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

Effects of silver ion-exchange on optical absorption (OA) and photoluminescence (PL) spectra of a cerium doped soda-lime-silicate glass at room temperature are investigated. The optical spectra are described in terms of the characteristic transitions 4f?5d originated in Ce³⁺ ions placed mainly in two different sites of the glass network. As Ag⁺ ions are introduced into the cerium doped glass, they are reduced to elementary silver (Ag⁰) which are favoured by the reaction Ce³⁺+Ag⁺→Ce⁴⁺+Ag⁰. Then, the number of Ce³⁺ ions decrease inversely with depth from the surface contrarily to Ce⁴⁺ ions does, and elementary silver diffuses and aggregates to form nanoparticles. As a consequence of these changes, the OA spectra of exchanged samples increase substantially in the UV range and the luminescence decreases significantly. The high sensitivity of PL together with deconvolution analysis of spectra, however, allows us to detect changes in the excitation and emission spectra from the earlier stages of ion-exchange. This indicates that during the ion-exchange we deal with fast processes (much shorter than 1 min). In fact, transmission electron microscopy observations of samples from the glass exchanged for a short time as 1 min at 325°C show the presence of a scanty number of silver nanoparticles, which confirms this point. Furthermore, with increasing the length of time of ion-exchange, PL spectra exhibit a progressive red shift indicative in part of a covalence increment in the oxygen–cerium coordinated bonding. We observe no luminescence from Ag⁺ ions and other silver molecular species in contrast with other preliminary PL studies on silver ion-exchange in soda-lime-silicate glasses free of cerium. The effect is discussed on the basis of a supplementary increase in the number of Ce⁴⁺ ions mainly due to the reaction Ce³⁺+Ag⁺→Ce⁴⁺+Ag⁰, which prevents efficiently the luminescence of the silver centers.