Photoluminescence of mesoporous silica films impregnated with an erbium complex
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Transparent mesoporous silica films were prepared by sol-gel spin coating on silicon wafers at room temperature. An erbium complex, erbium tris 8-hydroxyquinoline (ErQ), was homogeneously impregnated into the pores of the mesoporous silica films, and its concentration was easily controlled by using a solution immersing technique. The ErQ-impregnated mesoporous silica films show a room-temperature photoluminescence at 1.5 m.
Erbium-doped material films have received growing interest over the last decade due to their multiple applications such as use in integrated lasers or amplifiers for telecommunications.1 Since planar optical amplifiers have a smaller interaction length with respect to erbiumdoped fiber amplifiers, higher erbium concentration is required to obtain a sufficient optical gain. However, high doping levels of erbium quench the fluorescence emission and reduce the performance of the amplifier. Especially, the clustering of Er3+ ions is a main obstacle preventing concentration quenching because a silicabased inorganic matrix is fabricated by high-temperature processes such as flame hydrolysis deposition and chemical vapor deposition.2 To reduce concentration quenching, erbium ions should disperse uniformly on a molecular level. When Er3+ ions are surrounded by bulky organic ligands, the average minimum distance between Er3+ ions increases due to the steric hindrance. Thus, introduction of an erbium complex can be a solution to reducing concentration quenching. Er complex is generally used with a polymer matrix because of its solubility and the processing temperature. There have been several reports concerning room-temperature photoluminescence in polymer/Er complex systems.3,4 However, the polymer matrix is largely composed of a linear CH chain and thus large CH quenching can occur. Therefore, a general polymer matrix is not suitable to the incorporation of an Er complex. Theoretically, the most effective method for uniform dispersion is the periodic arrangement of erbium ions in a matrix when high doping levels of Er3+ ions are required. Thus, we selected mesoporous materials as the host matrix. Mesoporous materials were developed for constructing a periodic pore structure, which has pores of a few nanometers in size.5 They can also be made of various inorganic components, such as silica and alumina, which have low optical losses. J. Mater. Res., Vol. 18, No. 5, May 2003
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Recently, mesoporous materials were used for encapsulating organic dyes to prevent aggregation of the dye molecules.6 Impregnation of Er complex into mesoporous silica has some advantages over incorporation of Er complex in the matrix. First, the mesoporous silica has a periodic pore distribution such that the impregnated Er ions are expected to be uniformly dispersed. Moreover, the absorption cross section can increase compared to Er3+ ion by doping Er complex into a low loss silica matrix.7 Although the mesoporous film is fabricated through a high-temperature process, there i
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