Lithium and sodium dissolved in zinc sulfide act either as activators of fluorescence, or as quenchers, according to whether chlorine is present or not. The fluorescence occurs only at low temperatures and is excited by short-wave ultraviolet. The lithium band has a maximum at 4380A in the sphalerite modification of ZnS; the sodium band has a maximum at 3940A in sphalerite and at 3800A in the wurtzite modification.
The difference in the position of the bands for wurtzite and sphalerite and a shift found upon incorporation of CdS proves that we are dealing with electron-transfer bands. The centers of fluorescence are supposed to consist of lithium or sodium and chlorine ions occupying normal lattice sites. The levels involved in the fluorescence transitions are levels due to lattice ions, changed by the presence of the monovalent ions (indirect activation).
The quencher centers are supposed to consist of Li2S and Na2S incorporated in ZnS in such a way that the alkaline ions occupy two cation sites, while of two anion sites one is occupied by a monovalent sulfur ion and the other by an electron.
© 1949 Optical Society of AmericaFull Article | PDF Article
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