importantly, second-harmonic generation results of (TMA) 3 Sb 2 X 9 (X = Cl, Br) are about 0.7 and 0.8 × KH 2 PO 4 (KDP), respectively. Interestingly, (TMA) 3 Sb 2 Cl 9 single crystals undergo a reversible structural transition from Pc (No. 7) at room temperature to P 2 1 / c (No. 14) at 400 K, while the (TMA) 3 Sb 2 Br 9 single crystals belong to the noncentrosymmetric space group R 3c (No. 161), which clarifies the previous results. This work not only deepens the understanding of the role in lone pair electrons and organic cations in the structural induction in antimony-based halide perovskite materials but also provides guidance for subsequent nonlinear optical explorations.

Introducing electronegative species into organic constituents was considered to be one effective strategy for adjusting crystal symmetry and designing new nonlinear optical (NLO) materials. By substitution of C4 in piperidine (C 5 H 11 N) with electronegative oxygen, organic morpholine (C 4 H 9 NO) was easily obtained. Therefore, to design NLO crystals, we focused on combinations of stereochemically active lone-pair (SCALP) cation (Pb 2+ )-based chloride and bromide with morpholine molecules. In this work, two lead halide hybrid perovskite (C 4 H 10 NO)PbX 3 (X = Cl, Br, abbreviated as MPbCl 3 and MPbBr 3 , respectively) single crystals with moderate nonlinear optical properties were synthesized by a slow evaporation method. The two title crystals belong to orthorhombic space group P 2 1 2 1 2 1 with one-dimensional (1D) chainlike perovskite structures. Theoretical calculations revealed that the second harmonic generation (SHG) responses mainly originate from distorted {PbX 6 } octahedrons of the inorganic framework. Remarkably, moderate phase-matching SHG effects of about 0.70 and 0.81 times KH 2 PO 4 , large birefringences of 0.098 and 0.111 at 1064 nm, and large laser damage thresholds (LDTs) of 19.94 and 46.82 MW/cm 2 were estimated for MPbCl 3 and MPbBr 3 , respectively. This work provides a novel strategy for new purpose-designed hybrid NLO crystals by adjustment and modulation of chemical modification.

Organic-inorganic hybrid Pb-halide perovskites have attracted tremendous interest due to their potential application in photovoltaic and optoelectronic fields. However, the toxicity and poor stability of Pb-halide perovskites have become key bottlenecks toward their future commercialization and industrialization. Therefore, in this work, two novel hybrid lead-free perovskite nonlinear optical (NLO) crystals (2-AMP) 2 BiX 7 ·H 2 O (X = Cl, Br) with high stability were successfully synthesized. Both the crystals belong to the orthorhombic P 2 1 2 1 2 1 space group, displaying a zero-dimensional perovskite structure. The thermal, environmental, and solvent atmospheric stabilities were comprehensively investigated, with high thermal stability up to 170 °C and high environmental and high solvent atmospheric stability observed for (2-AMP) 2 BiBr 7 ·H 2 O. First-principles calculations were carried out to study the relationship of the structure and properties. A large birefringence of 0.1368@1064 nm was determined for (2-AMP) 2 BiBr 7 ·H 2 O, which was derived from the strong aeolotropic conjugated π-electron distribution of planar 2-aminomethylpyridium. A second-harmonic generation (SHG) effect that was 0.25 and 0.32 times that of KH 2 PO 4 (KDP) was measured for (2-AMP) 2 BiCl 7 ·H 2 O and (2-AMP) 2 BiBr 7 ·H 2 O, respectively, and the stronger SHG response of bromide was attributed to the larger distortions of {BiBr 6 } octahedrons. This work may offer new guidance for exploration of low toxicity and high stability of perovskite NLO materials.

To design nonlinear optical (NLO) materials, we focused on combinations of d 10 metal cation (Cd 2+ )-based chloride and morpholine molecules to form organic-inorganic hybrids. The O of morpholine containing lone-pair electrons can be integrated with Cd 2+ by a ligand-to-metal charge transfer (LMCT) strategy to build acentric structures benefiting from the second-order Jahn-Teller effect. Introduction of the high-electronegativity chlorine can make polyhedrons of acentric crystals more distorted and conducive to a strong second harmonic generation (SHG) response. Therefore, (Morpholinium) 2 Cd 2 Cl 6 crystals were constructed and synthesized by a solvent evaporation method. (Morpholinium) 2 Cd 2 Cl 6 belongs to the orthorhombic P 2 1 2 1 2 1 space group and shows a one-dimensional (1D) structure with distorted [CdCl 6 ] and [CdCl 4 O 2 ] octahedrons. The short cutoff edge of (Morpholinium) 2 Cd 2 Cl 6 was determined to be about 230 nm. The SHG response of (Morpholinium) 2 Cd 2 Cl 6 exhibited an intensity of approximately 0.73 × KDP as estimated by the powder second harmonic generation technique. Furthermore, related theoretical calculations were performed to study the relationship of the band structure, refractive anisotropy, electronic state, and nonlinear optical response. Besides, (Morpholinium) 2 Cd 2 Cl 6 showed relatively good thermal stability. This work can serve as a guide for the design and synthesis of new large NLO hybrid crystals with d 10 transition metals.

To study stability issues of three-dimensional perovskites, there is a strategy to introduce the thiocyanate ion (SCN - ) into CH 3 NH 3 PbI 3 (MAPbI 3 ) to solve these problems. Here, we report the bulk growth of layered perovskite MA 2 Pb(SCN) 2 I 2 single crystals by different growth methods in an ambient atmosphere. We also investigate the structural determination and refinements, band gap, and photoluminescence of MA 2 Pb(SCN) 2 I 2 single crystals. More importantly, the phase transition and stability of MA 2 Pb(SCN) 2 I 2 are systematically demonstrated. MA 2 Pb(SCN) 2 I 2 undergo the reversible single-crystal to single-crystal phase transition in the orthorhombic systems from the space group Pmmn (no. 59) to the space group Pmn 2 1 (no. 31) at low temperature. Moreover, the temperature-dependent recovery behaviors of MA 2 Pb(SCN) 2 I 2 single crystals, powders, and thin films at high temperature are studied in detail. Besides, the moisture stability of MA 2 Pb(SCN) 2 I 2 is described when exposed to moisture condition by the experiment and theoretical calculations. It would be interesting to not only conduct a comprehensive study on the crystal structures and the phase transition processes of layered perovskites but also provide guidance for further optoelectronic applications of these perovskite materials.