Dominic Anthony Cusano

Transparent Phosphor Coatings

Transparent coatings of a number of luminescent materials have been deposited on glass surfaces by chemical reaction of the components in the vapor state. The best of these so far obtained is zinc sulfide. Arsenic, copper, manganese, phosphorus, or zinc have been successfully introduced as activators. Under cathode ray excitation, some of these have given brightness as high as 40 foot-lamberts at 20 kv and 1 microampere per sq cm. The uv response of these films is low, but varies with the conditions of preparation. The properties of these nonscattering phosphor screens are described and their advantages over powder phosphors considered.

Titanium Dioxide Films as Selective Reflectors of the Near-Infrared

Owing to the high refractive index of TiO2, films of this material show a great difference in reflection between the spectral regions of constructive and destructive interference. A glass slide coated on one side with a film of such thickness as to give its first order reflection maximum at 11 000A and its reflection minimum at 5500A, will reflect approximately 30 percent at 11 000A and 8 percent at 5500A. If the glass is coated on both sides, it will reflect in the neighborhood of 40 percent of the integrated infrared from a tungsten lamp operated at 2700°K, while it reflects only 8 percent at 5500A. A series of experiments with incandescent lamps was undertaken to determine the effect of such coatings applied to the bulbs. Uniform TiO2 coatings of the proper thickness were deposited on the inside and outside of clear spherical bulbs, and the light output measured from compact filaments when carefully centered inside a coated bulb and when centered in an uncoated bulb. It was found that, for a given power input, the light output from the coated bulb was as much as 20 percent higher than from the uncoated bulb. For the same light output, 10 percent less power input was required in the coated bulb. Because this result was obtained only when spherical nonfrosted bulbs with accurately centered small filaments were used, it is questionable whether this process will have any practical applications in connection with incandescent lamps.

The Physics of Solid-State Light Amplifiers

An essential component of present light amplifying screens is a layer of inorganic, luminescent material. The ability of this layer to derive energy from an electric field to which it is subjected and convert this energy into visible light (i.e., electroluminescence) is fundamental to, but not alone sufficient for the realization of solid-state light amplification. What must be included is some means whereby the luminescent response to the field can be strongly controlled by incident radiation. In one case this has been obtained through the discovery of a phosphor film with the necessary properties, and in another by the utilization of a photoconducting material in contact with an electro-luminescent layer. In the latter case the photoconductor is the radiation-sensitive element, which serves to modify the potential across the luminescent component. The main characteristics of these light amplifying screens will be described, with particular emphasis on the interpretation of the phenomenon observed with the single phosphor film. The behavior, as it is relevant to their possible use in radiation detection will be discussed.