Highly Uniform Tm3+-Doped NaYbF4 Microtubes: Controlled Synthesis and Intense Ultraviolet Photoluminescence

Here, we present a facile and controlled synthesis of high-quality and uniform hexagonal phase NaYbF4 microtubes by a rational hydrothermal method. In addition, highly uniform and monodisperse NaYbF4 nanospheres and nanocubes are synthesized by simply tuning the reaction parameters, including sodium fluoride content, reaction temperature and reaction time. Under excitation with a 980 nm laser diode, intense ultraviolet (UV) and blue upconversion emissions were achieved from a single dopant ion (Tm3+) in NaYbF4. The effect of the crystal phase on the upconversion emission properties is also investigated. The results demonstrate that upconversion emission intensities from hexagonal phase NaYbF4 microtubes are much more efficient than the nanocubes by 2 orders of magnitude. These microtubes with unique upconvertion emissions demonstrate that NaYbF4 is an excellent host material, as compared with some of its other fluoride and oxide counterparts, and that it may find applications in UV and visible solid-state lasers or the fiber lasers.