Synthesis, Structural Characterization, and Emission Properties of NaYF4:Er3+/Yb3+ Upconversion Nanoluminophores
We propose a new method to prepare Er3+/Yb3+-codoped β-NaYF4 upconversion nanoluminophores, allowing creation of single-crystalline-phase β-NaYF4: Er3+/Yb3+ with concentrations up to 20 mol.% through a hydrothermal process. Using hexagonal-phase Y(OH)3 precursors with different nanostructures (nanosheets, nanorods, nanotubes, etc.), one can obtain many types of one-dimensional nano-NaYF4:Er3+/Yb3+ materials and significantly improve the multiphase phenomenon, which is a common challenge facing many research groups that use a hydrothermal process for synthesis of NaYF4 compounds. Upon near-infrared laser excitation at 976 nm, the obtained β-NaYF4:Er3+/Yb3+ nanorods emit in green (2H11/2, 4S3/2 → 4I15/2) and red (4F9/2 → 4I15/2) spectral regions with high intensity. Moreover, it is shown that one can change the luminescence integrated intensity ratio between the red and green emissions by varying the concentration and components of Er3+ and Yb3+ in the NaYF4 host material. Comparative studies on the luminescence kinetics of the NaYF4:Er3+/Yb3+ nanoluminophores were also conducted to explain the influence of Yb3+ ion on the upconversion processes.