The Luminescence Properties Of YBO₃: Eu～(3+) Nanocrystal

Great attention has been paid to the nanosized material because of its unique properties in comparison with the bulk. Nano-science and technology will play an important role in the 21^st century. For the large surface to volume ratio in nanosized materials, the influence of surface effect cannot be negligible in understanding its spectroscopic properties.In this thesis, rare earth doped nanocrystals were prepared, spectroscopic properties were studied and compared to that in the corresponding bulk material, and the influence of the surface effect was discussed.Trivalent Europium ion has been successfully applied as a spectral probe for detecting local environment in various materials. YBO₃:Eu³⁺ nanoparticles were prepared via hydrothermal method. Particle sizes ranged from 30-80nm were obtained. By adjusting the pH value, the average size and morphology of the nanoparticles could be controlled. The samples were characterized by XRD and TEM. Spectra of YBO₃:Eu³⁺ nanoparticles at room temperature indicates that with the decreasing of the particle sizes the branch ratio I(⁵D₀-⁷F₂)/I (⁵D₀-⁷F₁) increases, thus makes the chromaticity varied. Besides, the luminescence intensity decreases, and new spectral lines may appear. These phenomena are all related to surface effect. As the particle size decreases, the number of the luminescent ions close to the surface increases, their energy level split differently with the ions near the particle center. As the site occupied by Eu³⁺ changes from the particle center toward the surface, local symmetry decreases. A large portion of the doped rare earth ions located at the sites with micro-environments affected by the surface, Such an influence could enhance the Judd-Offelt Ω₂ parameter, and hence increase the relative intensity of the Eu^{3+ 5}Do→⁷F₂ emission and improve the chromaticity of the red phosphor. The temperature dependence of the ⁵D₀→⁷F₁ emission spectra was also measured at different temperatures. The emission intensity decreases since the additional nonradiative transition path aroused by quench centers at the surface.