Local deviations of the refractive index or the absorption coefficient from their average values in solid result in scattering of light. Deviations of this type in solid can be caused by ions formed by ionizing radiation or by charge carriers injected to insulator such as anthracene crystal.
Bearing in mind that the effect of light scattering is small sensitive modulation techniques were applied to study this phenomenon. The concentration of ions, under conditions of injection currents limited by space charge, was modulated by external voltage. Observation of the light scattered by anthracene crystals was carried out using a photomultiplier coupled to a selective, phase sensitive nanovoltmeter. The scattered light was examined as a function of the amplitude of variable voltage, the angle of observation as well as the wavelenght of the incident light. It has been found that the phenomenon of light scattering by anthracene ions is strongly affected by the ion absorption coefficient because the modulation effect of the scattered light follows its absorption by ionic states of the anthracene crystal.