Optical Materials最新文献

Due to its exceptional thermal stability and high conductivity, Yttrium stabilized zirconia (YSZ) has become an essential material in the field of infrared camouflage. Although YSZ exhibits relatively low emissivity within the 3–5 μm wavelength range, the increasing operating temperatures of aircraft necessitate further reduction in infrared emissivity within this specific band, in accordance with the Wien displacement law. This study focuses on the preparation of ceramic samples of YSZ doped with varying concentrations of Yb₂O₃ through a high-temperature solid-state reaction. It aims to investigate the influence of different doping concentrations on the microstructure, crystal structure, and infrared radiation characteristics of YSZ ceramic blocks. The experimental results demonstrated that the addition of Yb₂O₃ induces changes in the grain size and phase content of YSZ. Notably, as the amount of Yb₂O₃ doping increases, the infrared emissivity of YSZ samples in the 3–5 μm wavelength range exhibits a pattern of initial decrease followed by an increase. Remarkably, at a doping amount of 3 % mol, YSZ ceramics demonstrated the lowest emissivity, with the average emissivity of the 3–5 μm wavelength range decreasing from 0.41 to 0.38.

The long-duration memory effect in thermotropic liquid crystal (LC) materials has long been a topic of substantial interest and numerous pioneering works. Although the idea of exploring the memory effect had been started from the nematic (N) phase of LC itself, but due to its very short duration, it was soon shifted to the other LC phases such as ferroelectric LC (FLC) or their derivatives and composites. Therefore, we demonstrate here the prolonged memory effect in a smectic A (SmA) phase of a pristine thermotropic LC material namely 4-octyl-4′-cyanobiphenyl (8CB). The memory effect has also been investigated in the N phase to estimate its duration as compared to the SmA phase. To examine the memory effect, firstly, we measured the dielectric permittivity using the dielectric spectroscopic technique with and without 40 V DC biasing. Furthermore, these results have been confirmed by means of optical textures recorded through a polarizing optical microscope. Moreover, we have also observed the removal and retrieval of two stable states by sequent application of heat and DC biasing to examine the cyclability of the LC compound under testing. We anticipate that our results will definitely bridge the gap that occurred in the advancement of emerging futuristic LC-based memory devices.

In the current study, Sr-doped ZnO thin films were fabricated through a sol-gel route on a silicon substrate (100). The structural, optical, and morphological studies were examined through XRD, UV–vis, PL spectroscopy, and SEM. The crystalline superiority is enhanced through increasing Sr content while the optical bandgap is reduced because of lattice distortion and the production of active imperfections in ZnO, which may be the reason for bandgap tailing. The grain sizes observed are 53, 54, and 60 nm for ZnO, ZnSr1%, and ZnSr2%. Microstructural and strain were explored through Scherrer, W–H, and SSP methods. Furthermore, peak broadening was investigated using these methods. UV–Vis spectroscopy was employed to investigate the band gap of all grown thin films, which are 3.37, 3.28, and 3.20 eV of ZnO, ZnSr1% and ZnSr2%. The optical study was carried out to investigate the band gap, including different parameters such as Absorbance (A), transmittance (T), absorption coefficient ($\alpha )$, band gap (E_g) using different methods, band gap by derivative method, urbach energy (E_u), skin depth (δ), optical density (OD), refractive index (n), extinction coefficient (k), optical conductivity (σ_opt), dielectric constants (ε_r, ε_i), and Tan (α) were also explored. PL spectroscopy was used to study the defects in grown thin films. SEM was employed to examine the morphology of all fabricated thin films. ZnO thin film is widely studied for optoelectronics applications.

The lithium-calcium-borate (LiCaBO₃) glass co-doped with Ce³⁺ and Sm³⁺ ions were successfully fabricated by the conventional melt quenching method. Annealing heat at 710 °C for 2 or 4 h formed the nanocrystals in the glass matrix. The X-ray diffraction patterns have proved the formation of the nanocrystals in materials. The appearance of these nanocrystals changed the glass lattice structure as well as the physical and optical properties of the material. The radiative properties of the LiCaBO₃ glass and glass ceramics were analyzed within the framework of Judd-Ofelt theory. The thermoluminescence (TL) properties of the materials were studied by analyzing the glow curve and the TL spectra. The application potential of the materials in the field of dosimetry was proposed based on the investigation results of the parameters such as TL response to irradiation dose, fading rates, and the standard deviation.

A set of powder samples of Y₃AlGa₄O₁₂ doped with Dy³⁺ and Sm³⁺ with different concentration of Sm³⁺ ion were prepared via sol-gel synthesis. X-ray diffraction (XRD), scanning electron microscope (SEM), energy dispersive (EDS), Fourier transform infrared (FTIR) and photoluminescence spectral studies were carried out. All the diffraction peaks matched the cubic lattice Y₃AlGa₄O₁₂, as given by the XRD. The SEM images revealed aggregated spherical particles ranging from 50 to 130 nm. The EDS analysis confirmed the presence of the initial chemicals in the synthesized samples. FTIR spectrum was used to examine the vibrational modes in the sample. Under a 366 nm excitation wavelength, the emission spectrum showed the peaks at 492 nm (blue), 580 nm (yellow), 673 nm (red), and 760 nm (near-infrared) corresponding to the characteristic transitions ⁴F_9/2 → ⁶H_{15/2,13/2,11/2,9/2} of the Dy³⁺ ion, respectively. In comparison, the peaks at 568 nm, 614 nm, 664 nm, and 711 nm corresponded to the characteristic transitions ⁴G_5/2 → ⁶H_{5/2,7/2,9/2,11/2} of the Sm³⁺ ion. Under near ultraviolet light excitation, the superposition of these blue, yellow and red colours produced excellent white light emission. The intensities of these transitions varied with the concentration of Sm³⁺ ion and the excitation wavelength. The emission spectrum of Dy³⁺ overlapped with the excitation spectrum of Sm³⁺, indicated possible energy transfer from Dy³⁺ to Sm³⁺. According to Inokuti-Hirayama's theory of energy transfer, the mechanism of energy transfer was understood to be quadrupole-quadrupole interaction. The CIE chromaticity co-ordinates and correlated colour temperature values showed that these samples were suitable for light-emitting diode applications.

GaN-based nanorod light emitting diodes (LEDs) are key to the development of high brightness, small pixel size, and long lifetime for high-resolution display applications. To manufacture individual nanorod LEDs as compact light sources, it is necessary to separate the nanorod LEDs from the substrate and transfer them to the electrode. Dielectrophoresis (DEP) is a highly suitable technique for transferring the individual nanorod LEDs. However, there are still challenges in achieving a high alignment yield. In this work, nanorod LEDs are successfully fabricated and separated to enhance the horizontal alignment in interdigitated electrodes via insulator-based DEP (iDEP). In iDEP, a structure is formed by inserting an insulating layer between the electrodes. This structure manipulates the electric field generated around the electrodes due to polarization by the insulating layer. This results in a relatively uniform electric field distribution on the surface of the insulating layer, thereby enhancing the horizontal alignment of the nanorod LEDs. Herein, the iDEP structure achieves significant nanorod LED alignment yield of up to 91.9 %, compared to 45.5 % for the electrode-based DEP (eDEP) technique. Furthermore, the use of a patterned insulator makes it possible to restrict 1 or 2 aligned nanorod LEDs within a specific pixel region, which is suitable for high-resolution display technologies based on nanorod LEDs.

Our paper presents a combined experimental and theoretical study of the lattice dynamics of Bi₁₂GeO₂₀ crystal. Polarized Raman spectra were measured in two x-ray oriented single crystals. In a crystal of cubic symmetry, phonon modes of A- and E-types are spectroscopically indistinguishable. Using a special experimental technique, we separated the phonon modes that transform according to A and E irreducible representations. Since the number of E-type lines observed in Raman scattering is higher than theoretically allowed by group theory, we performed a first-principles calculation of the Bi₁₂GeO₂₀ lattice dynamics to accurately identify the symmetry of phonon modes. All experimental lines observed in Raman scattering are classified according to irreducible representations of the cubic I23 group. Using samples of different thicknesses, 10 mm and 0.120 mm, we have demonstrated that the optical activity plays an insignificant role at Raman backscattering in Bi₁₂GeO₂₀ crystal.

All inorganic perovskite quantum dots (PQDs) have great application prospects in the lighting and display fields due to their excellent photoelectric properties. However, their instabilities in water and high temperature lead to photoluminescence (PL) quenching, and colloidal synthesis methods usually use a mass of organic solvents, limiting their practical application. Herein, we successfully synthesized mesoporous silica (m-SiO₂) and employed a confinement effect to successfully synthesize CsPbBr₃@m-SiO₂ powders using a simple high-temperature solid-phase synthesis method in an air atmosphere. When the m-SiO₂ content is 0.2 g, optimal green luminous intensity is achieved with a peak wavelength of 522 nm and a full width at half maximum (FWHM) of 23 nm. CsPbBr₃@m-SiO₂ powders have excellent thermal stability, the PL spectral shapes do not change and the PL intensity can maintain 88.1 % of the original level after 10 heating cycles (200 °C). In addition, CsPbBr₃@m-SiO₂ powders exhibit excellent water stability, which can still be well dispersed after 30 days exposure to water, and the PL strength remain basically unchanged. This study presents a novel approach for the advancement of stable perovskite luminescent materials.

In this work, resistive type photodetectors were fabricated using Gd³⁺ ions doped NiO nanoparticles to improve the detection of ultraviolet (UV) light. The occurrence of the simple cubic phase in NiO systems has been shown by X-ray diffraction patterns. The crystalline size of the NiO nanoparticles doped with different concentrations of Gd³⁺ at levels of pure, 1 %, 2 %, and 3 % were 6 nm, 8 nm, 9 nm, and 12 nm, respectively. The presence of dopants in the material was established by the Raman spectrum analysis. Transmission electron microscopy (TEM) pictures were used to validate the morphological properties of Gd³⁺ doped NiO nanoparticles nanoparticles at different degrees of dopant concentration (0 %, 1 %, 2 % and 3 %). The introduction and concentration of dopants alter the shape of NiO material. Based on the findings of UV–visible absorption spectroscopic studies, it can be concluded that the addition of Gd³⁺ ions to the system improved the absorption characteristics. The measured bandgap values for various degrees of Gd³⁺ doping, namely 0 %, 1 %, 2 %, and 3 %, are 3.51 eV, 3.45 eV, 3.36 eV, and 3.23 eV, respectively. According to the measured photoluminescence spectrum, Gd³⁺ ions may efficiently trap and maintain excited electrons within an energy level between the ground and excited states. This process greatly extends the lifespan of excitons from immediate recombination. The use of Gd³⁺-doped NiO sensors in UV photodetection resulted in a significant increase in conductivity and photocurrent. The photodetector fabricated using a 3 % concentration of Gd³⁺ doped NiO, has a responsivity of 24 × 10⁻² AW⁻¹, a detectivity of 14 × 10⁹ Jones, and an external quantum efficiency (EQE) of 62 %.

The two-dimensional organic-inorganic hybrid perovskites demonstrate significant potential for use in photodetectors and white light-emitting diodes. In this study, we successfully synthesized pure and Mn²⁺-doped (PEA)₂PbBr₄ perovskite via rapid crystallization. The morphology, structure, magnetic properties, and optical characteristics of them were comprehensively characterized. The unusual behavior of free exciton emission is mainly attributed to electron-phonon coupling and negative thermal quenching effects. The self-trapped exciton emission results from self-trapped excited states and electron-phonon coupling. Moreover, energy transfer phenomena are observed between free exciton emission, self-trapped exciton emission, and Mn²⁺ emission. These findings offer valuable insights into the luminescence mechanism of two-dimensional layered perovskites.