The mechanisms responsible for spontaneous silver precipitation in silver-d
oped sol-gel materials are identified. The chemistry of the solvent phase i
s found to be the critical factor in controlling this phenomenon. The addit
ion of HCl as catalyst leads to the formation of AgCl and subsequent format
ion of silver upon light exposure. Another factor leading to silver precipi
tation is the reducing capability of methanol radicals. Silver precipitatio
n is inhibited by simply washing out the pore solvents by a solvent exchang
e method.