Fluorescent Lifetimes of Rare Earth Salts and Ruby

The mean lives of the resonance levels of the trivalent ions of Sm, Eu, Gd, Tb, and Dy in pure crystalline compounds have been determined by a direct measurement of the decay of the fluorescence. They decrease from a maximum of nearly 0.01 sec for Gd+++ to either side to less than 10—5 sec for Sm+++ and Dy+++. The intensity of the observed fluorescence decreases with the mean life, which except for Gd+++ is controlled by interactions of the rare earth ion with the crystal lattice.