Using the effective medium approximation[1–4] and the theory of photoemission from small particles, we look into the design-rules of infrared materials based upon the metalsemiconductor random heterostructures with Ag particles embedded in the semiconductor. It is found that semiconductor host matrices with higher dielectric constants show better optical absorption in the infrared and that optical properties are closely related to microstructural parameters such as volume fraction of metal particles, percentage of aggregation and particle size. Cu, Ag and Au particles all show similar characteristics. We synthesized materials with small silver particles embedded in Si. Their microstructures are analysized using X-ray diffraction, electron microscopy and sputter Auger profiling. Finally, we present the optical properties of these materials and make comparisons with our theoretical results.