Evolution and Eu3+ Doping of Sol−Gel Derived Ternary ZnxTiyOz - Nanocrystals

Alloyed Zn x Ti y O z nanostructures were prepared by a thermal condensation process employing ethanolic mixtures of zinc acetate dihydrate and titanium alkoxide, without additional use of additives. It has been found that the nanocrystal growth takes place at temperatures above 350 °C yielding cubic spinel Zn 2 TiO 4, cubic ZnTiO 3, or hexagonal ilmenite ZnTiO 3 . Their preferential appearance and size tuning between 5 and 80 nm was possible by varying the starting sol condensation conditions, Zn/Ti-ratio and sintering temperature. The electronic transitions in these ternary oxide semiconductor nanocrystals were observed at photon energies between 3.6 and 3.8 eV that reflects the presence of a wider optical gap than that known for the corresponding binary oxides ZnO and TiO 2 . We also noticed a strong influence of Eu 3+ doping on the resulting structural and optical properties. Despite its large ionic size, this lanthanide efficiently intervenes in the evolution process by blocking the nanocrystal growth and the cubic-to-hexagonal transformation in ZnTiO 3 . Its preferential incorporation into spinel phase is manifested by the activation of a strong red intrashell fluorescence and a significant Stark splitting of the 5 F J states. The comparison of the spectral response and asymmetry ratio values deduced from the experimental Eu 3+ luminescence data collected on structurally similar Zn 2 TiO 4 and ZnTiO 3 nanophases suggests the hypothesis that cubic ZnTiO 3 has a structure of an inverse defect spinel. Our study has not confirmed the existence of the previously reported and often recalled defect spinel Zn 2 Ti 3 O 8 .