Deciphering the Microstructures and Electronic Properties of the YVO₄:Re (Re = Pr, Nd, and Tm) Crystals: A Theoretical Insight

Rare-earth ion (Pr³⁺, Nd³⁺, and Tm³⁺)-doped yttrium vanadate (YVO₄) crystals have aroused great research interest owing to their excellent laser performances. However, the microstructures, which underlie the optical properties of these crystals, are still unclear. In this paper, the stable crystal structures of the YVO₄:Re (Re = Pr, Nd, and Tm) systems are predicted by using the crystal structure analysis by the particle swarm optimization (CALYPSO) structure search method. The unique tetragonal structures with the <i>P</i>4̅<i>m</i>2 (no. 115) space group for the YVO₄:Re crystals are identified for the first time. It is found that the rare-earth ions (Pr³⁺, Nd³⁺, and Tm³⁺) can accurately occupy the Y³⁺ sites and successfully fuse into the YVO₄ host crystals. The simulated X-ray diffraction (XRD) patterns of the YVO₄ and YVO₄:Re (Re = Pr, Nd, and Tm) are consistent with the experimental measurements, demonstrating the possibility and rationality of the predicted structures. Furthermore, we are motivated to clarify the electronic properties of the pure YVO₄ and YVO₄:Re (Re = Pr, Nd, and Tm) crystals based on density functional theory (DFT). The calculated electronic band structures of YVO₄:Re (Re = Pr, Nd, and Tm) indicate reductions in the band gaps. With the increase in f-electrons, the energies of the f-electrons in the conduction bands decrease slightly. The calculated electron localization functions (ELF) of YVO₄:Re (Re = Pr, Nd, and Tm) show that the bonding characteristics of Y-O, Pr-O, Nd-O, and Tm-O are all ionic. These theoretical results could provide important information for further research on the rare-earth-doped laser materials.