First-principle Investigation On Fluoride Upconversion Material Doped With Triple Rare Earth Ions And Its Preparation

Up-conversion luminescent materials show a great deal of potentials in solar energy, because of the ability of converting the infrared light excitation to the visible light emission, which could modify the efficiency of utilizing solar spectrum for photovoltaics.Currently, lanthanide-doped NaYF4, with low phonon energy, has been proved to be the most efficient one among kinds of UC materials. In the present article, the software Materials Studio, which is based on the first-principle theory, is used to simulate the crysital β-NaYF4 which is triply doped with different rare earth ions. Meanwhile, these materials were synthesized by hydrothermal approach after investigation on the impact of crystal phase and morphology through controlling experimental terms, such as heat preservation time, temperature and pH. And the luminescent properties of all obtained samples were characterized in detail.The results of first principle investigation of pure β-NaYF4 and rare earth ions doped β-NaYF4 demenstrate that although the cell volum would be enlarged by ions with larger radius, the stability of crystal systems could stay normal standard. And the band structures changed as the gaps decreased so much that electrons could transit with lower photon energy when excitated by the infrared light.The powders of β-NaYF4 doped with triple rare earth ions were prepared by hydrothermal approach and characterized by X-ray and SEM. And the results show that longer heat preservation time, higher temperature and acid condition are more beneficial to the generation of hexagonal crystal than cubic crystal. Finaly, under 180℃, pH=3 and 48 hours, samples of hexagonal phase and nearly perfect morphology were obtained successfully. Upconversion luminescence phenomenon could be observed in all of the three samples, under excitation of 980 nm and 1550 nm.