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The persistent luminescent (PSL) phosphors Sr 2- x - y MgSi 2 O 7 : x Eu2+, y Dy3+ (x = 0∼0.08, y = 0∼0.08) were synthesized by a solid-state reaction method in a weak reductive atmosphere of 5%-H 2 /N 2. Comprehensive measurements were carried out to study the effects of Eu2+ and Dy3+ doping amount on the crystal phase, photoluminescence (PL), afterglow decay properties, and trap energy levels. The results indicated that the impurity phases decreased and disappeared, and crystalline grains tended to be larger and denser with the doping amount of Eu2+ and Dy3+ increasing. We shed light on the origination of asymmetric PL peak, concentration quenching of Eu2+ ions, time evolution of PSL specture and chromaticity of Eu2+, Dy3+ co-doped phosphors. Based on the deconvolutions of X-ray photoelectron spectroscopy (XPS) spectra and thermoluminescence (TL) spectra, the types and energy depth of traps in these phosphors were systematically studied. According to the data of PL, PLE, and TL, we deduced a schematic diagram of the energy level and discussed the mechanism of PSL of the phosphors. As Dy3+ dopant increases, the Eu2+, Dy3+ co-doped phosphors not only generate more defects of V O •• and V Sr ʺ, but also introduce Dy Sr • defect with proper trap depth, meanwhile, a thermally assisted tunneling mechanism will gradually dominate during the persistent luminescence, which is responsible for that the phosphor with x = 0.02, y = 0.01 presents the best long afterglow property. [ABSTRACT FROM AUTHOR]

To improve ablation resistance of SiBCN ceramics, an ultra-high temperature ceramics (UHTCs) phase of HfC was introduced into SiBCN ceramics via high-energy ball milling and hot press sintering methods. The microstructures, phase compositions, ablation properties and mechanism of SiBCN/HfC composites under a plasma flame ablation environment were investigated. The composite exhibited excellent ablation resistance under a heat flux density of 4.02 MW/m2 for 60 s. The mass ablation rate of the SiBCN/HfC composite is evaluated to be 2.3 × 10−5 mg/mm2·s, which is an order of magnitude lower than that of SiBCN-based ceramics. The result showed that the introduction of HfC provided a skeleton support structure for the oxide layer that can significantly improve the ablation resistance. Furthermore, HfO 2 that originated from the oxidation of HfC can serve as the skeleton for reducing the fluidity of the continuous SiO 2 glass protective layer. It also suggests that HfC can be an optional addition to improve the ablation properties of the SiBCN ceramic. [ABSTRACT FROM AUTHOR]