Role of Ag Ions in Determining Ce Optical Properties in Fluorophosphate and Sulfophosphate Glasses.

Understanding the interactions among dopant species and the role of the host lattice is of fundamental importance for the chemical formulation of optically active glasses. Here, we consider the archetypal dopant pair of Ag-Ce in complex fluorophosphate (PF) and sulfophosphate (PS) matrices, in which variable bonding environments and ligand selectivity exert distinct effects on dopant properties. The addition of Ag to PF glasses blue-shifts the ultraviolet (UV) cutoff wavelength of Ce and enhances its photoluminescence (PL) intensity. In PS matrices, the exact opposite effect is observed: red-shifting the UV cutoff and lowering the PL intensity. No Ag-Ag pairs or cluster species were found in either matrix material; however, in PS, such clustering could be triggered by secondary broad-band UV-visible irradiation. The optical properties of Ag-Ce-codoped glasses are a result of the ionocovalent character of the Ag-O-Ce bond, the cross-relaxation process between Ag and Ce, and the redox ratio of Ce/Ce. In the PF glasses, the enhancement of the Ce PL intensity is due to energy transfer from Ag to Ce and a redox shift from Ce to Ce. The more covalent Ag-O-Ce interactions in the PS series decrease the Ce/Ce ratio. Moreover, photoinduced Ag clustering is facilitated in the more covalent environment, which indicates that glasses commonly used for Ag nanoparticle formation, such as silicate glasses, also possess more covalent Ag-O bonding.