Rare‐Earth Ions in LiNbO₃ Nanocrystals from the View of Spectroscopy and Force‐Field Calculations

The intrinsic and extrinsic defects in LiNbO₃ (LN) bulk crystals have been investigated with experimental and theoretical methods for many years. However, nowadays, scientific attention has turned to nanocrystals (e.g., for quantum nanophotonic applications). Herein, the results of spectroscopic measurements and theoretical calculations on Yb³⁺‐ or Er³⁺‐doped LN nanocrystals are presented. A series of congruent LN nanocrystals doped with Er³⁺ or Yb³⁺ have been produced by grinding process under wet conditions in a high‐energy ball mill. The effect of size reduction on the rare‐earth (RE) ions has been followed by absorption measurement of the characteristic electronic transitions using a Fourier‐transform infrared spectrometer. Out‐diffusion of the RE ions from the nano‐LN particle and the appearance of an unordered phase have been concluded from the experimental results. GULP software has been used to make force‐field calculations on a Li₂₄₅Nb₂₄₅O₇₃₅ unit to model the nano‐LN structure containing Er³⁺ or Yb³⁺ dopants. From the calculations taking into account, one Er³⁺ or Yb³⁺ ion, their out‐diffusion, and the appearance of the ions in the unordered phase have been demonstrated, while in the double‐doped case, independent RE incorporation has been found.