Carbon aerogels are highly porous, lightweight materials with a three-dimensional network structure composed predominantly of carbon nanoparticles or nanofibers. Their unique architecture and composition give rise to distinctive optical properties, including light absorption, scattering, and emissivity, which are critical for optoelectronic applications. These properties stem from their nanoscale morphology, high surface area, and tunable electronic structure, making them suitable for devices such as photodetectors, solar absorbers, and thermal emitters.

The light absorption characteristics of carbon aerogels are primarily governed by their carbonaceous composition and porous structure. Carbon, in its various forms, exhibits broadband absorption across the ultraviolet, visible, and infrared spectra due to its electronic transitions and defect states. The interconnected carbon networks in aerogels facilitate multiple scattering events, enhancing the effective absorption path length. Studies have shown that carbon aerogels can achieve absorption efficiencies exceeding 90% in the visible and near-infrared ranges, attributed to their low reflectance and high internal surface area. The absorption can be further tuned by adjusting the pyrolysis temperature during synthesis, which modifies the graphitic content and defect density. Higher pyrolysis temperatures generally increase the degree of graphitization, leading to stronger absorption in the infrared region due to free carrier absorption.

Scattering in carbon aerogels arises from their heterogeneous pore structure and the refractive index contrast between the solid carbon phase and the air-filled pores. The pore sizes, typically ranging from nanometers to micrometers, interact with light through Mie and Rayleigh scattering mechanisms. Smaller pores scatter shorter wavelengths more efficiently, while larger pores affect longer wavelengths. The overall scattering behavior can be engineered by controlling the aerogel density and pore size distribution. For instance, lower-density aerogels with finer pores exhibit stronger scattering in the UV-visible range, whereas denser aerogels with larger pores show increased scattering in the infrared. This tunability is advantageous for applications requiring light trapping or diffuse reflection, such as in solar thermal collectors or optical diffusers.

Emissivity, the ability of a material to emit thermal radiation, is another key optical property of carbon aerogels. Their high emissivity in the infrared spectrum makes them effective thermal emitters for applications like radiative cooling and infrared camouflage. The emissivity is influenced by the material’s electronic structure and surface morphology. Carbon aerogels with a higher sp² carbon content exhibit stronger emissivity due to the vibrational and electronic transitions associated with graphitic domains. Additionally, the porous structure enhances emissivity by increasing the effective emitting surface area. Measurements have demonstrated that carbon aerogels can achieve emissivity values above 0.9 in the mid- to far-infrared range, comparable to blackbody emitters. This property is particularly useful for optoelectronic devices requiring efficient thermal radiation management.

The combination of these optical properties enables carbon aerogels to perform multiple functions in optoelectronic systems. For example, their broadband absorption and high emissivity make them ideal for solar-thermal energy conversion, where they can efficiently absorb sunlight and re-emit thermal energy. Their scattering properties can be harnessed in light-management layers for photovoltaic devices, improving photon absorption in active materials. Furthermore, their mechanical flexibility and low density allow for integration into flexible optoelectronics, such as wearable sensors or foldable displays.

The optical performance of carbon aerogels can be further optimized through compositional and structural modifications. Doping with heteroatoms like nitrogen or sulfur can alter the electronic structure, introducing additional absorption bands or modifying emissivity. Controlling the precursor chemistry and gelation conditions allows for precise adjustment of the pore network, enabling tailored scattering profiles. For instance, resorcinol-formaldehyde-derived carbon aerogels exhibit different optical behaviors compared to those derived from cellulose or graphene oxide, due to variations in their carbon bonding and porosity.

In optoelectronic applications, the environmental stability of carbon aerogels is another advantage. Unlike many organic or plasmonic materials, carbon aerogels are chemically inert and thermally stable, maintaining their optical properties under harsh conditions. This durability is essential for long-term operation in devices exposed to high temperatures or corrosive environments.

The following table summarizes key optical properties of carbon aerogels and their relevance to optoelectronic applications:

| Property | Characteristics | Optoelectronic Application |
|-------------------|------------------------------------------|--------------------------------------|
| Absorption | Broadband, UV to IR, >90% efficiency | Solar absorbers, photodetectors |
| Scattering | Tunable with pore size, Mie/Rayleigh | Light trapping, optical diffusers |
| Emissivity | High (>0.9), IR-dominated | Radiative cooling, thermal emitters |

In conclusion, carbon aerogels exhibit a unique combination of light absorption, scattering, and emissivity, driven by their nanoscale architecture and carbon-based composition. These properties are highly tunable through synthesis parameters, enabling their use in diverse optoelectronic applications. Their robustness and versatility make them promising materials for next-generation optical and thermal devices, where performance and durability are critical. Future research may explore further refinements in microstructure control and hybrid compositions to expand their functionality in advanced optoelectronic systems.