Glass network engineering enables efficient nir cut-off in Cu²⁺ blue glasses

Near-infrared (NIR) cut-off filters play a key role in imaging systems by blocking NIR interference on CMOS sensors, thereby preventing image ghosting and distortion. However, current commercial Cu²⁺-doped blue glasses struggle to balance high visible transmittance with complete NIR cut-off because of the uncontrolled formation of Cu⁺ and Cu²⁺ and the difficulty of regulating the Cu²⁺ ligand field. Herein, we propose a network-engineering strategy to modify the fluorophosphate glass network through alkali-metal (AM) doping. Large-size AM ions in the glass provide high optical basicity and an oxidizing atmosphere, resulting in a Cu²⁺/Cu⁺ ratio as high as 29.87. Meanwhile, they regulate the glass network structure to reduce the octahedral distortion of the CuO₄F₂ unit, leading to a redshift of the NIR cut-off wavelength. As a result, the as-prepared blue glass exhibits both high visible transmittance and efficient NIR cut-off, outperforming commercial counterparts. Images captured using the present blue glass show higher saturation and more realistic color reproduction without NIR-light interference. This work provides a new strategy for addressing key bottlenecks in commercial blue glasses and offers an alternative material for advanced imaging.