Nd<sup>3+</sup>:GdScO<sub>3</sub> crystal field energy level and fitting
Authors: Fan Ying , Zhang Qing-Li , Gao Jin-Yun , Gao Yu-Xi , Huang Lei , Liu Yao ,   Institutes of Physical Science and Information Technology, Anhui University, Hefei 230601, China,   Anhui Provincial Key Laboratory of Photonic Devices and Materials, Anhui Institute of Optics and Fine Mechanics, Hefei Institutes of Physical Science, Chinese Academy of Sciences, Hefei 230031, China,   Advanced Laser Technology Laboratory of Anhui Province, Hefei 230037, China,   University of Science and Technology of China, Hefei 230022, China
Published: November 2023

Gadolinium scandate (GdScO<sub>3</sub>) crystal has a perovskite structure, belonging to an orthogonal system, and its space group is <i>Pnma</i> (No. 62). Due to the disordered distributions of Sc<sup>3+</sup> and Gd<sup>3+</sup> ions, different cation sites can be replaced by doped ions, which indicates that GdScO<sub>3</sub> crystal has a high tolerance for structural distortion. Compared with other oxide crystals, GdScO<sub>3</sub> crystal has lower phonon energy of about 452 cm<sup>–1</sup>, which reduces non-radiative relaxation between adjacent energy levels and has strong thermal stability. In addition, GdScO<sub>3</sub> crystal birefringence is large, and as a laser material, it can eliminate the adverse effects caused by thermal birefringence, such as thermal depolarization loss. As an active ion, Nd<sup>3+</sup>(4f<sup>3</sup>) is an ideal four-level system. Therefore, Nd<sup>3+</sup>:GdScO<sub>3</sub> crystal has a broad application prospect as a laser crystal matrix material. However, the study of Nd<sup>3+</sup>:GdScO<sub>3</sub> crystal field energy level fitting and crystal field parameters has not been reported to the authors’ knowledge. Neodymium-doped gadolinium scandiate (Nd<sup>3+</sup>:GdScO<sub>3</sub>) crystal is grown by the Czochralski method. The absorption spectrum in a range of 250—2650 nm is tested at a low temperature (8 K), and the emission spectrum at room temperature is also tested. The experimental energy levels of Nd<sup>3+</sup> are analyzed and 66 experimental Stark levels of Nd<sup>3+</sup>:GdScO<sub>3</sub> are identified. For the doped trivalent rare earth ion crystals, the energy level structure of rare earth ion is related to its luminescence characteristics, so it is necessary to study its energy level structure. In recent decades, parametric crystal field models have been widely applied to various rare-earth ion doped garnet crystals. The parametric model is used to analyze and fit the crystal field energy levels of Nd<sup>3+</sup> doped orthogonal GdScO<sub>3</sub>. The fitted root mean square error is 13.17 cm<sup>–1</sup>. The resulting free ion parameters and crystal field parameters are calculated and analyzed, and the crystal field intensity is calculated. Fitting results show that the parameterized Stark levels are in good agreement with the experimental spectra, and the results are ideal. Comparing with Nd<sup>3+</sup>:YAP and Nd<sup>3+</sup>:YAG, the crystal field strength of Nd<sup>3+</sup>:GdScO<sub>3</sub> is weak. The weak crystal field strength may be one of the reasons for the excellent laser properties of Nd<sup>3+</sup>:GdScO<sub>3</sub> crystals. But its microscopic mechanism needs further studying. All the data presented in this paper are openly available at https://www.doi.org/10.57760/sciencedb.15702.