Luminescence Properties of Eu- and Mg-Codoped Sol-Gel 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 2.0？mol% 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 614？nm and 590？nm 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. 1. Introduction The sol-gel technique that involves the simultaneous hydrolysis and condensation reaction of the metal alkoxide is one of the most common methods of synthesizing silica nanoparticles [1]. It is an efficient technique for the synthesis of phosphors due to the good mixing of starting materials and relatively low reaction temperature resulting in more homogenous products than those obtained by the solid-state reaction synthesis method. Lanthanide ions have been employed as optically active centers due to unique electronic configurations, which result in special spectroscopic properties. Thus, these ions have played prominent role in lighting and light conversion technologies. However, their optical properties, not only depend on the nature of the active ions, but also on the site environment provided by the host lattice. Rare earth ions or lanthanides in a silica host matrix have a wide range of applications in active materials for solid-state lasers, amplifiers, electro-optic devices and sensors because of their well-known fluorescing property [2–9]. In particular, europium is of great interest since it displays both a sharp luminescence in the orange-red as trivalent ion and a broad band one from UV to blue-green in its divalent configuration. Eu3+ ions are widely used as activators in various materials for their