The Research On Luminescence Properties Of ZrO₂ And La₂O₃ Doped With Rare-Earth

In this dissertation, after the investigation on the optical properties of nanocrystalline and bulk materials ZrO₂ and La₂O₃ doped with RE³⁺ ions and the calculation of the parameterΩbased on the Judd—Ofelt theory for the samples doped with Eu³⁺ ions, some conclusions taken are as follows:The optical properties of the two kinds of samples doped with RE³⁺ ions are associated with dopant concentration, preparation process and annealing temperature. To the different types of nanocrystal samples doped with Eu³⁺ ions, under continuous ultraviolet (394nm) irradiation, the strongest emission intensity change of different samples are as a function of irradiation time. However, those phenomena can not be observed in the bulk materials. In addition, under the identical conditions, the emission intensity of the bulk samples doped with Eu³⁺ ions is greater than that of corresponding nanocrystals. The fluorescent properties of the nanocrystalline samples doped with Eu³⁺ ions are related to aging time, the longer the aging time, the weaker the emission intensity. About the two kinds of nanocrystals doped with Er³⁺ ions, it is difficult for the excitation spectra to be observed. Under the identical measurement conditions, the upconversion of the nanocrystals is weaker than that of corresponding bulk materials, whose only green emission can be found under 380nm excitation in the codoped system of Yb³⁺ and Er³⁺ ions, in which the peak position at around 560nm is changeless and the peak position at about 545nm changes as Yb³⁺ ion concentration varies. Their upconversion emission intensity at 980nm excitation is strongly dependent on the Yb³⁺ ion concentration. The emission intensity ratio of green to red upconversion remarkably diversifies as Yb³⁺ ion content increases. Additionally, the parametersΩ₂ andΩ₄ are calculated on the basis of the Judd-Ofelt theory and emission spectra for the two kinds of samples doped with Eu³⁺ ion including nanocrystals and bulks. We obtained the rate of resonant energy transfer of ⁵D₀→⁷F₂ transition caused by the interaction between electric diple and electric multiple.At low dopant concentration, the rate of resonant energy transfer for the ⁵D₀→⁷F₂ transition between Eu³⁺ ions is smaller than that of its spontaneous emission. Accordingly, the energy transfer between Eu³⁺ ions can be neglected. By comparison with the optical properties of the two kinds of materials doped with identical rare earth ions, we found the emission intensities of La₂O₃:RE³⁺ was greater than those of ZrO₂:RE³⁺ under the identical conditions including dopant content, preparation methods and measurement condition, in other words, La₂O₃ is a better optical material than ZrO₂.