Abstract <p>The processes of emission and absorption by micro- and nanoparticles are calculated using the formalism of the mode theory of radiation using the dependence of the quality factor of electrically small radio antennas on their relative (in relation to the length of the emitted wave) sizes. The formation of a radian sphere filled with evanescent waves (TE, TM) around the surface of an emitting particle is considered. These waves are not emitted into free space and represent oscillations of electric and magnetic fields at frequencies ν <i>&lt; c</i>/λ_cutoff (for example, for a spherical particle λ_cutoff <i>=</i> 2.221<i>D</i>, where <i>D</i> is the diameter). For radiation at wavelengths greater than λ_cutoff, the particle ceases to be an effective antenna. For such particles, the role of antennas radiating into the far zone is played by the radian spheres surrounding them. Particles that are larger than the emitted wavelengths are themselves effective antennas. Using the proposed method, calculations of the powers and radiation coefficients of micron and nanometer particles were carried out.</p>