Improvement of the far-infrared optical property for glasses by plasma-assisted dispersion of fluorocarbon species into the shallow surface

Owing to global warming together with the demands for thermal energy storage in diverse fields, there is demand for transparent glasses achieving reflection of the short-wave far-infrared (IR) light from solar radiation while also absorbing the longer wavelength part. Here, we performed the plasma-assisted ion implantation using a desktop-type low-pressure fluorocarbon plasma generator system to improve the optical properties of transparent soda-lime glasses. Investigations using positron annihilation techniques for the plasma-treated glass demonstrated that the fluorocarbon species occupy the sub-nanoscale interstitial sites available in the glass network of the soda-lime glass as the intrinsic open spaces, forming an implantation layer in the shallow-surface region around a depth of 50 nm. As revealed by optical spectroscopy, the subsurface layer, due to the implanted fluorocarbon species, significantly cuts off the short-wave far-IR light around a wavelength of ∼3 µm and also acts as the absorber of the longer wavelength region from 7 to 12 µm. Plasma treatment could be a promising tool to improve the optical properties in the IR light region for various materials.