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Combining a single-component white-light phosphor with ultraviolet light emitting diode chips emerges as a promising method to produce white-light-emitting diodes (WLEDs). Nevertheless, it is still a challenge for synthesizing single-component white-light phosphors with a high color rendering index (CRI). Herein, Bi3+/Te4+ co-doped Cs2ZrCl6 perovskite white-light phosphor is presented with a high CRI of 91.7 and good stability against oxygen, water, and heat. The Cs2ZrCl6 microcrystals were prepared using an ultrasound-assisted hydrochloric acid method with controllable Bi3+ and Te4+ dopant contents. By manipulating the excitation wavelength, the emission light can be altered between cold and warm white. The Bi3+/Te4+ co-doped Cs2ZrCl6 phosphor can also emit the warm-white light, showing a high photoluminescence quantum yield of 82.9%. The presented Bi3+/Te4+ co-doped Cs2ZrCl6 perovskite phosphors with a high CRI and great environmental stability offer a new approach for the synthesis of single-phase white-light phosphors and have high potentiality for the application of WLEDs.

The spatiotemporal distribution of terahertz (THz) radiation from plasma has been demonstrated with the technology of THz focal-plane imaging. It has been found that the spatiotemporal distribution will vary with the frequency, as well as the length of plasma. A doughnut-shaped distribution appears in the lower frequency range, while the bell-shaped distribution corresponds to the higher frequency range. For plasmas with different lengths, their generated THz images in the time domain are similar, the THz images in the frequency domain as well. The spatiotemporal distributions are simulated with the off-axis-phase matching theory. All the findings will renew the understanding of the THz generation from plasma induced by two-color pulses.

A circularly polarized vortex beam possesses similar focusing properties as a radially polarized beam. This type of beam is highly valuable for developing optical manufacturing technology, microscopy, and particle manipulation. In this work, a left-hand circularly polarized terahertz (THz) vortex beam (CPTVB) is generated by utilizing a THz quarter wave plate and a spiral phase plate. Focusing properties of its longitudinal component Ez are detailedly discussed on the simulation and experiment. With reducing the F-number of the THz beam and comparing with a transverse component Ex of a general circularly polarized THz beam, the simulation results show that the focal spot size and intensity of its Ez component can reach 87 and 50% of Ex under a same focusing condition. In addition, the experimental results still demonstrate that the left-hand CPTVB can always maintain fine Ez focusing properties in a broad bandwidth, which manifest the feasibility of this class of THz beams.

Abstract Electric‐field‐induced phase transitions in Bi0.5Na0.5TiO3‐based relaxor ferroelectrics are essential to the control of their electrical properties and consequently in revolutionizing their dielectric and piezoelectric applications. However, fundamental understanding of these transitions is a long‐standing challenge due to their complex crystal structures. Given the structural inhomogeneity at the nanoscale or sub‐nanoscale in these materials, dielectric response characterization based on terahertz (THz) electromagnetic‐probe beam fields is intrinsically coordinated to lattice dynamics during DC‐biased poling cycles. The complex permittivity reveals the field‐induced phase transitions to be irreversible. This profoundly counters the claim of reversibility, the conventional support for which is based upon the peak that is manifest in each of four quadrants of the current–field curves. The mechanism of this irreversibility is solely attributed to polar clusters in the transformed lattices. These represent an extrinsic factor, which is quiescent in the THz spectral domain.

The basic concept of effective stress describes the characteristics of fluid and solid interaction in porous media. In this paper, based on the theory of fractal geometry, a fractal model was built to analyze the relationship between the microstructure and the effective stress of porous media. From the microscopic point of view, the influence of effective stress on pore structure of porous media was demonstrated. Theoretical analysis and experimental results show that: (i) the fractal model of effective stress can be used to describe the relationship between effective stress and the microstructure of porous media; (ii) a linear increase in the effective stress leads to exponential increases in fractal dimension, porosity and pore number of the porous media, and causes a decreasing trend in the average pore radius. Keywords: Porous media, Effective stress, Porosity, Fractal dimension, Size distribution