The Fluorescence of Phosphors in Rare Gases

Abstract

Experiments were performed to investigate the fluorescence of phosphors when excited by discharges in rare gases and mixtures of them as a possible substitute for mercury vapor. A special tubular discharge lamp was built that contained a glass strip upon which numerous patches of fluorescent material were painted. Measurements were made on the brightness of the individual patches as the rare gases, mixtures of them, pressures, and tube currents were varied. From a large amount of such data the following conclusions could be drawn: (1) All phosphors showed fluorescence to some degree to all gases or mixtures and operating conditions but the efficiencies were low compared to mercury excitation. Zinc silicate phosphors were always the brightest. The resultant light depended upon the glow from the gas as well as upon the light from the phosphor. (2) Highest efficiencies were obtained with the rare gases at low pressures. The shapes of the curves indicated that resonance radiation was the principal agent in producing fluorescence. In pure gases the optimum pressures were too low to be usable in a commercial lamp. (3) With certain gas mixtures the high light output of low pressures could be carried over to higher pressures. Argon, krypton, or xenon mixed with helium or neon gas showed this desirable characteristic, and is analogous to mercury vapor of a few microns pressure in a gaseous atmosphere of argon at several mm pressure. (4) The highest efficiency is attained with neon gas but the light is predominately the orange-red glow from neon. Neon might become a competitor of mercury only in pink fluorescent lamps. (5) Several interesting relationships associated with the atomic numbers of the rare gases were found.