Optical processes in PMMA, SiO2, and hybrid organic-inorganic sol-gel films colored with rhodamine 6GDN

The sol-gel technique was used to incorporate rhodamine 6GDN (Rh 6GDN) into thin layers of SiO2 and into an organic-inorganic hybrid matrix (OIHM). The OIHM is composed of a mixture of SiO2 and an acrylic copolymer. The Rh 6GDN was also incorporated into poly(methyl methacrylate) (PMMA) matrices. To investigate the influence of the different matrices on the optical behavior of the Rh 6GDN-colored layers on glass substrates, the optical absorption and photoluminescence were measured and analyzed. The absorption spectra show the presence of two main bands related to the monomer and dimer absorption, the relative intensity of these band depends on the type of matrix and on the hydrolyzation/condensation time. The strongest luminescence intensity was observed when the dye was embedded in the PMMA matrix; it was 20% larger than that observed in the OIHM layers. The weakest luminescence corresponds to the dye in the SiO2 matrix, which was up to 90% below the values observed when PMMA matrices were used. The absorption spectra of the dye show an unusual intense band at a wavelength of 310 nm when it is embedded in the PMMA matrix. A band in this position, which emits at 308 nm, is desirable for excimer laser applications. A simple quantum mechanical model is used, which treats the dye molecules as two-dimensional potential wells for delocalized electrons. The model fits reasonably well the experimental optical transitions determined from absorption and fluorescence spectra.