Photocatalytic reduction of CO_2 using a novel upconvertion luminescence agent coated with TiO_2 photocatalyst

A novel upconvertion luminescence agent,CaF_2:Na_xAl_yF_(x+3y)(0.3x0.5,0y0.1) without rare-earth elements was prepared by using hydrothermal method.The fluorescence spectrum and time-resolved spectrum tests showed that it can transform visible light(575～630 nm) into ultraviolet light(295~350 nm).The emission intensity exhibited a rising process from the beginning and a decaying process after 15 ms,and the phosphorescence life time of the emission was greater than 18.0 ms.Additionally,a visible-light-driven photocatalyst,TiO_2/CaF_2:Na_xAl_yF_(x+3y),is prepared by the ultrasonic dispersion and annealing methods for photocatalytic reduction of CO_2.The surface morphology of the samples was observed using the scanning electron microscopy(SEM),and the upconvertion luminescence mechanism of the CaF)2:Na_xAl_yF_(x+3y) has been discussed based on the tests results of X-ray diffraction and fluorescence spectrum.The experimental results indicated that the visible light(λ515 nm) catalytic activity of TiO_2 could be initiated under the existence of CaF_2:Na_xAl_yF_(x+3y).The mechanism of photocatalytic reduction of CO_2 on TiO2/CaF_2:Na_xAl_yF_(x+3y) was proposed as well.