US2121636A - Photoelectric device - Google Patents

Description

June '21, 1938. R, KQLLER 2,121,636

PHOTOELECTRIC DEVICE Filed May 26, 1937 1762/17/14 SENS/77107 Y WAVE zflmfi/M/W'smwvs) I Ve t or Lewis R. Kol Ier,

by 70 6000A His tcorney.

Patented June 21, 1938 UNlTE STATES- PA pl General Electric Company, a corporation of New York Application May 26, 1937, Serial No. 144,895

2 Claims.

The present invention relates to light-sensitive devices and more particularly to photo-electric tubes which respond to ultraviolet light.

Ultraviolet radiation is used for many purposes such as sterilization, health promoting effects, etc. In order to obtain the optimum effects from this type of radiation, it is necessary to measure and regulate the intensity of the light. For this purpose, special types of photo-electric tubes have been devised which respond to light of this character. However, since the light is limited to a restricted range in the spectrum, it is difiicult to design and. manufacture a tube which will have its optimum response in that range. It is even more difficult to duplicate tubes of this character.

Objects of the present invention are to devise a photo-electric tube which will respond efficiently to ultraviolet radiation or to radiation in a restricted portion of the ultraviolet region of the spectrum; to improve the manufacturing processes of these tubes to the extent that they can be readily duplicated, even on a quantity production basis, and to provide a tube in which the response curve in the ultraviolet region may be accurately predetermined. In carrying out these objects, a light-sensitive material of known composition is obtained by vaporization from a source of similar composition which can be varied and accurately controlled. The invention will be better understood when reference is made to the following specification and the accompanying drawing in which Fig. 1 is an elevational view of a photo-electric tube improved in accordance with the present invention; Fig. 2 is a view partly in section of the tube shown in Fig. 1; and Fig. 3 is a graph showing the response curves of various types of improved ultraviolet tubes.

In Figs. 1 and 2, numeral l designates a glass envelope containing an anode 2 and a lightsensitive cathode 3. The anode may take the form of a metal ring supported on the end of a rigid rod 4 which serves as the leading-in conductor. The cathode consists of a composite material which is sensitive to ultraviolet radiation, and contact is made with the material by means of a rod 5 which terminates in a platinum ribbon secured to the glass. The conductors are connected to contact pins 6 secured in a base 1. The envelope terminates in a stem 8 in which the conductors are sealed, the stem carrying an exhaust tubulation indicated at 9. A mica disk I is secured to the conductor 4 by means of an angle piece II. This disk is of a size snugly to fit the interior of the small neck portion of the envelope and serves to prevent deposition of active material on the stem. There is an opening l2 in the disk sufficiently large so that the rod can pass through without touching the disk. This prevents short-circuiting of the electrodes by the material which condenses on the disk. Shield l3 prevents active material which passes through the opening from depositing on the stem 8.

For introducing the light-sensitive material into the envelope, a capsule I4 is provided. This capsule may be supported from the rod 4. An alloy having predetermined amounts of cadmium and magnesium is made and placed in the capsule. After the capsule and the anode have been mounted in position, the envelope is evacuated and the bulb is baked out for an hour at 300 deg. C. At temperatures higher than this, there is danger of vaporizing the cadmium out of the alloy in the capsule. After the bake-out, the alloy is vaporized by heating the capsule by high frequency induced currents until the bulb is covered with an opaque mirror-like deposit. The thickness of the deposit is determined by the amount of alloy contained in the capsule. A window [5 is then formed by torching with a soft bunsen flame after which the tube is again baked for ten minutes at 100 deg. C. to insure uniformity of the deposit. The envelope may be based in the usual manner. The bulbous portion of the envelope except for the window I5 is therefore coated with an alloy of cadmium and magnesium, which I have found profusely emits photo-electrons when exposed to ultraviolet light.

It has also been found that by varying the cadmium and magnesium, the region within which the tube has its optimum response in the ultraviolet region of the spectrum can be varied. This is clearly shown in Fig. 3. As the cadmium is decreased and the magnesium increased, the sensitivity curve moves to the right, indicating an optimum response at a longer wave length. Thus, increasing the concentration of magnesium increases the relative response to long-Wave radiation, while increasing the concentration of cadmium increases the relative response to shortwave radiation. It may be desirable to cut off or materially reduce the sensitivity of the tube at wave lengths less than 2700 Angstroms. In this case, the envelope may be made of a glass such as Corex which absorbs light of the undesired wave lengths. The curves shown in Fig. 3 were obtained from a tube of this character, and for that reason the maximum values of the curves are not true characteristics of the cathode but are determined by the falling transmission of the Corex glass toward the shorter wave lengths.

The process as described, which involves the use of an alloy or composition within a capsule for obtaining a light-sensitive layer composed flashing the alloy or composition so that the composite light-sensitive layer will represent in prop-.

er proportion'the elements contained within the capsule. It is apparent that the improved proc-; 'ess may be employed on a quantity production basis, because the light-sensitive layer is, of a predetermined character and can be accurately controlled. 7

What I claim as Letters Patent of the United States, is:

1. A photo-electric tube comprising an envelope containing a light-sensitive cathode and an anode, said-cathode including cadmium and magnesium. V

2. A photo-electric tube comprising an envelope containlng a light-sensitive cathode and an anode, said cathode consisting of cadmium and-magnesium, the cadmium ranging from 5% new and desire to secure 'by a in A i'JERTIFIUKTEUFWRBEGTION- Patent No; 2,121,656. June 21, 1958.

LIMIS R, KOLLER.

It ishereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: Page 2, first column, line 11, for the word "as" read at; and that the said Letters Patent should be read with this correction therein that the same may conform to the record of the case in the Patent Office,

Signed and sealed this 9th day of August, A. D. 1958.

Leslie Frazer (Seal) Acting Commissioner of Patents.

' f 'omm'irl'cpz" E"'OFUGRRE' 'G'TION'T" Patent No; 2,121,656. June 21, 1958 LEWIS R0 KOLLER.

It ishereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: Page 2, first column, line ll, for the word "as" read at; and that the said Letters Pate nt should be read with this correction therein that the same may conform to the record of the case in the Patent Office,

Signed and sealed this 9th day of August, A. D. 1958.

Leslie Frazer (Seal)- Acting Commissioner of Patents.

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