The optical properties of clusters with metallic spherical particles embedded in an insulating matrix are studied. A theoretical approach is proposed for the calculation of the macroscopic dielectric response for a collection of spheres at random positions embedded in a homogeneous medium. While accounting for the dipole-dipole interaction between particles, we have considered the frequency dependence behavior of the imaginary part of the effective dielectric constant in this system with two kinds of particles of different sizes. © 2000 American Institute of Physics.
͓S0003-6951͑00͒05014-2͔The Maxwell-Garnett ͑MG͒ 1-3 approximation and its various updatings have frequently been used 4-13 as the description for the optical properties of composites consisting of a dielectric matrix with embedded metallic inclusions. The main purpose of 4-13 consists of accounting for the multipole interaction between inclusions. We shall consider here the method of cluster expansion developed in works. [8][9][10][11] In this method the effective dielectric constant of the composite is represented as a series where each term consistently takes into account the two-particle, three-particle, and higher interactions between inclusions. The difficulty of this method is that at each stage it is necessary to solve the electrostatic problem for sets of particles ͑two, three, etc.͒ in an external field and to know the appropriate multiparticle distribution functions of inclusions in the matrix.In the present letter, we propose to generalize the method 8 for the case of a composite containing spherical inclusions of various radii. We will take into account only the pair multipole interaction between inclusions ͑first correction in the MG approximation͒. A general expression for and its imaginary part as functions of the composite parameters containing inclusions of two different radii of the same material is considered using this approximation. We shall consider a system that consists of the continuous dielectric matrix with embedded spherical particles of different kinds ͑noted below by indices a,b,c...͒. The dielectric permittivity of the matrix is 0 while the dielectric constants of the particles a , b , c ... . Let the number of spheres of kinds a, b, c, etc. be N a ,N b ,N c ..., respectively. The total number of particles is Nϭ⌺ ␣ N ␣ . The system is located in the external field proportional to e Ϫit with a wavelength ϭ2c/, which is much larger than the sphere radius and mean distance between particles; n a ϭN a /V, n b ϭN b /V,... are the concentrations of particles of the kinds a,b,... .Generalizing the method of cluster expansion [8][9][10][11] in this case, we can develop the following expression for the calculation of the system effective dielectric permittivity:whereis a usual dipole polarizability of the particle of kind a, ⌽ a,b (R ab ) is the two-particle distribution function of particles in the matrix, and R ab ϭ͉r a Ϫr b ͉, where r a and r b are the origins of spheres a and b, respectively. Equation ͑1͒ is a generalizatio...