Effective enhancement of Bi near-infrared luminescence in silicogermanate glasses via silver–sodium ion exchange

The Ag ions were introduced into the Bi doped silicogermanate glasses by Ag+ for Na+ ion exchange method. After ion exchange, the X-ray photoelectron spectroscopy (XPS) spectrum implied the Ag ions were mainly in ionic form (Ag+) within the glasses. With the increase of the Ag+ concentration, more relaxation of local structure would be induced at the non-bridging oxygen (NBO), meaning that the network gave more negative sites. Bi3+ ions could be reduced to lower valence states of Bi containing Bi near infrared (NIR) active centers with the depolymerization of glass network, resulting in the enhancement of the Bi NIR luminescence. After heat treatment, the XPS, absorption spectra and transmission electron microscope (TEM) images revealed Ag nanoparticles (Ag NPs) formed in glasses. With the increase of the Ag NPs concentration, more NBOs released from Ag+, which led to reduce more Bi3+ ions to lower valence states of Bi containing Bi NIR active centers, resulting in further enhancement of the NIR luminescence. Our research may extend the understanding of structural modulation in Bi valence states and offer a valuable way to enhance the NIR luminescence of Bi in glasses.