Hydrothermal synthesis of β-NaYF4 nanotubes by in situ ion exchange reaction using Y(OH)3 nanotubes as templates

► Hexagonal NaYF4 nanotubes were prepared through in situ ion exchange reaction. ► The as-prepared β-NaYF4 preserved the basic morphology of the initial Y(OH)3 nanotubes. ► β-NaYF4 nanotubes could only be obtained at proper pH value. ► Yb3+/Er3+ codoped NaYF4 emitted bright green and red light.