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

Abstract

Pure A-La 2 Si 2 O 7 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 P 4 1, a = 6.83565(1) Å, and c = 24.84133(1) Å. The 29 Si and 139 La 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 Eu 3+ -doped A-La 2 Si 2 O 7 (%Eu = 3– 40). The analysis of the unit cell volumes indicated that Eu 3+ replaces La 3+ in the unit cell for all Eu 3+ 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-La 2 Si 2 O 7 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 Eu 3+ 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.