Tunable Light Polarization Information from Single Upconverting Fluoride Microcrystal

Abstract The key components in display, imaging, data communication, and photoelectric detection fields are low‐dimensional micro‐/nanomaterials with highly anisotropic optoelectronic properties manifesting polarized light. However, for anisotropic upconversion (UC) materials, obtaining tunable polarization characteristics remains a significant challenge. Herein, based on a detailed investigation of the crystal structure, local symmetry, and properties of rare‐earth ions (RE³⁺), the authors successfully realized a tunable UC light polarization characteristic (UCLPC) with dependence on excitation polarization using a series of RE³⁺ single‐ or co‐doped β‐NaYF₄ microrods. By simulating the electron cloud distribution and bonding structure based on density functional theory calculations, it is shown that: i) Yb³⁺ with a unique electron cloud distribution adjusts the UCLPC of the activator via energy transfer processes; ii) co‐doping with RE³⁺ having a larger dipole polarizability improves the UCLPC of the activator by performing its electric field distribution toward anisotropy; and iii) increasing the activator concentration strengthens the UCLPC. By exploiting the unique UCLPC from different doping combinations, applications in optical storage, encryption, and anti‐counterfeiting are illustrated. Simultaneously, the findings obtained in this work will provide new and exciting fundamental insights into understanding the polarization properties of RE³⁺ in an anisotropic structure.