Frank J. Studer

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.

Modification of Spectrum of Tungsten Filament Quartz–Iodine Lamps due to Iodine Vapor

The iodine atmosphere in typical quartz–iodine lamps modifies the spectrum of the emitted light by selective absorption in a broad band in the green-yellow region. Results of a study of the spectral emission of a series of quartz–iodine lamps with different amounts of iodine are given.

Optical Properties of Calcium Silicate Phosphors

Calcium silicate phosphors activated with varying amounts of manganese luminesce yellow to orange under cathode-ray excitation, but are not excited by ultraviolet λ2537. If a small amount of lead is added with the manganese, the resulting material responds to λ2537 to give the same color as that produced by cathode rays, and in addition to the visible luminescence, there is an ultraviolet band at λ3400. The spectral distribution in the visible is dependent upon manganese concentration and on temperature.If lead alone is used as an activator, the product gives emission entirely in the ultraviolet. Three emission bands are evident at approximately 3000A, 3340A, and 3500A, any one of which may be predominant, depending upon the conditions of preparation. The excitation spectrum also varies widely, having several maxima between 2000A and 3000A. When the phosphor is excited by 2288A line from a low pressure cadmium arc, a fourth broad band appears in the emission, which peaks about 3850A and extends far enough to the longer wave-lengths to be easily observed visually.X-ray analysis with a Philips Geiger counter spectrometer demonstrates that the emission band at 3000A is due to the α-metasilicate, the one at 3500A to the β-metasilicate, while the 3340A band is due to the β-orthosilicate. During the firing process the orthosilicate is formed first by the reaction between the calcium oxide and silica in equi-molar proportions, and it reacts thereafter with additional silica to form metasilicate.

Čerenkov Radiation from a Co 60 Source in Water

The spectral distribution of the Cerenkov radiation induced in deionized water by gamma rays from Co60 has been obtained. A 3400-curie Co60 source provided adequate light emission in the water surrounding it to allow a direct measurement with a grating spectrometer. In the observed spectral range, 3200A to 6000A, the spectral distribution is in agreement with the prediction of the Frank and Tamm theory and is offered as a quantitative check on this theory.

The Phosphorescence Decay of Halophosphates and Other Doubly Activated Phosphors

The decay rates of three doubly activated phosphors, namely, calcium halophosphate (Mn, Sb), calcium silicate (Mn, Pb), and zinc fluoride (Mn, Ti, or W) have been investigated under λ2537 excitation. The halophosphates studied all show initially a very rapid and abrupt decay, followed by a second stage of decay having a very slow rate. Both stages are of the exponential type. Investigation shows that the rapid rate (decay constant ≈ 1500 sec.−1) is to be ascribed to the antimony emission and the slow rate (k ≈ 75 sec.−1) to the manganese emission.Calcium silicate behaves in a similar fashion, the ultraviolet emission due to lead decaying rapidly (k ≈ 480 sec.−1) and the visible more slowly (k ≈ 60 sec.−1). The doubly activated zinc fluorides show similar behavior, though the great spectral width of the tungsten band makes separation of the two emission bands difficult.The fact that in all these cases, the two activators each retain their characteristic decay rates in the presence of the other indicates that two types of centers exist in each of which the process of luminescence functions independently of the other.

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.

Optical Properties of Zinc Fluoride Phosphors

When activated with manganese alone, zinc fluoride emits an orange fluorescence under excitation by 2537A whose brightness is very weak because its peak excitation lies at 2200A. Other activators, cerium, tungsten, and titanium, shift the peak excitation to 2500–2600A and produce a higher absorption in the range 2000–2600A. The emission of tungsten and titanium lies mainly in the visible; that of cerium consists of a series of bands in the ultraviolet.Combinations of these elements with manganese produce greater fluorescence brightness. With tungsten or titanium, the normal orange emission of manganese is increased manifold with no change in the spectral distribution nor in the unique exponential decay of its afterglow except that the decay is raised to a higher brightness level. With cerium, the individual emission of each activator persists, with no reduction in intensity of the ultraviolet cerium bands and with only a slight increase in the intensity of the manganese band.As explanation of this apparent discrepancy, evidence was found that only tungsten and titanium are present in the same phase as manganese, namely, zinc fluoride. Cerium combines to form a separate phase, an aggregate of zinc and cerium fluorides.

A method for measuring the spectral energy distribution of low brightness light sources.

A method is described by which it has been found possible to determine satisfactorily the spectral energy distribution for luminous surfaces whose brightness is only a few footlamberts. A standard spectrometer is used in conjunction with a photo-multiplier tube. Relative energy is found by direct comparison with a tungsten lamp calibrated for color temperature. Results obtained with this arrangement for various fluorescent lamps are in good agreement with measurements made on a large double monochromator, indicating that the scattered light in the single prism instrument does not introduce serious errors.

Grainless Phosphor Screens for TV Tubes and a Light Amplifier

A luminescent coating deposited as a grainless layer avoids the diffusely scattered light associated with a conventional powder phosphor in television tubes. Such transparent phosphor screens of zinc sulfide can be made by a vapor phase reaction as will be described. With a screen of this kind, higher resolution and contrast are possible. Phosphor layers produced in this way may also be used as light amplifying screens.

A Method for Automatically Plotting Spectral Energy Distribution of Luminescent Materials

A method is described for measuring automatically the spectral energy distribution of luminescent materials or of other light sources. A photo-multiplier operated on d.c. is used with a standard constant deviation spectrometer for measuring the energy in the spectrum. A compensator has been built in the spectrometer so that the output of the photo-cell is proportional to incident energy of any wave-length. A drive mechanism sweeps the spectrum across the exit slit at constant wave-length rate, and the photo-cell output appears on the chart of a standard photoelectric recorder. Errors, due chiefly to inaccuracies in milling the compensator, are less than 5 percent except in the extreme violet. Curves repeat within 1 or 2 percent. Spectral curves can be taken of surfaces whose brightness is as low as 1 foot lambert. The time to obtain a distribution curve may be varied from one-half to two minutes by a change of gears.