Showing papers on "Glass transition published in 2019"
TL;DR: A review of the state of the art of dynamic relaxation in metallic glassy system, as well as a comparison with other glassy systems, is presented in this paper, where the correlation between dynamic relaxation and various properties of MGs are established and summarized.
248 citations
TL;DR: The design and discovery approach, exemplified by the identification of high-strength, high-temperature bulk metallic glasses, bodes well for enabling the discovery of other glassy alloys with exciting properties.
Abstract: Since their discovery in 19601, metallic glasses based on a wide range of elements have been developed2. However, the theoretical prediction of glass-forming compositions is challenging and the discovery of alloys with specific properties has so far largely been the result of trial and error3–8. Bulk metallic glasses can exhibit strength and elasticity surpassing those of conventional structural alloys9–11, but the mechanical properties of these glasses are critically dependent on the glass transition temperature. At temperatures approaching the glass transition, bulk metallic glasses undergo plastic flow, resulting in a substantial decrease in quasi-static strength. Bulk metallic glasses with glass transition temperatures greater than 1,000 kelvin have been developed, but the supercooled liquid region (between the glass transition and the crystallization temperature) is narrow, resulting in very little thermoplastic formability, which limits their practical applicability. Here we report the design of iridium/nickel/tantalum metallic glasses (and others also containing boron) with a glass transition temperature of up to 1,162 kelvin and a supercooled liquid region of 136 kelvin that is wider than that of most existing metallic glasses12. Our Ir–Ni–Ta–(B) glasses exhibit high strength at high temperatures compared to existing alloys: 3.7 gigapascals at 1,000 kelvin9,13. Their glass-forming ability is characterized by a critical casting thickness of three millimetres, suggesting that small-scale components for applications at high temperatures or in harsh environments can readily be obtained by thermoplastic forming14. To identify alloys of interest, we used a simplified combinatorial approach6–8 harnessing a previously reported correlation between glass-forming ability and electrical resistivity15–17. This method is non-destructive, allowing subsequent testing of a range of physical properties on the same library of samples. The practicality of our design and discovery approach, exemplified by the identification of high-strength, high-temperature bulk metallic glasses, bodes well for enabling the discovery of other glassy alloys with exciting properties. Bulk metallic glasses made from alloys of iridium, nickel, tantalum and boron are developed by combinatorial methods, with higher strength at high temperature than those previously produced.
159 citations
TL;DR: In this paper, annealing was identified as a suitable post-processing method to improve the interlayer tensile strength of extrusion-based 3D printed composites, and two different thermoplastic polymers, which are common in 3D printing, were selected to study the enhancement of interlayer strength of composites by additive manufacturing: an amorphous polyethylene terephthalate-glycol (PETG), and a semi-crystalline poly (lactic acid) (PLA).
Abstract: Previous studies have shown that 3D printed composites exhibit an orthotropic nature with inherently lower interlayer mechanical properties. This research work is an attempt to improve the interlayer tensile strength of extrusion-based 3D printed composites. Annealing was identified as a suitable post-processing method and was the focus of this study. Two distinct thermoplastic polymers, which are common in 3D printing, were selected to study the enhancement of interlayer tensile strength of composites by additive manufacturing: a) an amorphous polyethylene terephthalate-glycol (PETG), and b) a semi-crystalline poly (lactic acid) (PLA). It was determined that short carbon fiber reinforced composites have lower interlayer tensile strength than the corresponding neat polymers in 3D printed parts. This reduction in mechanical performance was attributable to an increase in melt viscosity and the consequential slower interlayer diffusion bonding. However, the reduction in interlayer tensile strength could be recovered by post-processing when the annealing temperature was higher than the glass transition temperature of the amorphous polymer. In the case of the semi-crystalline polymer, the recovery of the interlayer tensile strength was only observed when the annealing temperature was higher than the glass transition temperature but lower than the cold-crystallization temperature. This study utilized rheological and thermal analysis of 3D printed composites to provide a better understanding of the interlayer strength response and, therefore, overcome a mechanical performance limitation of these materials.
142 citations
TL;DR: The results show that the thermal properties of the composites are improved in comparison with the neat epoxy, and the composite presents an increased glass transition temperature, high thermal stability and lower coefficient of thermal expansion.
Abstract: With the development of electronic devices such as integrated circuits toward the continual increase in power density and consumption, the efficient heat dissipation and low thermal expansion of materials become one of the most important issue. However, conventional polymers have the problem of poor thermal dissipation performance, which hinder application for electronic devices. In this work, the two-dimensional material, MXene (Ti3C2), is used as the reinforcement additive to optimize the thermal properties of polymers. We reported the preparation of multilayer Ti3C2 MXene by HF etching method and obtained few-layer Ti3C2 MXene by simple ultrasonication. Meanwhile, Ti3C2/epoxy composites were prepared by a solution blending method. The results show that the thermal properties of the composites are improved in comparison with the neat epoxy. Thermal conductivity value (0.587 W/mK) of epoxy composite with only 1.0 wt% Ti3C2 MXene fillers, is increased by 141.3% compared with that of neat epoxy. In addition, the composite presents an increased glass transition temperature, high thermal stability and lower coefficient of thermal expansion. This work is of great significance for the research of high-performance composite materials.
115 citations
TL;DR: In this paper, a mixture of biobased poly(ethylene terephthalate) and isopropyl alcohol fractioned hardwood organosolv lignin was used to obtain a turbostratic carbon phase and a smooth surface.
105 citations
TL;DR: The FTIR and Raman studies clearly revealed that the glass network mainly comprises of [BiO3], [BO6], [BO3] and [BO4] units.
Abstract: Nickel doped Bismuth Borate glasses with composition (70B2O3-(30-x)Bi2O3-xNiO) where x = 0,0.5,1.0,1.5,2.0 (wt%) have been synthesized by conventional melt quenching technique. X-Ray Diffractograms have confirmed the amorphous nature of the prepared glasses. The calculated physical parameters such as density, molar volume, average boron‑boron separation, ion concentration and inter ionic distance provided the information about the structural stability of glass samples. DTA and OPD confirmed the decrease in glass transition temperature (Tg) with increase in Ni content. The FTIR and Raman studies clearly revealed that the glass network mainly comprises of [BiO3], [BiO6], [BO3] and [BO4] units. It is also observed that the introduction of dopant (Ni) and modifier (Bi) leads to the conversion of [BO3] trigonal units into the [BO4] tetragonal units due to the increase in non-bridging oxygen atoms which results in the increase of degree of disorder in the glass network. The optical absorption measurements (UV) carried out for well polished glass samples show a decrease in optical band gap with the increase in Ni doping. This observation was further supported by the urbach energy calculations and metallization criterion of the prepared glass samples. The electronegativity and electronic polarizability values revealed the ionic character of glass samples.
103 citations
TL;DR: The modulated differential scanning calorimetry (MDSC) relies on the accurate detection of complex transitions and the possibility of distinguishing reversible events (dependent on the heat capacity) from non-reversible events ( dependent on kinetics).
Abstract: Phase transition issues in the field of foods and drugs have significantly influenced these industries and consequently attracted the attention of scientists and engineers. The study of thermodynamic parameters such as the glass transition temperature (Tg), melting temperature (Tm), crystallization temperature (Tc), enthalpy (H), and heat capacity (Cp) may provide important information that can be used in the development of new products and improvement of those already in the market. The techniques most commonly employed for characterizing phase transitions are thermogravimetric analysis (TGA), dynamic mechanical analysis (DMA), thermomechanical analysis (TMA), and differential scanning calorimetry (DSC). Among these techniques, DSC is preferred because it allows the detection of transitions in a wide range of temperatures (-90 to 550 °C) and ease in the quantitative and qualitative analysis of the transitions. However, the standard DSC still presents some limitations that may reduce the accuracy and precision of measurements. The modulated differential scanning calorimetry (MDSC) has overcome some of these issues by employing sinusoidally modulated heating rates, which are used to determine the heat capacity. Another variant of the MDSC is the supercooling MDSC (SMDSC). SMDSC allows the detection of more complex thermal events such as solid-solid (Ts-s) transitions, liquid-liquid (Tl-l) transitions, and vitrification and devitrification temperatures (Tv and Tdv, respectively), which are typically found at the supercooling temperatures (Tco). The main advantage of MDSC relies on the accurate detection of complex transitions and the possibility of distinguishing reversible events (dependent on the heat capacity) from non-reversible events (dependent on kinetics).
96 citations
TL;DR: In this article, a multi-arm hyperbranched polyethylenimine macromolecule was used to develop epoxy superadhesives for metal/polymer composite interfaces.
96 citations
TL;DR: The SiO2@metal organic framework (Universitetetet i Oslo-66, UiO-66) core-shell microspheres were constructed through covalent linkage between amine groups in Uo-66-NH2 and epoxy groups on the surface of silica as discussed by the authors.
Abstract: The SiO2@metal organic framework (Universitetet i Oslo-66, UiO-66) core–shell microspheres were constructed through covalent linkage between amine groups in UiO-66-NH2 and epoxy groups on the surface of silica. The morphology and size of the SiO2@UiO-66 core–shell microspheres could be simply controlled by tuning the ratio between UiO-66-NH2 and epoxy terminated silica (E-SiO2). As observed by TEM, the SiO2@UiO-66 hybrids showed better dispersion state within epoxy matrix compared to either E-SiO2 or UiO-66-NH2. The incorporation of SiO2@UiO-66 hybrids slightly promoted the thermal degradation of the resultant epoxy composites but improved residual yield. The dynamic mechanical analysis results indicated that the SiO2@UiO-66 hybrids slightly increased the glass transition temperature and the modulus. The SiO2@UiO-66 hybrids exhibited higher efficiency in reducing the heat release rate and the smoke production rate compared to either E-SiO2 or UiO-66-NH2. The influence of the component ratio in SiO2@UiO-66 on flame retardancy of the epoxy composites was also studied by cone calorimeter. Specifically, the SiO2@UiO-66 hybrid with medium ratio (SiO2@UiO-66-2) exhibited maximum reduction in peak heat release rate (−31%), total heat release (−23%) and total smoke production (−16%). The char residues were investigated by the Fourier transform infrared spectra, scanning electron microscopy and X-ray photoelectron spectroscopy, which demonstrated that the enhanced flame retardancy of EP/SiO2@UiO-66-2 was attributable to the continual morphology and high thermal resistance originated from the presence of the silicon and zirconium complex. These favorable characteristics including high flame retardant efficiency and good smoke suppression make SiO2@UiO-66 hybrids promising for flame retardant polymers application.
83 citations
TL;DR: High energy X-ray scattering and electro-static levitation in combination with molecular dynamics simulation are used and it is shown that the height of the first peak of the structure function, S(Q) − 1, follows the Curie-Weiss law.
Abstract: We present the results of a structural study of metallic alloy liquids from high temperature through the glass transition. We use high energy X-ray scattering and electro-static levitation in combination with molecular dynamics simulation and show that the height of the first peak of the structure function, S(Q) − 1, follows the Curie-Weiss law. The structural coherence length is proportional to the height of the first peak, and we suggest that its increase with cooling may be related to the rapid increase in viscosity. The Curie temperature is negative, implying an analogy with spin-glass. The Curie-Weiss behavior provides a pathway to an ideal glass state, a state with long-range correlation without lattice periodicity, which is characterized by highly diverse local structures, reminiscent of spin-glass.
79 citations
TL;DR: In this paper, the authors used SiO2 as the modified molecular and investigated the effects of exfoliated hexagonal boron nitride (h-BN) and siO2 nanoparticles-modified-exfoliated h-BN on the storage modulus, the glass transition temperature, the filler dispersion and the thermal conductivity of polyvinyl alcohol (PVA) composites prepared by a solution mixture method.
TL;DR: Berthier et al. as mentioned in this paper developed Monte Carlo methods for two-dimensional glass-forming liquids that allow us to access equilibrium states at sufficiently low temperatures to directly probe the glass transition in a regime inaccessible to experiments.
Abstract: Liquids cooled towards the glass transition temperature transform into amorphous solids that have a wide range of applications. While the nature of this transformation is understood rigorously in the mean-field limit of infinite spatial dimensions, the problem remains wide open in physical dimensions. Nontrivial finite-dimensional fluctuations are hard to control analytically, and experiments fail to provide conclusive evidence regarding the nature of the glass transition. Here, we develop Monte Carlo methods for two-dimensional glass-forming liquids that allow us to access equilibrium states at sufficiently low temperatures to directly probe the glass transition in a regime inaccessible to experiments. We find that the liquid state terminates at a thermodynamic glass transition which occurs at zero temperature and is associated with an entropy crisis and a diverging static correlation length. Our results thus demonstrate that a thermodynamic glass transition can occur in finite dimensional glass-formers. Identifying the nature of the glass transition is challenging because relevant experiments or analytical descriptions are hard to achieve. Here, Berthier et al. develop a Monte Carlo numerical tool to investigate two-dimensional glasses and find a zero-temperature thermodynamic glass transition.
TL;DR: In this paper, a solution casting of polyethylene oxide/carboxymethyl cellulose (PEO/CMC)/barium titanate (BaTiO3) was performed using the solution casting technique.
TL;DR: A review of the theories and assumptions related to the concept of the glass transition and the response of different food components such as moisture, carbohydrate, protein, and lipid at the glassy state is provided in this paper.
Abstract: Background Stability of food is a great challenge that encompasses the interaction among the constituents, processing conditions and thermal history. The frozen storage of food sometimes incurs possible harmful effect due to the formation of large ice crystal and destruction of the cell structure. Glass transition state is a second-order transition of matter where a system reaches a thermodynamically non-equilibrium state due to the immobility of molecules, and it is a universal phenomenon observed when liquid goes to supercooled vitreous state because of extensive cooling or change in the composition. The cryostabilisation or storage at glassy conditions has been studied widely as it can prevent the quality degradation due to freezing. Scope and approach The review provides an overview of the theories and assumptions related to the concept of the glass transition and the response of different food components such as moisture, carbohydrate, protein, and lipid at the glassy state. Influences of processing conditions including moisture removal, freezing rate, annealing time on the relaxation process or the glass transition are also elaborated. In addition, the effects of novel freezing techniques such as ultrasound assisted, high pressure assisted, electric and magnetic field assisted freezing are also discussed in the current review. Key findings and conclusions The glass transition is highly dependent on the presence of moisture and carbohydrate molecules for its great affinity to make hydrogen bond and increase viscosity. The fat and protein glass transitions take place at very low temperatures, at which commercial frozen storage is not considered feasible. Conventional freeze drying and dehydrofreezing require removal of water, which increases the glass transition temperature. Storage at or below the glass transition temperature is desired to increase stability and prevent any quality deterioration. Novel freezing processes such as high pressure, ultrasound, electric and magnetic assisted freezing incur changes in microstructure and metastable glassy states. The current review provides valuable information for designing products with optimized processing techniques and conditions.
TL;DR: In this article, a combination of thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), polarized light microscopy (PLM), differential scanning calorimetry (DSC), and broadband dielectric spectrography (BDS) were employed to study the polymer-filler interaction, crystallization and molecular mobility.
TL;DR: In this article, the authors report a strategy that resulted in a novel family of closo-boron-cluster based room temperature ionic liquids (RTILs), which make them excellent candidates as electrolytes for rechargeable batteries and hybrid devices.
Abstract: Due to their high glass transition temperatures, ionic liquids based on closo-boron clusters have been long discounted from consideration in energy storage applications. Here, we report a strategy that resulted in a novel family of closo-boron-cluster based room temperature ionic liquids (RTILs). Their very low glass transition temperatures, high cathodic and anodic stabilities and compatibility with Li and Mg metals make them excellent candidates as electrolytes for rechargeable batteries and hybrid devices.
TL;DR: Measurements of crystallization kinetics of Ge2 Sb2 Te5 with heating rates spanning over six orders of magnitude reveal a fourfold decrease in Kissinger activation energy for crystallization upon the glass transition, which enables rapid crystallization above the glass Transition temperature Tg .
Abstract: Controlling crystallization kinetics is key to overcome the temperature-time dilemma in phase change materials employed for data storage. While the amorphous phase must be preserved for more than 10 years at slightly above room temperature to ensure data integrity, it has to crystallize on a timescale of several nanoseconds following a moderate temperature increase to near 2/3 Tm to compete with other memory devices such as dynamic random access memory (DRAM). Here, a calorimetric demonstration that this striking variation in kinetics involves crystallization occurring either from the glassy or from the undercooled liquid state is provided. Measurements of crystallization kinetics of Ge2 Sb2 Te5 with heating rates spanning over six orders of magnitude reveal a fourfold decrease in Kissinger activation energy for crystallization upon the glass transition. This enables rapid crystallization above the glass transition temperature Tg . Moreover, highly unusual for glass-forming systems, crystallization at conventional heating rates is observed more than 50 °C below Tg , where the atomic mobility should be vanishingly small.
TL;DR: In this paper, the glass transition phenomenon for polymers, glass transition theories and characterization techniques are discussed, and previous studies on the glass-transition phenomenon of conjugated polymers are reviewed.
Abstract: Conjugated polymers are emerging as promising building blocks for a broad range of modern applications including skin-like electronics, wearable optoelectronics and sensory technologies. In the past three decades, the optical and electronic properties of conjugated polymers have been extensively studied, while their mechanical properties, especially the glass transition phenomenon which fundamentally represents the polymer chain dynamics, has received much less attention. Currently, there is a lack of design rules that underpin the glass transition temperature of these semi-rigid conjugated polymers, putting a constraint on the rational polymer design for flexible stretchable devices and stable polymer glass that is needed for the devices’ long-term morphology stability. In this review article, the glass transition phenomenon for polymers, glass transition theories and characterization techniques are first discussed. Then previous studies on the glass transition phenomenon of conjugated polymers are reviewed and a
TL;DR: Curing degrees, glass transition temperatures, and storage moduli of the formulated multifunctional nanocomposites prove their potential for application as functional structural materials.
Abstract: Reversible Hydrogen Bonds (RHB) have been explored to confer self-healing function to multifunctional nanocomposites. This study has been carried out through a sequence of different steps. Hydrogen bonding moieties, with the intrinsic ability to simultaneously perform the functions of both hydrogen donors and acceptors, have been covalently attached to the walls of carbon nanotubes. The epoxy matrix has been modified to adapt the formulation for hosting self-healing mechanisms. It has been toughened with different percentages of rubber phase covalently linked to the epoxy precursor. The most performant matrix, from the mechanical point of view, has been chosen for the incorporation of MWCNTs. Self-healing performance and electrical conductivities have been studied. The comparison of data related to the properties of nanocomposites containing incorporated functionalized and nonfunctionalized MWCNTs has been performed. The values of the electrical conductivity of the self-healing nanocomposites, containing 2.0% by weight of functionalized multiwalled carbon nanotubes (MWCNTs), range between 6.76 × 10−3 S/m and 3.77 × 10−2 S/m, depending on the nature of the functional group. Curing degrees, glass transition temperatures, and storage moduli of the formulated multifunctional nanocomposites prove their potential for application as functional structural materials.
TL;DR: In this article, an amino-silane treated e-glass fiber and iron(III)oxide particles were reinforced with UP/epoxy polymer blend to improve thermal and mechanical properties.
Abstract: In this current effort a study was made on UP blended epoxy thermosetting polymer and their properties when amino-silane treated e-glass fibre and iron(III)oxide particles were reinforced. The primary goal of this work is to toughen the brittle epoxy resin by blending low strength unsaturated polyester resin. Blending of low strength polyester reduced the brittleness of epoxy with inferior in some mechanical and thermal properties; hence silane treated e-glass fibre and iron(III)oxide particles was reinforced with UP/epoxy polymer blend to improve thermal and mechanical properties. Particle size of 200 nm and glass fibre of 600 g/m2 was used as reinforcements. Fibres and particles were surface treated by an amino silane (APTMS). Usefulness of particles and fibres addition was unveiled by mechanical, thermal, and dielectric properties. The reduced mechanical properties were increased when e-glass fibre and iron(III)oxide filler was reinforced. Glass transition temperature and degradation stability was less for UP/epoxy systems than pure epoxy whereas addition of filler increased Tg and degradation stability. The dielectric results showed increased dielectric constant and loss for UP blended epoxy composite.
TL;DR: In this paper, flexible segments were introduced into the backbones of rigid polar aromatic polymers to increase the flexibility of dipoles, which revealed multiple strong sub-glass transition (sub-Tg) relaxation peaks with low activation energies.
Abstract: Advanced polymers with high energy density and high efficiency are urgently needed in pulse power capacitor applications. Here, we present a practical design approach towards all-organic polymers with high energy density and high efficiency by enhancing dipolar polarization at the molecular level. Flexible segments were introduced into the backbones of rigid polar aromatic polymers to increase the flexibility of dipoles. Dielectric spectroscopy measurements of designed polymers revealed multiple strong sub-glass transition (sub-Tg) relaxation peaks with low activation energies, which indicated the enhanced movement freedom of dipoles below the glass transition temperature. As a result, dielectric constants were increased up to 46% when compared with their base polymers and D–E loop measurements showed that all these designed polymers had high energy densities above 11 J cm−3 with efficiencies above 90%. These results unveiled a novel approach towards high dielectric constant organic polymers for electrical energy storage.
TL;DR: Observations indicate that the addition of polyols as plasticizers could regulate the microstructure as well as the properties of chitosan films, which is essential for their usage in food industry.
TL;DR: Poly(ethylene oxide) (PEO) is the most widely used compound as a solid-state (solvent-free) polymer electrolyte for Li batteries as mentioned in this paper.
Abstract: Poly(ethylene oxide) (PEO) is the most widely used compound as a solid-state (solvent-free) polymer electrolyte for Li batteries, mainly due to its low glass transition temperature (Tg) and ability...
TL;DR: In this article, polyvinyl alcohol (PVA)/poly(ethylene) glycol (PEG) 600g/mol cross-linked membranes with different alumina (Al2O3) content were synthesized.
TL;DR: In this paper, the structural relaxation, potential energy states, and mechanical properties of a model glass subjected to thermal cycling are investigated using molecular dynamics simulations, and the simulation results indicate that the yielding peak as a function of the cycling amplitude for quickly annealed glasses represents a lower bound for the maximum stress in glasses prepared with lower cooling rates.
Abstract: The structural relaxation, potential energy states, and mechanical properties of a model glass subjected to thermal cycling are investigated using molecular dynamics simulations. We study a non-additive binary mixture which is annealed with different cooling rates from the liquid phase to a low temperature well below the glass transition. The thermal treatment is applied by repeatedly heating and cooling the system at constant pressure, thus temporarily inducing internal stresses upon thermal expansion. We find that poorly annealed glasses are relocated to progressively lower levels of potential energy over consecutive cycles, whereas well annealed glasses can be rejuvenated at sufficiently large amplitudes of thermal cycling. Moreover, the lowest levels of potential energy after one hundred cycles are detected at a certain temperature amplitude for all cooling rates. The structural transition to different energy states is accompanied by collective nonaffine displacements of atoms that are organized into clusters, whose typical size becomes larger with increasing cooling rate or temperature amplitude. We show that the elastic modulus and the peak value of the stress overshoot exhibit distinct maxima at the cycling amplitude, which corresponds to the minimum of the potential energy. The simulation results indicate that the yielding peak as a function of the cycling amplitude for quickly annealed glasses represents a lower bound for the maximum stress in glasses prepared with lower cooling rates.
TL;DR: A set of 12 glass compositions with distinct structural features have been designed over a broad composition space in the per-alkaline region of the Na2O -Al2O3 -SiO2 ternary system as discussed by the authors.
Abstract: A set of 12 glass compositions with distinct structural features have been designed over a broad composition space in the per-alkaline region of the Na2O – Al2O3 – SiO2 ternary system. As expected from a per-alkaline system, aluminum has been found to be tetrahedrally coordinated in all the glasses using 27Al magic angle spinning – nuclear magnetic resonance (MAS-NMR) spectroscopy and from structure models generated using molecular dynamic (MD) simulations. The physical properties of glasses, for example, density, coefficient of thermal expansion (CTE), glass transition, elastic moduli and Vickers hardness and brittleness have been measured experimentally and their trends have been explained based on the atomic structure of glasses, from both simulations and experiments. A reasonable agreement has been observed between the composition – structure – property relationship trends obtained experimentally when compared with those predicted by MD simulations. This demonstrates that MD simulation is a promising technique for predictive modeling and designing novel glass compositions for functional applications.
TL;DR: In this article, a benzimidazole monomer was designed as a H-bonding cross-linking monomer to prepare poly(ethylene terephthalate)-based copolyesters (PET-co-PBMs).
TL;DR: In this article, a series of Dy3+ ion doped tellurite glasses in the (50-x)TeO2-25WO3-25Li2O-xDy2O3 system were synthesized using conventional melt quenching technique to investigate colorimetric and radiative properties of dy3+ ions in a new and stable host for their evaluation as solid-state lighting materials.
Abstract: In the present work, a series of Dy3+ ion doped tellurite glasses in the (50-x)TeO2-25WO3-25Li2O-xDy2O3 system were synthesized using conventional melt quenching technique to investigate colorimetric and radiative properties of Dy3+ ions in a new and stable host for their evaluation as solid-state lighting materials. Physical and structural properties were studied through density calculations, refractive index measurements, and Fourier-transform IR spectroscopy analysis. Thermal properties of glasses – glass transition (Tg) and crystallization (Tc/Tp) temperatures and temperature difference (ΔT) – were determined using differential scanning calorimetry. Optical absorption spectra of glasses were recorded with Vis-NIR spectrophotometer. CIE color coordinates, correlated color temperature, color rendering index and yellow to blue emission intensity ratio values were obtained through photoluminescence analysis. Radiative properties such as, radiative transition probability, stimulated emission cross-section, branching ratio and optical bandwidth gain were calculated according to Judd-Ofelt theory. The obtained optical spectroscopy results were found to be comparable or better than other reported glass systems. From the derived results, glasses with Dy3+ ion concentration lower than 0.5 mol% were found to show the closest CIE color coordinate values to pure white light and highest CCT and CRI values revealing good potentiality to be used for applications in white LEDs and solid-state lasers.
TL;DR: In this paper, two kinds of hydroxyl-terminated polyurethanes (HTPU1 and HTPU2) with different molecular weights were used to investigate the influence of phase structure on the overall resin performances.