Fluorescence of Silicate Phosphors

Abstract

An hypothesis is proposed for the fluorescence of silicate phosphors connecting the absorption and emission bands with the energy levels of the activator ions. It is shown that the energy levels of the ions must be radically changed as the ions enter the lattice of the solid.In the case of Mn activated zinc silicate, the absorption of 2537A light is attributed to a transition from a 3d5 level to a 3d44p level with an energy change of 40,000 cm−1 in the solid as opposed to 112,000 cm−1 for the free ion. The emission of visible light is due to a transition from an excited 3d44p level to a 3d44s level, after which there are non-radiating transitions to the unexcited level. Fine structure considerations indicate the possibility of two or more emission bands for excited manganese.The results of beryllium additions to zinc silicate are discussed, and it is pointed out that the effectiveness in inducing new emission bands will vary with the cube root of the volume concentration. The behavior of alkaline earth silicates, activated by manganese, is also briefly discussed, and a reason for their excitation by cathode rays, but not by 2537 radiation, is suggested.In lead activated alkaline earth silicates the light absorption is attributed to a transition from the 6s2 level to the 6s6p (1P1°) level, after which there is a non-radiating transition to the 6s6p (3P0°) level from which the electron falls back to the 6s2 level with radiation of blue or ultraviolet light.