Structural and Optical Characterization of Pure and Lanthanum Substituted Nd_1-xLa_xAlO₃ Prepared by Sol-Gel Method

This work demonstrates the tuning of crystal-field parameters of Nd rare Earth ion in NdAlO₃ through lanthanum (La) substitution; for this purpose, this work has prepared the polycrystalline samples of pure and La-substituted NdAlO₃ using the sol-gel synthesis method. The purity of the phase of Nd_1-xLa_xAlO₃ (x = 0, 0.1, 0.2, 0.3, 0.4, 0.5) samples has been confirmed via X-ray diffraction measurements. This work found that with La substitution, the lattice parameters systematically increase. The values of lattice parameters "a" and "b" changed from 5.315 Å (x = 0) to 5.339 Å (x = 0.5). The lattice parameter "c" also increased from 12.926 to 13.025 Å in these samples. Additionally, the Nd/LaO bond length increased from 2.419 to 2.469 Å. The NdONd bond angle shifted from 169.7° to 171.4°, whereas the AlOAl bond angle varies from 165.5° to 167.8° and the value of the tolerance factor from 0.9640 to 0.9700, indicating improvement in the structural distortion. The crystal-field transitions are investigated using optical absorption spectroscopy; this work found that La-substitution leads to changes in the transition peak 4F_9/2, which is shifted from 676.99 nm for sample (x = 0) to 675.44 nm for sample (x = 0.5).