Photocatalytic Properties of Nanocrystalline TiO2 coupled with Up-Conversion Phosphors

NaYF4:(Yb3+, Er3+) up-conversion phosphor was synthesized with the combustion method and coated with TiO2 nanoparticles by means of a sol-gel technique. Emission peaks of the up-conversion phosphor were located at 523, 544 and 655 nm under irradiation with a 980 nm infrared (IR) dot laser light with 40 mW. TiO2-coated NaYF4:(Yb3+, Er3+) phosphor showed similar emission peaks with reduced intensities. The photocatalytic activity of the TiO2-coated up conversion phosphor particles was investigated based on the degradation of aqueous methylene blue (MB) solution under irradiation with a 200-W visible light of wavelength > 410 nm. TiO2-coated NaYF4:(Yb3+, Er3+) phosphor particles showed enhanced photocatalytic activity compared with pure TiO2 powders. The mechanism for enhanced photocatalytic activity was explained in relation to the energy band structure that exists at the interlayer between the NaYF4:(Yb3+, Er3+) phosphor and TiO2 nanoparticles.