Enhancing Upconversion Luminescence Efficiency via Chiral β-NaYF 4 :Er 3+ /Yb 3+ Microcrystals Based on Mesoscale Regulation.

Chirality, universal characteristics of nature, introduces asymmetry in synthetic materials. Revealing the microscopic asymmetry of macroscopically symmetric materials is the key to control the growth of chiral materials and give full play to their application potential. Materials for photon upconversion (UC) are of great interest for many applications owing to their anti-Stoke luminescence process, especially for chiral UC materials. For the preparation of UC materials, a tiny change in reaction parameters will lead to variations in morphology, phase components, and fluorescence intensity, as well as its chirality. Because of the strict reaction conditions for the formation of chiral UC materials, there are no reports of the successful synthesis of chiral UC materials. Therefore, a facile method for the controllable synthesis of chiral UC materials is highly desired. Herein, chiral-assembled hexagonal prisms of β-NaYF:Er/Yb microcrystals were synthesized to realize the smart manipulation of their morphology as well as a great improvement of the fluorescence efficiency. We proposed a three-stage doped β-NaYF crystal growth mechanism on mesoscale regulation, where the fluorescence enhancement principle of chirality was revealed. The enhancement of fluorescence efficiency of chiral UC materials endows their promising application in luminescent displays.