FLUORESCENCE OF EU2+-ACTIVATED PHASES IN BINARY ALKALINE EARTH ORTHOSILICATE SYSTEMS

The dependence of the emission spectra on compositional variations has been studied in binary alkaline earth orthosilicate systems activated by divalent europium. Isotherms at 1200°C were run in the systems (i) Ba2SiO4-Sr2SiO4, (ii) Ca2SiO4-Sr2SiO4, and (iii) Ca2SiO4-Ba2SiO4. Phosphors produced in the Ba2SiO4-Sr2SiO4 system were considerably more efficient than those in either of the other two systems and consequently were studied in much greater detail. A complete series of crystalline solutions exist between the end-members at 1200° C. The corresponding emission spectra vary in a fairly continuous manner from 505 nm for the pure barium end-member to 575 nm for the pure strontium end-member. X-ray diffraction data revealed complete crystalline solution between β-Ca2SiO4 and Sr2SiO4 at 1200°C. However, the low level of brightness and the pronounced asymmetry of the emission peaks rendered this system less amenable to a detailed investigation. Emission spectra indicated the formation of an intermediate compound in the Ca2SiO4-Sr2SiO4 system. The existence of this compound, Ba5Ca3Si4O16, was verified by x-ray diffraction. The emission spectrum of this compound peaks at a considerably lower wavelength (~490 nm) than those of its bounding compositions. The two later systems were further complicated due to the polymorphism of Ca2SiO4. Frequently the Ca2SiO4 phase was partially converted from β-Ca2SiO4 to γ-Ca2SiO4. © 1968, The Electrochemical Society, Inc. All rights reserved.