Physics of the Solid State最新文献

We report on a numerical study of the effect of InAlGaN interlayers on the efficiency of InGaN‑based red light-emitting diodes (LEDs). The introduction of interlayers in red LED structures was found to increase the turn-on voltage from approximately 2.64 V (without interlayer) to 2.68, 3.05, and 3.08 V for devices incorporating GaN, Al_0.20Ga_0.80N, and partially strain-relaxed In_0.08Al_0.35Ga_0.57N interlayers, respectively. Among the four LED configurations studied, the structure with an In_0.08Al_0.35Ga_0.57N interlayer exhibited the best performance, emitting at 632 nm with an internal quantum efficiency of 0.67, an external quantum efficiency of 33.5%, and a wall-plug efficiency of 21.2%. The partially strain-relaxed In_0.08Al_0.35Ga_0.57N interlayer effectively modifies the band structure by increasing electron and hole barrier heights, enhancing carrier confinement, and reducing polarization-induced fields. Furthermore, this device demonstrated superior stability of the electroluminescence peak wavelength under increasing bias voltage compared to the other structures.

TiO₂ is a multifaceted and economical material for its appropriateness in various technical and scientific areas, including optoelectronics, photoelectrodes, and photocatalysis. This paper presents the fabrication and characterization of TiO₂ film deposited on a glass substrate by the sol–gel-driven screen-printing approach followed by sintering at 400°C. The fabricated TiO₂ film was analyzed via electrical resistivity measurement, UV-visible (transmission) spectroscopy, X-ray diffraction, and energy-dispersive X-ray spectroscopy. The X-ray diffraction analysis exposed the emergence of a pure TiO₂ anatase phase with a favored orientation along the (101) direction. Scanning electron microscopy exhibits the distribution of nano-sized particles on the entire surface, whereas energy-dispersive X-ray spectroscopy approves the composition of Ti and O elements. The film shows an absorption band edge around 380 nm in the transmission spectrum corresponding to the direct bandgap of 3.25 eV for TiO₂. Electrical resistivity unveiled the semiconducting nature of the film, having a resistivity of ⁓10⁵ Ω cm. This study suggests the fabrication of TiO₂ film at a relatively low cost by a sol–gel-driven screen-printing approach for the potential use of these films in different technical and scientific areas.

Solar collectors play a crucial role in harnessing and utilizing solar energy, making their thermal performance a key factor in the efficiency of solar energy systems. Surface materials and coatings significantly influence heat absorption and retention, impacting overall energy efficiency. This study explores the thermal properties of various surface types, including granite, chrome-based alloys, and high-performance steel (HPS), under controlled conditions. By evaluating their heat absorption and retention characteristics, the study aims to provide insights into the optimal material configurations for enhancing solar collector performance. A series of surface types were evaluated, ranging from solid granite to fully alloyed materials and HPS. Heat retention efficiency and average heat performance were recorded to compare the effectiveness of each surface. Results reveal that solid granite surfaces exhibit a high heat retention efficiency of 92% at an average temperature of 88.1°C, while a fully alloyed surface achieves superior performance with a retention efficiency of 98% and an average heat of 91.2°C. The highest performance was observed with HPS, demonstrating 99% heat retention efficiency and 93.5°C average heat. In contrast, tempered glass and thermal-insulated surfaces yielded significantly lower efficiencies of 74 and 42%, respectively, with corresponding average heat values of 68.5 and 39.3°C. Ambient conditions provided a baseline with minimal heat retention (35%) at an average temperature of 35.2°C.The study highlights the superior performance of alloy-rich surfaces, particularly HPS and fully alloyed configurations, in optimizing thermal efficiency. The findings provide a basis for selecting surface materials and coatings to improve solar collector efficiency. The goal of this study is to contribute to the development of more effective solar energy systems by characterizing the thermal performance of granite and chrome-based selective coatings.

Core-shell quantum dots (CSQDs), are a special class of nanostructures where a lower band gap core is encased in a higher band gap shell, leading to enhanced carrier confinement, stability, and reduced recombination. In CSQDs, the point of contact of the two dissimilar materials leads to the formation of a heterojunction. At this heterojunction, lattice mismatch arises inducing strain, which directly affects the CSQDs’ optical and electrical properties by altering band lineups. In our study, through theoretical analysis we focused on varying the shell width while keeping the core size constant and vice versa influencing the strain at the junction, thus impacting band alignment and the material’s optical and electronic properties. We considered a model using a TiO₂ core enclosed within a ZnS shell layer. It has been observed that for a fixed core width, the strain imposed on TiO₂ increases with increasing core size, while that imposed on ZnS is seen to diminish for the same. This strain has a direct impact on the band lineup of the CSQD, thereby impacting the bandgap of the material. For increasing shell width, the bandgap decreases for both TiO₂ and ZnS. For the case of constant shell and varying core width, the opposite trend is noted across all outcomes. An interesting observation that has been derived from our work was that, as the core:shell ratio remains constant, the strain, band alignment and related properties remain consistent, irrespective of the absolute thickness of the core and shell.

Ethyl cellulose (EC) is a non-toxic, tasteless and biocompatible polymer derivative of Cellulose. Due to its biocompatible and hydrophobic nature, EC is extensively used as an encapsulating material for the controlled release of drugs. Gamma radiation sterilization has proven to be the most efficient and acceptable method worldwide for sterilizing the final drug products. Gamma sterilization has more advantages than convention methods like high penetrating power, isothermal character and non-residual. It assures killing the micro-organisms by breaking nucleic acid and halts cell division. In the present study, dried EC was packed in a thin polyethylene sheet and are irradiated with Co-60 gamma source, delivering doses 30, 60, and 90 kGy. Irradiation has produced the radicals of type ( - {{{text{C}}}_{{text{2}}}}{{{text{H}}}_{{text{5}}}}{{dot {text{O}}}}), which appeared only at higher doses, i.e., 60 and 90 kGy. X-ray diffraction depicts a gradual decrease in crystallinity following radiation dose, though EC is semi-crystalline. Differential scanning calorimetry thermograms indicate a slight decrease in melting temperature following radiation dose. Significant changes were observed in Infrared spectra on irradiating to higher doses. Scanning electron microscope images indicate that EC granules are irregularly shaped with rough patches. The physicochemical properties of irradiated EC were studied and it is observed that there are minimal effects of radiation on EC up to 30 kGy.

Synthesis of (MgCa)₂Bi₄Ti₅O₂₀ powder ceramics activated with (0.2 mol %) Eu³⁺, Tb³⁺, Sm³⁺, and Dy³⁺ ions was achieved via solid-state reaction method and aimed to investigate the optical properties comparatively. Notably, the emission spectra revealed distinct characteristics for each dopant. Eu³⁺ shows prominent emission band at 615 nm on excitation at 393 nm, while an excitation at 376 nm in Tb³⁺ exhibited green emission at 542 nm. Similarly, Sm³⁺ displayed intense reddish-orange emission at 599 nm with an excited wavelength at 405 nm, and Dy³⁺ emitted yellow light at 583 nm with an excitation wavelength of 426 nm. These findings emphasized significant luminescent performance of the rare earth ion-doped (MgCa)₂Bi₄Ti₅O₂₀ ceramic host. Among these rare earth ions, Sm³⁺:(MgCa)₂Bi₄Ti₅O₂₀ ceramic powder has shown strong luminescence intensity with its characteristics and energy band structure. Furthermore, structural and morphological analyses have been carried out by using XRD, SEM, and EDAX techniques, providing comprehensive insights into the characteristics of the ceramic powders.

The nanostructured transition metal dichalcogenides, ranging from two-dimensional layers, one-dimensional nanotubes or rods, and zero-dimensional quantum dots, have been investigated extensively in the recent past because of their unique and promising properties, including a suitable non-zero band gap that can be tailored, tuned, and engineered by varying different extrinsic parameters, making them suitable for targeted applications. Tungsten disulfide, which belongs to the transition metal dichalcogenide group, is suitable for various types of electronic and optoelectronic applications. The properties of transition metal dichalcogenides, suitable for different applications, depend on the method of synthesis and are even influenced by variations in synthesis parameters for a particular method. Different top-down and bottom-up methods of synthesis have been reported for nanostructured WS₂, mentioning the advantages and disadvantages of each method, different types of synthesis parameter variations, and possible permutations and combinations—comparing methods, mapping them to the quality of the end product, and then to the targeted applications. This paper reviews recent reported advances in the synthesis of WS₂, with underlying opportunities and challenges, with emphasis on different types of reported applications. This review will provide a roadmap for future work related to further advancements in the synthesis of nanostructured WS₂ and its applications.

A comparative theoretical investigation of A₃PI₃ (A = Ca, Ba, Mg) has been performed using full potential linear augmented plane wave method (FP-LAPW) performed by WIEN2K code based on the density functional theory (DFT) within the generalized gradient approximation (GGA). The volume optimization is performed using the Birch–Murnaghan equation of states. The compound belongs to the space group 221. The structural, electronic and optical properties including the band structure and density of states are obtained. The band structure analysis revealed direct bandgaps of 1.465 eV (Ca₃PI₃), 0.842 eV (Ba₃PI₃), and 0.566 eV (Mg₃PI₃). Optical calculations showed high static dielectric constants, notable at 1 eV for Ba₃PI₃, and significant absorption in the visible region, with Ca₃PI₃ exhibiting the most suitable optical profile. Mg₃PI₃ displayed the highest reflectivity (~0.72), indicating potential for photonic applications. The novelty of this work lies in the first comparative study of these A₃PI₃ systems, identifying Ca₃PI₃ as the most promising candidate for lead-free solar cell applications due to its optimal bandgap and balanced optical response. Fortunately, A₃PI₃ compounds are used for photovoltaic purposes because of their optical and thermoelectric properties. It also contributes to the low-cost, nontoxic and earth—abundant materials.

Controlling crystallization dynamics through thermal annealing emerged as a critical strategy for enhancing the power conversion efficiency (PCE) of monolithic perovskite solar cells (mPSCs). This study systematically investigates the influence of annealing temperatures (100, 200, 300, and 400°C) on the photovoltaic performance of mPSCs. Current–voltage (I–V) characterization reveals that higher annealing temperatures produce superior film morphology, reducing defect density and improving charge carrier mobility. Among the tested conditions, 400°C yields the optimal PCE of 10.82%, surpassing devices processed at lower temperatures by mitigating defect density and improving interfacial charge extraction. The obtained results demonstrate that the thermal annealing as a critical scalable parameter for optimizing perovskite based solar cells.

A low-cost polyol synthesis route was used to prepare Y₂Zr₂O₇ (YZO) phosphors doped with Bi³⁺ (1–2.5 at %) and co-doped with Tb³⁺ (1–3 at %). The structural, morphological, and optical properties were characterized using XRD, FESEM, UV-Vis, and PL spectroscopy. The Rietveld refinement of the XRD patterns confirmed that the undoped YZO host crystallizes in a cubic pyrochlore structure with the Fd({{bar {3}}})m space group. The FESEM images revealed agglomerated granule-like particles with an average size of ~105 nm. The UV-Vis absorption spectra showed characteristic peaks of Bi³⁺ and Tb³⁺ ions. The Photoluminescence studies demonstrated a blue emission at ~430 nm from the Bi³⁺ (³P₁ → ¹S₀ transition) under 305 nm excitation, with an optimal composition of YZO:1.5% Bi³⁺. Further, Co-doping with Tb³⁺ and exciting at 225 nm produced weak blue emissions and a dominant green emission at 545 nm from the ⁵D₄ → ⁷F₅ transition of Tb³⁺ ions. The optimal composition of the phosphor sample is identified to be Y_1.965Zr₂O₇:1.5% Bi³⁺, 2% Tb³⁺ which exhibits tunable blue–green emissions supported by lifetime decay analysis and energy transfer between Bi³⁺ and Tb³⁺ ions. The CIE chromaticity coordinates indicate its potential for display applications.