Hexagonal Beta-Na(Y,Yb) F-4 Based Core/Shell Nanorods: Epitaxial Growth, Enhanced And Tailored Up-Conversion Emission

To meet the increasing requirement, much effort has been devoted to enhance the emission intensity and tailor the emission color of rare earth phosphors. However, limited contributions have been made to the up-conversion (UC) of nanorods by complete epitaxial growth on each facet to achieve this requirement. In this study, we propose a facile epitaxial growth route to grow anisotropic hexagonal beta-NaYF4:Yb3+/Ho3+@beta-NaYbF4:Er3+, beta-NaYF4:Yb3+/Ho3+@beta-NaYF4, and beta-NaYbF4:Er3+@beta-NaYF4 core/shell nanorods, which were realized by adding hexagonal beta-NaYF4:Yb3+/Ho3+ or beta-NaYbF4:Er3+ nanorods as a corenanostructure into a solution containing cubic alpha-NaYbF4:Er3+ or alpha-NaYF4 nanoparticles as the shellprecursor. During epitaxial growth-induced phase transformation, the precursor nanoparticles disappeared gradually in the solution and consequently corresponding beta-phased shell yielded on each outer facet of each b-phased nanorod core. Eventually, the nanorod core was covered completely with a uniformly grown beta-NaYbF4:Er3+ or beta-NaYF4 shell. The UC emission of either beta-NaYF4:Yb3+/Ho3+ or beta-NaYbF4:Er3+ core can be enhanced by the outer shell due to the decrease in the number of surface defects. In addition, tailored UC emissions could be obtained by controlling the shell components and thickness, typically in the core/shell nanorods of beta-NaYF4:Yb3+/Ho3+@beta-NaYbF4: Er3+. The tunable colors with improved emission in these core/shell nanorods may find wider applications in multicolor labeling and anti-counterfeiting.