UV-VIS SPECTROSCOPICAL INVESTIGATIONS ON THE FORMATION AND DECOMPOSITION OF LIGAND PROTECTED SILVER CLUSTERS AND COLLOIDS IN AQUEOUS-SOLUTIONS IN PRESENCE OF PROTECTIVE COLLOIDS

The East chemical reduction of silver ions in aqueous solutions contai ning protective colloids leads to silver sols whose UV-visible absorpt ion spectra display cluster bands at 300 nm [Ag-9(+),Ag-3],340 nm [Ag- 5], 360 nm [Ag-7, big clusters consisting of any tens silver atoms] as well as colloid bands at 390 nm and 410 nm [plasmon absorption band o f metallic silver particles with a diameter around 4 nm, complexated b y Ag+ ions]. If the cluster growth is restrained (e.g. sodium polyacry late, lowered temperature) only the 340 nm band exists for a short tim e and, if exposed to air, it disappears completely. If the cluster gro wth is accelerated (e.g. raised temperature) in addition to the 340 nm band a weak 410 nm absorption maximum and a broad absorption region p eaking at 360 nm, occur. At admission of air at first the region peaki ng at 360 nm, and finally the 340 nm absorption band disappear. Simult aneously an absorption in the 420 nm to 570 nm range raises. In presen ce of gelatin only a stable plasmon absorption band at 390 nm occurs, shifting to 410 nm if exposed to air accopanied by raising of an absor ption in the 420 nm to > 600 nm range. It is concluded, that Ag-7 clus ters and/or bigger clusters with any tens silver atoms are the start p oint for a further growth to bigger metallic silver particles and-coll oids.