Three-primary-color upconversion luminescence in rare earth-doped β-NaLuF4 microtubes

Lanthanide ions-doped NaLuF4 hexagonal-prismatic microtubes have been successfully synthesized via a facile hydrothermal approach for the first time. The as-grown microtubes are determined to be pure hexagonal (β-) NaLuF4 phase with an outermost diameter of about 3 μm and a length of approximately 40 μm. The Yb3+/Er3+(Tm3+)-codoped NaLuF4 microtubes emit bright three-primary-color (red, green, and blue) light under 980 nm laser diode excitation undergoing an upconversion. Mechanisms for the excitation and emission were analyzed based on the emission spectra, the plot of luminescence intensity to pump power and a simplified energy level diagram.