Synthesis and multicolor upconversion of Tm3+/Er3+/Yb3+ doped Na (Y1.5Na0.5) F6 single-crystal nanorods

Er3+/Tm3+/Yb3+ tri-doped Na (Y1.5Na0.5) F6 single-crystal nanorods were synthesized by a facile hydrothermal treatment method. The tri-doped sample was characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM). The sample showed a pure hexagonal phase structure with space group P63/m and nanorod morphology. Under 980 nm excitation, intense red, green and blue upconversion emissions were observed. The red and green upconversion are consistent with 4F9/2 → 4I15/2 and 2H11/2, 4S3/2 → 4I15/2 transition of Er3+, respectively, while the blue upconversion originates from 1G4 → 3H6 transition of Tm3+. Moreover, the Er3+/Tm3+/Yb3+ tri-doped Na (Y1.5Na0.5) F6 nanorods exhibit strong red and green emission which is ascribed to the sensitization of Tm3+ to Er3+. The energy transfer upconversion mechanisms for the fluorescent intensity are also discussed.