Excitation power controlled luminescence switching in Yb3+–Tm3+ co-doped hexagonal NaYF4 nanorods

Intense infrared-to-visible up-conversion (UC) emissions were obtained in hexagonal Yb3+–Tm3+ co-doped NaYF4 nanorods under excitation at 980 nm. Especially, luminescent switching between different UC emission wavelengths at 800, 480 and 450 nm were observed by adjusting excitation powers. Based on power-dependent spectral analyses, it was found that the cooperative energy transfer between Yb3+–Yb3+ pairs and Tm3+ ions play a key role on the luminescent switching besides the saturation effect of Yb3+2F5/2 and Tm3+1G4 excited states. Our results indicate that hexagonal NaYF4 nanostructures have potential applications in miniaturized solid-state laser, optical processing sensors and fluorescent biolabels.