Applied Physics A Solids and Surfaces

The hexagonal series AMnO3 (A = Lu, Sc) (space group: P63cm) is an excellent model system for the investigation of magnetic frustration as the magnetic sublattice is made up of edge sharing triangles with nearest neighbour antiferromagnetic exchange. At low temperatures the Mn3+ moments form a 120° long range ordered state. In LuMnO3 (TN=91 K) the magnetic moments are in the ab-plane and perpendicular to the hexagonal axis, whereas ScMnO3 (TN=130 K) undergoes an in-plane spin-reorientation transition below T=70 K. Powder neutron diffraction experiments for the substitutional solid solution ScxLu(1-x)MnO3 (0.0≤x≤1.0) show the evolution of the spin-reorientation as a function of x.

In this work, a generalized solution for the thermoelastic plane wave in a semi-infinite solid induced by pulsed laser heating is developed. The solution takes into account the non-Fourier effect in heat conduction and the coupling effect between temperature and strain rate, which play significant roles in ultrashort pulsed laser heating. Based on this solution, calculations are conducted to study stress waves induced by nano-, pico-, and femtosecond laser pulses. It is found that with the same maximum surface temperature increase, a shorter pulsed laser induces a much stronger stress wave. The non-Fourier effect causes a higher surface temperature increase, but a weaker stress wave. Also, for the first time, it is found that a second stress wave is formed and propagates with the same speed as the thermal wave. The surface displacement accompanying thermal expansion shows a substantial time delay to the femtosecond laser pulse. On the contrary, surface displacement and heating occur simultaneously in nano- and picosecond laser heating. In femtosecond laser heating, results show that the coupling effect strongly attenuates the stress wave and extends the duration of the stress wave. This may explain the minimal damage in ultrashort laser materials processing.

The surface tension and specific heat for liquid ternary Ti–6Al–4V alloy were measured by the oscillating drop method and drop calorimetry, respectively, under containerless condition over broad temperature ranges. The solidification microstructures at different undercoolings appeared as the basket-weave morphology. The relationship between dendritic growth velocity of β phase and undercooling was determined as a power function, and the growth velocity attained 22.21 ms−1 at the maximum undercooling of 252 K (0.13 T L). The mechanical property of this alloy solidified at different undercoolings was determined through compression tests, while its thermal diffusivity in the solid state was measured by the laser flash method.

Heterojunction nanostructures are gaining popularity due to their extensive use in catalytic activities, such as pollutant removal and biomedical applications. In this study, a novel Th(MoO4)2/TiO2 hybrid nanocomposite with heterogeneous assemblies was fabricated and characterized for a potent use in toxic pollutant detection and degradation. Analytical techniques, such as powder XRD, FTIR, UV–DRS, PL, FESEM, HRTEM, EDX, and XPS, were used to examine the prepared nanocomposite. The crystallite sizes of the various heterostructures were determined by XRD patterns to be 27.91 nm, 25.79 nm, 17.91 nm, and 36.63 nm, respectively. The interaction between the heterojunction nanostructure and the surface oxygen vacancies on Th(MoO4)2–TiO2 hybrid nanostructure was investigated using X-ray photoelectron spectroscopy. The PL bands at the long wavelength side of the heterojunction have been attributed to the oxygen vacancies (OVs). The cyclic voltammetry (CV) technique was used to detect dichlorvos (DDVP) using a Th(MoO4)2–TiO2-modified electrode. The surface coverage concentration of the modified Th(MoO4)2–TiO2 electrode was calculated to be 2.8923 × 10–4. The composite was also tested as a photocatalyst for the degradation of Congo red (CR) dye in visible light. Within 130 min, the photocatalyst degraded approximately 97% of the dye in acidic medium. The results revealed that the Th(MoO4)2–TiO2 nanocomposite exhibits excellent photocatalytic, cytotoxic, and antibacterial properties and will be useful in real-world applications.

The fractal dimensions of six differently mechanically pre-treated stainless steel samples were investigated using five fractal algorithms. The surfaces were analyzed using a profiler, atomic force microscopy (AFM), scanning electron microscopy (SEM) and light microscopy (LM), and thereafter adhesively bonded and tested in single-overlap joints to test their tensile strength. All samples showed different fractal behavior, depending on the microscopic methods and fractal algorithms. However, the overall relation between fractal dimension and tensile strength is qualitatively the same, except for the SEM images. This verifies that tensile strength is correlated to fractal dimension, although only within the length-scale of the profiler and the light microscope (≈0.5–100 μm). The AFM method was excluded in this comparison, since the limitation in the z-direction for the AFM scanner made it difficult to scan the rougher parts of the blasted samples. The magnitude of the surfaces is a parameter not often considered in fractal analysis. It is shown that the magnitude, for the Fourier method, is correlated to the arithmetic average difference, Ra, but only weakly to the fractal dimension. Hence, traditional parameters, such as Ra, tell us very little about the spatial distribution of the elevation data.

Creating microvoids, cracks or refractive index modifications within dielectrics focusing intense laser radiation into the transparent material offers many promising applications, such as holographic data storage, laser-written waveguides or optical gratings. For further improvements in the quality of the named applications, a deep understanding of the involved processes during interaction of laser radiation with material is necessary. In this work, the change in the laser intensity distribution of focused laser radiation into PMMA by spherical aberration, caused by the transition of the radiation from air to matter, is discussed. Theoretical and numerical investigations including nonlinear effects of laser radiation material interaction as well as multi-physical approaches, such as combined calculation of the beam propagation, the temperature distribution and induced tensions, require a lot of effort and long computation time. Therefore, simple linear simulations are performed including calculation of the beam propagation without nonlinear optical effects, like self-focusing. Comparing the calculated intensity distributions with experimental data, regarding the lateral and axial size as well as the position of the laser-generated voids within PMMA, the applicability of the simulation approaches is demonstrated. The different simulation approaches are characterized in regard to their calculation time and accuracy depending on the simulation task.

A novel orange-red luminescent single-phase Sm3+ activated Ba9Y2Si6O24 phosphor was prepared via a conventional solid-state reaction approach. The crystal structure and luminescence characteristics of the synthesized phosphor were investigated in detail by using X-ray diffraction (XRD), photoluminescence excitation (PLE) spectra, photoluminescence (PL) spectra and temperature-dependent spectra. The Ba9Y2Si6O24: Sm3+ phosphor shows a series of sharp peaks ranging from 500 to 700 nm under the excitation of 404 nm, and the strongest peak was at 603 nm. Considering the concentration quenching mechanism, the optimal Sm3+ doped concentration is determined to be 0.06. Further research on the thermal quenching performance of Ba9Y2Si6O24: 0.06Sm3+ phosphors, indicating that Ba9Y2Si6O24: 0.06Sm3+ phosphors present excellent thermal stability, even the temperature goes up to 423 K, the emission intensity is 62.7% of that at 298 K. The above results demonstrate that Ba9Y2Si6O24: Sm3+ phosphor has ideal luminous performance and excellent thermal stability. As an orange-red luminescent material, Ba9Y2Si6O24:Sm3+ phosphor has broad development prospects in the application of white light- emitting diodes.

LaBMoO6:Dy3+ phosphor is successfully synthesized in the air by the solid-state reaction method. The luminescence properties and crystal structures are researched. LaBMoO6:Dy3+ phosphor with excitation at 388, 398, 426, and 451 nm emits yellow light. The emission spectrum of LaBMoO6:Dy3+ phosphor in the range of 450–780 nm contains four emission bands peaking at ~ 480, 570, 658, and 750 nm because of the 4F9/2 → 6H15/2, 6H13/2, 6H11/2, and 6H9/2 transitions of Dy3+ ion, respectively. The optimal Dy3+ ion concentration is ~ 6 mol% in LaBMoO6:Dy3+ phosphor. The lifetime of LaBMoO6:Dy3+ phosphor decreases from 0.467 to 0.279 ms with increasing Dy3+ ion concentration from 2 to 10 mol%. The energy-level diagram of Dy3+ ion is used to explain the luminous mechanism of LaBMoO6:Dy3+ phosphor. The experimental results indicate a potential application of LaBMoO6:Dy3+ phosphor as yellow phosphor for light-emitting diode based on near ultraviolet and blue chips.