| With the increasing global environmental problems,there are more and more researches to solve environmental pollution problems and explore new energy sources.Although TiO2 possesses broad research and application prospects for its photoelectric properties,its response to solar light is limited by its absorption edge.How to solve this problem has drawn a great deal of attention in order to improve its photocatalytic activity or photoelectric conversion efficiency.The researchers have found the upconversion luminescent materials and TiO2 composites could improve extend the light response to the near infrared light,such as NaYF4:Yb,Tm and TiO2 composite.The application of NaYF4:Yb,Er in this field is restrained for its upconversion emission peak in the ultraviolet band is weak.To solve this problem,we has realized the response of NaYF4:Yb,Er/TiO2 to the near infrared light by doping nitrogen into TiO2 to extended its absorption edge and introduction of Zr4+,Hf4+ into NaYF4:Yb,Er to improve the upconversion luminescence intensity.This paper can be devided into three parts.Firstly,the modified P25 and NaYF4:Yb,Er composite was fabricated.The industrial product P25 was calcined with urea and to prepare nitrogen doped P25.The samples were characterized by XRD,SEM,EDS,upconversion emission spectroscopy and UV-Vis absorption spectroscopy.The RhB photocatalytic degradation test was carried out with xenon lamp with a 420nm filter.The degradation curves were recorded by UV-Vis spectrophotometer.We also use the electrochemical i-t curve to study its photoelectric conversion performance.The results showed that the photoelectric conversion performance of NaYF4:Yb,Er&P25(N)sample displayed best property.Secondly,we enhanced the upconversion luminescence properties of NaYF4:Yb,Er by Zr4+ co-doping,and fabricated the NaYF4:Yb,Er,Zr@TiO2 core-shell structure.In order to investigate the relationship between microstructure and upconversion characteristics and photoelectric properties,we used XRD,SEM,EDS,upconversion emission spectroscopy,UV-Vis absorption spectra and electrochemical i-t curves.From the results,it was found that the upconversion intensity all emission bands of the NaYF4 synthesized by hydrothermal method increased,when the Zr4+ codoping concentration rose to 6mol%,while Zr4+ co-doping also extended its lifetime.Zr4+codoping modulated the microstructure of NaYF4 and improve the asymmetry of the rare earth ions for the upconversion properties to be increased.We also found that the NaYF4:Yb,Er,Zr@TiO2 had a tight core-shell structure,and the codoping of Zr4+improved the photoelectric conversion ability of the composites.Thirdly,we synthesized Hf4+ codoping NaYF4:Yb,Er and NaYF4:Yb,Er,Hf@TiO2.In order to investigate the relationship between microstructure and upconversion characteristics and photoelectric properties,we used XRD,SEM,electron energy dispersive spectroscopy,upconversion emission spectroscopy,UV-Vis absorption spectra and electrochemical i-t curves.From the results,it was found that the upconversion intensity of the 378nm and 408nm emission of the NaYF4 increased to about to 12 times of that of the non-Hf4+ NaYF4,when the Hf4+ co-doping concentration rose to 6mol%,with extended lifetime.Compared with Zr4+,Hf4+ with similar ion radius anticipated the energy transition between lanthannide ions for their 4f orbitals and improved three-photon upconversion as a migrator for short band emission intensity to be enhanced obviously.Hf4+ co-doping can further improve the photoelectric conversion ability of the composite.In this paper,the influence of ion co-doping on the matrix structure of the upconversion material and the relationship between the matrix structure and the upconversion luminescence properties were investigated.The photoelectric effect of the upconversion material and the photocatalyst was also investigated,which may contribute to the future high performance upconversion luminescent materials and high performance photoelectric conversion composites. |
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