Tunable Light Polarization Information From Single Upconverting Fluoride Microcrystal

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 beta-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.