| Abstract
| - A series of Eu3+-doped silica sol−gels are prepared under various conditions: (1) pH values of the sols arecontrolled at 3.0, 5.5, and 7.5; (2) the counterions of dopants are selected from acetate, chloride, and nitrateof europium (III) compounds; (3) two chelating agents, namely ethylenediaminetetraacetic acid (EDTA) andethylenediaminetriacetic (HEDTA) are used for complexing the europium (III) dopants; (4) a sol−gel matrixcontaining low O−H functionality is synthesized by using deuterated solvents (D2O and C2D5OD) and underan extremely dry N2 environment; and (5) a mixture of 1% of aluminum or antimony alkoxide and 99% ofsilicon alkoxide is adopted as precursors. The conditions that these differences have on the network structuresof a gel matrix are examined in order to determine the optimal conditions for the creation of structural defectsin an SiO2 network, generation of electron−hole centers and utilization of them to reduce Eu3+ to Eu2+during the sol−gel processing. Both differential scanning calorimetric (DSC) measurements and thermogravimetric and differential thermal analysis (TG/DTA) are employed to illustrate which gel samples are themost liquidlike and have the greatest cross-linking density. The results from thermoanalysis are then correlatedto the emission intensity and lifetimes of each Eu3+-doped sample. The relative emission intensity of Eu2+/Eu3+ gives the degree of conversion of Eu3+ to Eu2+ which is produced from the defect electron−hole pairgeneration. The absolute emission intensity of Eu3+ and Eu2+ is strongly quenched by the presence of OHgroups in xerogels and is shown to be enhanced by laser irradiation due to water evaporation. The resultsshow that a basic gel prepared by the mixed metal alkoxides most efficiently converts Eu3+ to Eu2+ becauseof its liquidlike nature, reduced cross-linking density, and low OH quenching.
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