Up-conversion luminescence properties of Yb^3＋ and Ho^3＋ co-doped Bi3.84W0.16O6.24 powder synthesized by hydrothermal method

Using polyethylene glycol (PEG) as the surfactant, Bi3.84W0.16O6.24 up-conversion luminescence nano-crystal co-doped with Yb3+ and Ho3+ ions was synthesized by the hydrothermal method. The structure and properties of luminescence powder were studied by X-ray diffraction (XRD) and scanning electron microscope (SEM). It was of cubic system when the sample was synthesized at a low temperature and the particle size was about 30 nm. The results showed that adding surfactants was useful to improve the powder agglomeration and the grain crystal was spherical. The green emission peak at 546 nm and red emission peak at 655 nm, corresponding to the ( 5F4, 5S2)→ 5 I 8 and the 5 F 5 → 5 I 8 transitions of Ho 3+ , respectively, were simultaneously observed at room temperature under excitation of 980 nm semiconductor laser. The up-conversion luminescence intensity was the strongest when the concentration ratio of Yb3+ /Ho3+ was 6:1 and the concentration of Ho 3+ ion was 1.5 mol.%. The up-conversion mechanism was also studied. The green and red emission peaks were the two-photon absorption according to the relationship between the pump power and the luminescence intensity.