Chemical analyses and x-ray powder photographs have shown that thermal treatment of hexagonal ZnS:Cu,C1 phosphors in atmospheres of H2S and of He containing ZnC12 results in structural transformations and solubility changes of activator and co-activator. The temperature at which these changes occur depends on the copper concentration. Our results demonstrate the role of a separate phase of copper sulfide in promoting the growth of cubic zinc sulfide and thus effecting the hexagonal-to-cubic transformation.The two crystalline modifications of zinc sulfide are well known. The high-temperature hexagonal and the low-temperature cubic forms exhibit a reconstructive transformation at a transition temperature of approximately 1020~ In these studies, previously crystallized hexagonal ZnS: Cu,C1 phosphors (ZnS phosphors with Cu activator and C1 co-activator) were thermally treated in either H2S atmospheres or mixed atmospheres of He and ZnC12, with or without additional activator present, and the resulting structural and chemical changes were determined by x-ray diffraction and chemical analyses. The results of these experiments demonstrate the role of a separate phase of copper sulfide in promoting the growth of cubic zinc sulfide and thus effecting the hexagonal-to-cubic transformation.Earlier studies have been made of the influence of foreign atoms and the regions of stability of wurtzite and sphalerite. Work in this area has included that of Skinner and Barton (1) on the effect of oxygen on increasing the stability of wurtzite below the transition temperature. Aven and Parodi (2) have discussed the role of copper and silver in effecting the hexagonal-to-cubic transformation during the crystallization of ZnS phosphors in H2S.All of these studies have dealt with transitions encountered during the crystallization of ZnS. It is well known that hexagonal ZnS can persist in the region of cubic stability. Studies have been published on the effect of grinding in causing the hexagonal form to convert to the cubic. Little work has been done on determining chemical factors that influence the transformation. Our research has placed emphasis on the influence of copper on the transformation of previously crystallized hexagonal phosphors subsequently fired in the range of cubic stability.
Articles you may be interested in Line shape and intensity considerations in microwave optical magnetic resonance induced by electrons and related experimentsAn examination of the theoretical relationship between absorption and crystal response in a Stark-effect microwave spectrograph indicates that a direct proportionality exists between the absorption coefficient and the component of crystal current at the modulation frequency, provided that certain reasonable conditions are fulfilled.An experimental method is described which utilizes this principle to obtain measurements of the ratio of one absorption coefficient to another. This method involves a matching of the modulation frequency component of crystal current against an adjustable reference signal. These measurements may be used to determine the energy separation of the lower states of the lines observed, thus yielding microwave data on vibrational or torsional energy levels. Line breadth and saturation can be measured equally well with minor modifications in method.This experimental method was tested by measuring the known ratios of absorption coefficients of the carbonyl sulfide lines near 24000 mc which are assigned to various isotopic species. The range of deviation of measured ratio from known ratio was 25 percent, and this discrepancy is attributed to reflections in the microwave transmission line, particularly at the ends of the Stark electrode. The determination of molecular vibrational or torsional energy levels is discussed.
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