Upconversion (UC) luminescent materials have received much attention due to their unique luminescent properties and potential applications in various fields. Yb 3+ /Tm 3+ codoped NaBiF 4 UC material has been successfully synthesized through a solvothermal method. With the excitation of 980 nm laser light, NaBiF 4 :Yb 3+ /Tm 3+ powder show strong UC luminescence. Especially, the near-infrared (NIR) UC emission band of NaBiF 4 :Yb 3+ /Tm 3+ centered at 800 nm is 49 times stronger than the blue emission band. The temperature-dependent UCL properties of NaBiF 4 :Yb 3+ /Tm 3+ were investigated systematically under 980 nm excitation. The results show that all the UC emission peaks of NaBiF 4 : Yb 3+ /Tm 3+ in the region from 300 to 900 nm decrease with the temperature increase except for the emission peak at 697 nm which is positively correlated with temperature. And the UC emissions of NaBiF 4 : Yb 3+ /Tm 3+ exhibits high temperature sensitivity between 303 and 443 K. Therefore, NaBiF 4 : Yb 3+ /Tm 3+ material with strong NIR UCL could be a potential candidate for sensitive temperature sensor .
NIR light accounts for 50% of total solar energy, but only a small amount of the energy is applied to photocatalytic reactions. The incorporation of upconversion nanoparticles with semiconductor materials is an effective tactics to exploit NIR-driven photocatalyst . In this work, we report a composite material that can convert NIR light into UV–Vis photons. The light conversion material is composed of NaBiF 4 : Yb 3+ , Tm 3+ up-conversion nanocrystals . The petal-like Bi 2 WO 6 is used as a semiconductor photocatalyst to directly degrade model pollutants, such as RhB. By controlling the morphology of Bi 2 WO 6 , the contact area between the semiconductor photocatalyst and the pollutant molecules is increased. The preparation of “double bismuth” composite material NaBiF 4 :Yb 3+ , Tm 3+ /Bi 2 WO 6 provides the possibility to make full use of sunlight. Under the excitation of simulated sunlight, the photocatalyst of NaBiF 4 :Yb 3+ , Tm 3+ /Bi 2 WO 6 reaches the highest degradation efficiency of 98% in 27 min. Compared with Bi 2 WO 6 , the prepared composite photocatalyst shows better photocatalytic performance, which is attributed to the effective energy transfer between NaBiF 4 :Yb 3+ ,Tm 3+ and Bi 2 WO 6 . The capture tests were used to detect active species used in the degradation process. After four continuous photocatalytic cycles, about 95% of RhB solution is degraded. Under the simulated solar light illumination, the photocatalytic mechanism of the composite photocatalyst is discussed. The results propose a promising system to improve the photocatalytic activity through the efficient use of sunlight.
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