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In this paper, the high-quality factor mullite microwave dielectric ceramic is employed to introduce in dielectric resonator antenna (DRA). The microwave dielectric properties of ɛr ∼ 5.8, Q × f ∼ 31 240 at 9.66 GHz, and loss tangent tanδ = 1/Q ∼ 2.7 × 10−4 can be obtained by the solid-state reaction method in mullite microwave dielectric ceramic sintered at 1700 °C. On this basis, the resonant modes of the proposed broadband high-gain rectangular DRA are analyzed by using a dielectric waveguide theoretical model and the antenna performance is evaluated by a commercial CST Microwave Studio 2021® software. It has been found that the proposed rectangular DRA can provide a broad bandwidth of 35.9%, a maximum gain of 10 dBi at 3.61 GHz, and a radiation efficiency of 90% in the range of 3.13–4.42 GHz. For demonstration, adequate consistency between the simulation results and the measurement results was achieved. The proposed DRA has great application potential and value in 5G communication scenarios requiring wideband and high-gain antenna. [ABSTRACT FROM AUTHOR]

Highly transparent Ho:Y2O3 ceramics for laser diode lighting were prepared using the vacuum sintering method with 0.3 at.% Nb2O5 as a sintering additive. The microstructures, transmittance, and luminescence properties of the Ho:Y2O3 ceramic samples were investigated in detail. The transmittance levels of all samples with various Ho3+ concentrations reached ~81.5% (2 mm thick) at 1100 nm. Under the excitation of 363 nm (ultraviolet) or 448 nm (blue) light, Ho:Y2O3 transparent ceramic samples showed that green emission peaked at 550 nm. The emission intensity was strongly affected by the concentration of Ho3+ ions, reaching its highest level in the sample doped with 1 at.% Ho3+. The CIE coordinates of the luminescence were in the green region (i.e., the CIE coordinates of the sample doped with 1 at.% Ho3+ were [0.27, 0.53] and [0.30, 0.69], under the excitation of 363 nm and 448 nm light, respectively). The possibility of its application as laser diode lighting was reported. Under the excitation of 450 nm blue laser, the sample doped with 0.5 at.% Ho3+ had the best performance: the saturated luminous flux, lumen efficiency, and the luminescence saturation power densities were 800 lm, 57.7 lm/W, and 17.6 W/mm2, respectively. Furthermore, the materials have high thermal conductivity and mechanical strength due to their host of rare-earth sesquioxide. Thus, Ho:Y2O3 transparent ceramics are expected to be a promising candidate for green-light-emitting devices for solid-state lighting, such as laser diode lighting. [ABSTRACT FROM AUTHOR]

Highly transparent Er:Y2O3 ceramics (1–9 at.% Er) were fabricated by hot pressing sintering with ZrO2 as the sintering additive. The microstructures, transmittance, luminescent properties, thermal conductivity, and mechanical properties of the Er:Y2O3 ceramic samples were investigated in detail. The samples all exhibited dense and fine grain microstructures; the average grain sizes were about 0.8 μm. The transmittance levels of the samples with various Er concentrations (2 mm thick) at the wavelengths of 600 and 2700 nm were ~74 and ~83%, respectively. As the Er doping concentration increased from 1 to 9 at.%, the up-conversion luminescence of the samples gradually changed from green to red, with the intensity ratio of red/green light increasing from 0.28 to 2.01. Meanwhile, the down-conversion luminescence properties of the specimens were also studied. When the samples were under 980 nm excitation, the emission bands were detected at 1552, 1573, 1639, and 1661 nm. The thermal conductivity of the samples was found to decrease from 8.72 to 5.81 W/(m·K) with an increase of the Er concentration from 1 to 9 at.%. Moreover, the microhardness and fracture toughness of the samples with 1 at.% Er concentration were ~8.51 GPa and ~1.03 MPa·m1/2, respectively. [ABSTRACT FROM AUTHOR]

The oxidation behavior and mechanism of aluminum oxynitride (AlON) powder exposed to air at elevated temperatures between 800°C and 1300°C was investigated by X‐ray diffractometry (XRD), scanning electron microscope (SEM), electron spin resonance (ESR), nuclear magnetic resonance (NMR), and simultaneous thermogravimetry, differential thermal analysis, and mass spectrometry techniques (TG‐DTA‐MS). The weight of AlON gradually increases to a maximum value at 1150°C and then decreases with further heating. Meanwhile, AlON powder undergoes chemical changes, as evidenced by lattice expansion, and turns eventually into alumina. ESR spectra reveal the occurrence of lone pair electrons in the oxidized products and the intensity of corresponding resonance signal increases before disappearing with the increase in temperature. Combined with the results of NMR and TG‐DTA‐MS, the measured data suggest that Al‐N in [AlO3N] tetrahedron and [AlO5N] octahedron are gradually oxidized into Al‐O‐N group with lone pair electrons, which causes continuous weight gain and lattice expansion. Further oxidation at higher temperatures results in alumina and N2. [ABSTRACT FROM AUTHOR]