The detailed temperature-dependent IR and Raman spectra were used to study and understand the mechanism of structural phase transition occurring at 175 K in manganese hypophosphite templated with ...formamidinium (FA+) ions, FAMn(H2POO)3, which adopts a perovskite-like architecture. The structural transformation between the C2/c and the P21/c monoclinic phases has a complicated nature and is mainly driven by re-orientational motions of the FA+ cations but it is also accompanied by a significant distortion of the MnO6 octahedral units as well as steric-forced changes of the PH2 groups determining the off-center shifts of FA+ cations in the cages. The re-orientational motions of formamidinium cations at 175 K are followed by slight changes of their geometry and re-arrangement of hydrogen bonds (HBs). The strong temperature-dependences of bands corresponding to vibrations involving hydrogen bonding reveal the highly-dynamic character of this phase transition and strong nature of created HBs. The most pronounced changes are observed for the modes corresponding to the formamidinium cation, proving that the phase transition has an order-disorder character.
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•The Mn2+-hypophosphite framework with FA+ cations has been studied using vibrational spectroscopy.•The assignment of observed IR and Raman bands has been proposed.•The mechanism of PT at 175 K has been explained.•PT involves order-disorder process along with deformation of the framework.
•CsPbCl3:x%Yb3+ concentration series prepared by a solid state method is reported.•XRD diffractograms confirmed the phase purity of the materials.•SEM images showed significant morphological changes ...with impurity concentration.•It turned out that the optimal dopant concentration in the host is 10%.•TL of the CsPbCl3:Yb3+ exhibits two types of traps.
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Inorganic halide perovskites are interesting materials that are characterized by a small energy gap and tunable exciton luminescence achieved by exchanging the halide ion in the structure. They are mainly obtained in the form of colloids or thin films, resulting in small grain sizes with narrow distribution. The unique physicochemical properties of perovskites give them great application potential, which is additionally increased by doping with optically active ions. In this paper, the structural and spectroscopic properties of the CsPbCl3:x%Yb3+ (x = 1, 5, 10, 15, 20%) concentration series prepared by the solid state method are investigated. Besides the measurements of X-ray diffraction, Raman spectroscopy, diffuse reflectance, excitation, emission and decay curves, a thermoluminescence analysis was also performed for the first time for CsPbCl3:Yb3+. It was found that the dopant content strongly influences the obtained results. The introduction of more than 10% of Yb3+ ions into the host lattice leads to a deterioration of the optical properties.
The temperature-dependent IR and Raman spectroscopy has been used to study the phase transitions in manganese-azide frameworks with either dimethylammonium (DMA+) or tetramethylammonium (TMA+) ...cations which adopt a perovskite-like crystal structure. The phase transition in DMA-analogue seems to be associated with cooperative tilting of MnN6 octahedra and order-disorder of hydrogen bonds while in TMA-analogue it is more complex and composed of several processes, including the motions of both manganese-azide framework and tetramethylammonium cations and their possible coupling. Our results are in agreement with the data received from crystallographic and dielectric measurements in the case of TMA-analogue and we have demonstrated the importance of order-disorder of hydrogen bonds in the case of DMA-analogue which previously has not been taken into account.
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•Two manganese-azide frameworks templated with DMA+/TMA+ cations have been studied by vibrational spectroscopy.•The mechanisms of phase transitions (PT) are complex with a significant contribution of order-disorder processes.•In DMA-analogue PT involves NH2+ motions which affect the manganese-azide framework.•In TMA-analogue the cooperative librations of MnN6 octahedra seem to play the most important part in PT.
We report on temperature-dependent infrared (IR) and Raman studies of (CH3)2NH2M(HCOO)3 metal–organic frameworks (MOFs) with M=Zn, Fe. Based on Raman and IR data, an assignment of the observed modes ...to respective vibrations of atoms is proposed. Temperature-dependent studies revealed abrupt changes below 160K that are attributed to the onset of first-order structural phase transition. The most pronounced changes are observed for the modes corresponding to the dimethylammonium cation, especially those involving motion of hydrogen atoms. This behavior proves that the phase transition has an order–disorder character and is associated with the ordering of protons. The abrupt splitting of some modes related to the formate ion indicates that this transition is also associated with significant distortion of the metal-formate framework.
GTSN: Nd (GeO2-TeO2-SrF2-Nb2O5–Nd2O3) glasses of varying (0.2–3%) Nd concentration were obtained using the melt-quenching method. Their thermal properties were evaluated using differential scanning ...calorimetry, showing highly favorable glass thermal stability. Glass structure was analyzed using XRD, IR and Raman spectroscopy. Combining the advantages of germanate, tellurite and fluoride optical systems, a promising glass laser material was achieved, as proven with optical spectroscopy methods, such as absorption, emission and fluorescence lifetime spectroscopies. Utilizing the fluorescence intensity ratios between emission bands from Nd excited levels, several models for luminescent thermometry were established for GTSN: Nd. One of the models was tested in a laser power-dependence experiment, allowing to estimate temperature increase during high power optical excitation. Great thermal stability and spectroscopic performance of the material, along with a built-in method for contactless temperature measurement, make GTSN: Nd a promising material for glass-based optically active elements.
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•High thermal stability of novel GTSN germanotellurite glasses.•Influence of dopant concentration on thermal and spectroscopic properties.•Significant peak emission cross-section of 2.08 × 10−20 cm2 at 1060 nm.•Four temperature sensing models based on NIR Nd fluorescence intensity ratios.•Luminescent thermometry model tested out in practical conditions.
Thermally induced reconstruction of ceria nanocubes into {111}-nanofacetted structures was investigated by XRD, TEM and Raman spectroscopy. The beneficial role of reducing atmosphere on the surface ...reconstruction processes was observed and is discussed. The activity of ceria nanoparticles with various surface morphology in catalytic oxidation of CO was investigated. The order of catalytic activity of the particles: smooth ceria nanocubes > {111}-nanofacetted ceria nanocubes > smooth octahedra correlates with the concentration of Ce3+ - oxygen vacancy pairs determined by Raman spectroscopy.
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•Edges of ceria nanocubes transform into (111) nanofacetted structures when annealed at T ≥ 500 °C.•Reducing atmosphere promotes the reconstruction of (110) surfaces at edges of ceria nanocubes.•The reconstruction process declines catalytic activity of ceria nanocubes in CO oxidation.
Lake thermal dynamics have been considerably impacted by climate change, with potential adverse effects on aquatic ecosystems. To better understand the potential impacts of future climate change on ...lake thermal dynamics and related processes, the use of mathematical models is essential. In this study, we provide a comprehensive review of lake water temperature modeling. We begin by discussing the physical concepts that regulate thermal dynamics in lakes, which serve as a primer for the description of process‐based models. We then provide an overview of different sources of observational water temperature data, including in situ monitoring and satellite Earth observations, used in the field of lake water temperature modeling. We classify and review the various lake water temperature models available, and then discuss model performance, including commonly used performance metrics and optimization methods. Finally, we analyze emerging modeling approaches, including forecasting, digital twins, combining process‐based modeling with deep learning, evaluating structural model differences through ensemble modeling, adapted water management, and coupling of climate and lake models. This review is aimed at a diverse group of professionals working in the fields of limnology and hydrology, including ecologists, biologists, physicists, engineers, and remote sensing researchers from the private and public sectors who are interested in understanding lake water temperature modeling and its potential applications.
Plain Language Summary
Lake thermal dynamics are fundamental in controlling mixing processes and have significant implications for biological and geochemical processes. Consequently, the impacts of climate change on these dynamics can have severe consequences for the health of lakes and their aquatic ecosystems. In this context, mathematical models are essential for understanding the potential effects of future climate change on lake thermal dynamics and related processes. This manuscript offers a comprehensive review of lake water temperature modeling. It covers the fundamental physical concepts that govern thermal dynamics in lakes and provides an overview of various sources of observational water temperature data, including in situ monitoring and satellite data used in these models. The study evaluates different types of lake water temperature models, including statistical, process‐based, and hybrid models. It explores emerging modeling approaches such as forecasting, digital twins, combining process‐based modeling with deep learning, ensemble modeling, and climate‐lake models coupling. Model performance is also discussed, highlighting suggested evaluation metrics and providing a comprehensive analysis of the state‐of‐the‐art optimization methods to assess model accuracy. This review targets researchers in limnology, hydrology, ecology, biology, physics, engineering, and remote sensing from the private and public sectors interested in lake water temperature modeling and its applications.
Key Points
Lake thermal dynamics are central in shaping mixing processes and the health of aquatic ecosystems, and climate change alters these dynamics
Mathematical models are essential to understand past and project future climate change impacts on lake thermal dynamics
This study reviews lake water temperature modeling, covering concepts, data sources, and model evaluation for applications across disciplines
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•The structural and spectroscopic properties of Sc2(MoO4)3: Cr3 + were investigated.•The influence of synthesis conditions on the structural properties was studied.•The emission ...spectra of samples doped with 0.1–2.0 % of Cr3 + were investigated.•The broadband NIR luminescence from Cr3+ ions may be attractive for LED applications.
The structural and spectroscopic properties of Sc2(MoO4)3 molybdate containing various concentrations of Cr3+ ions were investigated in a temperature range of 80–300 K. The samples were prepared using hydrothermal as well as solid-state reaction methods. The influence of synthesis conditions and the molybdenum source on the structural properties was studied by X-ray diffraction (XRD), IR (infrared), and Raman methods. The optical properties of Sc2(MoO4)3 samples doped with 0.1, 0.5, 1.0, and 2.0 % of Cr3+ ions were investigated. The broadband near-infrared (NIR) luminescence spectra generated from the 4T2 and 2E levels of Cr3+ ions may be attractive for NIR light-emitting diode (LED) applications. Emission decay profiles and the crystal field parameters of Cr3+ ions are discussed. In particular, the mechanism of photoluminescence generation and the thermal quenching path are described in detail.
We report the structural, phonon and luminescence properties of Eu3+-doped Gd3-xEuxNbO7 niobates prepared by conventional solid state reaction. Although a few different crystal structures of pure ...Gd3NbO7 have been reported so far, their properties still remain controversial and the mechanism of their structural phase transition is not well understood. The temperature-dependent IR and Raman spectra show a structural phase transition occurring at 340 K. The detailed analysis of vibrational spectra and correlation diagrams as well as theoretical factor group considerations allowed us to propose the detailed assignment of the observed bands, define the symmetry of low and high-temperature phases and explain the mechanism of their structural transformation from the Pmcn to the Cmcm centrosymmetric orthorhombic space group. Powder X-Ray diffraction patterns confirm our analysis. The temperature-dependent emission, room-temperature excitation spectra and luminescence decay times are reported to achieve more information on structural and optical properties of the studied niobates.
•Gd3Nb2O7 niobates doped with Eu3+ ions were prepared using solid state reaction method.•Factor group analysis was applied to explain Raman and IR spectra.•Low- and high-temperature phases were described and the mechanism of phase transition was proposed.
In the present work we report detailed structural, magnetic and phonon properties of NiCr2O4 powders synthesized via a simple coprecipitation method. Temperature-dependent XRD as well as ...temperature-dependent IR studies reveal that cubic to tetragonal phase transition is lowered due to size effects. Observed changes in the IR spectra indicate that the paramagnetic–ferrimagnetic phase transition taking place at 74K is related to further lowering of symmetry to orthorhombic system. Assignment of modes was proposed and factor group analyses in three possible symmetries were carried out. Our results show strong anomalies due to the Jahn–Teller tetragonal distortion and weak due to the orthorhombic distortion and onset of collinear ferrimagnetic order. Shifts of wavenumbers observed below 31K, where the onset of antiferromagnetic ordering occurs, were attributed to spin–phonon interactions.
XRD pattern of NiCr2O4 sample synthesized via a coprecipitation method followed by calcination at 1000oC. Display omitted
•NiCr2O4 starts to crystallize near 750°C.•Coexistence of cubic and tetragonal phases of NiCr2O4 was revealed.•Temperature of the Jahn–Teller distortion is lowered due to the size effects.•Evidences of tetragonal and orthorhombic distortions were found.•Weak spin–phonon interactions were evidenced.
