Controllable Synthesis And Spectral Characteristics Of Eu³⁺ Doped TiO₂Micro/Nanomaterials

In recent years, rare-earth (RE) ions doped materials have attracted a greatamount of interest due to their unique optical properties and are used as lasers, opticalfibres, high-performance luminescent devices, catalysts, time-resolved fluorescencelabels for biological detection, and other functional materials. It is well known thatthe luminescence efficiency of materials depends on the interaction between rareearth ions and the host. Moreover, the composition and microstructure of the hostplay an important role in controlling the chemical, physical, optical, and electronicproperties of the rare earth ions doped materials. Due to its low cost, hightransparency in the visible-light region, and good thermal and chemical properties,TiO2is a promising host material for RE ions and has potential applications in thefield of luminescent material. In our work, TiO2was used as the host, and uniformEu3+-doped TiO2nanotubes, solid microspheres, and core-shell microspheres weresuccessfully prepared through a simple solvothermal process. Modern analysistechniques including scanning electron microscopy (SEM), transmission electronmicroscopy (TEM), X-ray diffraction (XRD), thermogravimetric analyzer (TGA),and fluorescence spectrophotometer were used to investigate the characteristics of theas-prepared materials. Moreover, we studied the formation mechanisms of theas-synthesized samples and the effects of the morphology on the luminescentproperties in detail. The main research results in our work are summarized asfollows： 1、Uniform TiO2:Eu3+nanotubes have been successfully prepared through asimple solvothermal process with carbon nanotubes (CNTs) as templates, free of anysurfactant or catalyst. The as-obtained TiO2:Eu3+nanotubes with a pure anatase phaseare uniform in size and distribution. The TiO2:Eu3+nanotubes have an average outerdiameter of ca.40nm and an average inner diameter of ca.24nm, and the length isabout5~10μm. The synthesis process of TiO2:Eu3+nanotubes is briefly composed oftwo steps. At first, the carbon nanotubes templates were coated with a homogeneousTiO2layer by solvothermal method. Secondly, the TiO2:Eu3+nanotubes weresuccessfully synthesized by the calcination of carbon nanotubes. The luminescentspectrum shows that TiO2:Eu3+nanotubes exhibit a strong red emission due to the f–ftransition of Eu3+ions, which may find potential applications in the fields of lighting,displays, and biomedicine.2、 Uniform and monodisperse TiO2:Eu3+microspheres were successfullyprepared by a facile one-step solvothermal method using polyethylene glycol (PEG)as the soft template and ethanol as the solvent. The diameter of the as-synthesizedTiO2microspheres is approximately2.0~2.5μm. The dosage of ethanol in the systemhas a remarkably impact on the morphology of the TiO2:Eu3+microspheres. When thedosage of ethanol is18mL, the as-prepared samples are almost entirely composed ofsolid TiO2microspheres with smooth surfaces. When the dosage of ethanol rises to30mL, the as-obtained products contain a large number of core-shell structured TiO2microspheres with rough surfaces. This is mainly due to the different hydrolysiskinetics of tetrabutyl titanate. Under UV light excitation, the TiO2:Eu3+microsphereswith two kinds of morphology exhibit the red emission. In addition, the luminescenceintensity of the TiO2:Eu3+solid microspheres is stronger than that of the TiO2:Eu3+core-shell structured microspheres, which is due to less defects of the TiO2:Eu3+solidmicrospheres with smooth surfaces. Furthermore, this method is a facile, simple, andgreen route for the synthesis of rare-earth ion doped materials.