A series of Eu3+-doped silica sol-gels are prepared under various condition
s: (1) pH values of the sols are controlled at 3.0, 5.5, and 7.5; (2) the c
ounterions of dopants are selected from acetate, chloride, and nitrate of e
uropium (III) compounds; (3) two chelating agents, namely ethylenediaminete
traacetic acid (EDTA) and ethylenediaminetriacetic (HEDTA) are used for com
plexing the europium (III) dopants; (4) a sol-gel matrix containing low O-H
functionality is synthesized by using deuterated solvents (D2O and C2D5OD)
and under an extremely dry N-2 environment; and (5) a mixture of 1% of alu
minum or antimony alkoxide and 99% of silicon alkoxide is adopted as precur
sors. The conditions that these differences have on the network structures
of a gel matrix are examined in order to determine the optimal conditions f
or the creation of structural defects in an SiO2 network, generation of ele
ctron-hole centers and utilization of them to reduce EU3+ to EU2+ during th
e sol-gel processing. Both differential scanning calorimetric (DSC) measure
ments and thermogravimetric and differential thermal analysis (TG/DTA) are
employed to illustrate which gel samples are the most liquidlike and have t
he greatest cross-linking density. The results from thermoanalysis are then
correlated to the emission intensity and lifetimes of each Eu3+-doped samp
le. The relative emission intensity of Eu2+/EU3+ gives the degree of conver
sion of EU3+ to EU2+ which is produced from the defect electron-hole pair g
eneration. The absolute emission intensity of EU3+ and EU2+ is strongly que
nched by the presence of OH groups in xerogels and is shown to be enhanced
by laser irradiation due to water evaporation. The results show that a basi
c gel prepared by the mixed metal alkoxides most efficiently converts EU3to Eu2+ because or its liquidlike nature, reduced cross-linking density, an
d low OH quenching.