Patent GB-824242-A (GB)
Title: Improvements in and relating to apparatus embodying electroluminescent devices
Inventor: LINDSAY HENRY RUDOLPH
IPC: H05B44/00
Filed: 1954-10-21
Abstract: 824,242. Colour television tubes ; electroluminescence in colour. THORN ELECTRICAL INDUSTRIES Ltd. Oct. 21, 1955 [Oct. 21, 1954; Oct. 29, 1954], Nos. 30398/54 and 31395/54. Class 39(1). [Also in Group XL(b)] An electroluminescent colour receiver comprises a screen the colour of which is changed by varying the frequency of the exciting field. Zinc sulphide activated by copper and lead is green-luminescent at 50 cycles and blue at 1500-2000. A mixture of yellow emitting and blue emitting phosphors will emit yellow at 400 c.p.s. and blue at 2000-3000 c.p.s. The screen 10 comprises such a material formed as a layer or layers between a set of transparent conductive strips 11 and a further set of opaque conductive strips 13, e.g. graphite, powdered metal electro- or vacuum-deposited metal or lead dioxide, at right angles thereto. Each light-producing layer comprises a plurality of groups of two different strips of luminescent material. Conductors 11, 13 are connected to motor driven commutators 14, 15, which apply suitable voltages to the conductors to cause a spot of light to scan across the screen. The frame commutator may be replaced by a delay line, Fig. 3 (not shown) ; or both commutators may be replaced by an electronic switch or switches, Fig. 4 (not shown). In the frame sequential receiver of Fig. 2, the R. F. amplifier 20 feeds a signal separator motor control circuit 21 for the commutators, and the video signal from the amplifier 20 controls variable gain amplifiers, 24, 25 for green and blue and a switch 22 governing the sequence of the outputs of the amplifier. Each amplifier is coupled to an oscillator 27, 28 of the frequency which excites a colour in the electroluminescent layer. Similar receivers can be used for line and dot sequential systems or for the simultaneous production of all colours. The conductors of the screen may have one set as concentric circles and the other as radii or diameters of the circles. In an alternative receiver, Figs. 5, 6, the screen of a CRT comprises a layer 31 of fluorescent material and a glass plate 32 forming the end wall of the tube, in combination with a convertor comprising conductive layers 33, 37 a photoconductive layer 34, e.g. selenium, an electroluminescent material or mixture of materials giving a range of colour for different frequencies and an enclosing glass plate 38. An opaque layer 35 preferably of high dielectric constant and light reflecting may be provided between the photoconductive and electroluminescent layers. A video signal from R.F. amplifiers 40 controls the brightness and contrast of the tube image and signal to signal separator 42 and synchronizer 44 control the scanning of the tube and the switching of the two oscillators 46, 47, or a single variable oscillator to control the colour sequence. In Fig. 8 (not shown) a receiver uses a luminance signal combined with two chrominance signals. The chrominance information is fed to amplifiers which control the electroluminent image intensifier in conjunction with oscillators determining the colours. The devices may be used in signs, stage-lighting and photographic or cinematographic projectors. The image falling on the convertor may be infra-red, ultra-violet or X-rays. The CRT and the image converter may be spaced and provided with an optical system, Figs. 7A, 7B (not shown).