[1]United States Pate@@nt Office 2@765@419 2,765,419 ELECTROLUMP-TSCENT CtLi 5 Shepard Roberts, Scotia, N. Y., assignor to General Electric CoMpany, a corporation of New York Application November 3, 1951# Serial No. 254,709 10 7 Claims. (Cl. 313-108) This inven'tion relates to an ele@troluminescett cell Ij of the tybe known as ;i lumin6ug capacitor. More particul arly, the invention ielai6s to dn e le@ciiolumi@nesdent cell which dispeiises W'ith the necessity bf using a layer of trdnsparent conducting material iii Order to be vi8ibie. Elect roluminescent @elis br I;uminous capacit0is arC 20 lightemitting devices which rese,mble a flat plat6 @ondeiis dr or capacit6r in constrti etion ekeept that dn-e of the plate s is con@posed of gl@ss With a tr@Lnspatent @ofiducting mate rial siich as tin oxide on oiie 'surface ahd the space beiw een th-- conducting surfaces is filied with a dielectri'c 2@,5 mate rial in which a phosphor is suspolided. . Wheil an alter' nating current flow8 ihr6ugh stich A cAp6Ldit6r, vi@ibi.- light einitted by the phosohoi may be 8een througli tho laye r of transpareni condtictin@ matetidi. Sinc e the only presciitly known metho@ of formi@ @ 30 a tratis 'pa.-ent conductii@ layer is to c@6at tin o@tde on glass, i; elect roluminescent cells up t6 the present ime have been limit dd as to their iii@Lterials of construction. While plastics hdve been considered desirable, their @sd has bodil rule d oiit becaiise a tin ;oxide l@ay'er c'")@6i b@e mad6 t6 ;5 adhe re to a plastic. It is, therefore, an object of this.invention,to produce an electrolumine@cent cell which will eiriit visible light with out resorting t6 the iise of a tr;@nsp@a@rdnt conducting laye r. 0 it is a:nother objeci of this invention to providd dn electroluminescenf &ell ha@ing 14yer c I omposed lqtgely of 6@aque condiicfi@g iiiaferi@l having gaps throifghW'.-iidh vigible light may b6 6bserved. it is a@iiother objeci 6t this inve'niion to providd an 45 electrolumi,iescent ceft Wfiicii may be viewed thr6iigh plastic N@,hich has a layer of opaque conducting material in contact therewith@ It is a further object of this iliventfoii to providd an elect rolumineseent cell which will av6id diete@e'tri@ bt6'6Lkr)o dow n of the insulating layer wheii the'pow'dr i's' fiirned dn' or off. Brie fly stated, in accordance with one embodiment of my invention, I substitute a fine-line grid of opaque conducti ng material for the layer of transparent conducting r,5 mate rial normaily used and back this layer of opaque mate rial with a coating of transparent plastic or glass. In addition, I include a high resistance element in the oper ating circuit of my cell to avoid dielectric breakdow n at the moment of energization or deenergization of 60 the cell. My invention will be better understood from the followi ng description taken in conjunction with the accompany ing drawing wherein Fig. 1 illustrates an electrolumi nescent cell of the type presently known; Fig. 2 is ' 65 sche matic perspective drawing of one embodiment of my inve ntion; and Fig. 3 is a schematic perspective view of still another embodiment of my invention. In Fig. I a base plate 10 of conducting material has an overlying layer 11 of transparent dielectric material 70 in which a phosphor such as zinc sulfide is suspended. Zinc sulfide electroluminescent phosphors are well known Patented Oct. 2, 1956 2 to the art, and may be found described in a.n article entitled, "The new phenomenon of electrophotoluminescence and its possibilities for the investigati6ns of crystal latiice," by Pro@. G. bestriau in the Philosophical Magazine, October 1947, vol. 38, page 700. A top plate 12 of glass having a thin layer 13 of tin oxide overlies the dielectric layer. When an alternating current circuit is connected to layers io a@nd 13 in the.manner shown, light is emitted by the phosphor suspended in the dielectric layer 11., This light i@ visible through the glass 12. The cell of Fig. 2 is similar t6 that of Fig. I insofar as having ihe conducting base 16 is concerned and also the dielectric layer 11 in which the phosphor suspelided. However, insiead 6f the transparent conducting layer 13 I provide a grid 14 composed of fine lines of aq opaque conducting material such ds silver paste or vapoiized metal. The line@ of ihe @rid 14 are a few thousandths of an, inch in width and are sepa@rated by a similar distance. Where, conducting substances sucli. as silver paste, are used, the line may b6 applied to the plastic using. Wellknown printiiik techniques suc.h as the silk screen process in which ce@rtain parts of a piece of silk cloth are made impervious in accordance wlift @ pattern. The rest of the silk cloth oi screen may then be impregnated with silver paste ,@hich will p6netraie the screen and apply 6n th6 s@rfac(@ of ihe PlAstic in accordance with the pattern of the screeii. I hdve discov6red that An opaque conducting mat or web @uch as that described above allows a considerable amouni bf light to eme through the interstitial spaces. rge If the pattern is in the form ol' a clock dial or instrumeiit ace, the -ht f efe6trolumin6seent cell provides sufficient 11, for e@sy visibility. A pr6tective lay,-r 15 of paint or plastic may be p6sitioned over the grid 14. Fig. 3 illustrates an alternative embodiment of my in-@eniibn wherein th6 f,@i6 c6iiducting layeis are coplanar and intdrwoven but ard ifi u'lat6d froni each other. As in the case of Fig. 2, the phosphor is embedded -in a di616ciiie tayer 11. However, th6 alternati@g ci-irrent flows between two grids 16 and 17 both 6f which are in enga'gem6nt With the @dni6 side of the dielectric leiyer 11. The 9' rids 16 aiid@ 17 a:ie held in'position by an overlying layer of plastic 15. in Fi s. 1, 2 Eind 3 th6 6ondiicting layers are con@ected .9 togeth&r thrbtigh a @n alternatin-- ctirrent circuit 18. The luminous intensity of the' 6lectroluminesceht cell varies dire6tly With the fre4uen6@. 6f th6 ctirrent up to a' certain poiiit an(I Witlf the -@oltage. An overvoltage will restilf in diel6ctric br6akdow,n in the same manner as with any othet type of 4@aPacitor. Diiiing energiiation and deeiadrgi2aticin 6f thd c6ll th&re is' a high voltage surge which eifddiigdfs' the dielectric. I have di@covered' that the incorporation of a resistance element 20 in the alternating circuit will minimize the effect of this surge and prevent dielectric breakdown. The thickness of the layers shown is considerably exaggerated for purposes of illustration. While the base plate 10 and top plate or layer 15 may be rnade quite thick to impart stiffness to the cell, the dielectric layer ][I is of a thicki3ess of the order of a few mils and the conducting grids 14, 16 and 17 are even thinner. The spacing of the grid lines is also considerably exaggerated. My invention enables a transparent plastic to be used as a backing for one of the conducting layers instead of glass. However, glass may also b-. use-i fcr this putpose. In one embodirnent of my inve-.ition I provide a top plate 15 made of glass or transparent plastic. The conductin.mat in coiatact therewith rnay be com. posed of parallel or intersecting stripes of silver paste printed by th,- abovementioned silk screen process or aluminum which has been evaporated onto the top plate. A phosphor embedded in a layer of plastic is then sprayed over the conducting
[2]3 layer. The second conducting layer may now be sprayed, painted or printed silver paste or evaporated aluminum or aluminum foil. These materials readily lend themselves to use in this invention, but it is obvious that other materials which will conduct an electric current could be subsfituted for the silver or aluminum. In a sccond emboditnent of my invention, the top plate is glass or transparent plastic, as before. However, in this embodirnent parallel conducting stripes with alternate stripes connected to opposing electric terminals as shown in Fig. 3 are used. A phosphor paint is then applied over the conducting layers. in accordance with a third embodiment of my invention, the base material is a plastic film with phosphor particles incorporated therein. On one side of this film parallel or intersecting conducting stripes are applied. A continuous coating of conducting material is then applied to the other side. in accordance with a fourth embodiinent, a cell is made starting with a base of conducting material. A phosphor suspended in a plastic material is applied over this conducting material. Conducting stripes are then applied over this plastic layer and electrical connections are made between the base metal and the conducting stripes. In accordance with this embodiment a protecting layer of plastic over the conducting stripes is utilized to reduce corona and provide mechanical protection. The several embodiments described above are illustrated in Figs. 2 and 3 except that in certain cases one of the non-conductin- layers is omitted. Any of these cells, when incorporated in an alternating electric circuit having a resistance 20 of about 100,000 ohms in series, will have a long life and will operate satisfactorily on 60cycle house current. While the present invention has been described by reference to particular embodiments thereof, it will be understood that numerous modifications may be made by those skilled in the art without actually departing from the invention. 'fherefore, I aim in the appended claims to cover all such equivalentvariations as come within the true spirit and scope of the foregoing disclosure. What I claim as new and desire to secure by
