p. LENARD, H. KAMERLINGH ONNES and W. E. PAULI. “The behaviour 
of the phosphorescent sulphides of the alkaline earths at various 
temperatures, and particularly at very low temperatures.” 
Fig. 1. 
Fig. 2. 
Excitation-distribution. Band. 
1. Excited intensity during illumination (momentary ^-permanent excitation). 
2. Excited intensity in the afterglow (permanent excitation). 
Proceedings Royal Acad. Amsterdam Vol. XII. 
