GENERAL DISCUSSION OF FLUORESCENCE SPECTRA. 



11 



ordinary spectroscope, has a spectrum which seems to consist of a 

 single very broad band. A spectrophotometric study reveals, how- 

 ever, two neighboring and overlapping bands. These have then- crests 

 in the red and green respectively and are complex. (See fig. 3.) 



TABLE 1. Approximate wave-lengths of visible crests in the spectrum of a phosphorescent 



strontium sulphide (Sr; Bi; Na 2 SO), No. 13. 



The components of the band in the green are members of a series 

 having a constant frequency interval of 70 (see table 2), while the 

 components of the band in the red form a series with an interval of 



L & K. No. 33. BA. CU. NA^ B 4 7 



-15 



-10 



FIG. 3. 



26.6. The two series overlap, as may be seen from figure 3. In this 

 example the spectrum as a whole forms a heterogeneous complex made 

 up of two homogeneous complex bands which are partially super- 

 imposed. 



The fluorescence spectrum of commercial anthracene affords an 

 example of a heterogeneous complex easily resolved into a group of 



