Energy-saving glasses based on sodium tungsten bronze-like (Na5W14O44) functional units: Facile synthesis, NIR-shielding performance, and formation mechanism

Near-infrared (NIR)-shielding glasses for energy-saving window applications were prepared by forming sodium tungsten bronze-like (Na 5 W 14 O 44 ) functional units in the 29SiO 2 –43B 2 O 3 –28NaF glass matrix. The glasses were synthesized by a facile melt-quenching process where 4–8 mol.% H 2 WO 4 was added as the W source. The optimal glass was produced using 6 mol.% H 2 WO 4 , which had a low NIR transmission of 15.4% and a high visible light transmission of 59.8%. The possible mechanism for the formation of Na 5 W 14 O 44 in glasses were discussed based on XRD , Raman, XPS , XANES and EXAFS characterization of the glass samples, the glass samples after further crystallization, and the samples produced by staged heating of the starting materials. Crystalline or amorphous Na 5 W 14 O 44 formed during heating partially due to the protection by molten B 2 O 3 . Subsequently, amorphous Na 5 W 14 O 44 clusters are present in the glass acting as NIR-shielding functional units. This study sheds a light on further development of non-film-based and highly efficiency energy-saving windows.