In order to use the sunlight efficiently, a new titanium dioxide (TiO2) photocatalyst with high catalytic activity under visible light irradiation was prepared with sol-gel technique. In this work, an upconversion luminescence agent, crystallized Er3+: Y3Al5O12, was synthesized and its characters were determined. It is found that this crystallized Er3+:Y3Al5O12 can emit three upconversion fluorescent peaks below 387 nm under the excitation of 488 nm visible light. Hence, this upconversion luminescence agent could transform visible light into ultraviolet light, which could satisfy the genuine requirement of TiO2 photocatalyst. Additionally, the upconverison mechanisms were also discussed. Meanwhile, the prepared TiO2 photocatalysts coating upconversion luminescence agent were characterized by powder X-ray diffraction (XRD) and transmission electron microscopy (TEM). The photocatalytic activity of prepared TiO2 powder was tested through the degradation of congo red in aqueous solution as a model compound under visible and sunlight irradiation. To affirm the complete mineralization, the ion chromatography and total organic carbon (TOC) were used to observe the mineralized anions and organic residues. The experimental results proved that the prepared TiO2 photocatalyst coating crystallized Er3+:Y3Al5O12 behaved much higher photocatalytic activity under visible light and sunlight irradiation, and was able to decompose the congo red in aqueous solution efficiently. Therefore, this method may be envisaged as a novel technology for treating dyes wastewater using solar energy, especially for textile industries in developing countries. (c) 2007 Elsevier B.V. All rights reserved.