Deciphering the Structural Evolutions and Electronic Features of Nd3+:K2YF5 Nanocrystals

Neodymium (Nd3+)-doped K2YF5 nanophosphors have attracted considerable attention due to their promising application in fiber lasers, luminescence thermometry and bioimaging. However, the structural evolutions and electronic properties of Nd3+-doped K2YF5 nanocrystals have not been comprehensively studied, which is exactly the basis of spectral formation. In this letter, the ground structure of Nd3+:K2YF5 crystals are first obtained by crystal structure prediction in conjunction with density functional theory. Our results reveal a new stable phase with Pm (No. 6) space group for the Nd3+:K2YF5 nanocrystals, and Nd3+ ions replace the position of Y3+ ions. Additionally, we have identified the presence of a local polyhedron [NdF7]4-, wherein the crystallographic site with Cs symmetry is occupied by Nd3+ ions. The excellent agreement observed between our simulated X-ray diffraction patterns and the experimental data serves as compelling evidence supporting the validity of the ground-state structure. The electronic band structure calculation of Nd3+-doped K2YF5 employing the enhanced modified Becke-Johnson methodology demonstrates a closure of the insulator band gap (4.01 eV). Our analysis of the electron localization function for Nd3+-doped K2YF5 crystal indicates a dominant ionic bond interaction between Nd and F ions. These results offer valuable insights into the structural evolution and enable the exploration of properties when encountering other rare-earth-doped materials.