Optical Properties of Powders. Part I. Optical Absorption Coefficients and the Absolute Value of the Diffuse Reflectance. Part II. Properties of Luminescent Powders

Abstract

The optical properties of powders are determined for the case of particles, large compared with the wave‐length of light. The solution for the diffusion of light in a quasi‐infinitely thick powder is applied to relate certain measurements obtained on powders with the corresponding properties of the bulk material. In Part I, the diffuse reflectance R of a powder is first derived in general form in terms of the parameters of the individual particle, taking into account both internal and external scattering. Parameters are then obtained for a model for randomly shaped particles, and used to relate the diffuse reflectance to the optical absorption coefficient, the index of refraction, and the particle diameter. The relationship is compared with measurements on materials of different refractive indices. Part II deals with applications to luminescent powders, the calculation of the characteristics of emission in the presence of optical absorption, and the calculation of cascade transfer yields.