io4 



STUDIES IN LUMINESCENCE. 



It is evident that two bands are represented in the preceding curves. 

 Any one of these curves is probably made up by the superposition of two 

 curves, each of these component curves representing the flash for one of the 

 bands. If one considers the first flash in Figs. 107 and 108, it will be seen 

 that the curves resemble closely corresponding curves obtained with Sidot 

 blende. The maximum intensity increases with length of excitation and 

 occurs later and later. The areas included between the curves and thecoor- 



150 300 



Seconds 



Fig. 109. 



Maximum intensity of the first flash plotted against length of excitation. 

 Curve i, temp, of furnace 339 C (from Fig. 108). 



2. " 277 (from Fig. 107). 



3. " " " 222 



4. 148 



dinate axes increase with the excitation. The effect of saturation is shown 

 both by the change in areas and by the change in the maximum intensities. 

 The observations have been plotted in Fig. 109 so as to show the relation 

 between maximum intensities and lengths of excitation, in which case if one 

 considers the first flash alone the curves are similar to those already given 

 for Sidot blende. The effect of changing the temperature of the furnace 

 is shown in Fig. no. 



too 



Fig. no. 



The second flash does not always follow the laws of the first flash, as can 

 be seen in Fig. 108. As the length of excitation is increased, the maximum 

 intensity of the first flash occurs later and later, while the maximum of the 

 second flash occurs earlier and earlier. This effect is not well defined in 

 Fig. 107, due perhaps to the fact that the flash is of smaller intensity and 

 consequently more difficult to follow accurately. The effect of saturation 



