금속이온을 국소적으로 밀집하게 첨가한 TiO₂ 나노입자의 상전이와 분광학적 특성

Abstract

Metal ion doped and pure TiO2 nanoparticles were prepared by the reverse micelles and solvothermal processes. Mn, Co, Ni, Fe, Cr, Pb, Eu, and Tb ions had been doped in TiO2 nanoparticles and the doping ratios were 2% for all the metal ions. Their crystalline structure, surface morphology, and the phase transformation of TiO2 under the annealing process had been investigated by XRD, ESR, and TEM measurements. The anatase phase of the pure TiO2 began to transform into rutile phase at 750℃ and fully converted at 850℃ with the crystalline size of about 50nm. It had been observed the doped Mn and Co ions promoted the phase transformation from anatase to rutile and enhanced the grain growth, whereas Eu and Tb ions prevented phase transformation and inhibited grain growth under the annealing processes. The Eu, Tb doped TiO2 were not transformed into rutile at even 900℃ and crystalline grains grew more slowly than the pure ones. Co, Ni, Pb, Eu, Tb doped TiO2 produced the new products such as CoTiO3, NiTiO3, PbTi3O7, Eu2Ti2O7, Tb2Ti2O7 respectively, at the beginng temperatures of phase transformation. The spectroscopic characteristics of the Eu doped TiO2 nanoparticles which were synthesized by core-shell and solvothermal processes were studied. The critical doping amount of the concentration quenching was 20%, much higher than that of the dilutely doped materials. The photoluminescent spectra of these nanostructured materials were broad and there were no excitation spectra caused by the CTB and host band absorptions. They showed the luminescent characteristics of the materials which the Eu3+ ions were confined and concentrated at the small area. In the relaxation processes the excited Eu3+ ions were deexcited by the energy migration processes.