Trivalent iron (0.21-1.21 mol% equivalent Fe2O3) was introduced into s
ilica gel monoliths prepared via sols obtained from tetraethyl orthosi
licate and metal salts at different final sol pH values. The UV-visibl
e spectra indicated a change from an octahedral to tetrahedral Fe3+ en
vironment as the pH increased. An electron paramagnetic resonance spec
tral resonance at g = 4.22 appeared, in addition to that at g = 2.0, a
s the final pH increased. The resonance at g = 4.22 was also observed
for some gels upon heat treatment. Colloidal precipitation of Fe2O3 wa
s noted with increase in cation concentration and temperature of heat
treatment. The effects of processing on fight transmission of gels wer
e measured. The results indicated several processing conditions leadin
g to total cut-off of ultraviolet light through the doped gel monolith
s.