Irradiation of halophosphate lamp phosphors by a low-pressure mercury arc causes a loss in luminescent efficiency, changes in the absorption spectra, and thermoluminescence. The 1849A wavelength is primarily responsible for these changes, which are partially reversed by longer wavelength radiation or by heat. X-radiation produces larger changes in the absorption spectra, which are compared to observations on unactivated halophosphates. The relation between luminescent efficiency and color center formation is discussed.The effect of ultraviolet radiation on phosphors is of considerable interest with respect to their stability in fluorescent lamps. The decrease in luminescent efficiency previously reported for several phosphors (1) was found to occur for the alkaline earth halophosphate phosphors. Production of color centers has been described resulting from u.v. and x-radiation of the luminescent (2, 3) and nonluminescent (4) forms of the halophosphates. The conditions which result in a decrease of luminescent efficiency and the formation of color centers have been examined further. These studies relate to the phosphors alone and are not directly applicable to operation in practical lamps where additional effects due to binders, gases, and the supporting glass may be of great importance. Experiments and ResultsBoth commercially manufactured and laboratoryprepared halophosphate phosphors were studied. These have the general formula M5 (PO4)3 X: Sb, Mn where M is Ca and/or Sr; X is C1 and/or F; Sb is a sensitizer as well as an activator which produces a blue luminescence in the region of 4800A; and Mn is an activator which produces a peak in the 5800A region. Table I shows the qualitative composition of the phosphors studied. In addition, a sample of self-activated barium titanium phosphate was examined.

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The reaction of oxygen at a polycrystalline tungsten surface has been studied over a temperature range from 1300° to 2450°K and for oxygen pressures from ∼10−5 to ∼10−8 torr. A mass spectrometer was used to measure the oxygen pressure. In determining absolute pressures care was taken to avoid errors which may arise due to spurious currents in a Bayard—Alpert ion gauge. The efficiency of removal of carbon impurity from tungsten, by heating in oxygen, was determined. After obtaining a low carbon content, the rates of removal of oxygen at the tungsten surface were determined as a function of temperature. At temperatures below ∼2000°K evaporation of oxides of tungsten occurs at predictable rates. At higher temperatures atomic oxygen is produced and the observed rate of removal of oxygen is strongly influenced by the specific surfaces present in the entire system. For example, a silver surface efficiently reacts with oxygen atoms, without apparent saturation, to give a large apparent increase in the pumping speed at a tungsten surface enclosed in a glass system.

Solution of Argon in Layers of Krypton 1011 (2800 A.) in benzene is similar to other cases where Bayliss and Hulme19 have noted a specific enhancement when the solute has an absorption band close to one of the solvent; however it is difficult to see why acetone does not behave similarly. The high (19) N. S. Bayliss and L. Hulme, Australian J. Chem,, 6, 257 (1953). intensity of crotonaldehyde (3300 A.) in water must be due to some other cause. We feel that further comment at present would be premature.The authors gladly acknowledge assistance from the University Research Fund, including the grant of a studentship to one of us.

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