Cs+ substitution-enabled precision spectral engineering in Fe2+ doped phosphosilicate glass: Achieving high optical transparency and ultra-broadband thermal management for sustainable building integration

Energy-efficient windows are crucial for enhancing energy efficiency. However, developing novel window materials that simultaneously achieve high visible light transmittance, exceptional ultra-broadband near-infrared (NIR) shielding performance, neutral color appearance, long-term stability, cost-effectiveness, and sustainable production remains a formidable challenge. This study introduces a breakthrough material fulfilling all these requirements: ferrous ion-doped phosphosilicate glass (Fe 2+ -PSG), which emerges as a promising candidate for energy-efficient windows. Comprehensive characterization using UV–Vis-NIR transmittance/absorption spectroscopy and Raman spectroscopy reveals that Fe 2+ -PSG exhibits remarkable visible light transmittance of 83.7 ± 0.5%, a neutral color temperature of 6809 ± 53 K, and a high NIR shielding figure of merit of 1.80 ± 0.01. These exceptional properties primarily originate from the formation of colorless ferrous [FeO 6 ] units, influenced by phosphorus and cesium oxide incorporation. Moreover, Fe 2+ -PSG exhibits outstanding stability, retaining its optical performance for over 10 years under ambient conditions, and maintaining structural integrity after 24-hour immersion hot water (80 °C) and hot air (120 °C) exposures. These superior characteristics stem from unique structural modifications that modulate the crystal field splitting energy of Fe 2+ ions, enabling precise tuning of optical properties across the visible and NIR spectral ranges. Produced via a scalable, facile and low-cost melt-quenching process, Fe 2+ -PSG offers a feasible and sustainable solution for energy-efficient window fabrication. This innovation overcomes existing technological limitations and facilitates widespread practical applications.