College of Chemistry, Beijing Normal University, Beijing, 100875, China.
Dalton Trans. 2012 Oct 21;41(39):12175-84. doi: 10.1039/c2dt31249b.
Highly crystalline Eu(3+)-incorporated MgAl layered double hydroxides (LDHs) were synthesized by the homogeneous precipitation method. For the crystals as-prepared, after their calcination from 200-1000 °C, and, further, after restoration in a Na(2)CO(3) solution, the structural and luminescent changes were investigated for the first time. Eu(3+) ions with a coordination number of, probably, 8, were incorporated into the hydrotalcite layer, which led to a basal spacing (d(basal)) increase, microstrain formation, and crystalline morphology imperfections, while retaining the original lattice symmetry, R3[combining macron]m. In the deconstruction process due to calcination, the Eu(3+) ions restrained the formation of the spinel phase from the layered double oxide (LDO), but did not significantly change the memory effect, by which LDOs can convert to LDHs during the hydration process. For the reversible phase transformation between LDH and LDO, the morphology observation revealed that, in addition to the formation of pores on the surface, nano-slabs were formed, especially for the restored crystals. A layered phase with a d(basal) of 5.8 Å, due to bridging bidentate carbonates with the hydrotalcite layer, was formed in the calcination process at low temperature (300 °C) before the formation of LDO, but could not be restored to a large spacing. Typical (5)D(0) → (7)F(J) (J = 0-4) transitions of Eu(3+) at 579, 593, 615, 653, and 698 nm were observed in the photoluminescence spectra and the intensity of the dominating 615 nm band decreased with the LDH deconstruction and the formation of free water, and then increased with the formation of LDOs in the calcination process, and vice versa in the reconstruction process. The Eu(3+) ions had a probable 9- or 10-coordination mode in addition to the probable 8-coordination mode as the spinel phase appeared.
采用均相沉淀法合成了高度结晶的 Eu(3+)-掺入 MgAl 层状双氢氧化物（LDHs）。对于所制备的晶体，在 200-1000°C 下煅烧后，并且，进一步在 Na(2)CO(3)溶液中还原后，首次研究了结构和发光变化。Eu(3+)离子的配位数可能为 8，掺入水滑石层，导致基面间距（d(basal))增加，微应变形成和晶体形态缺陷，同时保留原始晶格对称性，R3[combining macron]m。在煅烧过程中的解构过程中，Eu(3+)离子抑制了层状双氧化物（LDO）向尖晶石相的形成，但并没有显著改变记忆效应，即 LDOs 在水合过程中可以转化为 LDHs。对于 LDH 和 LDO 之间的可逆相变，形态观察表明，除了表面形成孔外，还形成了纳米薄片，特别是对于还原晶体。在低温（300°C）煅烧过程中，在形成 LDO 之前，形成了具有 5.8 Å 的 d(basal)的层状相，这是由于与水滑石层桥联的双齿碳酸盐，但不能恢复到大间距。在光致发光光谱中观察到 Eu(3+)的典型（5）D(0) →（7）F(J)（J = 0-4）跃迁，在 579、593、615、653 和 698nm 处，观察到强度随着 LDH 解构和自由水的形成而降低，然后随着 LDO 在煅烧过程中的形成而增加，反之亦然在重建过程中。Eu(3+)离子除了可能的 8 配位模式外，还具有可能的 9 或 10 配位模式，因为尖晶石相出现。
