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Yb 2 O 3 :Ho 3+ nanocrystalline powders were synthesized through a solid state reaction method. X-ray diffraction analysis and field emission scanning electron microscopy were used to analyze the phase composition and morphology of the powders. Then under the 980 nm excitation of laser diode, the fluorescence of the crystals was studied via a fluorescence spectrometer. The green and red emissions centered on 551 and 668 nm were observed, and the green band dominated the emission spectrum. The effect of the concentration of Ho 3+ on the upconversion luminescence intensity was discussed and the possible upconversion emission mechanism was explained. It indicates that like other metal oxide nanoparticles, Yb 2 O 3 could also be a potential host material for doping to prepare the upconversion phosphor. [ABSTRACT FROM AUTHOR]

• A series of Tm3+/Yb3+-Bi 2 WO 6 catalysts hydrothermally prepared and characterized. • Tm3+/Yb3+-Bi 2 WO 6 showed excellent optical properties. • Significantly enhanced photocatalytic activity is achieved when degrading RhB. • This study provides a great way to obtain stable photocatalyst. Tm3+ and Yb3+ co-doped Bi 2 WO 6 up-conversion photocatalysts (Tm3+/Yb3+:Bi 2 WO 6) were synthesized via co-precipitation route at different calcination temperatures. Doping Tm3+ and Yb3+ into Bi 2 WO 6 lattice and substituting for the fractional Bi3+ were successfully confirmed by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) analysis. The morphology and optical property of the obtained samples were characterized by field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), UV–vis diffuse reflectance spectra (DRS) and up-conversion luminescence spectra (UC-PL). The photocatalytic results revealed that the Tm3+/Yb3+:Bi 2 WO 6 exhibited a much superior photocatalytic activity than the pure Bi 2 WO 6 and commercial Degussa P25 for the degradation of rhodamine B (RhB), and the degradation rate reached 97.6% in 25 min. The effects of Tm3+ and Yb3+ on the photocatalytic activity of Bi 2 WO 6 were studied in detail. The improved photocatalytic activity of Bi 2 WO 6 could be attributed to the efficient energy transfer between Tm3+/Yb3+ and Bi 2 WO 6 via infrared to visible up-conversion and the reduced recombination rate of photogenerated electron-hole pairs through co-doping of Tm3+/Yb3+ on Bi 2 WO 6 nanopaticles. [ABSTRACT FROM AUTHOR]