Excitation Position Sensitive Upconversion Emission of Lanthanide Ions Doped β‐NaYF₄ Single Microcrystals

Abstract The information about optical propagation properties and the directionality of emission light of individual microcrystal is essential for the applications of lanthanide ions doped (Ln‐doped) upconversion (UC) materials. In this work, we focus on the optical property of UC Yb³⁺ and Er³⁺ or Tm³⁺ doped β‐NaYF₄ single crystal microrods and microdisks. Their optical propagation properties and directionality of the UC emission are investigated by the UC photoluminescence (PL) spectra and microarea PL microscopy images. The emission colors, directionality and intensity to the edges of the microcrystals are evidently sensitive to the initial excitation laser position. The waveguide effect and the self‐absorption effect of the doping ions are responsible for such anisotropic emission and emission color changing. And the ray‐dynamical interpretation can give well explanation on the emission light distribution.