Journal of Sol-Gel Science and Technology 26, 625–628, 2003 c  2003 Kluwer Academic Publishers. Manufactured in The Netherlands. Reverse Saturable Optical Absorption of C 60 , Soluble Methanofullerenes, and Fullerodendrimers in Sol-Gel Mesoporous Silica Host Matrices Y. RIO AND D. FELDER Institute de Physique et Chemie des Mat´ eriaux de Strasbourg (Unit´ e Mixte 7504, CNRS-ULP), 23 rue du Loess, 67037 Strasbourg, Cedex, France G. KOPITKOVAS Institut of Materials Science and Applied Research, Vilnius University, Saulet ˙ ekio 10, Lithuania A. CHUGREEV Ioffe Physical-Technical Institut, Politekhnicheskaja 26, 194021 St. Petersburg, Russia J.F. NIERENGARTEN, R. L ´ EVY AND J.L. REHSPRINGER ∗ Institute de Physique et Chemie des Mat´ eriaux de Strasbourg (Unit´ e Mixte 7504, CNRS-ULP), 23 rue du Loess, 67037 Strasbourg, Cedex, France Abstract. Porous sol-gel glasses with various pore size distributions are prepared and either impregnated with pure C 60 or soaked with methanofullerenes or fullerodendrimers derivative solution. Induced absorption or “reverse saturable absorption” (RSA) has been studied in both types of solid materials. The samples impregnated by pure C 60 mainly contain well-dispersed fullerene molecules. Unlike crystalline films of C 60 , their absorption dynamics can be well described by a 5-level model, developed for non-interacting C 60 -molecules in solutions. Methanofullerene samples, on the other hand, show signs of micellar aggregation and therefore RSA dynamics, which are influenced by solid state effects. Fullerodendrimers derivatives lead to the highest quantum yield. Keywords: reverse saturable absorption, fullerene compounds, induced absorption, optical limiting 1. Introduction The protection of sensors or the human eye against intense pulsed laser sources is a field of growing inter- est. As these sources are no longer limited to single- wavelength emission, the use of simple colored filters for protection is no longer possible and one has to use broadband limiting devices. At low light intensi- ties, such a device should show a high transmission, which should rapidly decrease when the incoming flu- ence reaches a dangerous level for either the sensor or the human eye. For fluence values of about 1 J/cm, ∗ To whom all correspondence should be addressed. which are very easily achieved for the whole visible spectrum in the output of modern laser systems, ir- reversible damages can be obtained. An optical lim- iting device for protection against such laser sources has to satisfy several requirements. First, a low thresh- old value for the onset of decrease of transmission. Furthermore, the maximum transmission changes are of great importance, which means that at dangerously high fluences the transmission should drop as low as possible. The limiting process should show a very fast risetime. In addition the transmission at low light in- tensity should be as high as possible. Last but not least, there are also several practical aspects to be consid- ered, such as high mechanical and chemical stability,