The Microstructure and Electronic Properties of Yttrium Oxide Doped With Cerium: A Theoretical Insight.

Meng Ju,Jing Huang,Shichang Li,Jingjing Wang,Yunhong Chen,Chuanzhao Zhang,Weiguo Sun,Yuanyuan Jin

doi:10.3389/fchem.2020.00338

Abstract

Trivalent Cerium (Ce3+) doped Yttrium Oxide (Y2O3) host crystal has drawn considerable interest due to its popular optical 5d-4f transition. The outstanding optical properties of Y2O3:Ce system have been demonstrated by previous studies but the microstructures still remain unclear. The lacks of Y2O3:Ce microstructures could constitute a problem to further exploit its potential applications. In this sense, we have comprehensively investigated the structural evolutions of Y2O3:Ce crystals based on the CALYPSO structure search method in conjunction with density functional theory calculations. Our result uncovers a new rhombohedral phase of Y2O3:Ce with R-3 group symmetry. In the host crystal, the Y3+ ion at central site can be naturally replaced by the doped Ce3+, resulting in a perfect cage-like configuration. We find an interesting phase transition that the crystallographic symmetry of Y2O3 changes from cubic to rhombohedral when the impurity Ce3+ is doped into the host crystal. With the nominal concentration of Ce3+ at 3.125%, many metastable structures are also identified due to the different occupying points in the host crystal. The X-ray diffraction patterns of Y2O3:Ce are simulated and the theoretical result is comparable to experimental data, thus demonstrating the validity of the lowest energy structure. The result of phonon dispersions shows that the ground state structure is dynamically stable. The analysis of electronic properties indicate that the Y2O3:Ce possesses a band gap of 4.20 eV which suggests that the incorporation of impurity Ce3+ ion into Y2O3 host crystal leads to an insulator to semiconductor transition. Meanwhile, the strong covalent bonds of O atoms in the crystal, which may greatly contribute to the stability of ground state structure, are evidenced by electron localization function. These obtained results elucidate the structural and bonding characters of Y2O3:Ce and could also provide useful insights for understanding the experimental phenomena.

Highlights

The rare-earth Cerium ions doped crystals constitute an attractive class of materials that have been extensively used in many kinds of fields including scintillation phosphors, laser medium, and white light emitting diode phosphors (Han et al, 2019; Lin et al, 2019; Masanori et al, 2020)
We have systematically reported the structural evolutions, doping site locations and electronic properties of Y2O3 crystal doped with Ce3+ ions
The first four candidate isomers present different doping sites for Ce3+, which is helpful to investigate the structural evolution of Y2O3:Ce

Summary

Introduction

The rare-earth Cerium ions doped crystals constitute an attractive class of materials that have been extensively used in many kinds of fields including scintillation phosphors, laser medium, and white light emitting diode phosphors (Han et al, 2019; Lin et al, 2019; Masanori et al, 2020). Based on the obtained lowest energy structure of Y2O3:Ce, we thoroughly conduct a calculation of the electronic properties, which could provide powerful guidance for further experimental and theoretical studies. Apart from the ground state structure, the CALYPSO identifies a large number of candidate isomers that can be useful to study the structural evolution of the Y2O3:Ce. Figure 2 illustrates the first four metastable structures of Y2O3:Ce. The isomer (a) has the same R-3 space group as the lowest energy structure while the impurity Ce3+ ions are likely to substitute the Y3+ at the lattice vertexes.

Results

Conclusion