Optical Limiting in Fullerene Materials
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limiters into optical systems would extend the dynamic ranges of the sensors, allowing them to continue to function under harsher conditions. Optical limiting is a relatively "young" science [1]. A dozen inorganic clusters, organometallic complexes, and organic dyes have been found to possess optical limiting properties [27], most of which, however, have poor processibility, which significantly "limits" the scope of their practical applications. Buckminsterfullerene is such a typical example: it effectively limits strong laser pulses [8] but has very poor tractability. One approach to solve C60 's processibility problem is to incorporate the buckyball chemically into processable polymer and glass matrixes. How the chemical reactions involved affect C60's materials properties is a question of fundamental importance, which, however, has seldom been addressed. We have investigated the optical limiting behavior of a number of fullerene derivatives, polymers, and glasses prepared by different synthetic routes, including amination, polymerization, and sol-gel reaction, and have found that different chromophores attached to C60 alter the buckyball's limiting performance in quite different ways. We report here the structure-property relationships we observed for optical limiting in the fullerene materials with different molecular structures. EXPERIMENTAL All the experimental details including the procedures for preparing the fullerene materials and the set-ups for measuring their optical limiting properties can be found in our US Patent applications filed in 1995 and 1996 [9-10]. In brief, the C60 -PCs were prepared by irradiating C6 0/PC solutions with a UV lamp (UV-induced), by gently warming C60 /PC solutions in the presence of AIBN (AIBN-initiated), or by AICl 3 -catalyzed reactions of C 60 with PC (A1C1 3 69 Mat. Res. Soc. Symp. Proc. Vol. 479 01997 Materials Research Society
catalyzed). The C6 0 -PVCs were prepared by employing the AIBN-initiated fullerenation reaction. The C60-PSs, -PMMAs, and -CR-39s were prepared by radical copolymerizations of C60 with the corresponding vinyl monomers. The HxC 6 0(NHR)x derivatives were prepared by amination reactions of C6 0 with the corresponding amines. The 1-3/SIO 2 glasses were prepared by acid-catalyzed sol-gel reactions of tetraethyl orthosilicate (TEOS) in the presence of 1-3, while the 4-SIO 2 glasses were prepared by sol-gel reactions of 4 with TEOS using propyltrimethoxysilane (PTMS) or 2-hydroxyethyl methacrylate (HEMA) as drying-control chemical additives (DCCA). All the fullerene materials were carefully purified and fully characterized using spectroscopy methods. The optical limiting experiments were performed at 532 nm with 8 ns pulses from a frequency-doubled Q-switched Nd:YAG laser (Quanta Ray GCR-3) operating in a near-Gaussian transverse mode with a repetition rate of 10 Hz. All the limiting data were taken from the mean values of at least 10 shots. For the optical stability tests, the samples were continuously irradiated by the laser pulses of a nearly-cons
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