Luminescence Properties of Eu- and Mg-Codoped Sol-Gel SiO2 Glasses.

A series of SiO₂ nanostructures codoped with Eu³⁺; Mg²⁺ ions were obtained by a sol-gel method. The gels synthesized by the hydrolysis of Si(OC₂H₅)₄, Eu(NO₃)₃·6H₂O, and Mg(NO₃)₂ were heated in air at 600°C for 2 hours. Firstly, the total amount of Eu³⁺ ions was varied from 0 to 2.0mol% to investigate the effect of self-damping, while in the second case, the Eu³⁺ ions were kept constant in the experiment at 0.5 mol% total doping and Mg²⁺ ions varied. The samples were characterized by X-ray diffraction, TEM, EDS, and UV lamp-excited luminescence spectroscopy. The Eu³⁺ ions were homogeneously dispersed in the silica and interacting with the small (1-5 nm) amorphous silica matrix. Strong red emissions located at 614nm and 590nm for doped and codoped SiO₂ were observed from the UV light excitation at room temperature. The composition of around 1.25 mol% Eu³⁺ gave highest emission intensity. SiO₂; Mg²⁺ ions portray strongly enhanced emissions due to energy transfer from Mg²⁺ to Eu³⁺, which is due to radiative recombination. An increase in luminescence intensity was observed as the Mg²⁺-to-Eu³⁺ ratio increased for the range investigated. The results show Eu³⁺ ion is located inside or at the surface of disordered SiO₂ nanoparticles. [ABSTRACT FROM AUTHOR]