Phosphor-converted white light-emitting diodes (pc-WLEDs) are emerging as an indispensable solid-state light source for the next generation lighting industry and display systems due to their unique properties including but not limited to energy savings, environment-friendliness, small volume, and long persistence. Until now, major challenges in pc-WLEDs have been to achieve high luminous efficacy, high chromatic stability, brilliant color-rending properties, and price competitiveness against fluorescent lamps, which rely critically on the phosphor properties. A comprehensive understanding of the nature and limitations of phosphors and the factors dominating the general trends in pc-WLEDs is of fundamental importance for advancing technological applications. This report aims to provide the most recent advances in the synthesis and application of phosphors for pc-WLEDs with emphasis specifically on: (a) principles to tune the excitation and emission spectra of phosphors: prediction according to crystal field theory, and structural chemistry characteristics (e.g. covalence of chemical bonds, electronegativity, and polarization effects of element); (b) pc-WLEDs with phosphors excited by blue-LED chips: phosphor characteristics, structure, and activated ions (i.e. Ce 3+ and Eu 2+ ), including YAG:Ce, other garnets, non-garnets, sulfides, and (oxy)nitrides; (c) pc-WLEDs with phosphors excited by near ultraviolet LED chips: single-phased white-emitting phosphors (e.g. Eu 2+ –Mn 2+ activated phosphors), red-green-blue phosphors, energy transfer, and mechanisms involved; and (d) new clues for designing novel high-performance phosphors for pc-WLEDs based on available LED chips. Emphasis shall also be placed on the relationships among crystal structure, luminescence properties, and device performances. In addition, applications, challenges and future advances of pc-WLEDs will be discussed.

Phosphors in phosphor-converted white light-emitting diodes: Recent advances in materials, techniques and properties

Dielectric polymer nanocomposites are rapidly emerging as novel materials for a number of advanced engineering applications. In this Review, we present a comprehensive review of the use of ferroelectric polymers, especially PVDF and PVDF-based copolymers/blends as potential components in dielectric nanocomposite materials for high energy density capacitor applications. Various parameters like dielectric constant, dielectric loss, breakdown strength, energy density, and flexibility of the polymer nanocomposites have been thoroughly investigated. Fillers with different shapes have been found to cause significant variation in the physical and electrical properties. Generally, one-dimensional and two-dimensional nanofillers with large aspect ratios provide enhanced flexibility versus zero-dimensional fillers. Surface modification of nanomaterials as well as polymers adds flavor to the dielectric properties of the resulting nanocomposites. Nowadays, three-phase nanocomposites with either combination of fillers...

Recent Progress on Ferroelectric Polymer-Based Nanocomposites for High Energy Density Capacitors: Synthesis, Dielectric Properties, and Future Aspects.

An insight into the analogies, state-of-the-art technologies, concepts, and prospects under the umbrella of perovskite materials (both inorganic-organic hybrid halide perovskites and ferroelectric perovskites) for future multifunctional energy conversion and storage devices is provided. Often, these are considered entirely different branches of research; however, considering them simultaneously and holistically can provide several new opportunities. Recent advancements have highlighted the potential of hybrid perovskites for high-efficiency solar cells. The intrinsic polar properties of these materials, including the potential for ferroelectricity, provide additional possibilities for simultaneously exploiting several energy conversion mechanisms such as the piezoelectric, pyroelectric, and thermoelectric effect and electrical energy storage. The presence of these phenomena can support the performance of perovskite solar cells. The energy conversion using these effects (piezo-, pyro-, and thermoelectric effect) can also be enhanced by a change in the light intensity. Thus, there lies a range of possibilities for tuning the structural, electronic, optical, and magnetic properties of perovskites to simultaneously harvest energy using more than one mechanism to realize an improved efficiency. This requires a basic understanding of concepts, mechanisms, corresponding material properties, and the underlying physics involved with these effects.

Mutual Insight on Ferroelectrics and Hybrid Halide Perovskites: A Platform for Future Multifunctional Energy Conversion.

The aim of this review article on recent developments of mechanochemistry (nowadays established as a part of chemistry) is to provide a comprehensive overview of advances achieved in the field of atomistic processes, phase transformations, simple and multicomponent nanosystems and peculiarities of mechanochemical reactions. Industrial aspects with successful penetration into fields like materials engineering, heterogeneous catalysis and extractive metallurgy are also reviewed. The hallmarks of mechanochemistry include influencing reactivity of solids by the presence of solid-state defects, interphases and relaxation phenomena, enabling processes to take place under non-equilibrium conditions, creating a well-crystallized core of nanoparticles with disordered near-surface shell regions and performing simple dry time-convenient one-step syntheses. Underlying these hallmarks are technological consequences like preparing new nanomaterials with the desired properties or producing these materials in a reproducible way with high yield and under simple and easy operating conditions. The last but not least hallmark is enabling work under environmentally friendly and essentially waste-free conditions (822 references).

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Hallmarks of mechanochemistry: From nanoparticles to technology

Heterocyclic pyrrole molecules are in situ aligned and polymerized in the -absence of an oxidant between layers of the 2D Ti3C2Tx (MXene), resulting in high volumetric and gravimetric capacitances with capacitance retention of 92% after 25,000 cycles at a 100 mV s(-1) scan rate.

Pseudocapacitive Electrodes Produced By Oxidant-Free Polymerization of Pyrrole Between the Layers of 2D Titanium Carbide (MXene)

Phase formation and microstructure evolution in mullite ceramics synthesized from mechanochemically activated oxide powders doped with Cr2O3

It is well known that, to produce ceramics, green bodies must be sintered at a certain high temperature for a given time duration to develop required microstructure and thus desired properties. In particular, transparent ceramics must be fully dense to achieve maximum optical transmittance. Sintering process is governed by a number of parameters, which can be used to build up interrelationships among processing, microstructure, properties, and performance. Sintering behavior and microstructure development have been extensively studied. Qualitative understandings include driving forces of sintering, the mechanisms of densification, controlling factors, such as particle size of precursor powders, sintering temperature, time duration and applied pressure, electrical current, and so on. This chapter serves to cover the fundamental issues of the conventional sintering technologies.

Sintering and Densification (I)—Conventional Sintering Technologies

Magnetic Nanomaterials for Electromagnetic Wave Absorption

In5SnSbO12 is being considered for use in thermoelectric applications. It has a satisfactory electrical conductivity and is expected to possess low thermal conductivity. However, it is difficult to densify In5SnSbO12 by conventional solid-state reaction method. In this work, we demonstrated that Ga doping could increase the relative density of In5SnSbO12, from ~ 60% (x = 0) to ~ 90% (x = 0.1). The improved densification may be attributable to the increased cationic occupancy after the addition of Ga and the reduced grain size induced by the presence of the secondary phase Ga2In6Sn2O16. The improved relative density led to a significant reduction in electrical resistivity; for example, for x = 0.1, the lowest electrical resistivity was ~ 0.002 Ω cm at 973 K, which was five times lower than that of the undoped sample (x = 0). The resultant power factor of this sample had a value of 3.4 × 10−4 Wm−1 K−2 at 973 K, which was nearly four times higher than that of the undoped sample. Although thermal conductivities were increased with Ga doping due to the enhanced densification, they were lower than that of In2O3. The highest thermoelectric performance was achieved in the sample with x = 0.05, specifically zT ~ 0.17 at 973 K. These results indicate that the addition of Ga to In5SnSbO12 results in a material which is more promising for thermoelectric applications.

Improved densification and thermoelectric performance of In5SnSbO12 via Ga doping

In last two chapters, both methods to harvest waste thermal energy through the conversion to electricity. In this chapter, energy storage as an alternative method to harvest waste thermal energy, especially by using phase change materials (PCMs), will be presented.

Tianshu Zhang

Papers

Phase formation and microstructure evolution in mullite ceramics synthesized from mechanochemically activated oxide powders doped with Cr2O3

Sintering and Densification (I)—Conventional Sintering Technologies

Magnetic Nanomaterials for Electromagnetic Wave Absorption

Improved densification and thermoelectric performance of In5SnSbO12 via Ga doping

Waste Thermal Energy Harvesting (III): Storage with Phase Change Materials