Stabilization of ultra-small [Ag 2 ] 2+ and [Ag m ] n+ nano-clusters through negatively charged tetrahedrons in oxyfluoride glass networks: To largely enhance the luminescence quantum yields.

Herein, three different silver species were stably formed in SiO2 -Al2 O3 -B2 O3 -Na2 O-ZnF2 -CaF2 glasses and were identified by their characteristic luminescence bands: violet blue luminescence (Ag+ : 4d9 5s1 → 4d10 ), green white molecular fluorescence (molecule-like [Agm ]n+ , named ML-Ag) and orange molecular fluorescence ([Ag2 ]2+ pairs). Due to the relatively low aggregation degrees of [Agm ]n+ and [Ag2 ]2+ , non-radiative transitions were highly suppressed, and the PL quantum yields (QYs) of ML-Ag and [Ag2 ]2+ pairs reached 73.7% and 89.7%, respectively. The substitution of 0.5B2 O3 -0.5Na2 O with SiO2 promoted the partial reduction of Ag+ to Ag0 and the subsequent aggregation of Ag+ and Ag0 to form [Agm ]n+ (ML-Ag). The absence of Na2 O also resulted in an increasing amount of Ag+ -Ag+ pairs with closing interionic distance to form [Ag2 ]2+ in glass. According to the X-ray photoelectron spectra (XPS) and magic angle spinning (MAS) nuclear magnetic resonance (NMR) spectra, a solubility strategy and a charge compensation model were proposed to describe the transformations between different silver species. The formation of ML-Ag was further controlled via the solubility of Ag+ in glass, whereas [Ag2 ]2+ centers could be effectively produced by lowering the total amount of other competitive charge compensators, such as Na+ , or by introducing negatively charged [BO4 ]- , [AlO4 ]- , and [ZnO4 ]2- tetrahedrons into the glass matrix.