Laser-Driven In Situ Phase-Selective Crystallization of NaYF 4

NaYF4 nanocrystals are excellent matrix materials for rare-earth luminescent compounds, as their crystalline phase directly determines the upconversion luminescence efficiency of doped rare-earth ions. Traditional chemical methods require complex designs to induce phase transitions, which currently hinder the straightforward and efficient preparation of deterministic single-phase crystals. This limitation severely restricts the development of rare-earth nanocrystals in micronano photonic integration. In this study, we propose a continuous wave light-driven in situ-integrated crystallization strategy that enables the rapid synthesis of NaYF4:Er/Yb nanocrystals under ambient temperature and pressure. By modulation of the laser parameters, localized crystallization and phase control were achieved in the same precursor environment, yielding cubic and hexagonal NaYF4:Er/Yb nanocrystals, respectively. The resulting micro/nanostructures exhibited excellent upconversion luminescence performance upon excitation at 980 nm. This technique broadens application prospects in multiple fields, including fluorescence imaging, nanolithography, and infrared light detection.