Sio <sub> 2 </ Sub> Gel / Rare Earth Doping Of Sio <sub> 2 </ Sub> Preparation And Properties Of Luminescent Materials

SiO₂ xerogel luminescent material, rare earth ion Eu doped and Eu, Dy co-doped sol-gel SiO₂ as the principal matrix luminescent xerogel and films were prepared. Kinds of complications influencing the luminescent properties of the materials and the luminescence mechanisms of the materials were discussed in order to look for a new path to prepare efficient luminescent material with SiO2 as the matrix.Using tetraethylorthosilicate Si(C₂H₅O)₄(TEOS) as starting material, SiO₂ xerogel luminescent material was fabricated by the hydrolysis and condensation of TEOS. The influences of the water content and the aging temperature on the gelation time of the SiO₂ were studied. The results showed that SiO₂ has the shortest gelation time when H₂O/TEOS=4(mole ratio) and the gelation time becomes shorter with the increasing of the aging temperature. FT-IR spectra showed that SiO₂ xerogel contains many structure defects such as Si-OH and Si-OR group, which indicated that SiO₂ xerogel has not formed integrity network structure.The photoluminescence property of SiO₂ xerogel was studied. Ultraviolet radiation band with a peak at 325nm and visible band with peaks at 422nm, 442nm, 590nm and 656nm respectively were observed in the emission spectra of SiO₂ xerogel. The emission peaks of the SiO₂ xerogel is related to the oxygen vacancy defects, the silica suspended bonds and the non-bridge oxygen centers formed in sol-gel progress. With the increasing of the annealing temperature, the net-structure of SiO₂ becomes integrated and the defects decrease, which make the PL intensity of the SiO₂ weaker.Using Eu(NO₃)₃ as the impurity, Eu ion doped SiO₂, SiO₂-Al₂O₃ and luminescent xerogel were prepared. The XRD analysis shows that SiO₂-Al₂O₃-B₂O₃the material annealed 850℃ has non-crystalline structure. The influence of the Eu³⁺ ions concentration and the annealing temperature on the PL intensity of Eu³⁺ were studied . The results show that the intensity of the red emission of Eu³⁺ ion has the maximum value as the xerogel annealed at 700℃. When the Eu³⁺ ion concentration changes in the range 0.1%¹.2%, the concentration quench is not observed. The PLspectra of 0.2%Eu: SiO2-Al2O3 annealed at 850℃ show a broad blue emission band of Eu2+ with two peaks at 440nm and 480nm and the red emission of Eu3+ is observed at the same time. Because the incorporation of Al3+ ion can increase the electron donation ability of oxygen in AIO4 tetrahedron around Eu3+ and reduces a part of Eu3+ ion to Eu2+.Boric acid (H3BO3) was added to the starting materials, the results showed that H3BO3 can increase the PL intensity of Eu3+ ions. The red emission intensity of Eu3+ increases with the increasing of boric acid content in the range H3BO3 / TEOS = 0.1 0.8.Eu, Dy co-doped SiO2-Al2O3-B2O3 xerogel were prepared. The broad blue emission band of Eu2+ becomes much stronger and the red emission of Eu3+ almost disappear in the sample annealed at 850°C. The energy transfer between Eu2+ and Eu3+ can be influenced by Eu, Dy co-doped. Because incorporating Dy3+ can decrease the probability of energy transfer from Eu2+ to Eu3+ and the energy transfer from Eu3+ to Dy3+ could occur.Eu: SiO2-Al2O3-B2O3 thin films coated on sodium-calcium glass substrate with red emission and Eu, Dy: SiO2-Al2O3-B2O3 films with blue emission were obtained by dip-coating method. The AFM pictures of the films indicated that there is no crackle on the surface of the film and the grains in the surface of the film are uniformly distributed. The size of grain is about 50⁶0nm.The influences of the concentration, the anneal technic and the layer number on the PL intensity of the films were studied. The result shows that the intensity of the 617nm emission peak of Eu3+ increases with the layers and then decreased when the layers exceed 9, it indicated that the film has the best PL intensity at certain thickness. The PL intensity of films with same layers increases with the Eu3+ ion concentration. The PL spectra of the Eu, Dy co-doped films annealed at 850℃ has two emission peaks located at 428nm and 468nm, which is due to the f-d transition of Eu2+.