Inkjet printing (IJP) is a versatile technique for realizing high-accuracy patterns in a cost-effective manner. It is considered to be one of the most promising candidates to replace the expensive thermal evaporation technique, which is hindered by the difficulty of fabricating low-cost, large electroluminescent devices, such as organic light-emitting diodes (OLEDs) and quantum dot light-emitting diodes (QLEDs). In this invited review, we first introduce the recent progress of some printable emissive materials, including polymers, small molecules, and inorganic colloidal quantum dot emitters in OLEDs and QLEDs. Subsequently, we focus on the key factors that influence film formation. By exploring stable ink formulation, selecting print parameters, and implementing droplet deposition control, a uniform film can be obtained, which in turn improves the device performance. Finally, a series of impressive inkjet-printed OLEDs and QLEDs prototype display panels are summarized, suggesting a promising future for IJP in the fabrication of large and high-resolution flat panel displays.

We present a freeform lens for application to light-emitting diodes (LED) road lighting. We propose a simple source–target luminous intensity mapping method based on Snell’s law and geometric-optics analysis. We calculated different contours of cross-sections to construct a freeform lens with a smooth surface. The computer simulation results show that the lighting performance of a single freeform lens is not sufficient for road lighting. For the road lamp simulation, we adopted an oval arrangement of freeform lenses on a printed circuit board. In addition, we performed tolerance analysis to determine the tolerance limits of manufacturing and installation errors. A road lamp at a height of 12 m can create rectangular illumination with an area of 40 m × 12 m, 69.7% uniformity, and average illuminance of 24.6 lux. This lighting performance can fully comply with the urban road lighting design standard.

The structural and magnetic properties, as well as the mechanism of magnetization, of Ni-implanted AlN films were studied. AlN was deposited on Al₂O₃ substrates by metalorganic chemical vapor deposition (MOCVD), and subsequently Ni ions were implanted into the AlN films by Metal Vapor Arc (MEVVA) sources at an energy of 100 keV for 3 h. The films were annealed at 900°C for 1 h in the furnace in order to transfer the Ni ions from interstitial sites to substitutional sites in AlN, thus activating the Ni³⁺ ions. Characterizations were performed in situ using X-ray diffraction (XRD), X-ray photoemission spectroscopy (XPS), and vibrating sample magnetometry (VSM), which showed that the films have a wurtzite structure without the formation of a secondary phase after implanting and annealing. Ni ions were successfully implanted into substitutional sites of AlN films, and the chemical bonding states are Ni-N. The apparent hysteresis loops prove that the films exhibited magnetism at 300 K. The room temperature (RT) saturation magnetization moment (M_s) and coercivity (H_c) values were about 0.36 emu/g and 35.29 Oe, respectively. From the first-principles calculation, a total magnetic moment of 2.99 μB per supercell is expected, and the local magnetic moment of a NiN₄ tetrahedron, 2.45 μB, makes the primary contribution. The doped Ni atom hybridizes with four nearby N atoms in a NiN₄ tetrahedron; then the electrons of the N atoms are spin-polarized and couple with the electrons of the Ni atom with strong magnetization, which results in magnetism. Therefore, the p-d exchange mechanism between Ni-3d and N-2p can be the origin of the magnetism. It is expected that these room temperature, ferromagnetic, Ni-doped AlN films will have many potential applications as diluted magnetic semiconductors.

This study considered the design of an efficient, high brightness polar InGaN/GaN light emitting diode (LED) structure with AlGaN capping layer for green light emission. The deposition of high In (>15%) composition within InGaN quantum well (QW) has limitations when providing intense green light. To design an effective model for a highly efficient InGaN green LEDs, this study considered the compositions of indium and aluminum for In_xGa_1−xN QW and Al_yGa_1−yN cap layers, along with different layer thicknesses of well, barrier and cap. These structural properties significantly affect different properties. For example, these properties affect electric fields of layers, polarization, overall elastic stress energy and lattice parameter of the structure, emission wavelength, and intensity of the emitted light. Three models with different composition and layer thicknesses are simulated and analyzed to obtain green light with in-plane equilibrium lattice parameter close to GaN (3.189 Å ) with the highest oscillator strength values. A structure model is obtained with an oscillator strength value of 1.18×10⁻¹ and least in-plane equilibrium lattice constant of 3.218 Å. This emitter can emit at a wavelength of 540 nm, which is the expected design for the fabrication of highly efficient, bright green LEDs.

The time delay (TD) signature is a critical parameter in optical chaos-based applications. The feasibility of extracting the TD has been a crucial issue that significantly influences the performance of these applications. In this paper, statistical analyses have been conducted to extract the TD signatures from different types of coupled optical chaos systems. More specifically, a mutually coupled semiconductor laser chaotic system, an intensity-coupled electro-optic chaotic system, and a phase-coupled electro-optic chaotic system are studied in detail. These systems are proposed to resist the attack strategies against the TD signature. They are proved to be effective under statistical analyzes, such as the self-correlation function (SF) and mutual information (MI). However, only a single output has been considered for the attack process in the existing research. We demonstrated that the TD signature can still be extracted by analyzing the mutual statistical relationship between the different output signals which are generated simultaneously by the coupled system. Furthermore, we find that the extraction strategy is effective for a wide parameter range in these schemes.

The streak tube imaging light detection and ranging (LiDAR) is a new type of waveform sampling laser imaging radar whose echo signals are stripe images with a high frame rate. In this study, the morphological and statistical characteristics of stripe signals are analyzed in detail. Based on the concept of mathematical morphology denoising, connected domains are constructed in a noise-containing stripe image, and the noise is removed using the difference in connected domains area between signals and noises. It is shown that, for stripe signals, the proposed denoising method is significantly more efficient than Wiener filtering.

Porous titanium dioxide (TiO₂) nanowires were synthesized via a surfactant-free hydrothermal method followed by acid-washing process and calcination. The structures and morphologies of products were characterized by field emission scanning electron microscopy (FESEM), Transmission electron microscopy (TEM), X-ray diffraction (XRD), and Brunauer-Emmett-Teller (BET) N₂ adsorption-desorption analyses. The analysis of FESEM suggested the precursor was composed of a vast of uniform nanostructures like wires. The nanowire-like precursor was transformed into the porous nanowire after acid-treatment and calcination at 500°C for 2 h in air. The surface area of as-synthesized TiO₂ nanowires calculated by BET is 86.4 m²/g. Furthermore, the photocatalytic properties of synthesized porous TiO₂ nanowires were evaluated through the degradation of methylene blue (MB) and Rhodamine B (RhB). The results clearly suggested that the as-prepared porous TiO₂ nanowires showed remarkable photocatalytic performance on the degradation of RhB and MB due to their small size of nanocrystallites and the porous naonstructure.

Efficient indium tin oxide (ITO)-free inverted polymer solar cells (PSCs) were fabricated by applying ultrathin metal transparent electrodes as sunlight incident electrodes. Smooth and continuous Ag film of 4 nm thickness was developed through the introduction of a 2 nm Au seed layer. Ultrathin Ag transparent electrode with an average transmittance of up to 80% from 480 to 680 nm and a sheet resistance of 35.4 W/sq was obtained through the introduction of a ZnO anti-reflective layer. The ultrathin metal electrode could be directly used as cathode in polymer solar cells without oxygen plasma treatment. ITO-free inverted PSCs obtained a power conversion efficiency (PCE) of 5.2% by utilizing the ultrathin metal transparent electrodes. These results demonstrated a simple method of fabricating ITO-free inverted PSCs.

The absorption coefficient and refractive index of tourmaline in different directions were characterized for the first time using terahertz time-domain spectroscopy. Results show that the absorption and refractive index of terahertz frequency are related to the structure of tourmaline. Absorption along the optical axis direction is more sensitive than that along the vertical direction. This result indicates that the identification and characterization of crystals as well as minerals can be realized by the terahertz method.