This study aims to elucidate the phase transformation of hexacelsian-to-celsian in 10 wt.% h -BN reinforced BaAl 2 Si 2 O 8 (BN/BAS) composites fabricated by hot-pressed at 1300 °C for different holding time. Results showed that the relationship between the transformation fraction of celsian and the holding time displays a typical “S” curve according to Johnson-Mehl-Avrami equation. During the hexacelsian-to-celsian transformation, a transitional phase of paracelsian was observed. Celsian tended to nucleate and grow up along the (110) P habit plane of paracelsian by a non-diffusive transition behavior. During transformation, celsian and paracelsian present an oriented intergrowth with orientation relations of (110) P //(020) M , [001] P //[101] M and [ 1 1 ¯ 0 ] P // [ 10 1 ¯ ] M .
The white LEDs with high performance and excellent luminous quality is of high importance for developing the current lighting industry, and high thermally stable blue phosphors play a critical role in the preparation of white LEDs. Herein, we reported a facile way to obtain highly efficient blue Eu 2+ -doped celsian phosphor with excellent thermal stability by a phase transformation of Ba 2+ -exchanged SOD Zeolite strategy. The structure of phosphors changed from nepheline to celsian with the doping of Ba 2+ , and the maximum emission intensity blue-shifts from 550 nm to 450 nm under the excitation of 370 nm. The PLQY is determined to be 56 %, 96 % and 82 % for the phosphor with Ba 2+ doping concentration being 0, 1.49 and 1.86, respectively, and the luminescence intensity at 423 K is can be 80 %, 102 % and 93 % of its intensity at room temperature. Finally, the package of the LED device based on our yellow and blue phosphors together with the commercial red CaAlSiN 3 :Eu 2+ phosphor is constructed to show warm white light with the CCT of 3705 K and a high CRI of 97.7. This study provides a facile way for obtaining satisfactory phosphors for high-quality lighting.
Monoclinic barium aluminosilicate (celsian) shows application potential owing to its high-temperature resistance, low thermal conductivity, and excellent oxidative reduction properties. Hexacelsian can easily undergo nucleation because of its favorably symmetric crystal structure, resulting in faster precipitation compared to than in the case of celsian. Celsian can only be formed through the sluggish transformation of hexacelsian at high temperatures. In this study, celsian doped with different contents of CaO was synthesized through a simple one-step solid-state reaction process at lower temperatures and in a shorter time and investigated using differential thermal analysis, phase characterization, microstructural observation, and FactSage thermodynamic calculations. Results showed that the addition of CaO could promote the solid-state reaction, affording products such as barium silicate, hexacelsian, and celsian at lower temperatures. Moreover, CaO could promote the synthesis of celsian in the form of solid solution, affording fully monoclinic celsian Ba 0.7 Ca 0.3 Al 2 Si 2 O 8 with only 3 h of holding time at 1400 °C. The optimal addition of CaO showed a decreasing trend with the increase in heat treatment temperature. An optimum CaO level of 0.1 ≤ x ≤ 0.3 was recommended to stabilize celsian. The effects of CaO addition and temperature on the physical, mechanical and thermal conductivity properties of Ba 1-x Ca x Al 2 Si 2 O 8 were investigated, and Ba 1-x Ca x Al 2 Si 2 O 8 also exhibited excellent antioxidant reduction properties.
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