Cerium doped soda-lime-silicate glasses: effects of silver ion-exchange onoptical properties

Effects of silver ion-exchange on optical absorption (OA) and photoluminesc ence (PL) spectra of a cerium doped soda-lime-silicate glass at room temper ature are investigated. The optical spectra are described in terms of the c haracteristic transitions 4f <----> 5d originated in Ce3+ ions placed mainl y in two different sites of the glass network. As Ag+ ions are introduced i nto the cerium doped glass, they are reduced to elementary silver (Ag) whic h are favoured by the reaction Ce3- + Ag+--> Ce4+ + Ag-0. Then, the number of Ce3+ ions decrease inversely with depth from the surface contrarily to C e4+ ions does. and elementary silver diffuses and aggregates to form nanopa rticles. As a consequence of these changes, the OA spectra of exchanged sam ples increase substantially in the UV range and the luminescence decreases significantly. The high sensitivity of PL together with deconvolution analy sis of spectra, however, allows us to detect changes in the excitation and emission spectra from the earlier stages of ion-exchange. This indicates th at during the ion-exchange we deal with fast processes (much shorter than 1 min). In fact. transmission electron microscopy observations of samples fr om the glass exchanged for a short time as 1 min at 325 degreesC show the p resence of a scanty number of silver nanoparticles, which confirms this poi nt. Furthermore. with increasing the length of time of ion-exchange, PL spe ctra exhibit a progressive red shift indicative in part of a covalence incr ement in the oxygen-cerium coordinated bonding. We observe no luminescence from Ag` ions and other silver molecular species in contrast with other pre liminary PL studies on silver ion-exchange in soda-lime-silicate glasses fr ee of cerium. The effect is discussed on the basis of a supplementary incre ase in the number of Ce4+ ions mainly due to the reaction Ce3+ + Ag+--> Ce4 + + Ag-0. which prevents efficiently the luminescence of the silver centers . (C) 2001 Elsevier Science B.V. All rights reserved.