PHENOMENA OF PHOSPHORESCENCE. 



217 



In case all three modes of recombination contribute to the phosphores- 

 cence we obtain a similar expression for Z - *, except that A and B now have 

 the values 



A-p*(*>+ ^) + ^ 1 a(i-, - kl<P ) 



D . &1<>0 k 2 (fO 



3 = PiCUfo ViO. Pz&~ 



m m 



20 



4.0 



60 



80 



Seconds 

 Fig. 189. 



100 



120 



14-0 



1 60 



Observed decay curves for different durations of excitation compared with curves computed 



from the equation 



i i/tii+at- 



V/ " V B(y+e->t) 



The times of excitation and the relative numerical values of the constants used in computation are as follows: 



Curve. 

 E 

 P 

 C 

 B 



Excitation. 

 60 sec. 

 37 

 1 1 .6 



54 



y 

 0.36 

 0.4 



O. I 



o. r 



1 /No 



72 

 167 

 336 

 650 



2.18I a =4.8 

 4 \m =0. 16 



4-35J 



In Fig. 189 several curves have been plotted for I~' J by means of this 

 equation. Values of the constants have been determined by trial so as 

 to make these curves correspond as nearly as possible with the series of 

 experimental curves obtained with Sidot blende by varying the time of 

 excitation. 1 Observational points are indicated by circles. It will be 

 seen that, except in the case of one point on curve D, the agreement is highly 

 satisfactory. 



To give an idea of the character of the decay curves which might result 

 from the presence of grouped ions (disturbances due to diffusion, absorp- 

 tion, etc., being neglected) we may write equation (7) in the form 



1 



V7 



i/tio-\-at 



(i/wo+a/). 



V B Vt + 



-mt 



V5 



'Nichols and Merritt, Physical Review, xxni. p. 45. See also Chapter IV. 



