Crystal Structure and Luminescent Properties of Eu3+-Doped A‑La2Si2O7 Tetragonal Phase Stabilized by Spray Pyrolysis Synthesis

Pure A-La2Si2O7 powder has been
synthesized through a spray pyrolysis method followed by calcination
at 1100 °C for 15 h. The crystallographic structure, refined
from the synchrotron powder diffraction pattern of the sample, showed
tetragonal symmetry with space group P41, a = 6.83565(1) Å, and c =
24.84133(1) Å. The 29Si and 139La NMR spectra
have been described here for the first time in the literature and
could be simulated with four Si and four La resonances, respectively,
in good agreement with the presence of four Si and four La crystallographic
sites in the unit cell. The same synthesis method was successful for
the synthesis of Eu3+-doped A-La2Si2O7 (%Eu = 3– 40). The analysis of the unit cell
volumes indicated that Eu3+ replaces La3+ in
the unit cell for all Eu3+ substitution levels investigated.
However, anomalous diffraction data indicated that the La/Eu substitution
mechanism was not homogeneous, but Eu much prefers to occupy the RE3
sites. The Eu-doped A-La2Si2O7 phosphors
thus synthesized exhibited a strong orange-red luminescence after
excitation at 393 nm. Lifetime measurements indicated that the optimum
phosphor was that with an Eu3+ content of 20%, which showed
a lifetime of 2.3 ms. The quantum yield of the latter was found to
be 12% at 393 nm excitation. These experimental observations together
with the high purity of the phase obtained by the proposed spray pyrolysis
method make this material an excellent phosphor for optoelectronic
applications.

纯净的 A-La2Si2O7 粉末通过喷雾热解法合成，随后在 1100 °C 下煅烧 15 小时。经同步辐射粉末衍射图谱精炼的晶体结构展现出四方对称性，空间群为 P41，晶胞参数 a = 6.83565(1) Å，c = 24.84133(1) Å。首次在文献中描述了 29Si 和 139La 的核磁共振光谱，分别可由四个 Si 和四个 La 的共振峰模拟，与晶体单元中四个 Si 和四个 La 晶格位的实际存在良好吻合。相同的合成方法成功用于 Eu3+-掺杂 A-La2Si2O7（%Eu = 3– 40）的合成。对晶胞体积的分析表明，所有研究的 Eu3+ 替代水平中，Eu3+ 替代 La3+ 发生在晶胞中。然而，异常的衍射数据表明，La/Eu 替代机制并非均匀，Eu 更倾向于占据 RE3 位点。因此合成的 Eu 掺杂 A-La2Si2O7 发光材料在 393 nm 激发后展现出强烈的橙红色荧光。寿命测量表明，最优的发光材料为 Eu3+ 含量为 20% 的样品，其寿命为 2.3 毫秒。在 393 nm 激发下，该材料的量子产率达到了 12%。这些实验观察结果与通过喷雾热解法获得的相的高纯度共同使得该材料成为光电子应用中极优的发光材料。