H2O Single Crystals Research Articles

From nonemission to nearly unity quantum yield: Breaking parity-forbidden transitions in rubidium indium chloride through 5s2 lone pair Sb-doping

Halide perovskites doped with ns2 metal ions have stimulated widespread research owing to their efficient and stable self-trapped emissions. Here we observe the strictly forbidden transition 3P0→1S0 is broken and afford nearly unity triplet orange self-trapped excitons (O-STEs) emission, through 5 s2 lone pair Sb cation doping in host Rb2InCl5·H2O single crystal. In particular, additional triplet blue self-trapped excitons (B-STEs) emission centered at 475 nm, stemming from partially allowed 3P1→1S0, is also observed. Spectroscopic characterization along with literature analysis demonstrates that the behavior of forbidden transition breaking originates from the mixing of 3P0 and 3P1 states. First-principles density-functional theory (DFT) calculations as well confirm the involvement of atomic orbitals in bandgap construction, as evidence of 5s5p-5 s2 transition, affording the STEs emission. Combining the efficient, stable broad emission Rb2In96.39 %Cl5·H2O: 3.61 % Sb3+ crystal with Cs3Cu2Cl5 and Cs3Cu2I5 phosphors, a lead-free white light-emitting diode with a high color rendering index of 93.4 has been achieved. Furthermore, the unique sensitive and steep temperature dependence photoluminescence (PL) lifetimes may prompt this type of self-trapped zero-dimensional (0D) perovskites to great potential in the field of thermometry application.

Unraveling dynamic Jahn-Teller effect and magnetism in FeTiF6×6H2O single crystal

Hydrated iron fluoridotitanate (FeTiF6 × 6 H2O) single crystals are fascinating magnetic materials with unique properties. To understand the underlying mechanisms, this study combines X-ray absorption near-edge structure (XANES) and X-ray magnetic circular dichroism (XMCD) techniques, complemented by density functional theory (DFT) calculations. Polarization-dependent X-ray absorption spectroscopy, encompassing XANES and XMCD, is a powerful technique for probing the local structures and magnetic properties of materials. It is element-selective, bulk-sensitive, and compatible with a wide range of experimental conditions. In this study, we used XANES and XMCD spectroscopies to investigate the local structures and magnetic properties of Fe and Ti in FeTiF6 × 6 H2O single crystals. XANES analysis revealed distinct local environments around Fe and Ti, providing insights into their coordination environments. Element-selective magnetization measurement at the Fe K-edge demonstrated that iron sites in the oxidation state Fe2+ have an unambiguous paramagnetic contribution to the magnetization along the b-axis. Notably, the absence of an XMCD signal at the Ti K-edge confirmed the absence of a magnetic moment in Ti atoms within the crystal. DFT calculations corroborate the experimental findings and provide insights into the electronic structure and magnetic interactions. The combined results provide a comprehensive understanding of the dynamic Jahn-Teller effect in FeTiF6 × 6 H2O single crystals, highlighting the significance of polarization-dependent X-ray absorption spectroscopy in unraveling the intricate magnetic behavior of such materials. This study contributes to the fundamental understanding of magnetism in these materials and paves the way for the development of novel magnetic materials with tailored properties.

Experimental and theoretical investigation on the SR method grown semi-organic Piperazinium Tetrachlorozincate Monohydrate (PTZM) single crystal for optoelectronic applications

Efficient semi organic nonlinear optical (NLO) Piperazinium Tetrachlorozincate monohydrate (PTZM) [C4H12N2][ZnCL4]·H2O single crystals have been grown by slow evaporation solution technique (SEST) and Sankaranarayanan-Ramasamy (SR) method using water as solvent. Single crystal X-ray diffraction (SXRD) analysis reveals the unit cell parameters of the grown crystal. The morphology of the grown crystal was identified by the single crystal XRD analysis. The electrical properties, dielectric constant, dielectric loss and piezoelectric (d33) coefficient were determined. The etch pit density of PTZM crystal has been calculated by using the chemical etching analysis. The laser damage threshold (LDT) analysis was investigated by Nd: YAG laser and the wavelength of laser is 1064 nm. The mechanical stability of the grown PTZM crystal was studied using Vickers microhardness measurement. Utilizing quantum chemical calculations, the PTZM compound is analyzed for vibrational properties, HOMO and LUMO characteristics, NBO interactions, and the determination of first-order hyperpolarizability. The nonlinear susceptibility and first-order hyperpolarizability results provide compelling evidence and affirm the PTZM molecule’s potential as a strong candidate for nonlinear optical (NLO) applications.

Unveiling the Structure-Luminescence-Stability relationship in 5s2-Based Antimony halides toward High-Performance emitters

Emerging low-dimensional metal halides have attracted enormous research interests due to their prominent photoluminescence (PL) properties and extensive application potentials. However, the systematic discussion on the structure-luminescence-stability relationship is still lacking. Herein, a series of novel lead-free metal halides are developed to unveil the underlying relationship. The as-synthesized (C6H5NH3)6SbCl9·H2O single crystal is structurally unstable that would spontaneously transform into (C6H5NH3)3ClSbCl5·H2O in the mother liquor, due to the strong antibonding Sb-5s2 lone pair with a spherical distribution in highly symmetrical geometry. To suppress this effect and stabilize the metastable phase, In3+ without ns electrons is introduced into the lattice of (C6H5NH3)6SbCl9·H2O, as a result, the changed coordination environment, including band structure, lattice constant and intermolecular electronic interaction, not only inhibits the structure transformation, but also leads to an enhanced PL efficiency (83.37 %) at ∼ 600 nm. This work promotes the understanding of structure-luminescence-stability relationship in organic–inorganic materials, and provides a new insight for further searching for high-performance lead-free perovskite luminescent materials.

Crystallization and characterization of K2NixCo1-x(SO4)2·6H2O mixed crystals for ultraviolet light filters and sensors

Mixed Tutton salts K2NixCo1-x(SO4)2·6H2O (KNICOSH) single crystals with x = 0, 0.20, 0.50, 0.80 and 1 were grown at 309 K using the slow evaporation of supersaturated aqueous solutions. X-ray diffraction analysis revealed the monoclinic structure, space group P21/a (C_2 h^5) and Z = 2, for each crystal obtained in this work. Thermal investigation showed several peaks that indicated the dehydration process, the exothermic reactions and melting points of K2NixCo1-x(SO4)2·6H2O crystals. The temperatures of these peaks increased with increasing x value, and it means that the crystals rich with Ni have higher thermal stability than those rich with Co. The infrared spectra of KNICOSH crystals showed three types of modes (internal modes of the sulfate ion, internal modes of water and librational modes of water). The wavenumber of internal modes of water increased systematically with increasing Ni content which indicate that the water molecules in KNISH crystal have hydrogen-bonding stronger than that of KCOSH crystal. The wavenumber of other infrared spectra modes changed unsystematically with increasing Ni content. K2Ni0.50Co0.50(SO4)2.6H2O crystal has the most absorption for the light at the visible range while at the ultraviolet region the absorption is low (high transmittance). This behavior enhanced its efficiency for using in ultraviolet light filters and sensors.

Growth, structural effects, and non-linear and spectroscopic properties of nanocomposites based on α-NiSO4·6H2O single crystals with TiO2 nanoparticles or sols

Nanocomposites based on nickel sulfate hexahydrate α-NiSO4·6H2O (NSH) with titanium (IV) oxide introduced in the form of nanoparticles (Hombifine N: anatase; Degussa P25: 85 % anatase + 15 % rutile; η-phase: 86 % η - phase + 14 % anatase, NSH:Ti(1)) or sols (NSH:Ti(2)) are synthesized for the first time. X-ray diffraction study reveals a single-phase nature of samples, the full occupancy of all crystallographic sites in the NSH:Ti(1) structures, and the presence of Ti4+ ions in interstitial sites near the vacant Ni site in the NSH:Ti(2) structures. A crystallization of the nanosized η-phase of the composition TiO2-x × mH2O directly in the NSH:Ti(1) crystalline matrix with the formation of TiO2 with the rutile structure, facilitated by the structural-geometric correspondence of 2D projections of NSH and rutile, is observed for the first time. The presence of TiO2 in the interblock space of NSH:Ti(1) crystals affects the unit cell parameters due to the induced stresses, which is practically not described in the literature. The intensity of SHG signals of NSH:Ti varies depending on both the prehistory of TiO2 samples and the crystal state, single-crystal or powdered, of the object under study: the highest values were observed for the NSH:Ti(2) powder with the lowest content of titanium ions. The UV–VIS study reveals similar absorption and transmission bands, but with little difference in band width and intensity, for NSH, NSH:Ti(1) and NSH:Ti(2), which can be perspective for UV filters operating in the solar-blind range.

Narrow‐Bandgap Mixed 0D/1D Bismuth Bromide Perovskite Hydrate Enabled by Aromatic Ditertiary Ammonium Spacer

AbstractPerovskite hydrates have attracted extensive attention in diverse fields with intriguing optoelectronic properties, while their structural distortions usually cause large band gaps, which yield inferior light absorption and diminished optoelectronic device performance. Herein, modulating the structural distortion by steric hindrance effects is reported. Specifically, an N,N,N′,N′‐tetramethyl‐1,4‐phenylenediammonium (TMPD)2+ is adopted to template regular BiBr5 chains by interacting with bismuth bromide via weakening and reorienting H‐bonds, yielding a mixed 0D/1D (TMPD)2Bi2Br10.H2O with a narrow bandgap of 1.89 eV. The 0D/1D (TMPD)2Bi2Br10.H2O can be reversibly transformed into 0D (TMPD)2Bi2Br10 (Eg = 2.55 eV) with good cycling behavior. The (TMPD)2Bi2Br10.H2O turns out to be more stable than (TMPD)2Bi2Br10, and a mechanism involving vacancy‐assisted bromide ion migration is proposed for understanding the formation of BiBr5 chains. Density functional theory (DFT) calculations indicate that the (TMPD)2+ triggered hydration has a crucial impact on the downshift of the conduction band edge, thus decreasing the band gap. Moreover, the (TMPD)2Bi2Br10.H2O single crystal exhibits promising photoconductive behavior under a high moisture atmosphere, showing superiority over the conventional CH3NH3PbI3 perovskites that cannot survive moisture. This finding offers new insights into developing narrow band gap perovskite hydrates toward practical optoelectronic applications.

Synthesis, crystal structure and optical properties of the quasi-0D lead-free organic-inorganic hybrid crystal (C6H14N)3Bi2I9·H2O

The organic-inorganic metal halide perovskite materials have remarkable semiconductor and light absorption characteristics. It shows excellent application prospects in the fields of optoelectronics and temperature sensors. In this work, zero-dimensional lead-free (C6H14N)3Bi2I9·H2O single crystals were synthesized by conventional solvothermal reaction. The crystal structure was analyzed using single crystal X-ray diffraction (SXRD). (C6H14N)3Bi2I9·H2O was crystallized in the orthorhombic crystal system with the space group Pmn21. The material is stable for long-term storage under ambient conditions and shows a reversible thermochromic phenomenon. Through ultraviolet–visible–near-infrared (UV–vis–NIR) absorption analysis, the band gap of (C6H14N)3Bi2I9·H2O at room temperature is found to be 2.12 ​eV and it gradually decreases as the temperature increases. This indicates that the thermochromism is probably caused by charge transfer. The response of material to optical signals was also studied and the maximum value of the responsivity (R) and external quantum efficiency (EQE) at 275 ​nm could reach 11 ​mA/W and 2.4%, respectively. It suggests that the material has a potential for applications in photovoltaic devices.

Lead-Free Hybrid Organic-Inorganic Ferroelectric: (3,3-Difluoropyrrolidinium)2ZnCl4·H2O.

Hybrid organic-inorganic ferroelectrics (HOIFs) have a wide range of applications in the optoelectronic field in terms of rich optoelectronic properties. Particularly, lead-free HOIFs have attracted extensive attention due to their environmental friendliness, low heavy metal toxicity, and low synthesis cost. However, there are few reports about Zn-based HOIFs due to their uncontrollable ferroelectric synthesis and other reasons. Here, we designed and synthesized a zinc-based zero-dimensional (3,3-difluoropyrrolidine)2ZnCl4·H2O (DFZC) single crystal, which undergoes a phase transition from ferroelectric to paraelectric phase (space group from Pna21 to Pnma) at 295.5 K/288.9 K during the heating/cooling process. The systematic study shows that the ferroelectric phase transition is a displacive type. The ferroelectric hysteresis loop of DFZC was obtained by the double-wave method and the Sawyer-Tower method, which has a spontaneous polarization (Ps) of ∼0.4 μC/cm2. This work reveals the strategy to design new zinc-based lead-free HOIFs for potential applications in optoelectronic fields.

Observation of the hyperfine structure and anticrossings of hyperfine levels in the luminescence spectra of LiYF4:Ho3+

Resolved hyperfine structure and narrow inhomogeneously broadened lines in the optical spectra of a rare-earth-doped crystal are favorable for the implementation of various sensors. Here, a well-resolved hyperfine structure in the photoluminescence spectra of LiYF4:Ho single crystals and the anticrossings of hyperfine levels in a magnetic field are demonstrated using a self-made setup based on a Bruker 125HR high-resolution Fourier spectrometer. This is the first observation of the resolved hyperfine structure and anticrossing hyperfine levels in the luminescence spectra of a crystal. The narrowest spectral linewidth is only 0.0022 cm−1. This fact together with a large value of the magnetic g factor of several crystal-field states creates prerequisites for developing magnetic field sensors, which can be in demand in modern quantum information technology devices operating at low temperatures. Very small random lattice strains characterizing the quality of a crystal can be detected using anticrossing points.

A Red-Emitting Hybrid Manganese Halide Perovskite C5H5NOMnCl2·H2O Featuring One-Dimensional Octahedron Chains.

Herein, we successfully synthesized a new organic-inorganic hybrid manganese halide perovskite C5H5NOMnCl2·H2O, in which organic molecules, water molecules (through O atoms), and Cl atoms coordinate with Mn atoms to form deformed [MnO3Cl3] octahedrons. Then, octahedrons form a chain through edge sharing, resulting in a 1D-chain single crystal structure. The high-quality C5H5NOMnCl2·H2O single crystal prepared by a simple solvent evaporation method produced bright red emission at 656 nm attributed to the d-d transition of Mn2+. Also, it has a photoluminescence quantum yield (PLQY) of 24.2%. Photoluminescence excitation and absorption spectra were both featured with multiple bands and were in good agreement with the Mn2+ 3d energy levels. The photoluminescence decay spectrum showed an average lifetime of 0.466 ms, which further proves the d-d transition mechanism. The C5H5NOMnCl2·H2O single crystal had a direct band gap of 1.43 eV. Moreover, a red light LED with a CCT of 1857 K was obtained based on the C5H5NOMnCl2·H2O powder, indicating its promising application in red-emitting LED.

Giant anisotropy of magnetic properties of hydrated iron fluoridotitanate single crystal

Study of the magnetic properties of the FeTiF6 ‧ 6 H2O single crystal has shown that this compound is a two-dimensional antiferromagnet with a N é еl temperature of TN = 8 K and its magnetic moment anisotropy attains 7000% at a temperature of T = 4.2 K. The Mössbauer spectroscopy data unambiguously indicate the paramagnetic state of iron cations in the temperature range of 4.2–300 K. However, a sharp change in the difference between the quadrupole doublet linewidths at 10 K has been observed, which is consistent with the temperature of magnetic ordering. It has been suggested that the long-range magnetic order is established in the crystal through the formation of the exchange coupling revealed by the electron spin resonance measurements on the oriented single crystals.

Te4+-doped Cs2InCl5·H2O single crystals for remote optical thermometry

Zero-dimensional metal halide perovskites have captured intense research interest owing to their unique optoelectronic properties. Particularly, metal halides with the ns2 electronic configuration are of great interest owing to the high-temperature sensitivity of their photoluminescence, which could be applied to remote optical thermometry (ROT). Herein, all-inorganic and lead-free halide perovskite Te4+-doped Cs2InCl5·H2O single crystals (SCs) were prepared through the hydrothermal method and showed a strong temperature dependence of photoluminescence lifetime. Upon Te4+ doping, the nonemissive Cs2InCl5·H2O SC exhibits a bright orange emission at 660 nm with a wide full width at half maximum of 180 nm. The strong phonon-exciton coupling promotes the formation of self-trapped excitons in the soft lattice of the zero-dimensional Te4+-doped Cs2InCl5·H2O SC. The Te4+ ions with the 5s2 electronic configuration endow the Te4+-doped Cs2InCl5·H2O SC with a strong temperature-dependent photoluminescence lifetime. This SC reaches a maximum specific sensitivity of 0.062K−1 at 320 K, thereby showing the potential advantages of indium-based metal halide perovskites in ROT applications.

Crystal growth and physico-chemical characterization of semi-organic [C4H12N2] ZnCl4·H2O single crystal for laser applications

Optical high-quality semi-organic piperazinium tetrachlorozincate monohydrate, [C4H12N2] ZnCl4·H2O (PTCZ), single crystals were grown by conventional solution method. The structure of grown crystal was confirmed by the single-crystal X-ray diffraction (SXRD) analysis. The material phase purities and its various (hkl) planes have been confirmed by the powder X-ray diffraction (PXRD) analysis at room temperature. The different functional groups were confirmed by the Fourier transform infrared (FTIR) spectroscopy. The optical quality of the PTCZ single crystal and band gap energy have been identified by the UV–Vis–NIR spectral analysis and also calculated refractive index of the material. The thermal stability of the PTCZ single crystal was investigated by TG–DTA. The hardness-related properties were analyzed by microhardness tester. The dielectric properties have been measured on the grown single crystal and the electronic polarizability value has been calculated with various theoretical approaches. The etching was carried out on the grown crystal to find the dislocation density. The crystal atomic perfection has been investigated by the high-resolution X-ray diffraction (HRXRD) or Rocking curve (RC) analysis. The Z-scan measurement has been carried out to find third-order optical susceptibility (χ(3)) of the grown single crystal using solid-state laser (640 nm).

Investigation on third-order nonlinear parameters, mechanical and dielectric behavior of alkali metal-organic C2HLiO4 H2O single crystal

A metal-organic lithium hydrogen oxalate hydrate single crystal was developed using the solution growth method. The single-crystal XRD analysis confirmed the triclinic structure and space group P1 along with the lattice parameters a = 3.439 Å, b = 5.097 Å, c = 6.141 Å, α = 78.50°, β = 84.89°, and γ = 81.41° of the grown crystal. The average crystallite size and strain within the material were calculated and compared using Debye Scherrer and Williamson-Hall method. The existence of diverse functional groups in the LHOH crystal was verified with the help of the FTIR analysis. The Z-scan method was carried out to acquire information about the developed material's third-order nonlinear characteristics that showed the material's self-focusing effect. The dielectric behavior of the compound was studied for various temperatures and frequencies. The Vicker’s microhardness analysis was carried out to collect information about the hardness number, yield strength, elastic stiffness, brittle index and fracture toughness of the grown crystal. The hardness number decreased when the applied load was increased, which indicated the normal indentation effect of the material.

Theoretical and experimental investigation of structural and vibrational properties of L-arginine·HClxBr1-x monohydrate crystals

In this work, five l-arginine·HClxBr1-x·H2O single crystals were grown through the slow evaporation method from a mixture of two aqueous solutions of l-arginine hydrochloride monohydrate and l-arginine hydrobromide monohydrate in proportions 0:1, 1:3, 1:1, 3:1, and 1:0, respectively. The crystals were grown by slow evaporation method from aqueous solutions at room temperature (25 °C). The grown single crystals were investigated by X-ray fluorescence (XRF) which presented: C6H14N4O2·HCl·H2O, C6H14N4O2·HCl0.14Br0.86·H2O, C6H14N4O2·HCl0.42Br0.58·H2O, C6H14N4O2·HCl0.63Br0.37·H2O and C6H14N4O2·HBr·H2O. X-ray diffraction (XRD), in association with Rietveld’s refinement, showed that all samples crystallized in the monoclinic system, with P21-space group. XRD experiments also evidenced that the unit cell volume of the LAHClxBr1-x crystals decreased as increasing Cl concentration. In addition, structure modeling and vibrational spectra calculations of the LAHClxBr1-x (x = 0.0, 0.5 and 1.0) crystals were performed at DFT/LDA level to be correlated with the experimental data. Raman spectroscopy experiments evidenced that bands associated with lattice modes undergo a blueshift as the Cl concentration was increased. This behavior can be explained by decreasing Cl mass as well as contraction of the unit cell towards LAHCl crystal, as observed by XRD data.

Realizing Tunable White Light Emission in Lead-Free Indium(III) Bromine Hybrid Single Crystals through Antimony(III) Cation Doping.

Low-dimensional metal halide hybrids (OIMHs) have recently been explored as single-component white-light emitters for use in solid-state lighting. However, it still remains challenging to realize tunable white-light emission in lead-free zero-dimensional (0D) hybrid system. Here, a combination strategy has been proposed through doping Sb3+ enabling and balancing multiple emission centers toward the multiband warm white light. We first synthesized a new lead-free 0D (C8NH12)6InBr9·H2O single crystal, in which isolated [InBr6]3- octahedral units are separated by large organic cations [C8NH12]+. (C8NH12)6InBr9·H2O exhibits dual-band emissions with one intense cyan emission and a weak red emission tail. The low-energy ultrabroadband red emission tail can be greatly enhanced by the Sb3+ doping. Experimental data and first-principles calculations reveal that the original dominant cyan emission is originated from the organic cations [C8NH12]+ and that the broadband red emission is ascribed to self-trapped excitons in [In(Sb)Br6]3-. When the Sb concentration is 0.1%, a single-component warm white-light emission with a photoluminescence quantum efficiency of 23.36%, correlated color temperature of 3347 K, and a color rendering index up to 84 can be achieved. This work represents a significant step toward the realization of single-component white-light emissions in environmental-friendly, high-performance 0D metal halide light-emitting materials.

Growth of mixed K2NixCo(1−x)(SO4)2 · 6H2O crystals for large supercooling without spontaneous crystallization in solution

A scheme for growing mixed K2NixCo(1−x)(SO4)2 · 6H2O (KCNSH) single crystals under conditions of supercooling at 5 °C–10 °C without spontaneous crystallization in solution for more than a month has been proposed and implemented. The growth method is implemented according to the ‘rotor crystallizer’ scheme. The crystals grown were characterized by optical spectroscopy and x-ray topography. The crystals obtained demonstrated the optical properties necessary to create effective UV filters.

Rod-like incipient ferroelectric SrTiO3 polycrystal with crystal-axis orientation

Strontium titanate (SrTiO3, ST) is an incipient ferroelectric material. Generally, a one-dimensional (1D) ST polycrystal is difficult to obtain because of its high aspect ratio and directional orientation. We prepared a 1D ST polycrystal from a layered H2Ti4O9·H2O (HT) single crystal via a solvothermal soft chemical process. The 1D ST polycrystal fabricated from ST nanocrystals has a [010] crystal axis, implying that it is a mesocrystal. The ST nanocrystals were grown not only on the surfaces but also in the interlayers of the original HT matrix. The formation mechanism of the ST mesocrystal is based on a topochemical mesocrystal conversion process. ST ceramics fabricated from ST mesocrystal powder present a lossy capacitor response and excellent energy-storage capabilities owing to the presence of locally oriented ST nanocrystals with a lattice mismatch in the rod-like ST mesocrystals. The investigations performed in this study can set a new benchmark for the development of new electric ST-based materials.

Enhanced lithium storage capability of FeF3·0.33H2O single crystal with active insertion site exposed

Iron fluoride cathode for lithium batteries intrigues researchers for decades due to high capacity and low cost, but suffers from poor electronic and ionic conductivity. Hierarchical micro/nano construction with preferred orientation growth can shorten ion diffusion pathway and facilitate electron transportation without inducing side reactions. Here, FeF3·0.33H2O hierarchical microspheres self-assembled by octagonal single crystal slices are prepared. Benefiting from the artful structure, SAED and XRD characterizations confirm that the octagonal single crystal slices provides more lithium ions intercalation positions (4c sites). Electrochemical tests demonstrate that the well designed FeF3·0.33H2O single crystal (FFH-S) delivers 30 mAh g−1 higher capacity (172 mAh g−1 at 0.1C) than the common FeF3·0.33H2O polycrystal (FFH-P). In-situ XRD combined with theoretic calculation elucidate the difference in lithium storage capacity. Instructive argument that single crystal octagon slices with [110] oriented growth provide more active sites for lithium ions intercalation contributes to the preparation of high performance iron fluoride cathode materials for rechargeable battery.