Structure and Optical Properties of Nanocomposites Prepared by the Incorporation of Organic Dyes into a SiO2 and SiO2–PMMA Glassy Matrix*

Electronic spectra of nine different types of organic colorants embedded in three different matrices (sol–gel SiO2 , PMMA, and SiO2–PMMA) were studied experimentally with the use of optical absorption, photoluminescence excitation, and emission techniques, as well as fluorescent microscopy and atomic force microscopy. We found a distinct set of energy levels for each type of dye. The type of matrix and the degree of aggregation of the organic molecules have relatively small effects on the spectra, although their influence on the optical density of the material is essential. The character of the energy spectra is mainly related with the shape of the dye molecule. A quantum mechanical description of the electronic spectra of these molecules was made on the basis of the free electron molecular orbitals approach. The molecules were considered as two-dimensional potential wells with different shapes. The effect of boundary conditions on the energy spectra was studied. The direct solution of the Schrödinger equation shows a good theory–experiment correlation.