A robust strategy for preparing Li-gradient LiNbO3: Yb/Er nanocrystals with improved dynamic force-optical response

The arrangement of lithium and niobium in the LiNbO 3 lattice is crucial to its notable ferroelectric, piezoelectric, ion conductive, and nonlinear optical properties. However, the synthesis of Li concentration-gradient nanocrystals remains a significant challenge. In this paper, we report a reliable method for synthesizing LiNbO 3 : Yb/Er nanocrystals with a Li-gradient through topochemical molten salt synthesis. We elucidate the Li-gradient characteristics using various analytical techniques, including depth-dependent elemental analysis. Variable-temperature upconversion luminescence spectroscopy provided insights into thermally induced surface and interior Li + diffusion. Our findings demonstrate that Li-gradient nanocrystals exhibit enhanced ferroelectric behavior and increased sensitivity to mechanical force in upconversion emission response. This study proposes a feasible universal strategy for synthesizing alkali metal niobate materials with controlled polarization, offering promising candidates for flexible, low-power optoelectronic devices.