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修后的晶体结构呈现出四角对称性，空间群为P41，晶胞参数a = 6.83565(1) Å，c = 24.84133(1) Å。本文首次在文献中描述了29Si和139La的核磁共振谱，分别与四个Si和四个La的共振峰相对应，与单元晶胞中存在的四个Si和四个La晶格位点相吻合。相同的合成方法对于合成Eu3+掺杂的A-La2Si2O7（%Eu = 3～40）也取得了成功。对单元晶胞体积的分析表明，在所研究的所有Eu3+取代水平上，Eu3+均取代了La3+。然而，异常的衍射数据表明，La/Eu的取代机制并非均匀，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激发后表现出强烈的橙色-红色荧光。寿命测量表明，最佳磷光体为含Eu3+量为20%的样品，其寿命为2.3毫秒。在393 nm激发下，其量子产率被发现为12%。这些实验观察结果以及通过所提出的喷雾热解法获得的相的高纯度，使该材料成为光电子应用的理想磷光材料。