lightabsorbing

Light-absorbing describes a material's ability to take in energy from incident light, reducing transmission and/or reflection. The extent and wavelength range of absorption depend on the material’s electronic, vibrational, and structural properties. In dyes and pigments, absorption is due to electronic transitions within molecules; in semiconductors, it is related to a band gap that permits electron promotion. Metals absorb light via plasmonic resonances and free-carrier absorption. Some materials absorb broadly, appearing black, while others absorb selectively and show color.

Quantities used to quantify absorption include absorbance, transmittance, and reflectance. Absorbance A is defined as A = log10(I0/I), with I0 the incident and I the transmitted light. For a uniform layer, A can be described by Beer-Lambert law, A = εcl, where ε is the molar extinction coefficient, c is concentration, and l is path length. In practice, A + T + R describes the total interaction with light.

Measurement methods such as UV-Vis spectroscopy and reflectance spectroscopy yield absorption spectra that identify materials, gauge concentration, or characterize coatings. These spectra inform applications by revealing which wavelengths are blocked or transmitted, guiding the design of solar cells, optical filters, and protective finishes.

Applications and examples: solar-energy devices rely on light-absorbing layers to generate charge or heat; pigments and coatings control color and reduce glare; infrared-absorbing films provide thermal management; camouflage and sensors exploit selective absorption properties.

Limitations and notes: absorption converts light energy to other forms, usually heat, though some materials fluoresce or phosphoresce. Absorption depends on thickness, microstructure, angle of incidence, and environment, and it can vary with temperature or aging.