Preparation And Luminescence Properties Of Rare Earth Ions Eu, Tb Doped The Unitary Or Binary System Of SiO₂ And TiO₂ Nano-materials

In this paper, the samples of SiO₂ with rare-earth Eu³⁺(Tb³⁺) doped have been prepared with the Stober Sol-gel method at first. The samples are sphericity nanoparticles with monodisperse and uniform size at a certain extent, which were investigated by transmission electron microscopy (TEM). The structure of the samples was examined by FT-IR and XRD. The results obtained in this study showed that the samples were in amorphous phase and SiO₂ net structure was still observed after annealling with the doped concentration of Eu³⁺(Tb³⁺). The luminescence properties of the samples was investigated by PL spectra indicating that nano-materials has lower efficient luminescence than bulk materials, but the concentration quenching has been improved in the nano-materials.In addition, A Stober Sol-gel (base-catalyst) and Sol-gel (acid- catalyst) methods have been used to prepare nano-materials TiO₂-SiO₂:Eu³⁺ in this paper. The structure of the samples was examined by FT-IR indicated the compound TiO₂ and SiO₂ have been reacted, forming the new chemical bond of Ti-O-Si, which also has been proved by TGA-DTA, XRD and SAED spectras. The TiO₂ disperse into amorphous phase of SiO₂ as lower proportion of TiO₂ / SiO₂, but the Si⁴⁺ will replace Ti⁴⁺ from phase of TiO₂ as higher proportion of TiO₂/ SiO₂. Radius of Eu³⁺(0.113nm) is larger than that of Ti⁴⁺ so that Eu³⁺ can't replace Ti⁴⁺ position but more evenly dispersed in the TiO₂ nano-crystalline, forming the bond Ti-O-Eu at the crystal interface of TiO₂. The samples catalyzed by acid after annealling from 300℃to 900℃(800℃, base-catalyzed) are still anatase phase that were investigated by XRD spectras, suggesting the bond of Ti-O-Si conducive to the stability of anatase phase and the samples have stability of anatase phase with perfect crystal under acid-catalyze. SEM and TEM of samples show that TiO₂-SiO₂:Eu³⁺ are sphericity nanoparticles with monodisperse and uniform size. From the excitation and emission spectras of samples, we obtained follow conclusion: First, there is emission peak of oxygen-vacancies at 469 nm that partly overlapped with the 7F0→5D2 transition of Eu³⁺, which changed the excitation wavelength from UV area to visible light. Second, the structure isoelectronic trap has been formed, as Si⁴⁺ into the TiO₂ lattice, replacing some of the Ti⁴⁺ position, and this structure is conducive to the dipole-electronic trasition of Eu³⁺ (5D0→7F2), Consequently the luminescence intensity of Eu³⁺ in compound-oxid is much higher than that in pure TiO₂. Third, the luminescence intensity of the samples catalyzed by acid is greatly strengthened and concentration quenching has been improved, compared to the samples catalyzed by alkaline. Fourth, the energy resonance transfer has been limited by nano-particles border due to the surface and interface effects, so the transfer- frequency of excitation energy descreased from luminescence center pass to quenching center, but increasing between luminescence centers. Therefore, we often get higher concentration in nano-materials doped with RE³⁺ than bulk materials.In all, there will be much potential value in nano-materials because of these special properties.