The optical properties of windows, in a broad spectral range in the visible and infrared, play an important role in the energy efficiency of buildings. Windows must block mid-to-far infrared radiation that carries, following Planck’s Law, the energy radiated by surfaces inside the building. This enables energy escape to be mitigated, thus helping to reduce the power consumption of heating systems during the cold season. At the same time, windows must efficiently transmit sunlight in the visible range to enable good indoor vision without artificial lighting. Reaching such goals simultaneously requires windows to be suitably designed.

To achieve suitable optical properties, Mohammad Ali Shameli and coauthors report a theoretical work that proposes to use a thin-film coating consisting of a transparent dielectric matrix containing randomly distributed, optically resonant, metallic potassium microparticles. Thanks to the low optical losses of this material in the visible compared with other metals, and its stronger losses in the infrared, the coating could display a 50% transmittance of visible light, while the transmission of mid-to-far infrared light would be suppressed by more than 10 dB in the wavelength range from 6 to 16 micrometers. Bringing this solution to the real world requires fabricating the coatings. This will enable benchmarking their global specifications in comparison with already existing solutions.

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