On the Interaction of Radiation with Matter and on Fluorescent Exciting Power

The interaction of radiation and matter is discussed on the basis of Einstein's theory. The distribution of energy in an enclosure containing quantized particles is indeterminate unless there is thermal or other non-radiative interaction between the particles; the latter process is therefore essential to the production of the black-body distribution. Fluorescence cannot lower the entropy of the system.Exciting power for fluorescence.---No sharp distinction can be drawn between thermal emission and fluorescence. If ψyx is the fluorescence of frequency νy excited by radiation of frequency νₓ and if αₓ, αy, uₓ, uy are the corresponding absorption coefficients and black-body densities, respectively, then on certain assumptions ψyx=kαₓαyuyνₓ, k being independent of νₓ and νy. Much more general assumptions lead to: ψyxψxy=νyuyνₓuₓ. These equations ought to apply to gas fluorescence, and it is quite possible that the latter may hold generally for liquids and solids and the former in those cases where the shape of the fluorescence band does not vary with the exciting frequency. The equations agree with the few data in existence.