Preparation And Properties Of Rare-earth Doped Bi₂WO₆

Up-conversion(UC)luminescence materials can transform near infrared(NIR)light into visible or ultraviolet light(UV)by means of multiple absorption or energy transfer processes,UC luminescence materials have exhibited good application foreground in optical temperature sensors,medical diagnostics,display devices,solar cells and photocatalysts,ect.UC luminescence materials doped with rare earth ions show the excellent luminous performance,it is attributed to the UC process of 4f electronic structure of rare earth ions and they can broaden the photo-response range.Bi2WO6 is a typically layered Aurivillius oxide and has attracted extensive attention from researchers because of its narrow band gap(2.6-2.8eV),low phonon energy,excellent optical and catalytic properties.In this paper,Bi2 WO6,as the multiple semiconductor oxide,was used as matrix material,we prepared a series of UC luminescence of rare earth doped Bi2WO6 nanopowders.The effect of some factors on UC luminescence properties was discussed in detail,and as visible light driven photocatalyst,photocatalytic activity of Bi2WO6 was further improved.The obtained results are as follows:(1)Orthorhombic Ho3+/Yb3+-Bi2WO6 powders were synthesized successfully through the hydrothermal route and a subsequent calcination process,the diameter of particles were about 50-100nm.The powders exhibited UC luminescence properties,under 980nm laser excitation,can transform infrared(NIR)light into strong green and weak red light.The effects of Ho3+ and Yb3+ ions concentrations and excitation pump power on UC luminescence intensity were analyzed in detail.The results showed that the strongest luminescence intensity was obtained when the concentration of Ho3+ and Yb3+ were 1mol%,5.0mol%respectively.Moreover,in the Ho3+/Yb3+ co-doped system,UC process is belong to the energy transfer between Holo and Yb3+ ions,and green and red emissions are involved a two-photon absorption process.(2)Orthorhombic 1mol%Ho3+/5mol%Yb3+-Bi2WO6 up-conversion luminescence powders by the hydrothermal route and a subsequent calcination process.The effect of the calcination temperature in the heat treatment process on UC luminescence intensity was discussed.The results showed that the UC luminescence intensity of obtained powder exhibited the better luminescence intensity.(3)Novel visible light driven Ho3+/Yb3+-Bi2WO6 photocatalyst was prepared by a simple hydrothermal method and a heat treatment process.Under visible light irradiation(?>420nm),the photocatalytic degradation efficiency of prepared photocatalyst for Rhodamine B(RhB)was investigated.The results showed that the photocatalytic activity was further improved owing to UC process,Ho3+/Yb3+-Bi2WO6 exhibited the excellent degradation efficiency(99.8%),which is 1.83 times higher than undoped Bi2WO6(54.5%).In addition,after four recycles of photodegradation of RhB,there was no great decrease for photocatalytic degradation rate of Ho3+/Yb3+-Bi2WO6,indicating that the compositions of Ho3+/Yb3+-BiZWO6 nanopowder was not photocorroded.Therefore,this study provides a better method that could obtain efficient and stable visible light photocatalysts.