Brazilian Journal of Physics最新文献

This work investigates the influence of Nb₂O₅ incorporation on the structural and luminescent properties of Eu³⁺–doped phosphate glasses. Raman spectroscopy revealed that the addition of Nb₂O₅ promotes the substitution of PO₄ units by NbO₆ octahedra, leading to depolymerization of the glass network and a reduction in phonon energy. Optical absorption spectra showed a redshift in the absorption edge and a decrease in the optical band gap, associated with an increased number of nonbonding oxygens. Photoluminescence spectra exhibited an enhancement in the hypersensitive ⁵D₀ → ⁷F₂ transition and increases in both the relative intensity ratio (R) and the Judd–Ofelt parameter Ω₂, indicating a rise in local asymmetry. Lifetime measurements revealed a reduction in the experimental lifetime, along with an increase in total radiative emission rate and suppression of non–radiative processes, yielding a quantum efficiency of up to 93%. These findings demonstrate that Nb₂O₅ incorporation significantly improves the red emission efficiency of Eu³⁺ ions in phosphate glass matrices.

Aluminium oxide nanoparticles (γ-Al₂O₃ NPs) were synthesized by a straightforward chemical co-precipitation method using aluminium nitrate and sodium hydroxide, followed by calcination at 600 °C. X-ray diffraction confirmed the formation of cubic γ-Al₂O₃ NPs with an average crystallite size of about 6.5 nm. Microscopic analyses (FESEM and HRTEM) revealed nearly spherical particles with sizes between 15 and 55 nm, and EDX mapping confirmed a uniform distribution of aluminum and oxygen across the sample. UV-visible spectroscopy showed a sharp absorption edge at 260 nm corresponding to a direct optical band gap of 5.51 eV, while FTIR spectra displayed the characteristic Al-O vibrational modes. Dielectric measurements on γ-Al₂O₃ NPs pellets (1–5 mm) across the frequency range 10^− 2-10⁵ Hz and temperatures of 25–100 °C showed that the dielectric constant, dielectric loss, and capacitance increased with temperature and thickness but decreased with frequency, consistent with Maxwell-Wagner interfacial polarization. Complex-modulus and Argand-plane analyses exhibited depressed semicircular arcs, confirming non-Debye relaxation, whereas AC conductivity increased with temperature and thickness, indicating thermally activated charge transport suggesting thermally activated hopping conduction. This study presents the first systematic correlation among thickness, temperature, and frequency on the dielectric relaxation and charge-transport behavior of γ-Al₂O₃ NPs, revealing a tunable dielectric response that highlights their promise for high-frequency electronic and energy-storage applications.

We develop a statistical mechanics framework for prefix coding based on variational principles, renormalization, and quantization. A Lagrangian formulation of entropy-optimal encoding under the Kraft–McMillan constraint yields a Gibbs-type implied distribution and completeness of the optimal code. A renormalization operator acting on codeword distribution laws produces a coarse-graining flow whose fixed points have iterated-log structure; discrete quantizations of these fixed points include Elias’ (omega) code as a special case. Extending the theory to mixed discrete–continuous source laws, we show how continuous codelength functions can be quantized into countable prefix codes and derive resolution-adjusted entropy bounds together with Heisenberg-type and Boltzmann-type relations. This provides a unified and physically motivated view of universal coding, with Elias’ (omega) code as a guiding example.

Topological photonic crystals have emerged as a powerful platform for achieving robust light transport, even in the presence of disorder. In this work, we theoretically investigate the formation of topological interface states (TIS) in a magnetized plasma-based topological photonic crystal (MPTPC). The interface state arises at the boundary between two magnetized plasma photonic crystals with distinct topological phases. We analyze the impact of three key physical parameters: magnetic field strength (varvec{B_{ext}}), electron density ((varvec{n_e})), and loss factor ((gamma)) on the transmittance spectra and localization properties of the TIS. Our results reveal that (varvec{B_{ext}}) and (varvec{n_e}) significantly influence the spectral position and width of the interface mode in opposing ways: increasing (|varvec{B_{ext}}|) leads to a blueshift and broadening, while increasing (varvec{n_e}) results in a redshift and narrowing of the mode. In contrast, variations in the loss factor (gamma) within the studied range have a negligible effect on the TIS. These findings highlight the need for a careful balance between (|varvec{B_{ext}}|) and (varvec{n_e}) to optimize the quality and stability of the interface mode. The tunability of the TIS in MPTPCs opens new avenues for designing reconfigurable and robust photonic devices.

Organic solar cells (OSCs) are no longer based on fullerene acceptors but instead on a newer form of non-fullerene acceptor (NFA). NFAs have significantly increased the power conversion efficiencies of OSCs, typically showing improvements ranging from 2.5% to 18% over fullerene-based devices.Such advantages of NFAs as the modifiable optical bandgaps, improved transport of charge and broad absorption spectra, can be attained effortlessly with synthesis variation methods and by simply altering chemicals. In this review, new developments in high-performance NFAs are discussed, including designing donor and acceptor materials in an intelligent fashion, control of the shape of blends and device construction. Also discussed in the review are how to ensure devices are more stable and can grow by the use of NFAs. In tandem designs, more sub-cells are connected which better utilizes the solar spectral range and reduces energy loss. It also discusses issues related to commercializing scaled OSCs and the future of materials and device engineering research.

Graphical Abstract

TiO₂ thin films were deposited on glass substrates using a precursor free spin-coating method, with spin speeds varied from 1000 rpm to 4000 rpm for microstructure optimization. Increasing the spin speed improved film uniformity and reduced nanoparticle agglomeration, with the 4000 rpm film exhibiting the most compact and defect-free morphology by FESEM analysis. XRD patterns confirmed the anatase phase, and FT-IR analysis was confirmed the presence of Ti–O–Ti bonds and hydroxyl groups on the surface. AFM and PL analyses indicated high crystallinity and low surface roughness at 4000 rpm. UV–Visible spectroscopy showed a bandgap of 3.13 eV with strong UV absorption, and contact angle measurements demonstrated enhanced hydrophilicity with increasing spin speed. The optimized TiO₂ thin film, when tested as a humidity sensor, exhibited a sensitivity of 89.7% (5–50% RH), a response time of approximately 240 s, a recovery time of less than 300 s, and a hysteresis of 8.1%, with minimal baseline drift. The precursor-free fabrication route is cost-effective, environmentally friendly, and compatible with scalable processing, confirming the suitability of the optimized TiO₂ thin film for humidity sensing at room temperature.

The history of the Wu–Shaknov experiment (1949), and its later reinterpretation by Bohm and Aharonov as an early experimental signature of quantum entanglement, reveals the nonlinear nature of scientific practice. What began as a test of Wheeler’s prediction later became central to debates on the Einstein–Podolsky–Rosen (EPR) paradox and subsequent Bell-type experiments. By foregrounding Chien-Shiung Wu’s experimental philosophy, this essay shows how scientific knowledge advances through reinterpretation, dissent, and the reframing of research questions, whilehighlighting the human and ethical dimensions of physis. It argues that training in the History, Philosophy, and Sociology of Science is essential for fostering critically reflective, socially responsible, and ethically engaged scientists.

We have studied the weak value amplification in photon number of an Optomechanical system driven by an external laser. Here, photon number acts as system, and the mirror acts as meter. In the weak coupling condition, post selection of the photon number operator enhance the value of mirror displacement. The displacement of the mirror depends on the weak value of the photon number operator ((A_w)) and on the value of relative phase ((phi)) between the pre and post selected system states. Amplification of the mirror can be seen for maximum coupling strength ((.25 Omega _m)) in weak coupling criteria for optomechanical systems, (Omega _m) being the mechanical frequency.

Er³-doped zinc fluoroborate glasses with the composition (45–x)B₂O₃–25ZnF₂–15K₂O–15LiF–xEr₂O₃ (where, x = 0.25, 0.5, 0.75 and 1.0 wt%) were synthesized via the conventional melt-quenching technique. These glasses were characterized using XRD, FTIR, optical absorption, excitation, visible and NIR emission spectroscopy. The broad scattering at lower angles in the XRD spectrum indicates the long-range structural disorderliness of the glasses and the pattern does not reveal any crystalline phase thus confirms the amorphous nature. FTIR spectra revealed the fundamental stretching and bending vibrations of borate groups like trigonal BO₃ and tetrahedral BO₄ units in the present glasses. Judd–Ofelt (JO) analysis of the absorption spectra was performed to extract JO intensity parameters as well as radiative properties, where a higher Ω₂ values indicated greater asymmetry around Er³ ions. The visible and near infrared luminescence spectra showed enhanced radiative properties such as transition probability (A), stimulated emission cross-section ((:{sigma:}_{P}^{E})), branching ratios (β_R) and radiative lifetime (τ_R) for the ²H_11/2+⁴S_3/2→⁴I_15/2 and ⁴I_13/2→⁴I_15/2 transitions, extending the application of the present glass system for waveguide laser and optical amplifier at 1.53 μm. The CIE 1931 chromaticity diagram confirmed that the (x, y) color coordinates fall within the green region, supporting the suitability of these glasses for green light emitting device applications. By using the Mc-Cumber theory, the absorption cross-section (σ_a), emission cross-section (σ_e), and gain coefficient (G_λ) for the NIR ⁴I_13/2→⁴I_15/2 transition, were calculated and reported. The transition ⁴I_13/2→⁴I_15/2 in ZFB0.5E glass exhibits higher stimulated emission cross-section, broad gain bandwidth, and substantial gain coefficient among the prepared glasses highlighting its potential as an efficient gain medium for 1.53 μm optical amplifiers and telecommunication photonic applications.

Single crystal of Zinc Sulphate Nickel Nitrate (ZN) was successfully grown using the slow evaporation method. Single crystal X-ray diffraction (SCXRD) analysis revealed that the crystal belongs to the monoclinic crystal system. The elemental composition and functional groups of the compound were confirmed through Energy Dispersive X-ray Analysis (EDAX) and Fourier Transform Infrared Spectroscopy (FTIR), respectively, indicating the presence of the expected constituents. Optical characterization using UV–Visible spectroscopy showed a sharp transmittance cut-off at 235 nm, and the Tauc’s plot revealed an optical band gap of 5.2 eV. Additional optical parameters, including refractive index, extinction coefficient, and reflectance, were also calculated. Photoluminescence (PL) studies demonstrated violet emission, suggesting potential optoelectronic applications. Cyclic voltammetry (CV) analysis indicated strong capacitive behavior, making the crystal a promising candidate for energy storage systems. Impedance spectroscopy further distinguished the contributions of bulk and grain boundary resistance. Antibacterial studies revealed that the Zn component exhibited significant antibacterial activity. This paper presents a thorough analysis and detailed discussion of the crystal’s properties.