Knowledge Bank

Investigation of optical properties of small metal clusters consisting of a few atoms presents a great interest from the point of view of study the transition from molecular state of substance to the condensed one. These clusters are very unstable under the common conditions and special efforts for their stabilization and further investigation are required. Solid matrices of inert gases limited by the range of low temperatures are traditionally used for investigation of optical properties of small metal clusters. In the present work to obtain and stabilize silver clusters at room temperatures we have used different polycrystalline matrices on the basis of silica with different pore size, titanium dioxide, aluminium oxide, organic stabilizers, alumosilicate and zeolites of different types. Absorption band corresponded to small silver clusters was observed in the region of 320 - 340 nm depending on the kind of matrix used. The similar band for silver clusters was also observed in solutions by $Henglein1$, Mostafavi $et.al.2$. Oxidation of silver clusters in oxygen and air atmosphere was found to lead to disappearance of the band 320 - 340 nm and appearance of the 270 - 290 nm band (not typical for massive oxide). Depending on kind of matrix and preparation method the time of cluster oxidation changed from several minutes to the period of more than a year. It was obtained that silver clusters in mordenite with absorption band at 320 nm are the most stable. In this case the matrix of zeolite functions both as stabilizer of unstable clusters and means of estimation of their size. The absence of channels more than 0.7 nm in diameter in mordenite permits to suppose that the size of silver clusters does not exceed this value.