Revisiting a (001)-oriented layered lead chloride templated by 1,2,4-triazolium: structural phase transitions, lattice dynamics and broadband photoluminescence.

This study revisits a (001)-oriented layered lead chloride templated by 1,2,4-triazolium, Tz2PbCl4, which recently has been an object of intense research but still suffers from gaps in characterization. Indeed, the divergent reports on the crystal structures of Tz2PbCl4 at various temperatures, devoid of independent verification of chiral phases through second harmonic generation (SHG), have led to an unresolved debate regarding the existence of a low-temperature phase transition (PT) and the noncentrosymmetric nature of the low-temperature phase. Now, by combining differential scanning calorimetry, single-crystal X-ray diffraction, dielectric, as well as linear and nonlinear optical spectroscopies on Tz2PbCl4, we reveal a sequence of reversible PTs at T1 = 361 K (phase I-II), T2 = 339 K (phase II-III), and T3 = 280 K (phase III-IV). No SHG activity could be registered for any of the four crystal phases, as checked by wide-temperature range SHG screening, supporting their centrosymmetry. The dipole relaxation processes indicate a decrease in activation energy with increasing temperature, from 0.60, 0.38, to 0.24 eV observed for phase IV (space group P21/c), phase III (Pnma), and phase II (Cmcm), respectively. This change is interpreted as a result of the diminishing strength of H-bonds as the system transforms from phase IV to III and subsequently to II. The weaker H-bonds facilitate the reorientation of Tz+ cations in the presence of an external electric field. The photoluminescence spectra of Tz2PbCl4 reveal an intriguing interplay of narrow and broadband emission, linked respectively to free excitons and excitons trapped on defects. Notably, as the temperature decreases from 300 K to 16 K, both the emission bands exhibit distinctive blue and red shifts, indicative of increased in-plane octahedral distortion. This dynamic behaviour transforms the photoluminescence of Tz2PbCl4 from greenish-blue at 300 K to yellowish-green at 13 K, enriching our understanding of 2D lead halide perovskites and highlighting the optoelectronic potential of Tz2PbCl4.

Highly Sensitive Temperature Sensors Resulting from the Luminescent Behavior of Sm3+-Doped Ba2MgMoO6 High-Symmetry Double-Perovskite Molybdate Phosphors.

We present double-perovskite molybdate with the formula of Ba2MgMoO6 doped with Sm3+ ions as a potential red phosphor to improve the color characteristics of white-light-emitting dioded (wLEDs). The new orange-red phosphor was synthesized using the co-precipitation (CP) method, and then its structural and spectroscopic properties were determined. Red emission at 642.6 nm dominates, which results from the electric dipole (ED) transition of the 4G5/2 → 6H9/2 type, and the materials are characterized by short luminescence decay times. BMM:Sm3+ is, to our best knowledge, the clearest example of dominant red emission of Sm3+ resulting from the location of the dopant in octahedral sites of high-symmetry cubic structure. In the sample containing 0.1% Sm3+, Sm3+ ions are located in both Mg2+ and Ba2+ sites, while at higher concentrations the Ba2+ site is less preferable for doping, as a result of which the emission becomes more uniform and single-site. The relative sensitivity calculated from FIR has a maximum of 2.7% K-1 at -30 °C and another local maximum of 1.6% K-1 at 75 °C. Such value is, to the best of our knowledge, one of the highest achieved for luminescent thermometry performed using only Sm3+ ions. To sum up, the obtained materials are good candidates as red phosphor to improve the color characteristics of wLEDs, obtaining a color-rendering index (CRI) of 91 and coordinated color temperature (CCT) of 2943 K, constituting a warm white emission. In addition to this, a promising precedent for temperature sensing using high-symmetry perovskite materials is the high sensitivity achieved, which results from the high symmetry of the BMM host.

Calcium carbonate polymorph selection in fish otoliths: A key role of phosphorylation of Starmaker-like protein.

Fish otoliths are calcium carbonate biominerals found in the inner ear commonly used for tracking fish biochronologies and as a model system for biomineralization. The process of fish otolith formation is biologically controlled by numerous biomacromolecules which not only affect crystal size, shape, mechanical properties, but also selection of calcium carbonate polymorph (e.g., aragonite, vaterite). The proteinaceous control over calcium carbonate polymorph selection occurs in many other species (e.g., corals, mollusks, echinoderms) but the exact mechanism of protein interactions with calcium and carbonate ions - constituents of CaCO3 - are not fully elucidated. Herein, we focus on a native Starmaker-like protein isolated from vaterite asteriscus otoliths from Cyprinus carpio. The proteomic studies show the presence of the phosphorylated protein in vaterite otoliths. In a series of in vitro mineralization experiments with Starmaker-like, we show that native phosphorylation is a crucial determinant for the selection of a crystal's polymorphic form. This is the first report showing that the switch in calcium carbonate phase depends on the phosphorylation pattern of a single isolated protein. STATEMENT OF SIGNIFICANCE: Calcium carbonate has numerous applications in industry and medicine. However, we still do not understand the mechanism of biologically driven polymorph selection which results in specific biomineral properties. Previous work on calcium carbonate biominerals showed that either several macromolecular factors or high magnesium concentration (non-physiological) are required for proper polymorph selection (e.g., in mollusk shells, corals and otoliths). In this work, we showed for the first time that protein phosphorylation is a crucial factor for controlling the calcium carbonate crystal phase. This is important because a single protein from the otolith organic matrix could switch between polymorphs depending on the phosphorylation level. It seems that protein post-translational modifications (native, not artificial) are more important for biomolecular control of crystal growth than previously considered.

Phase Transitions, Dielectric Response, and Nonlinear Optical Properties of Aziridinium Lead Halide Perovskites.

Hybrid organic-inorganic lead halide perovskites are promising candidates for next-generation solar cells, light-emitting diodes, photodetectors, and lasers. The structural, dynamic, and phase-transition properties play a key role in the performance of these materials. In this work, we use a multitechnique experimental (thermal, X-ray diffraction, Raman scattering, dielectric, nonlinear optical) and theoretical (machine-learning force field) approach to map the phase diagrams and obtain information on molecular dynamics and mechanism of the structural phase transitions in novel 3D AZRPbX3 perovskites (AZR = aziridinium; X = Cl, Br, I). Our work reveals that all perovskites undergo order-disorder phase transitions at low temperatures, which significantly affect the structural, dielectric, phonon, and nonlinear optical properties of these compounds. The desirable cubic phases of AZRPbX3 remain stable at lower temperatures (132, 145, and 162 K for I, Br, and Cl) compared to the methylammonium and formamidinium analogues. Similar to other 3D-connected hybrid perovskites, the dielectric response reveals a rather high dielectric permittivity, an important feature for defect tolerance. We further show that AZRPbBr3 and AZRPbI3 exhibit strong nonlinear optical absorption. The high two-photon brightness of AZRPbI3 emission stands out among lead perovskites emitting in the near-infrared region.

Chitosan and Its Carboxymethyl-Based Membranes Produced by Crosslinking with Magnesium Phytate.

Membranes produced by crosslinking chitosan with magnesium phytate were prepared using highly deacetylated chitosan and its N-carboxymethyl, O-carboxymethyl and N,O-carboxymethyl derivatives. The conditions of the membrane production were described. IR, Raman, electron absorption and emission spectra were measured and analyzed for all the substrates. It was found that O-carboxymethyl chitosan derivative is the most effectively crosslinked by magnesium phytate, and the films formed on this substrate exhibit good mechanical parameters of strength, resistance and stability. Strong O-H···O hydrogen bonds proved to be responsible for an effective crosslinking process. Newly discovered membrane types produced from chitosan and magnesium phytate were characterized as morphologically homogenous and uniform by scanning electron microscopy (SEM) and IR measurements. Due to their good covering properties, they do not have pores or channels and are proposed as packaging materials.

Effect of the Addition of Graphene Flakes on the Physical and Biological Properties of Composite Paints.

In this study, graphene flakes were obtained using an electrolytic method and characterized using X-ray diffraction (XRD), Raman and FTIR spectroscopy, scanning and transmission electron microscopy (SEM/TEM). Graphene-based composites with varying concentrations of 0.5%, 1% and 3% by weight were prepared with acrylic paint, enamel and varnish matrices. The mechanical properties were evaluated using micro-hardness testing, while wettability and antimicrobial activity against three pathogens (Staphylococcus aureus 33591, Pseudomonas aeruginosa 15442, Candida albicans 10231) were also examined. The results indicate that the addition of graphene flakes significantly enhances both the mechanical and antimicrobial properties of the coatings.

Effect of Gel Exposition on Calcium and Carbonate Ions Determines the Stm-l Effect on the Crystal Morphology of Calcium Carbonate.

Biomineralization of fish otoliths is regulated by macromolecules, such as proteins, whose presence is crucial for the functionality and properties of these mineralized structures. Special regulatory effects are exerted by intrinsically disordered proteins, such as the polyanionic Starmaker-like protein from medaka, a homolog of zebrafish Starmaker. In this study, we employed a set of bioinspired mineralization experiments with a single diffusion system to investigate the effect of the Starmaker-like protein on calcium carbonate biominerals with regards to the prior exposition of the protein to calcium or carbonate ions. Interestingly, the bioinspired minerals grown in the presence of the Starmaker-like protein in calcium- or carbonate-type experiments differ significantly in terms of morphology and protein distribution within the crystals. Our deeper analysis shows that the Starmaker-like protein action is a result of the environmental conditions to which it is exposed. These findings may be of special interest in the areas of biomineralization process pathways and biomaterial sciences.

Spectroscopic and optical properties of 1,2,4-triazolo[4,3-a]pyridin-3(2H)-one as a component of herbicides.

The herbicides azafenidin [(2-(2,4-dichloro-5-prop-2-ynoxyphenyl)-5,6,7,8-tetrahydro-[1,2,4]triazolo[4,3-a]pyridin-3-one)] and flumetsulam [(N-(2,6-difluorophenyl)-5-methyl-[1,2,4]triazolo[1,5-a]pyrimidine-2-sulfonamide)] were subjected to IR, Raman, UV-Vis and emission studies. As triazolopyridine is the most prominent and active component of these herbicides, this molecule was characterised by XRD studies, FTIR, Raman, UV-Vis and emission spectra. The experimental data were compared to the results of the DFT quantum chemical calculations carried out for its optimised structure, IR intensities and Raman activities, HOMO-LUMO transitions, and energies of the singlet and triplet states. The characteristics for triazolopyridine quantities were used in the analysis of the studied herbicides.

Structure, Luminescence and Temperature Detection Capability of [C(NH2)3]M(HCOO)3 (M = Mg2+, Mn2+, Zn2+) Hybrid Organic-Inorganic Formate Perovskites Containing Cr3+ Ions.

Metal-organic frameworks are of great interest to scientists from various fields. This group also includes organic-inorganic hybrids with a perovskite structure. Recently their structural, phonon, and luminescent properties have been paid much attention. However, a new way of characterization of these materials has become luminescence thermometry. Herein, we report the structure, luminescence, and temperature detection ability of formate organic-inorganic perovskite [C(NH2)3]M(HCOO)3 (Mg2+, Mn2+, Zn2+) doped with Cr3+ ions. Crystal field strength (Dq/B) and Racah parameters were determined based on diffuse reflectance spectra. It was shown that Cr3+ ions are positioned in the intermediate crystal field or close to it with a Dq/B range of 2.29-2.41. The co-existence of the spin-forbidden and spin-allowed transitions of Cr3+ ions enable the proposal of an approach for remote readout of the temperature. The relative sensitivity (Sr) can be easily modified by sample composition and Cr3+ ions concentration. The luminescent thermometer based on the 2E/4T2g transitions has the relative sensitivity Sr of 2.08%K-1 at 90 K for [C(NH2)3]Mg(HCOO)3: 1% Cr3+ and decrease to 1.20%K-1 at 100 K and 1.08%K-1 at 90 K for Mn2+ and Zn2+ analogs, respectively.

Optimization of the Electrochemical Method of Obtaining Graphene Nanoplatelets (GNPs).

Graphene nanoplatelets (GNPs) were prepared using the electrolytic exfoliation method on graphite foil in an ammonium sulfate solution. A series of experiments were conducted in order to optimize the production of the flakes by varying the pH of the solution, applied voltage and current, duration of electrolysis, temperature in the electrolytic system, and type and duration of the ultrasound interaction. The quality of the produced graphene nanoplatelets was analyzed using X-ray diffraction, Raman and IR spectroscopy, and TEM.

Otolin-1, an otolith- and otoconia-related protein, controls calcium carbonate bioinspired mineralization.

BACKGROUND: Otoliths and otoconia are calcium carbonate biomineral structures that form in the inner ear of fish and humans, respectively. The formation of these structures is tightly linked to the formation of an organic matrix framework with otolin-1, a short collagen-like protein from the C1q family as one of its major constituents. METHODS: In this study, we examined the activity of recombinant otolin-1 originating from Danio rerio and Homo sapiens on calcium carbonate bioinspired mineralization with slow-diffusion method and performed crystals characterization with scanning electron microscopy, two-photon excited fluorescence microscopy, confocal laser scanning microscopy and micro-Raman spectroscopy. RESULTS: We show that both proteins are embedded in the core of CaCO3 crystals that form through the slow-diffusion mineralization method. Both of them influence the morphology but do not change the polymorphic mineral phase. D.rerio otolin-1 also closely adheres to the crystal surface. GENERAL SIGNIFICANCE: The results suggest, that otolin-1 is not a passive scaffold, but is directly involved in regulating the morphology of the resulting calcium carbonate biocrystals.

Hybrid Chlorides with Methylhydrazinium Cation: [CH3NH2NH2]CdCl3 and Jahn-Teller Distorted [CH3NH2NH2]CuCl3.

The synthesis, structural, phonon, optical, and magnetic properties of two hybrid organic-inorganic chlorides with monoprotonated methylhydrazinium cations (CH3NH2NH2+, MHy+), [CH3NH2NH2]CdCl3 (MHyCdCl3), and [CH3NH2NH2]CuCl3 (MHyCuCl3), are reported. In contrast to previously reported MHyMIICl3 (MII = Mn2+, Ni2+, and Co2+) analogues, neither compound undergoes phase transitions. The MHyCuCl3 has a crystal structure familiar to previous crystals composed of edge-shared 1D chains of the [CuCl5N] octahedra. MHyCuCl3 crystallizes in monoclinic P21/c symmetry with MHy+ cations directly linked to the Cu2+ ions. The MHyCdCl3 analogue crystallizes in lower triclinic symmetry with zig-zag chains of the edge-shared [CdCl6] octahedra. The absence of phase transitions is investigated and discussed. It is connected with slightly stronger hydrogen bonding between cations and the copper-chloride chains in MHyCuCl3 due to the strong Jahn-Teller effect causing the octahedra to elongate, resulting in a better fit of cations in the accessible space between chains. The absence of structural transformation in MHyCdCl3 is due to intermolecular hydrogen bonding between two neighboring MHy+ cations, which has never been reported for MHy+-based hybrid halides. Optical investigations revealed that the bandgaps in Cu2+ and Cd2+ analogues are 2.62 and 5.57 eV, respectively. Magnetic tests indicated that MHyCuCl3 has smeared antiferromagnetic ordering at 4.8 K.

Metal-Organic Framework Optical Thermometer Based on Cr3+ Ion Luminescence.

Metal-organic frameworks with perovskite structures have recently attracted increasing attention due to their structural, optical, and phonon properties. Herein, we report the structural and luminescence studies of a series of six heterometallic perovskite-type metal-organic frameworks with the general formula [EA]2NaCrxAl1-x(HCOO)6, where x = 1, 0.78, 0.57, 0.30, 0.21, and 0. The diffuse reflectance spectral analysis provided valuable information, particularly on crystal field strength (Dq/B) and energy band gap (Eg). We showed that the Dq/B varies in the 2.33-2.76 range depending on the composition of the sample. Performed Raman, XRD, and lifetime decay analyses provided information on the relationship between those parameters and the chemical composition. We also performed the temperature-dependent luminescence studies within the 80-400 K range, which was the first attempt to use an organic-inorganic framework luminescence thermometer based solely on the luminescence of Cr3+ ions. The results showed a strong correlation between the surrounding temperature, composition, and spectroscopic properties, allowing one to design a temperature sensing model. The temperature-dependent luminescence of the Cr3+ ions makes the investigated materials promising candidates for noncontact thermometers.

Luminescence and Dielectric Switchable Properties of a 1D (1,1,1-Trimethylhydrazinium)PbI3 Hybrid Perovskitoid.

The synthesis and investigation of the physicochemical properties of a novel one-dimensional (1D) hybrid organic-inorganic perovskitoid templated by the 1,1,1-trimethylhydrazinium (Me3Hy+) cation are reported. (Me3Hy)[PbI3] crystallizes in the hexagonal P63/m symmetry and undergoes two phase transitions (PTs) during heating (cooling) at 322 (320) and 207 (202) K. X-ray diffraction data and temperature-dependent vibrational studies show that the second-order PT to the high-temperature hexagonal P63/mmc phase is associated with a weak change in entropy and is related to weak structural changes and different confinement of cations in the available space. The second PT to the low-temperature orthorhombic Pbca phase that corresponds to the high change in entropy and dielectric switching is associated with an ordering of the trimethylhydrazinium cations, re-arrangement and strengthening of hydrogen bonds, and slightly shifted lead-iodide octahedral chains. The high-pressure Raman data revealed two additional PTs, one between 2.8 and 3.2 GPa, related to the symmetry decrease, ordering of the cations, and inorganic chain distortion, and the other in the 6.4-6.8 GPa range related to the partial and reversible amorphization. Optical studies revealed that (Me3Hy)[PbI3] has a wide band gap (3.20 eV) and emits reddish-orange excitonic emission at low temperatures with an activation energy of 65 meV.

Mixology of MA1-x EA x PbI3 Hybrid Perovskites: Phase Transitions, Cation Dynamics, and Photoluminescence.

Mixing molecular cations in hybrid lead halide perovskites is a highly effective approach to enhance the stability and performance of optoelectronic devices based on these compounds. In this work, we prepare and study novel mixed 3D methylammonium (MA)-ethylammonium (EA) MA1-x EA x PbI3 (x < 0.4) hybrid perovskites. We use a suite of different techniques to determine the structural phase diagram, cation dynamics, and photoluminescence properties of these compounds. Upon introduction of EA, we observe a gradual lowering of the phase-transition temperatures, indicating stabilization of the cubic phase. For mixing levels higher than 30%, we obtain a complete suppression of the low-temperature phase transition and formation of a new tetragonal phase with a different symmetry. We use broad-band dielectric spectroscopy to study the dielectric response of the mixed compounds in an extensive frequency range, which allows us to distinguish and characterize three distinct dipolar relaxation processes related to the molecular cation dynamics. We observe that mixing increases the rotation barrier of the MA cations and tunes the dielectric permittivity values. For the highest mixing levels, we observe the signatures of the dipolar glass phase formation. Our findings are supported by density functional theory calculations. Our photoluminescence measurements reveal a small change of the band gap upon mixing, indicating the suitability of these compounds for optoelectronic applications.

Synthesis, Photoluminescence and Vibrational Properties of Aziridinium Lead Halide Perovskites.

Three-dimensional lead halide perovskites are known for their excellent optoelectronic properties, making them suitable for photovoltaic and light-emitting applications. Here, we report for the first time the Raman spectra and photoluminescent (PL) properties of recently discovered three-dimensional aziridinium lead halide perovskites (AZPbX3, X = Cl, Br, I), as well as assignment of vibrational modes. We also report diffuse reflection data, which revealed an extended absorption of light of AZPbX3 compared to the MA and FA counterparts and are beneficial for solar cell application. We demonstrated that this behavior is correlated with the size of the organic cation, i.e., the energy band gap of the cubic lead halide perovskites decreases with the increasing size of the organic cation. All compounds show intense PL, which weakens on heating and shifts toward higher energies. This PL is red shifted compared to the FA and MA counterparts. An analysis of the PL data revealed the small exciton binding energy of AZPbX3 compounds (29-56 meV). Overall, the properties of AZPbX3 are very similar to those of the well-known MAPbX3 and FAPbX3 perovskites, indicating that the aziridinium analogues are also attractive materials for light-emitting and solar cell applications.

Effect of Dimensionality on Photoluminescence and Dielectric Properties of Imidazolium Lead Bromides.

Hybrid organic-inorganic lead halide perovskites have emerged as promising materials for various applications, including solar cells, light-emitting devices, dielectrics, and optical switches. In this work, we report the synthesis, crystal structures, and linear and nonlinear optical as well as dielectric properties of three imidazolium lead bromides, IMPbBr3, IM2PbBr4, and IM3PbBr5 (IM+ = imidazolium). We show that these compounds exhibit three distinct structure types. IMPbBr3 crystallizes in the 4H-hexagonal perovskite structure with face- and corner-shared PbBr6 octahedra (space group P63/mmc at 295 K), IM2PbBr4 adopts a one-dimensional (1D) double-chain structure with edge-shared octahedra (space group P1̅ at 295 K), while IM3PbBr5 crystallizes in the 1D single-chain structure with corner-shared PbBr6 octahedra (space group P1̅ at 295 K). All compounds exhibit two structural phase transitions, and the lowest temperature phases of IMPbBr3 and IM3PbBr5 are noncentrosymmetric (space groups Pna21 at 190 K and P1 at 100 K, respectively), as confirmed by measurements of second-harmonic generation (SHG) activity. X-ray diffraction and thermal and Raman studies demonstrate that the phase transitions feature an order-disorder mechanism. The only exception is the isostructural P1̅ to P1̅ phase transition at 141 K in IM2PbBr4, which is of a displacive type. Dielectric studies reveal that IMPbBr3 is a switchable dielectric material, whereas IM3PbBr5 is an improper ferroelectric. All compounds exhibit broadband, highly shifted Stokes emissions. Features of these emissions, i.e., band gap and excitonic absorption, are discussed in relation to the different structures of each composition.

The Structural and Optical Properties of 1,2,4-Triazolo[4,3-a]pyridine-3-amine.

The structural and spectroscopic properties of a new triazolopyridine derivative (1,2,4-triazolo[4,3-a]pyridin-3-amine) are described in this paper. Its FTIR spectrum was recorded in the 100-4000 cm-1 range and its FT-Raman spectrum in the range 80-4000 cm-1. The molecular structure and vibrational spectra were analyzed using the B3LYP/6-311G(2d,2p) approach and the GAUSSIAN 16W program. The assignment of the observed bands to the respective normal modes was proposed on the basis of PED calculations. XRD studies revealed that the studied compound crystallizes in the centrosymmetric monoclinic space group P21/n with eight molecules per unit cell. However, the asymmetric unit contains two 1,2,4-triazolo[4,3-a]pyridin-3-amine molecules linked via N-H⋯N hydrogen bonds with a R22(8) graph. The stability of the studied molecule was considered using NBO analysis. Electron absorption and the luminescence spectra were measured and discussed in terms of the calculated singlet, triplet, HOMO and LUMO electron energies. The Stokes shifts derived from the optical spectra were equal to 9410 cm-1 for the triazole ring and 7625 cm-1 for the pyridine ring.

Physicochemical Characterization of the Loganic Acid-IR, Raman, UV-Vis and Luminescence Spectra Analyzed in Terms of Quantum Chemical DFT Approach.

The molecular structure and vibrational spectra of loganic acid (LA) were calculated using B3LYP density functional theory, the 6-311G(2d,2p) basis set, and the GAUSSIAN 03W program. The solid-phase FTIR and FT-Raman spectra of LA were recorded in the 100-4000 cm-1 range. The assignment of the observed bands to the respective normal modes was proposed on the basis of the PED approach. The stability of the LA molecule was considered using NBO analysis. The electron absorption and luminescence spectra were measured and discussed in terms of the calculated singlet, triplet, HOMO, and LUMO electron energies. The Stokes shift derived from the optical spectra was 20,915 cm-1.

Metal-Formate Framework Stiffening and Its Relevance to Phase Transition Mechanism.

In the last decade, one of the most widely examined compounds of motal-organic frameworks was undoubtedly ((CH3)2NH2)(Zn(HCOO)3), but the problem of the importance of framework dynamics in the order-disorder phase change of the mechanism has not been fully clarified. In this study, a combination of temperature-dependent dielectric, calorimetric, IR, and Raman measurements was used to study the impact of ((CH3)2NH2)(Zn(DCOO)3) formate deuteration on the phase transition mechanism in this compound. This deuteration led to the stiffening of the metal-formate framework, which in turn caused an increase in the phase transition temperature by about 5 K. Interestingly, the energetic ordering of DMA+ cations remained unchanged compared to the non-deuterated compound.