Influence of glass matrix SiO2–B2O3–NaF on the formation of NIR-shielding functional units in energy-saving window glasses

This work presents the influence of glass matrix SiO 2 –B 2 O 3 –NaF on the formation of near-infrared (NIR)-shielding functional units in energy-saving glass windows. The structural analyses by XRD , XPS , and Raman confirmed that the NIR-shielding performance is insensitive to SiO 2 or B 2 O 3 glass network formers but is significantly impacted by the concentration of NaF. This is because the presence of a reasonable amount of NaF provides the much-needed sodium for the formation of NIR-shielding functional units Na 5 W 14 O 44 but too much NaF (>22 mol.%) can inhibit the formation of Na 5 W 14 O 44 by transforming the W– O –W chain in the interconnected [WO 6 ] and [WO 4 ] polyhedrons into W–O - bonds. By adjusting NaF to the optimal level (16 mol.%) and adding only a small amount of H 2 WO 4 (1.9 mol.%) as the tungsten source in the raw materials, excellent optical properties and thermal insulation performance have been achieved in the produced bulk glass, with a high transmission of 65.8% at 550 nm in the visible light region and a low transmission of 6.6% at 1550 nm in the NIR region. This performance is much better than soda lime glass and ITO glass and is comparable to cesium tungsten bronze-based membrane coated glass. This study paves a way for glass composition design to achieve high NIR-shielding performance with the minimum amount of tungsten source, leading to cost-effective glass fabrication and enhanced mechanical strength of energy-saving glass windows.