Doping Sodium Tungsten Bronze-Like (Na 5 W 14 O 44 ) Near-Infrared Shielding Functional Units in Bulk Borosilicate Glasses for Energy-Saving Window Applications.

Tungsten bronze is an effective near-infrared (NIR) shielding material for fabricating energy-saving smart windows. While high-performing NIR-shielding glasses can be fabricated by coating a tungsten bronze film on window glasses, these glasses suffer a short lifespan due to the adhesion and degeneration of film. In this work, we show that tungsten bronze-like material Na 5 W 14 O 44 can be distributed in the bulk glass matrix during the facile melt-quenching glass fabrication process under an air atmosphere, overcoming the limitations of film-based glasses. X-ray diffraction, Raman spectroscopy, and X-ray photoelectron spectroscopy confirmed the presence of tungsten bronze-like Na 5 W 14 O 44 functional units in the SiO 2 -B 2 O 3 -NaF glass matrix. The addition of a small amount of H 2 WO 4 and Sb 2 O 3 is critical for the formation of Na 5 W 14 O 44 functional units because H 2 WO 4 provides W for Na 5 W 14 O 44 , and Sb 2 O 3 acts as a reducing agent that helps the formation of W 5+ in Na 5 W 14 O 44 under an air atmosphere. Furthermore, the NIR-shielding ability can be tuned by adjusting the concentration of Sb 2 O 3 in the range of 0-1.5 mol % and of H 2 WO 4 in the range of 4-6 mol %. The optimized composition containing 1.25 mol % of Sb 2 O 3 and 5 mol % of H 2 WO 4 exhibits excellent NIR-shielding ability (Δ T = 62.8%), high visible light transmittance ( T max = 67.7%), and excellent thermal insulation. This performance is comparable to cesium tungsten bronze film-based glasses and much better than soda lime glass and ITO glass under sun irradiation. This study sheds light on fabricating energy-saving windows in a simple and cost-effective way with flexibility for fine tuning of NIR-shielding performance.