Typical high-entropy fluorite oxides with five metal cations have exhibited improved thermomechanical properties . In this work, we have successfully prepared single-phase high-entropy (Zr 0.2 Ce 0.2 Hf 0.2 Y 0.2 Al 0.2 )O 2-δ fluorite oxides through the combination of sol-gel method and calcination , using metal nitrate/chloride, citric acid and absolute ethanol as the primary raw materials. A series of characterizations were employed for chemical, morphological and structural analysis of the calcined products. The five cationic elements were shown to be uniformly distributed in the nearly pure fluorite oxide without apparent segregation at the micro/nano-meter scales after 1500 °C calcination. Annealing and water quenching within the test temperature range did not witness any appreciable phase transition. It is revealed that the concentration of Ce 3+ in Ce ions reaches 33.84% and δ is equal to 0.234, yielding a nominal composition of (Zr 0.2 Ce 0.2 Hf 0.2 Y 0.2 Al 0.2 )O 1.766 . Cation and anion configurational entropy were found to be 1.609 R and 0.722 R, respectively, where R is the ideal gas constant, for a sum of the total configurational entropy of 2.331 R in the high-entropy system. Line defects inside the crystals and 3 types of crystalline boundary structures have been observed and identified among the mostly atomically sharp grain boundaries.
Ke Sun,Haibin Lin,Rui Zhang,Jinlong Zhu,Liping Wang,Songbai Han,Xiaofei Wang
The emerging laser-driven phosphor-converted white laser diodes (w-LDs) demand highly efficient and thermally stable color converters. To this end, the Ce 3+ luminescence in the rekindled La–Si–O–N host, and the impacts of NH 4 Cl flux and post-processing are investigated systematically. On the basis of the XRD results, well crystalline Ce 3+ -doped La 5 Si 3 O 12 N and LaSiO 2 N are obtained at 1600 °C for 5 h and 1500 °C for 4 h, respectively. Impressively, the representative La 5 Si 3 O 12 N:0.04Ce 3+ and LaSiO 2 N:0.03Ce 3+ exhibit a broad excitation band from 240 nm to 400 nm, peaking at around 360 nm, which is well matched with emission from near-UV (n-UV) chip. Under excitation by a n-UV laser, the La 5 Si 3 O 12 N:0.04Ce 3+ and LaSiO 2 N:0.03Ce 3+ produce bright blue light in a wide emission band from 360 nm to 550 nm. The CIE chromaticity diagram reveals the tunability of the hue of these phosphors. The quenching temperature is determined to be 396 K and 429 K for La 5 Si 3 O 12 N:0.04Ce 3+ and LaSiO 2 N:0.03Ce 3+ respectively, indicating superior thermal stability. The addition of 3 wt% NH 4 Cl flux much enhances the emission intensity of both La 5 Si 3 O 12 N:0.04Ce 3+ and LaSiO 2 N:0.03Ce 3+ . Furthermore, the post-treatments markedly improve the luminescence properties by increasing the crystallinity , reducing the surface defect , and changing the morphology. Therefore, it is believed that the present work has promising applications in LD lighting and promoting the development of laser display.
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