The compositions M II M 2 III ( S , Se ) 4 where M II = Eu , , Ca , Sr , Ba and M III = Al , Ga , In were prepared by reaction of the elements in evacuated silica tubes with iodine as a mineralizer. All members except Ba ( Ga , Al ) 2 S 4 , which is cubic, exhibit the pseudo‐orthorhombic PbGa 2 Se 4 type structure. They are high resistivity p‐type semiconductors; they exhibit Eu +2 ‐activated fluorescence which varies from red to blue as the electropositive character of the cations increase. Fluorescence activated by Yb +2 is seen at low temperature. Studies were made of the fluorescence decay lifetimes, temperature dependence, excitation spectra, and optical adsorption of SrGa 2 S 4 : Eu in order to relate the Eu +2 ‐activated fluorescence to the host bandgap. It is concluded that the most efficient phosphors are those in which the Eu +2 excited states lie farthest from the fundamental edge.
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Donohue et al. (1974) studied this question.