Concentration Dependence Curves of Y 2 O 2 S : Eu

Concentration dependence curves for over a range of excitation conditions have been determined for transitions from the to various 7 F levels. It is shown that the optimum Eu concentration for the transition is lower for cathode‐ray excitation than for photoexcitation. The absorption spectrum of has also been determined; it suggests the possibility that the change in optimum concentration might be qualitatively explained in terms of a preferential increase in reabsorption of the emission, however the calculated average population increase does not seem to be large enough to provide quantitative validation.