Recently, using microwave devices that emit electromagnetic waves and enhance the convenience of life have increased; however, they can be harmful to the environment. In this study, CuFe₂O₄ nanoparticles were prepared through the conventional sol-gel procedure and then were characterized by X-ray powder diffraction (XRD), vibrating sample magnetometer (VSM), field emission scanning electron microscopy (FE-SEM), Fourier transform infrared spectroscopy (FT-IR), and vector network analyzer (VNA) using S parameters. Results illustrated that pure crystal structure of magnetic nanoparticles has been synthesized by the sol-gel method with magnetic saturation (M_s) of 22 emu/g. Finally, CuFe₂O₄ nanoparticles were composited by silicone rubber to investigate its microwave absorption properties. Results showed that the CuFe₂O₄/silicone rubber nanocomposite absorbed more than 94.87% of the microwave irradiation at ku-band frequency with 1.7 mm thickness and the maximum reflection loss was −60.38 dB at 16.1 GHz. Magnetic and dielectric properties of the CuFe₂O₄ nanoparticles and silicone rubber polymeric matrix in the nanocomposite demonstrated desirable microwave absorption properties. Full article

Lately, silicone rubber, because of the desirable permittivity on the one hand, and various applications in the implants, membranes, solar cells, sensors, semiconductor devices, high frequency devices, photothermal therapy methods, acoustic metamaterials, and insulator materials on the other hand, has attracted considerable attention. In this research, CuCr₂O₄ nanoparticles were prepared according to the sol–gel method and then were identified by Fourier transform infrared (FT-IR), X-ray powder diffraction (XRD), field emission scanning electron microscopy (FE-SEM), and vibrating sample magnetometer (VSM). Results showed that monophase crystal structure with identical morphology of CuCr₂O₄ nanoparticles has been synthesized. Finally, CuCr₂O₄ nanoparticles and silicone rubber were composited and then microwave absorbing properties of the CuCr₂O₄/silicone rubber nanocomposite were investigated by vector network analyzer (VNA), exhibiting 48.56 dB microwave attenuation for the CuCr₂O₄/silicone rubber nanocomposite with 2.6 mm thickness at 10.9 GHz frequency, while having more than 92.99% microwave absorption along the x-band frequency. Full article

In this work, we report on the characterization and reliability/stability study of phosphorescent materials for lighting applications. More specifically, we investigated (a) phosphors directly deposited over light-emitting diodes (LED) chip, (b) remote phosphor (RP) solutions encapsulated in plastic medium for LED lighting, and (c) phosphors without binder for extreme high-intensity laser diode white lighting. The optical and thermal properties of phosphors were studied to develop a sample based on a mix of phosphor compounds in order to achieve different correlated color temperatures (CCT) and high color rendering index (CRI) LEDs. Thermal properties of cerium-doped YAG (Yttrium Aluminum Garnet) phosphor materials were evaluated in order to study thermal quenching. A maximum phosphor operating temperature of 190–200 °C was found to cause a sensible efficiency degeneration. Reduced efficiency and Stokes shift also caused a localized temperature increase in the photoluminescent materials. In the case of remote phosphors, heat did not find a low thermal resistance path to the heatsink (as occurred through the GaN LED chip for direct phosphor-converted devices) and thermal analysis indicated that material temperature might therefore increase to values in excess of 60 °C when a radiation of 435 mW/cm² hit the sample template. Reliability was also investigated for both plastic-encapsulated materials and binder-free depositions. Pure thermal reliability study indicated that phosphors encapsulated in polycarbonate material were stable up to temperature of approximately 100 °C, while binder-free phosphor did not show any sensible degradation up to temperatures of 525 °C. Full article

In the last decade, spinel structures have been widely explored due to widespread applications in antibacterial nanocomposites, memory devices, catalysts, photocatalysts, high-frequency devices, and electromagnetic absorbing materials. In this study, BaFe₂O₄ spinel structures were synthesized through the sol–gel method using a low sintering temperature and were identified by vibrating sample magnetometer (VSM), X-ray powder diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, field emission scanning electron microscopy (FE-SEM), and vector network analyzer (VNA) analysis. Results showed that uniform and pure crystal structures of BaFe₂O₄ nanoparticles were prepared based on the sol–gel method. Finally, BaFe₂O₄ nanoparticles were blended by silicone rubber to characterize the microwave absorption properties of the nanocomposite at the ku-band frequency. According to the VNA results, the BaFe₂O₄/silicone rubber nanocomposite with 1.75 mm thickness absorbed more than 94.38% of microwave irradiation along the ku-band frequency and the maximum reflection loss of the BaFe₂O₄/silicone rubber nanocomposite was 51.67 dB at 16.1 GHz. Full article