Study Of Temperature Dependence Research Articles

Effect of doping with carbon dots on the alignment and dielectric properties of nematic liquid crystal 4-cyano-4′-pentylbiphenyl in ITO sample cells without conventional alignment layers for low-cost display applications

The melding of nanomaterials with liquid crystalline materials is at the frontier of scientific research due to the transformative impact of nanoparticles on the functionalities of host liquid crystal materials. Here, we report the effect of doping of carbon dots (CDs) in the nematic liquid crystal (NLC), 5CB (4-cyano-4′-pentylbiphenyl) in indium tin oxide (ITO) sample cells without alignment layers (i.e., unaligned ITO (U-ITO) sample cells) using polarizing optical microscopy and dielectric spectroscopic techniques. Polarizing optical microscopy reveals largely dark optical textures under crossed polarizers confirming vertical alignment of Pure 5CB in U-ITO sample cells. However, defects present in the texture pose severe constraints on the use of induced vertical alignment in U-ITO sample cells for device applications. To improve the quality of vertical alignment, CDs of size 2.8 nm at concentrations of 0.03, 0.05 and 0.1 wt% are doped into 5CB. Optical texture studies show the quality of induced vertical alignment of the 0.03 wt% composite is better than pure 5CB and other composites. Frequency-temperature dependent dielectric studies verify the induced vertical alignment by observation of the short-axis molecular relaxation through. The stability of the vertical alignment throughout the nematic phase of 5CB is confirmed through temperature dependent dielectric and optical texture studies. The induced vertical alignment of 5CB in U-ITO sample cells could be attributed to the stronger LC-LC interaction than the ITO-LC interaction. The improvement in the quality of vertical alignment of CDs-5CB composites could be due to the CDs influencing LC-LC and ITO-LC interactions. Finally, the effect of CDs on the increasing dc electrical conductivity of 5CB in U-ITO sample cells is investigated. Our results clearly indicate that CD-5CB composites would be useful in cost-effective display and other photonic devices devoid of alignment layers.

‘Turn On’ fluorescent imine linked 1,2,3-triazole based chemosensor for detection of mercuric ions

The exorbitant use or erroneous management of metal ions has been incurred with catastrophic pollution of our ecological system, particularly in soil and water bodies, resulting in significant repercussions. Hence, precise identification and analysis of heavy-metal ions in intricate hydrological environments is imperative. Therefore, an imine conjugated 1,2,3-triazole derivative VPT was synthesized, characterized via FTIR, NMR (1H &13C), LCMS spectroscopic techniques and was employed for the exclusive identification of Hg2+ ions in the presence of various other metal ions via UV–Visible and fluorescence spectroscopy. The sensor VPT exhibited binding constant (Ka) value of 2.93 × 104 M−1 and detection limit value of 0.5 × 10−9 M in the ACN:H2O::4:1 medium. The stoichiometric ratio was determined using Job’s plot, which revealed a (1:1) ratio of VPT with Hg2+ ions. In addition, time-dependent, temperature-dependent, and pH titration studies were conducted via U.V-Visible spectroscopy to expand the sensor’s applicability. The viable configurations of probe VPT and its 1:1 stoichiometric with Hg2+ ion were optimized using the B3LYP/6-311G++(d,p)/LANL2DZ levels of theory in the Gaussian 09 program respectively and this semi-empirical quantum mechanics approach demonstrated a reduction in the energy gap confirming the stable formation of [VPT-Hg2+] complex. These insights facilitate the design offluorescent probe VPT for detecting Hg2+ in both environmental and biological context.

Temperature-dependent lattice dynamics study on phase stability, martensitic transformation mechanism, and vibrational entropy properties of B2-type Ni–Mn–Ti Heusler alloy

The all-d-metal Ni–Mn–Ti Heusler alloy with its good mechanical properties and colossal caloric effects has attracted significant attention for mechanocaloric refrigeration. However, the phase stability of the B2-type disordered structure at finite temperatures and the physical origin of large phase transformation entropy change in theoretical calculation remain unclear. In view of thermal and strongly anharmonic effects, we combined the first-principles and temperature dependent effective potential calculations to systematically study the phase stability, martensitic transformation mechanism, and vibrational entropy properties of B2 partial disordered structures for Ni8Mn5Ti3 and Ni8Mn6Ti2. Our results showed the austenitic structures of Ni8Mn5Ti3 and Ni8Mn6Ti2 both exhibit antiferromagnetic interaction behaviors at targeted temperatures, resolving the contradiction between previous calculations and experiments. By the analysis of phonon dispersion relations and Helmholtz free energies at low and high temperatures, we provided a deeper explanation for the underlying mechanism of martensitic transformation. Meanwhile, the phase transformation temperatures and vibrational entropy changes were accurately predicted compared with the experiment results. Specifically, we demonstrated that the large vibrational entropy change of Ni–Mn–Ti material originates from the contributions of both the tetragonal distortion ratio and volume change, which provides important theoretical guidance and has great practical significance for designing the solid-state material with large vibrational entropy change in the application of solid-state refrigeration.

Probing the impact of bent-core mesogen on the dielectric relaxations of ferroelectric liquid crystal

The modulation in dielectric relaxations of a conventional ferroelectric liquid crystal (FLC, SCE9) material by doping the bent-core mesogen (BCM) derived from the oxadiazole bisaniline moiety has been greatly investigated using frequency-temperature dependent dielectric spectroscopy. The application of probing ac voltage (i.e., oscillating voltage, 800 mV) has clearly shown the presence of partially unwound helical mode (p-UHM) along with Goldstone mode (GM). However, the temperature-dependent dielectric studies further demonstrate that p-UHM gets merged with GM at higher temperatures and hence becomes difficult to observe it separately. It appears that doping of BCM into FLC leads to the suppression of p-UHM at lower temperature, but with the increase in the concentration of dopant beyond a certain point, p-UHM mode reappears. Moreover, the significant decrement (∼9 °C) in SmC*-SmA* phase transition temperature of FLC with increase in the dopant BCM concentration up to 3 wt%. We believe that such studies would be certainly useful for the understanding of the plausible interaction between two different shaped mesogens (i.e., rod and bent-core) present in the mixture and could pave the way forward to the use of one type of mesogen in the modulation of the dielectric properties of other mesogen.

Temperature Effects and Activation Barriers in Aqueous Proton-Uptake Reactions.

Aqueous proton transfer reactions are fundamental in biology and chemistry, yet kinetics and mechanisms of strong base-weak acid reactions are not well understood. In this work, we present a temperature-dependent reaction kinetic study of the water-soluble photobase actinoquinol, in the presence and absence of succinimide, a weak acid reaction partner. We study the temperature dependence of the reaction and connect the observed dynamics to the reaction's thermodynamics. We find that actinoquinol reacts in associated complexes with water/succinimide, creating an intermediate complex that can undergo either dissociation to create products, or reverse proton transfer within the complex to recreate the initial reactants. We find that the intermediates' formation is energetically unfavorable with both reaction partners, which impacts the net reaction rates. We also find that the net reaction rate is additionally strongly influenced by the competition between the dissociation of the intermediates and their reverse reaction.

Isomeric Effects of Au28(S-c-C6H11)20 Nanoclusters on Photoluminescence: Roles of Electron-Vibration Coupling and Higher Triplet State.

The exploration of near-infrared photoluminescence (PL) from atomically precise nanoclusters is currently a prominent area of interest owing to its importance in both fundamental research and diverse applications. In this work, we investigate the near-infrared (NIR) photoluminescence mechanisms of two structural isomers of atomically precise gold nanoclusters of 28 atoms protected by cyclohexanethiolate (CHT) ligands, i.e., Au28i(CHT)20 and Au28ii(CHT)20. Based on their structures, analysis of 3O2 (triplet oxygen) quenching of the nanocluster triplet states, temperature-dependent photophysical studies, and theoretical calculations, we have elucidated the intricate processes governing the photoluminescence of these isomeric nanoclusters. For Au28i(CHT)20, its emission characteristics are identified as phosphorescence plus thermally activated delayed fluorescence (TADF) with a PL quantum yield (PLQY) of 0.3% in dichloromethane under ambient conditions. In contrast, the Au28ii(CHT)20 isomer exhibits exclusive phosphorescence with a PLQY of 3.7% in dichloromethane under ambient conditions. Theoretical simulations reveal a larger singlet (S1)-triplet (T1) gap in Au28ii than that in Au28i, and the higher T2 state plays a critical role in both isomers' photophysical processes. The insights derived from this investigation not only contribute to a more profound comprehension of the fundamental principles underlying the photoluminescence of atomically precise gold nanoclusters but also provide avenues for tailoring their optical properties for diverse applications.

Elucidating Uniaxial Negative Thermal Expansion and Reversible Phase Transition in β-AgVO3 Microrods: In Situ PXRD and Raman Scattering Studies

This study investigates the thermal behavior and structural transitions of silver vanadate microrods (AgVO3) synthesized via coprecipitation. The samples were characterized at room temperature using scanning electron microscopy, Powder X-ray Diffraction, and Raman scattering. The AgVO3 was obtained in the monoclinic phase (β-phase) with a Cm space group and rod-like morphology of micrometer-sized diameter. In situ temperature-dependent studies utilizing XRD and Raman spectroscopy revealed notable findings: at low temperatures (298 – 12 K), the β-AgVO3 phase exhibited thermal stability alongside uniaxial negative thermal expansion (NTE) along the b lattice parameter of microcrystals. Conversely, experiments at high temperatures (298 – 673 K) demonstrated a reversible structural transition from the monoclinic phase to a triclinic phase at 473 K (β → β’), with NTE observed along the b direction in both high-temperature phases. These temperature-induced structural modifications and the observed uniaxial negative thermal expansion in β-AgVO3 microrods constitute significant contributions to the field, providing valuable insights into their thermal behavior and potential applications.

In-plane and out-of-plane anisotropy in the optical and dielectric properties of YBa2Cu3O7-x superconducting film

YBa2Cu3O7-x (YBCO) is a crucial aspect of research in the field of superconducting applications, where its high anisotropy is generally undesirable in strong power transmission. However, from a dialectical perspective, a thorough investigation of material anisotropy can offer an additional degree of freedom to tune potential properties and design innovative devices. This work employed pulsed laser deposition to fabricate a high-quality YBCO thin film (Tc = 89 K) and used the Mueller matrix spectroscopic ellipsometer (MMSE) to determine the complete dielectric tensor of the YBCO film across the ultraviolet to near-infrared spectrum (245–1000 nm), enabling a comprehensive, quantitative study of the optical anisotropy of YBCO. It provided optical constants and dielectric function spectra for different axes. We found that YBCO exhibits birefringence and dichroism both in-plane and out-of-plane. By combining standard critical point (SCP) analysis and first-principles calculations, we identified specific interband transitions related to SCP in the YBCO dielectric spectra, revealing the physical essence of anisotropic optical transitions from a quantum mechanical standpoint. Temperature-dependent studies of the transitions and optical constants were conducted. The work fills a partial void in the optical parameters of the anisotropy of YBCO and holds relevance for understanding the origins of copper-based high-temperature superconductivity.

Leakage mechanisms of sub-pA InGaAs/GaAs nano-ridge waveguide photodetectors monolithically integrated on a 300-mm Si wafer

We report on a comprehensive temperature dependent dark current study of high-quality InGaAs/GaAs multi quantum well waveguide photodetectors monolithically integrated on silicon. They are integrated through metalorganic vapor-phase selective-area epitaxial growth in a 300 mm CMOS pilot line. Defects resulting from the metamorphic growth of III-V devices on Si make these devices susceptible to different leakage mechanisms at higher operating temperatures. For the high-temperature operation of complex photonics-electronics integrations, understanding the leakage mechanisms of the devices has critical significance. This will help to optimize designs promptly and ensure the reliability and longevity of such devices under extreme operating conditions. The photodetector devices exhibit dark currents below 1 pA, at room temperature and −1 V bias voltage, limited by the noise floor of the measurement setup. To resolve the different leakage mechanisms contributing to the dark current, the devices were measured at elevated temperatures and the results were cross-validated with device simulations. The devices exhibited very low dark currents, with a median below 0.1 nA at 195 °C, suggesting very high-quality material growth. Through device models, leakage mechanisms related to Shockley-Read-Hall (SRH) recombination at bulk volume defects are found to be the main factor contributing to the dark current. The surface SRH recombination is found to be limited, yet affecting the forward bias dark current due to the shortening of the diffusion paths of the majority carriers. Also, the device model shows that the actual dark currents at room temperature can be as low as 0.01 pA, more than 1-order lower than the measured levels. This study emphasizes the high quality of the III-V nano-ridge waveguide devices grown on Si, which can potentially expand the capabilities of silicon photonics platforms further.

Distinct Valley Polarization in Vertical Heterobilayers: Difference between Edge- and Center-Nucleated WS2/MoS2.

Structural imperfections can cause both beneficial and detrimental consequences on the excitonic characteristics of transition metal dichalcogenides (TMDs). Regarding valley selection, structural defects typically promote valley depolarization in monolayer TMDs, but defect healing via an additional growth process can restore valley polarization in vertical heterobilayers (VHs). In this study, we analyzed the valley polarization of center-nucleated and edge-nucleated VHs (WS2/MoS2) grown using a controlled growth process and discovered that defect-related photoluminescence (PL) is strongly suppressed in the center-nucleated VHs due to defect healing. Additionally, we demonstrated that the valley polarization of lower-lying intralayer excitons is more sensitive to the defect density of the sample than to higher-lying intralayer excitons. Despite defect healing in the center-nucleated VHs, the temperature-dependent PL study indicated that valley depolarization of the lower-lying intralayer excitons becomes significant below 100 K because of stronger hybridization of defect states. Also, we conducted a comprehensive study on the excitation intensity dependence to investigate the electron-doping-induced Auger recombination mechanism, which also contributes to valley depolarization of intralayer excitons via regeneration of intervalley trions. Our findings provide valuable insight into the development of VH-based valleytronic devices.

Solvent-Assisted Structural Modifications of Sulfur Dots Followed by Time-Dependent Emergence of a New Emissive State and Long-Lived Afterglow.

Sulfur dots are a new class of recently developed nonmetallic luminescent nanomaterials with various potential applications. Herein, we synthesized sulfur dots using a mild chemical etching method and then modified the structural features of the as-synthesized sulfur dots using a slow and defined solvent-assisted aggregation process. This increases the particle size and overall crystallinity along with the modifications of the surface functional groups, which eventually show a new emission band at longer wavelengths. Detailed photophysical and temperature-dependent luminescence studies confirmed that the new emissive state evolves due to interparticle interactions in the excited state. Furthermore, the occurrence of a new emissive state in a longer-wavelength region helped reduce the energy gap between the lowest excited singlet state and the lowest excited triplet state in modified sulfur dots, resulting in an aqueous stable room-temperature phosphorescence/afterglow emission through efficient intersystem crossing. This typical efficacious afterglow emission directly shows the potential applicability of structurally modified sulfur dots in encryption devices and can also be potentially effective in light emitting diodes (LED) and sensing devices.

Robust luminescent material with superior color purity: Sm3+ ion-doped CaAl4O7 phosphor synthesized in a cost-effective approach for solid-state lighting applications

This work reports the synthesis of Sm3+ ion doped calcium dialuminate phosphor by microwave-assisted combustion synthesis technique. Phase purity and the crystal structure of the phosphors were affirmed by PXRD analysis and was found to have monoclinic structure. SEM study was performed to analyze the surface morphology. FTIR study clarifies the existence of functional groups. The optical bandgap of 4.43 eV was determined for CaAl4O7:Sm3+ (x = 0.03) sample. The emission spectra of the sample recorded upon excitation at 403 nm suggest orange color emission around 601 nm pertaining to the transition 4G5/2→6H7/2 of Sm3+ ions. The optimal dopant concentration was established at 3 mol%. CIE chromaticity coordinates of (x = 0.6029, y = 0.3964) were established for the optimized sample. Correlated color temperature of 1620 K demonstrates the emission of light in warmer region. The superior color purity of 99.21 % and color rendering index of 77 for the optimized phosphor material was manifested. The photoluminescence (PL) decay time (for Sm3+ concentration = 0.03 mol) was found to be 0.73 ms. Thermal stability of the sample was investigated and the activation energy was determined to be 0.152 eV by temperature-dependent PL study. To explore the lighting ability of the phosphor, phosphor-in-glass (P-i-G) material was fabricated. CaAl4O7:Sm3+ (x = 0.03) based P-i-G material validates excellent luminous efficacy (360 lm/W) and luminous efficiency (52.70 %) which affirms its practical applications.

Direction Dependent Ferroelectricity and Conductivity in a Single Crystal 2D Halide Double Perovskite.

Halide ferroelectric materials have garnered a lot of interest because of their distinctive electrical and structural characteristics. In this study, the design and development of a new non-centrosymmetric 2D layered halide double perovskite material, Cl1.14Br2.86PA4AgInBr8 (CPAIn) is reported. This material shows ferroelectric properties above room temperature, with a Curie temperature of 190 °C. This behavior is achieved through the substitution of the halogenated A-site organic linker, 3-chloropropylammonium. CPAIn exhibits anisotropic ferroelectric behavior with higher spontaneous polarization of 6.25 µC cm-2 along the perpendicular direction to the octahedral layers, whereas the value decreases to 0.174 µC cm-2 between sheets. While using bottom contact to study the nature of polarity within a sheet, the P-E loop displays capacitive loop. The nature and value of polarization is highly direction dependent, and to further understand the mechanism of conduction, a combination of temperature-dependent impedance studies and poling dependent conductivity techniques are employed. These directional dependent properties hold immense potential in memory devices, sensors and photovoltaics, piezoelectric devices and energy storage.

The study of structural, frequency and temperature dependence of electrical and dielectric properties of CuO-substituted Ni-Zn nanocrystalline ferrites for MLCI applications

ABSTRACT The Cu2+ ion-substituted Ni-Zn ferrites were synthesised by the citrate gel auto-combustion method. The structural and micro-structural analyses of all samples were done using XRD and SEM, respectively. XRD studies confirmed that all samples belong to a cubic spinel structure. The cation distributions of all samples were estimated using relative X-ray intensity calculations. Room temperature, temperature variation, electrical resistivity, initial permeability and dielectric properties were carried out by an impedance analyser. The dielectric and permeability values decreased with increasing frequency. The addition of Cu2+ ions in the present system modifies the cation distribution which results in a gradual decrease of magnetisation values. The temperature dependence of initial permeability showed a sharp decrease with increasing temperature. This indicates the formation of a single phase of materials. The maximum permeability value obtained at x = 0.10 is directly related to the grain size. These temperature variation studies indicate that all these materials are well-suitable for MLCI applications.

A double perovskite BaSrTiMnO6: Synthesis, microstructural, transport and optical properties for NTC thermistor applications

The provided communication reports the synthesis and comprehensive characterization of the BaSrTiMnO6 (BSTMO) ceramic. Rietveld analysis suggests the formation of monoclinic crystal symmetry with average crystallite size of 75.3 nm and micro-lattice strain of 0.00174. Scanning Electron Microscope (SEM) analysis reveals uniform grain distribution with well-defined grain boundaries. Well-grown grains and grain boundaries actively contribute to the transport mechanism. Energy Dispersive X-ray Analysis (EDX) is employed to check the purity and compositional analysis of the prepared sample. Raman spectrum analysis confirms the presence of all constituent atomic vibrations. UV-visible spectrum investigation yields a bandgap energy of 1.94 eV, suitable for photovoltaic applications. Maxwell-Wagner type of polarization effect is observed from frequency-dependent dielectric constant and loss study. Modulus study confirms non-Debye relaxation nature. Temperature-frequency-dependent electrical impedance analysis shows negative temperature coefficient, non-Debye type relaxation. The study of temperature dependence of resistance suggests NTC thermistor behavior.

Photo-Oxidation of α-Pinene Oxidation Products in Atmospheric Waters - pH- and Temperature-Dependent Kinetic Studies.

The atmospheric α-pinene oxidation leads to three carboxylic acids: norpinonic acid (NPA), pinic acid (PA), and 3-methyl-1,2,3-butanetricarboxylic acid (MBTCA). In this study, the OH radical kinetics in the aqueous phase of these carboxylic acids were investigated at different temperatures and pH values of solutions. Activation parameters and the corresponding atmospheric lifetimes of the acids in the troposphere were derived. The overall second-order rate constants for the individual speciation forms of the acids (AH and A- for NPA; AH2, AH- and A2- for PA; and AH3, AH2-, AH2- and A3- for MBTCA) were determined. At 298 K, the rate constants for reactions of protonated forms (AHx) of NPA, PA, and MBTCA with •OH, were (1.5 ± 0.2) × 109 L mol-1 s-1, (2.4 ± 0.1) × 109 L mol-1 s-1, and (4.1 ± 0.6) × 108 L mol-1 s-1, respectively. For the fully deprotonated forms (Ax-) of studied acids, the second-order rate constants were (2.2 ± 0.2) × 109 L mol-1 s-1, (2.8 ± 0.1) × 109 L mol-1 s-1, and (10.2 ± 0.7) × 108 L mol-1 s-1 at 298 K, respectively. It was found that the reactions of NPA and PA with OH radicals are faster than with MBTCA. For MBTCA, the reaction rate depends on pH more strongly at elevated temperatures (>298 K). The atmospheric lifetimes of the acids considered due to their reactivity with •OH were calculated for different model scenarios at a temperature of 283 K and pH = 2 in the aqueous phase. For this purpose, liquid water content (LWC) was used for aerosols and clouds under storm conditions and at various aqueous-phase concentrations of OH radicals. The lifetimes decreased with increasing LWC (from 10-12 m3 m-3 in aerosol to 10-5 m3 m-3 in storms), indicating that the acids undergo significant aqueous processing under realistic atmospheric conditions. Besides, the aerosol systems appeared less effective in removing PA and NPA, with lifetimes ranging from hundreds of days to tens and hundreds of hours, respectively. Clouds were more effective, with lifetimes ranging from tens of hours to a single second or less. MBTCA, which dissolves better in water, was effectively removed in all systems, with the longest lifetime of approximately 90 min.

Temperature-dependent dielectric and electromechanical properties of co-modified calcium bismuth titanate (CaBi4Ti4O15) ceramics

Bismuth layer-structured ferroelectrics (BLSFs), Aurivillius-type ceramics, are of great interest primarily due to their exceptionally high Curie temperature (Tc), rendering them invaluable in various applications such as sensors, actuators, transducers, and micro-electro-mechanical systems designed for elevated temperature operations, including ferroelectric Random-Access Memory applications. This study delves into the dielectric and electromechanical properties of Cobalt-modified Calcium Bismuth Titanate (CaBi4Ti4O15, CBT) (CBT-xCo, with x = 2, 4, and 6 mol%) prepared using a conventional solid-state route followed by sintering. By incorporation of Co, insignificant structural changes were observed, disclosed by X-ray Diffraction analysis. Scanning Electron Microscope micrographs unveiled highly anisotropic grains. The sintered density measured by Archimedes method was maximum for x = 6 mol% with value of 99.1 %. A temperature-dependent dielectric study disclosed that the Curie temperature of the CBT ceramics improved with the increase in Co concentration. Notably, CBT-4Co exhibited the lowest dielectric loss of 0.0967 at 1 MHz and the highest resistivity value of 0.1975 × 105 (Ω cm) at a temperature of 775 °C. Moreover, the electromechanical coupling (kp) and mechanical quality factor (Qm) measured at elevated temperatures unveiled distinctive properties, asserting the potential of the ceramics for high-temperature piezoelectric applications up to 450 °C. CBT-4Co demonstrated the highest kp, with a negligible variation at high temperature, although Qm declined. Results confirmed that CBT-4Co stands distinguished showcasing high Tc, minimal dielectric loss, and consistent electromechanical properties making it the prime candidate for electromechanical applications spanning the gamut from room temperature to elevated temperatures.

Phonon Properties and Lattice Dynamics of Two- and Tri-Layered Lead Iodide Perovskites Comprising Butylammonium and Methylammonium Cations-Temperature-Dependent Raman Studies.

Hybrid lead iodide perovskites are promising photovoltaic and light-emitting materials. Extant literature data on the key optoelectronic and luminescent properties of hybrid perovskites indicate that these properties are affected by electron-phonon coupling, the dynamics of the organic cations, and the degree of lattice distortion. We report temperature-dependent Raman studies of BA2MAPb2I7 and BA2MA2Pb3I10 (BA = butylammonium; MA = methylammonium), which undergo two structural phase transitions. Raman data obtained in broad temperature (360-80 K) and wavenumber (1800-10 cm-1) ranges show that ordering of BA+ cations triggers the higher temperature phase transition, whereas freezing of MA+ dynamics occurs below 200 K, leading to the onset of the low-temperature phase transition. This ordering is associated with significant deformation of the inorganic sublattice, as evidenced by changes observed in the lattice mode region. Our results show, therefore, that Raman spectroscopy is a very valuable tool for monitoring the separate dynamics of different organic cations in perovskites, comprising "perovskitizer" and interlayer cations.

Электрофизические и температурные характеристики тонких слоёв квантовых точек Ag2S

This paper presents a study of the electrical properties of colloidal silver sulfide quantum dots thin films (Ag2S/SiO2 QDs) and silver sulfide quantum dots decorated with Au plasmon nanoparticles (Ag2S/SiO2/Au QDs). A study of the conductivity temperature dependences was carried out in the temperature range from 300 to 360 K. The activation energy values were obtained from linear approximations of the current-voltage characteristics in Arrhenius coordinates. It has been shown that decorating Ag2S/SiO2 QDs with Au plasmon nanoparticles leads to an increase in the band gap from 0.29 to 0.89 eV. In this work, the ideality factor is calculated and the main conductivity mechanisms of the presented thin-film structures are determined. It has been shown that decorating Ag2S/SiO2 QDs with Au plasmon nanoparticles leads to a change in the conductivity type. According to the Mott-Gurney model, the charge carriers mobility is calculated.

Fabrication of methylated carbon quantum dot-based fluorescent films for highly sensitive and stable temperature probes

Due to their distinct physicochemical characteristics and outstanding biocompatibility, carbon quantum dots have shown to offer enormous potential in the field of temperature sensing. However, there is still much to learn about the mechanism underlying carbon quantum dots' thermal sensing capabilities, and developing incredibly precise thermometers based on it is still an enormous obstacle. Herein, we successfully fabricated carbon quantum dots with variable luminescence wavelength and temperature-sensitive properties by adjusting the ingredients to modify the composition of functional groups (-NH2, -OH, -COOH and -CH2OH) on the surface of quantum dots in a simple hydrothermal synthesis process, followed by encapsulation with polyvinyl alcohol (PVA). Subsequently, structural/optical characterisation and temperature-dependent studies were utilized for investigations into the quantum dot fluorescence mechanisms as well as the thermal sensing characteristics connected to surface functional groups, respectively. Notably, the designed red-emitting methylenated carbon quantum dot film probe displayed more linear segmented temperature sensing properties (R2>0.99), a wider temperature applicability range (20–160 °C), and high temperature reversibility (20–80 °C, at least 4 cycles). Finally, the mechanism by which functional groups affect the thermal characteristics of carbon quantum dots was addressed, and we hypothesized that intramolecular and intermolecular hydrogen bonding interactions are important factors affecting the thermal properties of carbon dots. This work presents great promise and theoretical guidance for the development of highly reliable carbon quantum dot temperature sensing systems.