Meng Ju

Er3+-doped Sc2O3 (Er:Sc2O3), featuring low phonon energy, high thermal conductivity, and excellent optical properties, has become a promising laser gain material. Nevertheless, the microscopic mechanisms associated with its structural stability, electronic characteristics, and optical response remain insufficiently understood. In this study, the structural, electronic, electron localization, and optical properties of Er:Sc2O3 at different doping concentrations were systematically investigated through first-principles calculations based on density functional theory. The CALYPSO method was employed to predict the stable crystal structures, and subsequent calculations were performed using the VASP package within the generalized gradient approximation (GGA) + U framework. The results reveal that Er3+ substitution induces local lattice distortion and symmetry reduction from the cubic Ia3̅ phase to the trigonal R3̅ phase. Moreover, all optimized structures remain dynamically stable according to phonon dispersion calculations. Electronic structure analysis suggests that Er-related 4f states introduce impurity energy levels into the band gap and gradually reduce the band gap width with increasing doping concentration, while the insulating nature of the system is preserved. Additionally, the electron localization function and Bader analysis specify that the bonding characteristics remain predominantly ionic. Furthermore, Er3+ doping modifies the dielectric response and shifts the absorption edge toward lower energy, resulting in an expanded optical absorption range, as reflected in optical calculations. These findings provide a theoretical reference for understanding the microscopic effects of Er:Sc2O3.

Our study reveals the electronic structures and features of isotropically contracted Y ₂ O ₃ :Eu ³⁺ and anisotropically compressed Y ₂ O ₃ :Pr ³⁺ under pressure.

The pursuit of high-temperature superconductive superhydrides has recently moved into a brand-new era by going beyond extensively probed binary hydrides and paying attention to ternary ones with the distinguished hydrogen patterns that can be stabilized under modest pressures, such as XHn backbones and molecular H2 motifs. Herein, we raise a strategy for the rational design of high-Tc superconductors under moderate pressures by combining the BHn backbones and molecular H2 units in ternary transition-metal hydrides. Towards this goal, the structural stabilities and superconducting properties for ternary Sc-B-H compounds ranging from 25 to 400 GPa were conducted based on the evolutionary algorithm and the first-principles calculations. Six thermodynamically stable metallic configurations namely, P6/mmm-ScBH, P-6m2-ScB2H, P3m1-ScB2H, P6/mmm-ScB2H2, P-3m1-ScB2H2 and P21/m-ScBH5, are identified. Lattice dynamics calculations indicate that P-3m1-ScB2H2 is dynamically stable at the low pressure of 50 GPa with an estimated superconducting critical temperature of 26.97 K. Remarkably, the P21/m-ScBH5 phase exhibits superconductivity with a maximum Tc of 86.07 K under 150 GPa (μ* = 0.1) beyond the liquid nitrogen temperature (77 K) and can be dynamically stable down to 100 GPa with a reduced Tc of 29.95 K. This significant superconductivity mainly depends on the H-H interaction in molecular H2 motifs at high frequency as well as the B-H interaction from the BH2 units at midfrequency. Our consequences verify that ternary molecular superhydrides including XHn and molecular H2 units can become an excellent channel to design high-temperature superconductors at the modest pressures.

Our study successfully identified a novel cage-like structure of the Y ₂ O ₃ :Cr crystal for the first time.

A conspicuous ternary hydride Fm-3m-LaBeH8 superconductor with the particular Be-H alloy backbone was initially predicted in theory and subsequently synthesized in experiment with the measured superconducting critical temperature Tc of...

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 P4̅m2 (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.

In this study, the structural evolution, electronic properties, and optical characteristics of Er³⁺-doped Y₃Sc₂Al₃O₁₂ (YSAG) crystals were systematically investigated by the CALYPSO structure prediction methodology combined with density functional theory. The crucial findings are detailed as follows. (1) The ground state structure of Er³⁺:YSAG was determined. Er³⁺ ions substitute Y³⁺ sites to form [ErO₈]¹³⁻ coordination polyhedra with D ₂ point group symmetry, triggering space group transitions from I a 3 ¯ d to C 222 . The phonon spectrum and x-ray diffraction simulations confirmed the stability and accuracy of the structure. (2) Er³⁺ doping induced a band gap to narrow from 4.38 eV to 3.32 eV, attributed to the influence of the 4f electrons of Er³⁺ ions. Electron localization function and Bader charge analyses demonstrated the predominantly ionic nature of Er–O bonds. (3) Dielectric functions and absorption coefficients specified enhanced absorption in the vacuum ultraviolet region (25–35 eV) upon Er³⁺ incorporation. This study elucidated the structure-property relationships governing rare-earth doping effects in garnet-type laser crystals, providing fundamental theoretical insights for the microstructural design and performance optimization of rare-earth-doped laser materials.