CA1082445A - Fluorescent compositions and low-velocity electron excited fluorescent display devices utlizing the same - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
Fluorescent compositions which contain zinc oxide and one phosphor selected from the group hereinafter defined in a weight ratio within the range of 1/9 to 9/1, and fluo-rescent display devices having said fluorescent compositions in the form of a fluorescent screen, which can emit green, blue or rod light under low-velocity electron excitation, said group consisting of a copper and-aluminium activated zinc cadmium sulfide phosphor [(Zn1-x, Cdx)S:Cu, Al, wherein 0?x?0.1], a cerium activated yttrium aluminium gallium oxide phosphor [Y3(Al3-y, Gay)5O12:Ce, wherein 0?y?0.5], a manganese activated zinc silicate phosphor (Zn2SiO4:Mn), a terbium activated yttrium lanthanum oxysulfide phosphor [(Y1-z, Laz)2O2S:
Tb, wherein 0?z?1], a europium activated strontium gallium sulfide phosphor (SrGa2S4:Eu2+), a silver activated zinc sulfide phosphor (ZnS:Ag), and a europium activated yttrium oxysulfide phosphor (Y2O2S:Eu).

Description

108;~445 BACKGROUND OF THE INVENTION
Field of the Invention This invention relates to novel fluorescent compositions and low-velocity electron excited fluorescent display devices 5 . utilizing the same, and more particularly is concerned with novel fluoroescent compositions which can display emission having high luminance in a high state of color purity under low-velocity electron excitation, and low-velocity electron excited fluorescent display devices containing as a fluorescent screen these fluore-scent compositions.
Description of the Prior Art , As is commoniy known, a low-velocity electron excited I fluorescent display device (which is abbreviated as a "Fluorescent ~ display device" hereinafter) may be employed as a display device ¦ 15 for desk top electronic calculators and various kinds of measur-ing instruments . Demand for such fluorescent display devices is ¦ great because ofthe remar~able popularization in recent years of calculators and instruments in which they are employed. The fluorescent device of this kind in general has a fundamental . :;` 20 structure such that both an anodic plate having a fluorescent :
screen on one side thereof and a cathode standing face to face , : ~ with the above-described fluorescent screen are enclosed in an . ~ evacuated tube wherein the fluorescent screen placed on the anodic ~ : plate is excited by low-velocity electrons emitting from the J~
~:` 25 cathode to result in amission of light of certain wavelengths.
. ~
Both Figure 1 and Figure 2 give outlines of typical structures . ~ of fluorescent display devices, and they show a diode type display. ~ 2 -, ,~
~,......... , . ~ . . - -,~. . : . . ..
,; ,. , , , ~
, ~08'~445 tube and a triode type display tube, re~*ively. As s ~ n in both Figure 1 and Figure 2, one side of an anodic plate 11 made of, e.g., an al ~ num plate, has a fluorescent screen 12 thereon. me other s~e of the anodic plate 11 is supported by a ceramic base plate 13. The diode type display tube is equipped with a cathode standing face to face with the above-described fluorescent screen 12 placed on the one side of the anodic plate 11, and emission occurs by excitation of the fluorescent screen 12 which arises from low-velocity electrons emitted from the cathode 14. In particular, the triode type display tube shown in Figure 2 additonally has a grid electrode 15 between the cathode 14 and the fluorescent screen 12 so as to control or diverge low-velocity electrons emitted from the cathode 14. Moreover, when the surface of the fluorescent screen 12 has wide area, two or more cathodes may be additionally placed in both fluorescent display tubes shown in Figure 1 and Figure 2 wherein only one cathode is placed, and there is no particular limit to the number of cathodes that can be placed therein. The aforesaid anodic plate 11 having a fluorescent screen 12 on one side thereof, the ceramic base plate 13 and the cathode 14 (which are shown in Figure 1), or the aforesaid anodic plate 11 having a fluorescent , screen 12 on one side thereof, the ceramic base plate 13, the cathode 14 and the grid electrode 15 (which are shown in Figure 2) are enclosed in a transparent container 16, made of, for example, t glass, the pressure inside which is held at a high vacuum of 10 5 to 10 g Torr.
Zinc activated zinc oxide phosphors (ZnO:Zn) have ~een commonly ~nown as phosphors employed for the above-described . .;1 ~ fluorescent display devices which can emit light of high 3~

i~
, : . . ' ' . . ': . - ,. : --. ,: . - ~ - . .: . . .

~082445 luminance under low-velocity electron excitation occurring under certain conditions, particularly under acceleration potential below 100V. Phosphors of this kind can be prepared by firing zinc oxide ~ZnO) alone in a reducing atmosphere, or by firing ZnO contaminated with a slight amount of a certain zinc compound other than ZnO such as zinc sulfide ~ZnS) or the like in air, and they can give forth greenish white emission of high luminance when excited by low-velocity electrons. Fluorescent display devices havinq the fluorescent screen made of the aforesaid ~ZnO:Zn) have been commercially used as display devices for, e.g., desk top electronic calculators and various kinds of measuring instruments. However, aside from ~ZnO:Zn) almost no phosphors are known which can emit light under low-velocity electron ; excitation, and therefore, fluorescent display devices equipped with fluorescent screens containing phosphors other than (ZnO:Zn) are rare at the present stage of this art. Emission color of ~ZnO:Zn) is greenish white as described above, and therefore a fluorescent display device utilizing ~ZnO:Zn) has inadequate I color purity as a green emitting display. Accordingly, the 20 present invention is aimed at providing green emitting composi-tions and fluorescent display devices using them which can emit i~ green light in a high state of color purity. In addition, the present invention is also aimed at providing fluorescent composi-tions capable of emitting light of specific wavelengths, other than greenish ones, in high luminance and at providing fluorescent display devices utilizing them.
SUMMA~Y OF T~.E INVENTION
One object of the present invention is to provide novel ~J' ~
, .

.. . . .. .

108'~445 fluorescent compositions which can give forth emission of high luminance in a high state of color purity under low velocity electron excitation which occurs under certain conditions, particularly under acceleration potential below lOOV.
S Another object of the present invention is to provide novel green emitting compositions which can give forth green emission of high luminance in a high state of color purity under low-velocity electron excitation occurring under certain condi-tions, particularly under acceleration potential below lOOV.
A further object of the present invention is to provide novel blue emitting compositions which can give forth blue emission of high luminance in a high state of color purity under low-velocity electron excïtation occurring under certain condi-tions, particularly under acceleration potential below lOOV.
Still another object of the present invention is to provide novel red emitting compositions which can give forth red emission of high luminance in a high state of color purity under low-velocity electron excitation occurring under certain condi-tions, particularly under acceleration potential below lOOV.
Another object of the present invention is to provide fluorescent display devices which can display emission having b~th high luminance and high color purity.
A further object of the present invention is to provide fluorescent display devices which can display green emission hav-2S ing both high luminance and high color purity.
Still another object of the present invention is to provide fluorescent display devices which can display blue ~; emmission having both high luminance and high color purity.

i~ - 5 -: $

. . - . . . . .
,., : , .,. - ,. .... . . ... . : . .:-~ . . . - . . . . .. . . .
~.. . , . ~ .

108;~4~5 Another object of the present invention is to provide fluorescent display devices which can display red emission hav-ing both high luminance and high color purity.
Other objects of the present invention will become apparent from a consideration of the following description and examples.
These objects can be attained with fluorescent composi-tions containing zinc oxide and one phosphor selected from the following group in a weight ratio ranging from 1:9 to 9:1, said group consisting of a copper and aluminium activated zinc cadmium sulfide phosphor [(Znl x' Cdx)S:Cu, Al, wherein 0~x~0.1], a cerium activated yttrium aluminium gallate phosphor [Y3(All y, Gay)5Ol2:Ce, wherein 0Cy~0.5], a manganese activated zinc silicate phosphor (Zn2SiO4:Mn), a terbium activated yttrium lanthanum oxy-sulfide phosphor [(Yl z, Laz)2O2S:Tb, wherein 0~z~1], a europium activated strontium gallium sulfide phosphor (SrGa2S4:Eu2 ), a silver activated zinc sulfide phosphor (ZnS:Ag), and a europium activated yttrium oxysulfide phosphor ~Y2O2S:Eu).
Moreover, some objects of the present invention can be attained.with fluoresaent display devices having the above-described fluorescent compositions as a compound of a fluorescent screen.
When x equals zero in the aforesaid formula 1(Znl x' Cdx) S:Cu, Al], this formula represents the copper and aluminium acti-...... 25 vated zinc sulfide phosphor, but in the present discussion these . are dealt with as the special cases of copper and aluminium activated zinc cadmium sulfide phosphors.
Although the formulae ~Y3(All_y, ~ay)512 ':~`

.,.

.~ .: . . . - . , - . .

108'~45 [(Yl z, Laz)2O2S:Tb] under the conditions of y=0, z=0 and z=l represent a cerium activated yttrium aluminium phosphor, a terbium activated yttrium oxysulfide phosphor and a terbium activated lanthanum oxysulfide phosphor, respectiveLy, the former is dealt with as the special case of cerium activated yttrium aluminium gallium phosphor, and the latter two phosphors are dealt with as the special cases of terbium activated yttrium lanthanum oxysulfide phosphors analogous to the way mentioned above.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 and Figure 2 are structural outlines of typi-. cal examples of fluorescent display devices wherein a diode type display tube is shown in Figure 1 and a triode type display tube is shown in Figure 2, Figures 3A to 3J illustrate the dependence of luminance of emission on the mixing weight ratio of the amount of ZnO to that of the phosphor contained in a fluorescent composition pro-vided in the present invention under low-velocity electron exci-tation, Figures 4A to 4J are diagrams illustrating the relation-ships between brightness of emission, which each of the fluore-~ ~ scent compositions of the present invention and the phosphor s' alone comprised therein give forth, and the acceleration potential;l applied to each of them, t ~ 25 Figures 5A to 5K are emission spectra of the respective fluorescent compositions of the present invention and the conven-~ tional one, and ~ Figure 6 is a CIE standard chromaticity diagram plotted , ; . , , . , ' . ' ~ ' . ' . , ~, 108;~445 against the emission chromaticity under low-velocity electron excitation of the fluorescent compositions of the present inven-tion and the known fluorescent composition.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
All the fluorescent compositions provided in the present invention which contain a certain composition capable of emitting green, blue or red-light under low-velocity electron excitation are characterized by containing ZnO as an essential component.
Commercially available reagent grade ZnO (termed as "reagent ZnO" hereinafter), for example, Sazex 2000* manufactured by Saikai Chemicals, may be used as the ZnO which is one of the important components of the present invention without any purify-ing treatments. Besides reagent ZnO, zinc oxides produced by firing in air zinc compounds of the kind which can easily be converted to zinc oxide at high temperature, such as zinc carbon-ate, zinc sulfate, zinc oxalate, zinc hydroxide, etc., (termed as "fired ZnO" or "heat treated ZnO" hereinafter) can also be employed. Appropriate firing temperatures for producing fired ZnO were found to be below 1200C. Temperatures higher than 1200C were undesirable because ZnO commences sintering.
' The phosphors which correspond to the other component -~ of the fluorescent compositions provided in the present invention including phosphor (1) having the formula l(znl x' Cdx)S:Cu, Al], phosphor 12) having the formula [Y3(all_y, Gay)5O12:Cel, phosp ~3) having the formula-[Zn2SiO4:Mn], phosphor (4) having the formula l~Yl z, ~az)2O2S:Tbl, phosphor (5) having the formula (SrGa2S4:Eu 1, phosphor (6) having the formula [ZnS:Agl and - * denotes trade mar~ throughout the application , . . . . . . . . . . . . .
- . : -. . ~ ~ . . . .
.
- ~

108'~445 phosphor (7) having the formula [Y202S:Eu] can, in general, be produced in accordance with the following process.
Phosphor (1) may be prepared as follows: Chemically precipitated zinc sulfide (ZnS) and chemically precipitated cadmium sulfide (CdS) are mixed in a molar ratio of (l-x) mole of the former to x mole of the latter (, wherein the value x is within the range of O~x~0.1). To the resulting sulfide mixture there are added both the prescribed amount of a copper compound such as copper sulfate (CuSO4 5H2O) or the like and the pre-scribed amount of an aluminium compound such as aluminium sulfate [A12(SO4)3 18H2O] or the like, and they are mixed thoroughly.
Then, they are fired at a temperature ranging from about 900DC to about 1200C for periods of about one hour to about five hours in a sulfuric atmosphere such as an atmosphere of hydrogen sulfide, sulfure or the like to produce phosphor (1). The preferred amount of an activator corresponding to either Cu or Al which is suitable for phosphor ~1) is within the range of 10 5 to 10 3 gram, and more preferably 5 x 10 5 to 5 x 10 4 gram, per one gram of a host material (Znl_x, Cdx)S.
When the affix x has a value larger than 0.1, the phosphor (1) emits light of longer wavelength, from yellow to red, with increasing value of x. Therefore, those compositions are unsuitable for those of components which constitute fluorescent compositions employed for green emitting fluorescent display devices of the present invention.
Phosphor (2) may be prepared as follows: Yttrium oxide -~ (Y2O3) or an yttrium compound easily alterable to Y2O3 at a high - temperature, alluminium oxide (A1203) or an aluminium compound ' , ~ _ g _ .

, .

iO8;~445 easily alterable to A12O3 at a high temperature are mixed with Ga203 or a gallium compound easily alterable to Ga203 in a molar ratio of 5 moles of an oxide mixture, one mole of which is represented by the formula (All y Gay)203 wherein Y mole of Ga2O3 is mixed with (l-y) mole of A12O3 under the condition of 0~y~0.5, to 3 mole of Y203, and the prescri~ed amount of a cerium ion which is suitable for the phosphor (2) is further added to and mixed with the resulting oxide mixture in the form of cerium oxide (Ce203) or a cerium compound easily alterable to cerium oxide at a high temperature. The mixture is fired at a temperature within the range of about 1200C to about 1700C, and preferably about 1400C to about 1600C, for about one hour to about five hours in an air or in a weak-reducing atmosphere. It is preferred that the above-described firing treatment be repeated not less than twice.
The preferred amount of the activator Ce appropriate to the phosphor (2) is within the range of 10 4 to 10 1 gram atom and more particularly 10 3 to 5 x 10 2 gram~atom, per mole of a host 3 1 Y y 5 12- Among the compositions included within the scope of phosphor (2), those which have the affix y equal to a value larger than 0.5 were not suitable as a component of a fluorescent composition employed for the fluorescent display device of the present invention because of the fluorescent luminance decreases with increasing the value y.
Phosphor (3) may be prepared by mixing zinc oxide (ZnO) or a zinc compound easily alterable to ZnO at a high temperature with silicon dioxide (SiO2) or a silicon compound easily alter-able to SiO2 at a high temperature in a molar ratio of 2 mole of ZnO to 1 mole of SiO2, additionally mixing the resulting mixture ., . -- 10 --" . ~ ' ~ . ~ . : - -' ' , ' - ,: . ~ ' .

108~44S
oxide with the prescribed amount of manganese ion, an activator for the phosphor (3), in the form of manganese oxide (MnO) or a manganese compound easily alterable to MnO, and then firing them in air at a temperature within the range of about 10~0C to about 1400C, and more particularly about 1200C to about 1300C, for about one hour to about five hours. The above-described firing process should be repeated not less than 2 times. The preferred amount of the activator Mn suitable for the phosphor (3) was within the range of 10 4 to 10 1 gram atom, and more particularly 10 3 to S x 10 2 gram-atom, per mole of host material Zn2SiO4.
Phosphor (4) may be prepared by mixing yttrium oxide (Y2O3) with lanthanum oxide (La2O3) in a molar ratio of (l-z) mole of the former to z mole of the latter (wherein the value z is present within the range of 0~z~1), additionally mixing them with the prescribed amount of terbium oxide (Tb2O3), adding to the resulting rare earth oxide mixture 20 to 40 weight % of sulfur (S) and 20 to 40 weight % of sodium carbonate (Na2CO3) to act as a flux thereon, mixing them thoroughly, and firing the resulting mixture in air at a temperature within the range of about 1200C
to about 1300C for about one hour to five hours. The aforesaid rare earth oxide mixture group consisting of Y2O2, La2O3 and Tb2O3 may be produced simply by physically mixing these ingredients, but it should, in general, be prepared by once dissolving these ingredients in a mineral acid with the intention of improving

2~ upon the miscibility thereof, adding in aqueous solution of oxalic acid thereto to coprecipitate yttrium oxalate, lanthanum oxalate and terbium oxalate, and then pyrolyzing the resulting coprecipi-tated rare earth oxalate mixture. The preferred amount of the :'' -1~ ' ' , ~

', Y- : :

iO8'~445 activator Tb suitable for the phosphor (4) is within the range of 10 2 to 1.5 x 10 1 gram, and more particularly 5 x 10 2 to 6 x 10 gram, per 1 gram of host material (Yl z, Laz)2O2S.
Phosphor (5) may be prepared by adding gallium oxide (Ga2O3) of high purity to a strontium compound which is easily - alterable to the sulfide by heating in a sulfuric stream, such as strontium sulfate, strontium carbonate or strontium chloride, all of which must be of high purity, in equimolar amounts, addi-tionally adding as an activator the prescribed amount of europium ion in the form of europium sulfate [Eu2(SO4)3~, europium nitrate [Eu(NO3)3] or europium oxide [Eu2O3] to the aforesaid oxide mix-ture, thoroughly mixing the resulting mixture, and then firing it at a temperature within the range of about 700C to aboùt 1000C, and more preferably about ~00C to about 900C, for about 3 to about 5 hours in a sulfuric stream of such as sulfur vapor, hydrogen sulfide gas, carbon disulfide gas or the like.
The preferred amount of the activator Eu suitable for ISrGa2S4:
Eu2+] was within the range of 10 4 gram-atom to 5 x 10 1 gram atom, and more particularly 5 x 10 3 gram-atom to 10 1 gram.atom, per mole of host material SrGa2S4.
Phosphor (6) may be prepared by adding an appropriate amount of a silver compound such as silver nitrate or the like to reagent grade zinc sulfide (ZnS) and then ~iring the resulting mixture in a weak-reducing atmosphere at a temperature within the 2~ range of about ~OO~C to about 1200DC for about one hour to about five hours. The resulting IZnS:Ag~ is known to have two crystal systems; i.e., a cubic system and a hexagonal system. The phosphor [ZnS:Ag] crystal of the hexagonal system can be obtained .~ .

~ - 12 -. .

~,i ~ . . ,. : .
.
:, - : . . - - : . ;-.. ~ . , . : - - . . . .

~08'~445 by firing the aforesaid starting material at a temperature higher than about 1020C, and that of a cubic system can be produced by firing the aforesaid starting material at a temperature lower than about 1020C. [ZnS:Ag] of either the cubic crystal system or the hexagonal crystal system can be used as the component of the fluorescent composition. The preferred amount of the activa-tor Ag suitable for [ZnS:Ag] was within the range of 10 5 to 10 3 gramt and more particularly 5 x 10 5 to S x 10 4 gram, per gram of host material ZnS.
10Phosphor (7) may be prepared by adding the prescribed amount of europium oxide ~Eu2O3) to yttrium oxide (Y2O3), and then mixing them thoroughly to make a rare earth oxide mixture, further mixing the resulting mixturewith 20 to 40 weight % of sulfur (S) and 20 to 40 weight % of sodium carbonate (Na2CO2) to act as a flux, and then firing them in air at a temperature of about 1200C to about 1300C for about one hour to about five hours. The preferred amount of the activator Eu suitable for [Y2O2S:Eu] was within the range of 10 2 to 1.5 x 10 1 gram, and more particularly 5 x 10 2 to 6 x 10 2 gram, per gram of host material Y2O2S.
Fluorescent compositions of thepresent invention can be produced by mechanically mixing ZnO and one of the above-descri~èd phosphors (1) to (7). The mixing process may be carried out by use of a conventional mixing instrument such as a mortar, a ball-mill, a mixer-mill or the like.
~`~The two components are mixed in a weight ratio of the amount of zinc oxide to that of phosphor ranging from 1/9 to 9/1.
~Nhen~zinc oxide is present in an amount under the mixing weight `'~ - 13 -,i - .

., ,~ . , . ~ .

~ , .
. . - :

108'~45 ratio of 1/9, characteristics of the resulting composition are akin to those of the phosphor used. Therefore, substantially no emission is observed under low-velocity electron excitation. On the other hand, when zinc oxide is present in an amount in excess of the mixing weight ratio of 9/1, the resulting composition gives rise to very weak emission because of the small amount of phosphor. Accordingly, the mixing ratio of these two components isrequired tobe within the range of 1/9 to 9/1. This factis illustra-tedby thegraphs inFigures3A to 3Jas follows: Each of Figures 3A to 3J shows the relationship between the ZnO/phoshpor ratio (by weight) of one of fluorescent compositions to be examined in the present invention and the luminance of emission achievable under low-velocity electron excitation. Figures 3A to 3H each corresponds to the luminance of emission achieved under the acceleration potential of ~OV, while Figures 3I and 3J correspond to that achieved at 100V. Figures 3A, 3B, 3C, 3D, 3E, 3F, 3G, 3H, 3I and 3J show the results obtained using as phosphors (I) ZnS:Cu, A1 (pho5phor (1)-1), (II) (Zn0 95, Cdo 05)S:Cu, Al (phosphor (1)-2), (III) Y3A15O12:Ce (phosphor (2)-1), (IV) Y3(A10;6, GaO 4)5O12:Ce (phosphor (2)-2), (V) Zn2SiO4:Mn (phosphor

(3)), (VI) Y2O2S:Tb (phosphor (4)-1), (VII) La2O2S:Tb (phosphor

(4)-2), (VIII) SrGa2S4:Eu2+ (phosphor (5)), (IX) ZnS:Ag (phosphor (6)) and (X) Y2O2S:Eu (phosphor (7)), respectively. The curve a and the curve b in each of Figures 3A to 3H and Figure 3J
~5 show the case in which reagent ZnO is used and the case in which fired ZnO produced by firing at the temperature of 1000C is `~ used, respectively. The curve a, the curve ~ and the curve _ in ~igure 3I show the case wherein reagent ZnO is used, the case , .
. . : , ~ ., .
: .-, ., : : . ' .. . : - ~ - . . ~
: - :

1~82445 wherein fired ZnO produced by firing at 700~C is used and the - case wherein fired ZnO produced by firing at 1000C is used, respectively.
It is apparent from the aforesaid figures that the values of the luminance corresponaing to the values of the ZnO/
phosphor ratio smaller than 1/9 and larger than 9/1 were extremely small in all fluorescent compositions. The value of the ZnO/
phosphor ratio which provides the maximum luminance depends upon the kind of ZnO used. Namely, in each of Figures 3A to 3H and Figure 3J, maximal luminance is obtained with the ZnO/phosphor ratio of abour 1/1 when reagent ZnO is used and whatever kind of phosphor may be used therein ~as shown on the curve-a). How-ever, when fired ZnO is used, the ZnO/phosphor ratio capable of providing maximal luminance is gradually shifted to larger values than 1/1 (i.e., in the direction of increasing amount of ZnO) with rising firing temperature. For example, in the case where fired ZnO produced by firing at 1000C is employed, maximal luminance is obtained with a ZnO/phosphor ratio of about 7/3 whatever kind of phosphor may be used therein (as shown on the curve-b). A similar tendency to the above-described one can also be observed in Figure 3J which shows that maximal luminance is obtained with the ZnO/phosphor ratio of about 3/7 when reagent ZnO is used (as shown on the curve-a). However, when fired ZnO
is used, the ZnO/phosphor ratio capable of providing maximal 2~ luminance is gradually shifted to larger values than 3/7 (i.e., in the direction of increasing amount of ZnO) with rising firing temperature. For example, in the case of a firing temperature , ~ .
of 700~C (curve-b), maximal luminance is obtained with a ZnO/

, ~
, , ` ' . .. . .

'`' ' ' ' ' :

108'~4~5 phosphor ratio of about 1/1, and in the case of a firing tempera-ture of 1000C (curve-c), maximal luminance is obtained with a ZnO/phosphor ratio of about 7/3.
In addition, the fluorescent composition containing a combination of two or more kinds of phosphors selected ~rom the group consisting of the aforesaid phosphors (1) to (5) give results similar to the above, and it goes without saying that fluorescent compositions containing the combined phosphor in the ZnO/phosphor ratio in the range of 1/9 to 9/1 fall under the category of the present invention.
The fluorescent compositions of the present invention are characterized by producing emissions having high luminance and excellent color purity under low-velocity electron excitation.
Of the fluorescent compositions proposed in the present invention, those compositions containing the phosphors (1) to (5) emit green light, those compositions containing the phosphor (6) emit blue light and those compositions containing the phosphor (7) emit red llght. These results are particularly surprising in view of the fact that the phosphors comprised in the fluorescent compositions of the present invention themselves display emission at high luminance under electron excitation at an acceleration potential of several KV, ~ut display almost no emission under low-velocity electron excitation, particularly under an acceleration poten~ial below 100V.
Although the reason why compositions preparea from Zno ~ and phosphor of the ~ind which display hardly any emission under ;S ~low-velocity electron excitation by mixing them thoroughly can, when mixed thoroughly, display some emission under low-velocity . . . - - . . , : .. ... - :
-: . - - . - . , - .- : :
. .. . :-: , - . , . : , -.- .. . . : .
, . . . : : . . , - ., . .: : -:, - . : : : , .
.... . . . .. . . .

108Z4~5 electron excitation has not been clarified at the present, it is thought that the aforesaid phenomena occurs predominantly because of the improved excitation efficiency which becomes possible because the electric conductivity of the composition is raised S as a whole by the addition of ZnO having higher electric conduc-tivity than the phosphors (1) to (7), so that the charge-up phenomenon does not occur on the occasion of excitation.
~ he differences between the emission characteristics of the fluorescent compositions of the present invention and those of of phosphors present as a component therein are illustrated in detail with reference to Figures 4A to 4J. These figures show the dependence of luminance upon acceleration potential. In each figure, curve-a corresponds to the result for the fluorescent composition prepared in the present invention, while curve-b corresponds to that for the phosphor comprised therein itself.
That is to say, the curve-a in Figure 4A shows the result for the fluorescent composition prepared by mixing reagent ZnO with the phosphor (1)-l lZnS:Cu, Al], which contains both activators Cu and Al in the amount of 10 4 g/g, in an amount of an equivalent mixing ratio by weight in accordance with one of the examples hereinafter described, while the curve-b shows the result for the aforesaid phosphor (1)-l alone. The curve-a in Figure 4B shows the result for the fluorescent composition prepared by mixing reagent ZnO with the phosphor (1)-2 {(Zn0 95, Cdo 05)S:Cu, Al], which contains both activators Cu and Al in the samé amount of g/g, in an amount of an equivalent mixing ratio by weight in accordancewith another example hereinafter described, while the 1' . curve-b shows the result for the aforesaid phosphor (1)-2 alone.
., !, ~ 17 , . . - ~ .
,.
, - - ' '.. ' : ~ - .

108'~445 The curve-a in Figure 4C shows the result for the fluorescent composition prepared by mixing reagent ZnO with the phosphor (2)-1 1Y3A15O12:Ce], which contains the activator Ce in the amount of 10 2 gram-atom/mole, in an amount of an equivalent mix-ing ratio by weight in accordance with a further example herein-after described, while the curve-b shows the result for the aforesaid phosphor (2)-1 alone. The curve-a in Figure 4D shows the result for the fluorescent composition prepared by mixing reagent ZnO with the phosphor (2)-2 [Y3(Alo 6~ Ga~ 4)512 Ce3, which contains the activator Ce in the amount of 10 2 gram-atom/
mole, in an amount of an equivalent mixing ratio by weight in accordance with still another example hereinafter described, while ~he curve-b shows the result for the aforesaid phosphor (2)-2 alone. The curve-a in Figure 4E shows the result for the fluor-escent composition prepared by mixing reagent ZnO with the phos-phor (3) lZn2SiO4:Mn], which contains the activator Mn in the ; amount of 2 x 10 2 gram-atom~mole, in an amount of an equivalent ` mixing ratio by weight in accordance with another example herein-after described, while the curve-b shows the result for the aforesaid phosphor (3) alone. The curve-a in Figure 4F shows the result for the fluorescent composition prepared by mixing reagent ZnO with the phosphor (4~ Y2O2S:Tb], which contains ~ the activator Tb in the amount of 5 x 10 2 g/g~ in an amount of¦ an equivalent mixing ratio by weight in accordance with a further example hereinafter descri~ed, while the curve-b shows the result for the aforesaid phosphor (4)-1 alone. The curve-a in Figure 3 4G shows the result for the fluorescent composition prepared by~ .

mixing reagent ZnO with the phosphor (4)-2 [La2O2S:Tb~, which p ~i' ' ;'- -,~ ~ - 18 --1:~ . .
,, ~ , , , . . . .. , _ _ _ _ _ . . . . . . .
': - , . . .. ..
:, '- ' ' ' , . .
: . . . . .
.. . - : . . : . .- -' , ' ., - ~- . .~ ,. . .. :
.. . . . . . . .
~,~, ~, - . , 108'~445 contains the activator Tb in the amount of 5 x l0 g/g, in an amount of an equivalent mixing ratio by weight in accordance with a still another example hereinafter described, while the curve-b shows the result for the aforesaid phoshpor (4)-2 alone. The curve-a in Figure 4H shows the result for the fluorescent compo-sition prepared by mixing reagent ZnO with the phosphor (5) (SrGa2S4:Eu2+], which contains the activator Eu2~ in the amount of 3 x l0 2 gram.atom/mole, in an amount of an equivalent mixing ratio by weight in accordance with another example hereinafter described, while the curve-b shows the result for the aforesaid phosphor (5) alone. The curve-a in Figure 41 shows the result for the fluorescent composition prepared by mixing heat treated ZnO produced by firing at 1000C with the phosphor (6) [ZnS:Ag], which contains the activator Ag in the amount of l0 4 g/g, in the mixing ratio of 7 weight parts of the former to 3 weight parts of the latter in accordance with a further example of the present invention hereinafter described, while the curve-b shows the result for the aforesaid phosphor (6) alone. The curve-a in Flgure 4J shows the result for the fluorescent composition pre-pared by mixing reagent ZnO with the phosphor (7) lY2O2S:Eu],which contains the activator Eu in the amount of 5 x l0 2 g/g~
in an equivalent mixing ratio by weight in accordance with still another example of the present invention hereinafter described, ¦ while the curve-b shows the result for the aforesaid phosphor (7) ` 25 alone.
It is apparent from Figures 4A to 4~ that the fluor-escent compositions ofthe present invention emit green, blue or red light even under conditions that cause the luminance of the ,lg -.. . .

'': . : ' - ~ :
.- .- : - , :. , , ,,- . ~ :............ . .

108'~'~45 phosphors contained in the respective fluorescent compositions as essential components thereof, to decrease rapidly; i.e., under low-velocity electron excitation induced by acceleration poten-tials below 100V. For example, the luminance of each of the S fluorescent compositions shown in Figure 4A, 4B or 4F is about several hundred times that of said respective phosphors alone under low-velocity electron excitation induced by application of acceleration potential of 100V, and the luminance of each of the fluor~scent compositions shown in Figure 4C, 4D, 4E, 4G, 4H, 4I
or 4J is about one thousand times that of said respective phos-phors alone under the same conditions as mentioned abo~e.
The excellent emission spectrum characteristics of the fluorescent compositions of the present invention can be seen from Figures 5A to 5I. Among the fluorescent compasitions pro-posed in the present invention, all green-emitting compositions emit green light in a higher state of color purity that the well-known fluorescent composition lZnO:Zn3. Namely, Figures 5A to 5 and Figure 5I are graphs representing the emission spectra of fluorescent compositions of the present invention and tZnO:Zn], respectively, under low-velocity electron excitation. Figure SA
shows the emission spectrum of a fluorescent composition prepared by mixing ZnO and the phosphor (1)-1, Figure 5B shows the emis-sion spectrum of a fluorescent composition prepared by mixing ZnO
and the phosphor (1)-2, Figure 5C shows the emission spectrum of 25 a fluore9cent composition prepared by mixing ZnO and the phosphor (2~-1, Figure 5D shows the emission spectrum of a fluorescent ¦~ composition prepared ~y mixing ZnO and the phosphor (2)-2, Figure 5E shows theemission spectrum of a fluorescent composition , - 20 -.~,...~... .

~08~445 prepared by mixing ZnO and the phosphor (3), Figure 5F shows the emission spectrum of a fluorescent composition prepared by mix-ing ZnO and the phosphor (4)-1, Figure SG shows the emission spectrum of a fluorescent composition prepared by mixing ZnO and the phosphor (4(-2, Figure 5H shows the emission spectrum of a fluorescent composition prepared by mixing ZnO and the phosphor

(5) and Figure 5I shows the emission spectrum of the conventional fluorescent composition [Zno:Zn} alone.
All of the emission spectra in the aforesaid green emitting compositions of the present invention indicate a main peak at a wavelength closer to green than that ~f a well-known composition [ZnO:Zn3, and the h~lf-value width of each emission spectra is narrower than that of [ZnO:Zn]. Therefore, the emis-sion color of each green emitting composition of the present , 15 invention is a green of a higher color purity than the emission color of [ZnO:Znl.
Figure 6 shows CIE standard chromaticity diagrams where-in chromaticity points of the emission spectra obtained under low-l velocity electron excitation relating to the fluorescent composi-!; 20 tions ~llustrated in the examples of the present invention and ¦ lZnO:Zn], the emission spectra of which were shown in Figures 5A
, to 5I, are plotted. The chromaticity points A, B, C, D, E, F, G, . ~ H and I correspond to the emission spectra shown in Figures 5A, . ~ 5B, 5C, SD, 5E, 5F, 5G, 5H and 5I, respectively. As can be seen ~:~ 25 from Figure 6, the emission color-obtained for each of the fluor-:, ~, : ::
.~ escent compositions of the present invention (chromaticity points .' 5',~ A, B, C, D, E, F, G and H) is also a green of much more excellent color purity than that of lZnO:gn]. The fluorescent compositions A~ . 21 ~. . ; - ,. , ~ . . . , -- - .
,., . ~ ~ .

prepared in accordance with the present invention and having emission spectra as shown in Figures 5A to 5H each contains a single phosphor. It is, however, possible to produce other fluorescent compositions capable of emitting green light of higher color purity than [ZnO:Zn] by combining two or more phosphors selected from the aforesaid phosphors (l) to (S).
In addition, a fluorescent composition containing the phosphor (6) prepared in accordance with the present invention can give forth blue emi~sion of high luminance in a high state of color purity, and another fluorescent composition containing the phosphor (7) prepared in accordance with the present invention can give forth red emission of high luminance in a high state of color purity. Almost no fluorescent components of the kind which can emit blue or red light of high luminance and high color purity under low-velocity electron excitation have been know up to naw. The emission spectra of the above-described fluorescent compositions of the present invention are shown in Figure SJ and ln Figure 5X, respectively. As clearly shown in these figures, the emission spectrum of the fluorescent composition containing the phosphor (6) has a peak at about 450nm, and the resulting emission is blue of excellent color purity. On the other hand, the emission spectrum of the other fluorescent composition con-taining the phosphor (7) has a peak at about 625nm, and the ~ . .
resulting emission is red of excellent color purity. The fluor-i 25 escent compositions provided by the present invention are very i useful as phosphors for making fluorescent display devices, and each can retain its above-mentioned excellent inherent character-istics without impairment when employed as a fluorescent screen ,.
, ., . ~ . . : ~ .
- . . .,: . ; , . -. " .:, ~ - . , : - -~., . ~ .
.. ... . . , . . , , ~ .. ~ - .
.: .' . ., : - . :, . . - .. : , 1~824~5 enclosed in a fluorescent display tube.
The fluorescent display device provided in accordance with the present invention has essentially the same structure as the known fluorescent display tube described earlier. Namely, its basic structure includes an anodic plate having a fluorescent screen on one side thereof and a cathode standing face to face with the aforesaid fluorescent screen.

'1`

..
, s ' i~

., , , , .
. ,~,. .
. , ~ , :. ' , ' ' ': ' .
.: -. ~ , ' - .' . ', ~ ~ , ., ,. ~ ~

~08'~445 both of which are enclosed in an evacuated tube. The fluorescent display devicc of the present invention is characterized by the fluorescent composition which forms the fluorescent screen on the anodic plate. Therefore, aside from the fluorescent screen, all elements constituting th~ fluoresccnt display device of the present invention can be conventional ones as used in ordinary fluorescent display devices. Moreover, conventional techniques employed ~or producing conventional fluorescent display devices can be applied to the production of the fluorescent display devices of the present invention without modification. A concrete illustration of a typical method for manufacturing the fluorescent display device according to the present invention is given below.
First an anodic plate supported by a conventional ceramic base plate is coated with the above-described fluorescent ; 15 composition in accordance with the sedimentation coating method in order to make a fluorescent screen. Namely, an anodic plate is placed in an aqueous suspension of the fluorescent composition and the fluorescent composition is allowed to deposit on one side of the anodic plate as it settles because of its own i 20 weight, and then the water is removed from the aqueous suspension.
The resulting coated layer is then dried. In such a process, a small amount of water glass (about 0.01 to about 1~) may be added to the aforesaid suspension for the purpose of increasing the adhesive property of the resulting fluorescent screen to the ano~ic plate. The preferred ~mount of fluorcsccnt composition applied to the anodic plate is within the range of about 5 mg/cm to about 30 mg~cm2.
The above-described sedimentation coating method has been commonly and widely applied in making fluorescent screens.

... , 1 ......... . . , ,........ , . . ........ . . . ~

. .. . ; . . .; ..... .. ., . . . . , , -.. , . - . .. . . ... . .. . . . .... .

108'~445 l~owever, the method for making a fluorescent screen in accordance with the present invention is not to be interpreted as being limited to the aforesaid sedimentation coating method.
~ cathode made of a wire-heater covered with an oxide such as BaO, SrO, CaO or the like is placed opposite the fluorescent screen on the anodic plate at an interval of about 5mm, and then the resulting pair of electrodes is set in a transparent container made of ~lass or the like and air present in the containcr is cvacuated. After the pressure inside this container reaches a pressure of 10 5 Torr or less, the evacuation is stopped and the container is sealed. After sealing, the pressure inside the resulting container is additionally reduced by sputtering a getter. By the method ; described, a fluorescent display device capable of attaining the objects of the present invention can be obtained. Further, as shown in Figure 2, it is desirable to place a mesh-like control grid between the cathode and the fluorescent screen to function as a diverging electrode. Such an electrode is useful in diverging low-velocity electrons emitted from the cathode because the fluorescent screen on the anodic plate is flat while the cathode is a wire. In this case, better results are attained by using as fine a mesh as possible since a smaller mesh results in a smaller loss in emission and in better efficiency in the divergence of low-velocity electrons.
, 25 Specifically, meshes of below 500 micron and having an aperture ratio of not less than 50% are preferred. (Where the aperture ratio refers to the area of the holes capable of passing low-velocity electrons divided by the total area of the grid).

., I
'' , 1 `. .. . ..
.
:. . . - , - ~ . ~ . : .
. : : , : : ,., .. . . . . . . . .

108;~4~5 A charact~r, numbcr or l~atterns can be displayed by cutting the anodic plate in the form of the character, number or pattern to be displayed and selectively applying the acceleration potential suitable for the particular pair of separated anodes.
Moreover, multicolor fluorescent display devices can be produced by cutting the anodic plate into a desired form; e.g., the form of an array of dots or lines, applying a fluorescent screen which contains a first fluorescent composition consisting of ZnO and one phosphor onto some portions of the separated anode, and applying onto other portions of the anode a fluorescent screen comprising other phosphors which, under low-velocity electron excitation, can emit light of a color different from that of said first composition.
In accordance with the present invention, it is possible to provide fluorescent display devices which can display green emission of higher color purity than conventional devices having a fluorescent screen made of lZnO:Zn] and is further I possible to provide devices which can display blue emission or ¦ red emission. The present invention has very large utility value from a industrial point of view because almost no blue I or red emitting fluorescent display devices have been known up ¦ to now. It has further been found in accordance with the present invention that it becomes feasible to produce multicolor ~; low-velocity electron excited fluorescent display devices by using a fluorescent screen consistin~ of various kinds of fluorescent compositions suitable for low-velocity electron excitation which can display emissions of different colors ~, ~1~ -~ from one another.
~i -; , ~ ~ - 26 ~., , . ., , :
. , : ' ,' '; ' ' , ': ' ' ' ' ,. :- . , , , ,. . ,., . .: . . : .
''', ' ' ' ",' ... , ' ' .'". .; . ~

~08'~4S
The present invention will now be illustr~ted in greater detail by refcrence to the following examples.
Example l B One weight part of reagent ZnO (Sazex 2000 manufactured by Sakai Chemicals) and one weight part of LZnS:Cu, Al]
(phosphor (l)-l) containing as an activator Cu and Al in the equivalent amount of 10 4 g/g were mixed thoroughly by using a mortar. A fluorescent composition capable of displaying green emission having high luminance and hi~her color purity than thàt of [ZnO:Zn] under low-velocity electron excitation was obtained. In the same manner as the above, other fluorescent compositions having different mixing ratios within the range of l:9 to 9:1 (by weight) were prepared.
Example 2 lS Reagent ZnO (Sazex 2000 manufactured by Sakai Chemicals) was placed in an alumina crucible and fired at 1000C for one i hour in air. The resulting heat treated ZnO w~s fully ground i I to a fine powder by means of a ball-mill. 7 weight parts of this heat treated ZnO and 3 weight parts of [(Zn0 95, Cdo 05)S:Cu, Al] (phosphor (1)-2) containing as an activator both Cu and Al , in the equivalent amount of 10 4 g/g were thoroughly mixed by using a mortar. A fluorescent composition capable of displaying green emission having high luminance and higher color purity ~i I than that of ~ZnO:Zn~ under low-velocity electron excitation i 25 was obtained. In the same manner, fluorescent compositions having differcnt mixing ratios within the range of l:9 to 9:1 (by weight) were prepared.

' -:: .
.'~

. ' ' '"'' ' ;' ' ' ' . - ~ : . .. ...

10~ 445 ~xample 3 B One weight part of reagent ZnO (Sazex 2000 manufactured by Sakai Chemicals) and one weight part of [Y3A15O12:Ce~
~phosphor (2)-1) containing Ce in the activating amount of gram-atom/mole were thoroughly mixed by using a mortar.
Thus, a fluorescent composition capable of displaying green emission having high luminance and higher color purity than that of [ZnO:Zn] under low-velocity electron excitation was obtained. In the same manner, fluorescent compositions having different mixing ratios within the range of 1:9 to 9:1 (by weight) were prepared.
Example 4 Zinc oxalate (ZnC2O4) was placed in an a~umina crucible and fired at 1000C for one hour in air. The resulting heat ~15 treated ZnO was fully ground to a fine powder by means of a ball-mill. 7 weight parts of the thus obtained heat treated ZnO and 3 weight parts of [Y3(Alo.6, GaO.4)512 p (2)-23 containing cerium in the activating amount of 10 2 gram~atom/mole were well-mixed by using a mortar. The thus obtained fluorescent composition could display green emission having high luminance and higher color purity than that of ' l [ZnO:Zn] under low-velocity electron excitation. In the same manner, fluorescent compositions having different mixing ratios within the range of 1:9 to 9:1 (by weight) were prepared.
Example 5 Zinc carbonate ~ZnCO3~ was placed in an alumina crucible I and fired at 1000C for one hour in air. The resulting heat i treated ZnO was well-ground to a fine powder by means of ~ a ball-mill. 7 weight parts of the thus obtained heat treated ,.;:: I
~ 28 ` ~1 ~ !

, ,, i ~ , , . ~ .
, ~ ~ . . . .
.
, . . . . . . . .

, . . ~. . . : : . .
,. . . . . . ;. .

1~38'~445 ZnO and 3 weig~lt parts of [Zn2SiO4:Mn~ (phosphor (3)) containing manganese in the activating amount of 2 x 10 2 gram atom/mole were fully mixed by using a mortar. Thus, a fluorescent composition capable of disylaying green emission having high luminance and higher color purity than that of ~ZnO:Zn] under low-velocity electron excitation was obtained. In a similar manner, fluorescent compositions having different mixing ratios within the range of 1:9 to 9:1 (by weight) were prepared.
Example 6 1 B One weight part of reagent ZnO (Sazex 2000 manufactured by Sakai Chemicals) and one weight part of [Y2O2S:Tb] (phosphor (4)-1) containing tcrbium in the activating amount of 5 x 10 2 I g/g were thoroughly mixed by using a mortar. Thus, a fluorescent - composition capable of displaying green emission having high luminance and higher color purity than that of IZnO:Znl under low-velocity electron excitation was obtained. In a similar manner, fluorescent compositions having different mixing ratios within the range of 1:9 to 9:1 (by weight) were prepared.
I Example 7 ¦ 20 Reagent ZnO (Sazex 2000 manufactured by Sa~ai Chemicals) was placed in an alumina crucible and fired at 1000C for one ¦ hour in air. The resulting heat treated ZnO was well-ground I to a fine powder by means of a ball-mill. 7 weight parts of j I the thus obtained heat treated ZnO and 3 weight parts of ¦ 25 ~La2O2S:Tbl (phosphor (4)-2) containing as an activator Tb in the amount of 5 x 10 2 g/g were fully mixe~ by using a mortar.
~ Thus, a fluorescent composition capable of displaying green ¦ emission having high luminance and higher color purity than ... ., ~ . . . . .
-,: .. ,., . ~ : ..
. . : . : . ., . ~ . , - .
, ~ .

':

108~445 that of [ZnO:Zn] under low-velocity electron excitation was obtained. In a similar manner, fluorescent compositions having different mixing ratios within the range of 1:9 to 9:1 (by wcight) were prepared.
Ixalnple ~
B Two weight parts of reagent ZnO (Sazex 2000 manufactured by Sakai Chemicals), one weight part of [Zn2SiO4:Mn~ (phosphor (3)) containing as an activator Mn in the amount of 2 x 10 gram atom~mole and one weight part of [Y3(Alo 6~ GaO 4)512 Ce] (phosphor (2)-2) containing cerium in the activating amount of 10 2 gram-atom/mole were fully mixed by using a mortar. Thus, a fluorescent composition capable of displaying green emission having high luminance and higher color purity than that of [ZnO:Zn] under low-velocity electron excitation was obtained. In a similar manner, fluorescent compositions differing from one another in composition ~ were prepared by changing the weight ratio of the amount of I reagent ZnO to the total amount of the combined phosphors (2)-2 and (3) within the range of 1:9 to 9:1.
Example 9 Zinc carbonate (ZnCO3) was placed in an alumina crucible I and fired at 1000C for one hour in air. The resulting heat treated ZnO was well-ground to a fine powder by means of a ball-mill. Two weight parts of the thus obtained heat treated ,~ ZnO, one weight part of IZnS:Cu, Rl] ~phosphor (1)-1) containing as an activator both Cu and ~1 in the equivalent amount of 10 g/g and one weight part of 1Zn2SiO4:Mn~ (phosphor (3)) containing as an activator Mn in the amount of 2 x 10 2 gram~atom/mole ~¦ were fully mixed by using a mortar. Thus, a fluorescent composition ~1 .

. .
.:: : - , - .~
~ ~ `' : ` ; " ' :i, , .

~108;~'}45 capable of displaying green emission having high luminance and higher color purity than that of [ZnO:Zn~ under low-velocity electron excitation was obtained. In a similar manner, fluorescent compositions differing from one another in composition were prepare~ by changing the weight ratio of th~ amount of the heat treated ZnO to the total amount of the combined phosphors (1)-1 and (3) within the range of 1:9 to 9:1.
Example 10 Reagent ZnO (Sazex 2000 manufactured by Sakai Chemicals) and [SrGa2S4:Eu2 ] containing europium in the activating amount of 3 x 10 2 gram-atom/mole were well-mixed in equivalent weight parts by using a mortar, Thus, a fluorescent composition capable of displaying green emission having high luminance and higher color purity than that of ~ZnO:Zn] under low-velocity electron excitation was obtained. In a similar manner, i fluorescent compositions differing from one another in composition were prepared by changing the mixing weight ratio of the amount of reagent ZnO to that of the phosphor [SrGa2S4:Eu2+].
Example 11 Reagent ZnO (Sazex 2000 manufactured by Sakai Chemicals) was placed in an alumina crucible and fired at 1000C for one I hour in air. The resulting heat treated ZnO was well-ground I to a fine powder by means of a ball-mill. 7 weight parts of ; I the thus o~tained heat treated ZnO and 3 weight parts of ~SrGa2S4:Eu ~ containing europium in the activating amount of 3 x 10 2 gram-atom/mole were fully mixed by using a mortar.
Thus, a fluorescent composition capable of displaying green emission having high luminance and higher color purity than ' ~ , ' .,.' : ' ' ' -:

44$

that of [ZnO:~n] under low-velocity electron excitation was obtained. In a similar manner, fluorescent compositions differing from on~ another in composition were prepared by changing the mixing ratio.
~xa.nplc 12 Zinc oxalate (ZnC2O4) was placed in an alumina crucible and fired at 1000C for one hour in air. The resulting heat treated ZnO was well-ground to a fine powdcr by means of a ball-mill. 7 weight parts of the thus obtained heat treated ZnO
and 3 weight parts of 1SrGa2S4:Eu2+~ containing europium in the activating amount of 3 x 10 2 gram atom/mole were mixed thoroughly by using a mortar. Thus, a fluorescent composition capable of displaying green emission having high luminance and higher color purity than that of [ZnO:Zn] under low-velocity electron lS excitation was obtained. In a similar manner, fluorescent compositions differing from one another in composition were prepared by changing the mixing ratio.
Example 13 Zinc carbonate (ZnCO3) was placed in an alumina crucible and fired at 1000C for one hour in air. The resulting heat treated ZnO was wcll-ground to a fine powder by means of a ball-I mill. 7 weight parts of the thus obtained heat treated ZnO
¦ and 3 weight parts of ~SrGa2S4:Eu 3 containing europium in the activating amount of 3 x 10 2 gram-atom/mole were fully mixed by using a mortar. Thus, a fluorescent composition capable of disp7ayins green emission having high luminance and higher color i purity than that of ~ZnO:Zn~ under low-velocity electron excitation was obtained. In a similar manner, fluorescent compositions differing from one another in composition were . .
7 I prepared by changing the mixing ratio.
, , - 32 , . ~

~o8~,~,4~5 Example 14 B Thr~e weight parts of reagent ZnO (Sazex 2000 manufactured by Sakai Chemicals) and seven weight parts of [ZnS:Ag] containing silver in the activating amount of 10 4 g/g were well-mixed by using a mortar. ~hus, a fluoresccnt composition capable of displaying blue emission having high luminance and higher color purity was obtained. In a similar manner, blue emitting fluorescent compositions differing from one another in composition could be obtained by changing the mixing ratio.
Example 15 I Reagent ZnO (Sazex 2000 manufactured by Sakai Chemicals) was placed in an alumina crucible and fired at 700C for one hour in air. The resulting heat treated ZnO was well-ground to a fine powder by means of a ball-mill. One weight part of the thus obtained heat treated ZnO and one weight part of [ZnS:Agl containing silver in the activating amount of 10 g/g were fully mixed by using a mortar. The thus obtained blue emitting fluorescent composition had high luminance and high color purity under low-velocity electron excitation. In a similar manner, fluorescent compositions differing from one another in composition could be obtained by changing the mixing ratio.
Example 16 ' I ~eagent ZnO (Sazex 2000 manufactured by Sakai Chemicals) was placed in an alumina crucible and fired at 1000C for one hour in air. The resulting heat treated ZnO was well-ground to a fine powder by means of a ball-mill. 7 weight parts of ¦ the thus obtained heat treated ZnO and 3 weight parts of tzns:Ag3 1 .
. . , ' ' ' . , ' ' . .
', ,. :, .: ., ,, , ,,', ., ' , ' , ' ' ' : ' ,, . ~ ' ' ' ' ' ' ' ..' ' . ' .. ', . ,, ., . , ' , . ', , . . . .. . . ' .
' '~ ' ' " " ~ '' '' . ' ~ ". ' " ' ', ' ' ' 108~4~5 containing silver in the activatinc~ amount of 10-4 g/g were fully mixed by using a mortar. Thus, a fluorescent composition capable of emittin~ blue li~ht having high luminance and high color purity under low-velocity electron excitation could be obtained. In a similar manner, fluorescent compositions differing from one another in composition were preparcd by changing the mixing ratio.
Example 17 Zinc oxalate (ZnC2O4) was place~ in an alumina crucible ; 10 and fired at 1000C for one hour in air. The resulting heat treated ZnO was well-ground to a fine powder by means of a ball-mill. 7 weight parts of the thus obtained heat treated ZnO
and 3 weight parts of lZnS:Ag] containing silver in the activating amount of 10 4 g/g were fully mixed by using a mortar. Thus, lS a fluorescent composition capa~lc of displaying blue emission having high luminance and high color purity under low-velocity I electron excitation was obtained. In a similar manner, fluorescent ; I compositions differing from one another in composition were prepared by changing the mixing ratio.
, 20 Example 18 Zinc carbonate (ZnCO3) was placed in an alumina crucible i 1 and fired at 1000C for one hour in air. The resulting heat treated ZnO was well-ground to a fine powder by means of a ball-I mill. 7 weight parts of the thus obtained heat treated ZnO
and 3 weight parts of ~ZnS:Ag) containing silver in the activating amount of 10 g/g were fully mixed by using a mortar. Thus, a fluorescent composition capable of displaying blue emission having high luminance and high color purity under low-velocity ~;

~ 34 . ~.

iO8;~445 electron e~citation was obtained. In a similar manner, fluorescent compositions differing from one another in composition were prepared by changing the mixing ratio.
Example l9 Reagent ZnO (Sazex 2000 manufactured by Sakai Chemicals) and lY2O2S:~u] containing europium in the activating amount of 5 x 10 2 g/g were well-mixed in equivalent weight parts by using a mortar. Thus, a fluorescent composition capable of displaying red emission having high luminance and high color purity under low-velocity electron excitation was obtained. In a similar manner, fluorescent compositions differing from one another in composition were prepared by changing the mixing ratio of the amount of reagent ZnO to that of the phosphor [Y2O2S:Eu~.
, Example 20 Reagent ZnO (Sazex 2000 manufactured by Sakai Chemicals) was placed in an alumina crucible and fired at 1000~C for one hour in air. The resulting heat treated ZnO was well-ground to a fine powder by means of a ball-mill. 7 weight parts of the thus obtained heat treated ZnO and 3 weight parts of [Y2O2S:Eu] containing europium in the activating amount of 5 x 10 2 g/g were fully mixed. Thus, a fluorescent composition capable of displaying red emission having high luminance and high color purity under low-velocity electron excitation was obtained. In a similar manner, fluorescent compositions differing from one another in composition were obtained by changing the mixing ratio of the amount of fired ZnO to that ~ of the phosphor [Y2O2S:Eu~.
i ~
~, I

:, . , . . . , ~ - .

. , , , ., . - :
. ~ , , . , , ,: , .

~xample 21 Zinc oxalate (ZnC2O4) was placed in an alumina crucible and fired at 1000C for one hour in air. The resulting heat treated ZnO was wcll-ground to a fine powder by means of a ball-mill. 7 weight parts of the thus obtained heat treated ZnOand 3 weight parts of [Y2O2S:~u] containing europium in the activating amount of 5 x 10 2 g/g were fully mixed by using a mortar. Thus, a fluorescent composition capable of displaying red emission having high luminance and high color purity under low-velocity electron excitation could be obtained. In a similar manner, fluorescent compositions differing from one another in composition were prepared by changing the mixing ratio of the amount of fired ZnO to that of the phosphor [Y2O2S:Eu].
Example 22 Zinc carbonate (ZnCO3) was placed in an alumina crucible , and fired at 1000C for one hour in air. The resulting heat ; treated ZnO was well-ground to a fine powder by means of a ball-mill. 7 weight parts of the thus obtained heat treated ZnO
and 3 weight parts of [Y2O2S:Eu] containing europium in the activating amount of S x 10 2 g/g were fully mixed by using a mortar. Thus, a fluorescent composition capable of displaying red emission having high luminance and high color purity under , , low-velocity clectron excitation could be obtained. In a similar manner, fluorescent compositions differing from one another in composition were prepared by changing the mixing ratio of the amount of heat treated ZnO to that of the phosphor ~Y2O2S:Eu~.

; - 36 '~ : .

~. ~ ~ - , . . ~ ., ~
~ . .

: ' . . .
' " .' . .
- :'~ . ,, . :
-108;~445 Example 23 One weiqht part of reagent ZnO (Sazex 2000 manufactured by Sakai Chemicals) and one weight part of the phosphor (1)-1 containing both copper and aluminium in the activating amount of 10 4 g/g w~re well-mixed by using a mortar. A 200mg portion of the resulting mixture was dispersed into 100ml of distilled water containlng water ~lass in the concentiation of 0.01~.
The resulting suspension was applied to a 2cm x lcm alminium anodic plate supported on a ceramic base plate in accordance with the sedimentation coating method to ma~e a fluorescent screen. The amount of the fluorescent composition applied was about 10mg/cm2. Next, a cathode made of a tungsten wire-heater covered with an oxide was placed across from the fluorescent screen on the aluminium anodic plate at the interval of about 5mm. Then this pair of electrodes was set in a hard glass container and air present in thc container was evacuated, After the pressure inside the container reached 10 5 Torr or so, the evacuation was stopped and the container was sealed.
Next, the pressure inside the evacuated container was additionally reduced by sputtering a getter. Thus, a fluorescent display device having the structure as shown in Figure ~1) was obtained.
The resulting fluorescent display device displayed green emission having a luminance of 8.2 ft-L under an anodic plate potential of 80V, a cathode potential of 0.6V and a cathode current of 4OmA.
Example 24 , Reagent ZnO (Sazex 2000 manufactured by Sakai Chemicals) was placed in an alumina cruci~le and fired at 1~00C for one hour in air. The resulting heat treated ZnO was well-ground : I .
<! 1 .
~ ... . . . . . . ..
., , . .. . . .. ... . " - .
... . ... . . . . . . . . . . ...... .

. .

108;~4~

to a fine powd~r by mean~ of a ~all-mill. 7 weight parts of the thus obtained heat treat~d ZnO and 3 w~ight parts of the pllosphor (l)-2 containing both coppcr and aluminium in the activating amount of 10 4 g/g were fully mixed by using a mortar.
~ fluoresccnt display d~vice was prepared in the same manner as in ~xample 23 exccpt that thc thus obtained fluorescent composition was employed. This fluorescent display device displayed green emission having a luminance of 9.0 ft-L under an anodic platc potential of 80V, a cathode potential of 0.6V and a cathode current of 40mA.
Example 25 B One weight part of reagent ZnO ISazex 2000 manufactured by Sakai Chemicals) and one weight part of the phosphor (2)-1 containing cerium in the activating amount of 10 2 gram-atom/mole were fully mixed by using a mortar. A fluorescent display device was prepared in the same manner as in Example 23 except that the thus obtained fluorescent composition was employed.
This fluorescent display device displayed green emission having ¦ a luminance of 2.0 ft-L under an anodic plate potential of 80V, a cathode potential of 0.6V and a cathode current of 40mA.
~xample 26 j I Zinc oxalate (ZnC2O4) was placed in an alumina crucible ! I and fired at 1000~C for one hour in air. The resulting heat ~ treated ZnO was well-ground to a fine powder. 7 weight parts{ 25 of the thus obtained heat treated ZnO and 3 weight parts of ~ the phosphor (2)-l containing cerium in the activating amount t of 10 2 gram~atom/mole were fully mixed by using a mortar.

~r~ i A fluorescent display devices was prepared the same as in t~ 38 `f -' ' ' .- ' ' ' :
, `-- ,' , ' ,, '-~ ' ,, , ' , ' ' .

Example 23 e~cept that the thus obtained fluorescent composition was employed. This fluorescent display devices displayed green emission having a luminance of 2.5 ft-L at an anodic plate potcntial of 80V, a cathode potential of 0.6V and a cathode current of 4OmA.
Example 27 Zinc carbonate (ZnCO3) was placed in an alumina crucible and fired at 1000C for one hour in air. The resulting heat treated ZnO was well-ground to a fine powder by means of a ball-mill. 7 weight parts of the thus obtained heat treated ZnO and 3 weight parts of the phosphor (3~ containing manganese in the activating amount of 2 x 10 2 gram atom/mole were fully mixed by using a mortar. A fluorescent display device was prepared in the same manner as in Example 23 except that the thus obtained fluorescent composition was employed. This fluorescent display device displayed green emission having a luminance of 5.0 ft-L
under an anodic plate potential of 80V, a cathode potential of 0.6V and a cathode current of 40mA.
Example 28 0 One weight part of reagent ZnO (Sazex 2000 manufactured I I by Sakai Chemicals) and one weight part of the phosphor (4)-1 containing terbium in the activating amount of 5 x 10 2 g/g ¦ were fully mixed by using a mortar. A fluorescent display device was prepared in the same manner as in Example 23 except that the thus obtained fluorescent composition was employed.
This fluorescent display device displayed green emission having a luminance of 1.8 ft-L under an anodic plate potential of 80V, a cathode potential of 0.6V and a cathode current of 40mA.

- 3g ' : . . . : ; - -i . . , - .. ,' .. - : -: . , ., :: . :
: .. - . . , ., : .. . . - .

4~5 ~xample 29 12 ~
~L~ Reagent ZnO (Saz~x 2000 manufactured by Sa~ai Chemicals) was plac~d in an alumina crucible and fired at 1000C for one hour in air. 'l'he resulting heat treated ZnO was well-ground to a fine powder by means of a ball-mill. 7 weight parts of the thus obtained heat treated ZnO and 3 weight parts of the phosphor (4) containing t~rbium in the activating amount ~f 5 x 10 2 g/g were fully mixed by using a mortar. A fluorescent display device was prepared in the same manner as in Example 23 except that the thus obtained fluorescent composition was employed. This fluorescent display device displayed green emission having a luminance of 5.0 ft-L under an anodic plate potential of 80V, a cathode potential of 0.6V and a cathode current of 4OmA.
! 15 Example 30 - ¦ Two weight parts of reagent ZnO (Sazex 2000 manufactured ¦ by Sakai Chemicals), one weight part of the phosphor (3) containing ¦ manganese in the activating amount of 2 x 10 2 gram atom/mole and one weight part of the phosphor (2)-2 containing cerium in the activating amount of 10 2 gram atom/mole were fully mixed by using a mortar. A fluorescent display device was prepared in the same manner as in Example 23 except that the thus obtained fluorescent composition was employed. This fluorescent display ¦ device displayed green emission having a luminance of 4.5 ft-L
;¦ 25 under an anodic plate potential of ~0V, a cathode potential of ~l 0.6V and a cathode current of 40mA.
~` 1 :fi'~
~ 40 ,,i 1 1 . ~ ,,~ . . .. . .

108~445 Example 31 Zinc carbonate (ZnCO3) was placed in an alumina crucible and fired at 1000C for one hour in air. The resulting heat treated ZnO was well-ground to a fine powder by means of a ball-mill. Two weight parts of the thus obtained heat treated ZnO,one weight part of the phosphor (1)-1 containing both copper and aluminium in the activating amount of 10 4 g/g and one weight part of the phosphor (3) containing manganese in the activating amount of 2 x 10 2 gram atom/mole were fully mixed by using a mortar. A fluorescent display device was prepared the same as in Example 23 except that the thus obtained fluorescent composition was employed. This fluorescent display device displayed green emission having a luminance of 6.8 ft-L under an anodic plate potential of 80V, a cathode potential of 0.6V and a cathode current of 40mA.
Example 32 ! B Reagent ZnO (Sazex 2000 manufactured by Sakai Chemicals) ; and lSrGa2S4:Eu ~ containing europium in the activating amount of 3 x 10 2 gram~atom/mole were well-mixed in equivalent weight parts by using a mortar. A fluorescent display device was 3~ ¦ prepared in the same manner as in Example 23 except that the thus obtained fluorescent composition was employed. This fluorescent display device displayed green emission having ~; ~ a luminance of 6.6 ft-L under an anodic plate potential of 80V, ~; ~25 a cathode potential of 0.6V and a cathode current of 40mA.
~xample 33 Reagent ZnO ~Sazex 20~0 manufactured by Sakai Chemicals) was placed in an alumina crucible and fired at 1~00C for one hour in air. The resulting heat treated ZnO was well-ground , : . ~ . , ~. ' - . ': - . ' ~8Z445 to a fine powd~r by means of a ball-mill. 7 weight parts of the thus obtained heat treated ZnO and 3 weight parts of ~SrGa2S4:Eu ] containing europium in the activating amount of 3 x 10 2 gram-atom/mole were fully mixed by using a mortar.
A fluorescent display device was prepared in the same manner as in Example 23 except that the thus obtained fluorescent composition was employed. This fluorescent display device displayed green emission having a luminance of 7.2 ft-L under an anodic plate ` potential of 80V, a cathode potential of 0.6V and a cathode Z 10 current of 40mA.
Example 34 I Zinc oxalate (ZnC2O4) was placed in an alumina cruclble I and fired at 1000C for one hour in air. The resulting heat Zl treated ZnO was well-ground to a fine powder by means of a ball-mill. 7 weight parts of the thus obtained heat treated ZnO
and 3 weight parts of lSrGa2S4:Eu2 ] containing europium in the activating amount of 3 x 10 2 gram atom/mole were fully mixed by using a mortar. A f luorescent display device was prepared in the same manner as in Example 23 except that the thus obtained fluorescent composition was employed. This fluorescent display device displayed green emission having a luminance of 7.0 ft-L
~ under an anodic plate potential of 80V, a cathode potential of Z 0.6V and a cathode current of 40mA.
Example 35 2S Zinc carbonate (ZnCO3) was placed in an alumina crucible and fired at 1000C for one hour in air. The resulting heat ¦ ~ treated ZnO was well-ground to a fine powder by means of a ball-mi~11. 7 weight parts of the thus obtained heat treated ZnO

,:
, ~ , , : .
~," . , ~ . ~ -` 108'~445 and 3 weight parts of ~SrGa2S2:Eu2 ] containing europium in the activating amount of 3 x 10 2 gram atom/mole were fully mixed by using a mortar. A fluorescent display device was prepared in the same manner as in Example 23 except that the thus obtained fluorescent composition was employed. This fluorescent display device displayed green emission having a luminance of 6.8 ft-L under an anodic plate potential of 80V, a cathode potential of 0.6V and a cathode current of 40mA.
Example 36 Bl Three weight parts of reagent ZnO ~Sazex 2000 manufactured by Sakai Chemicals) and 7 weight parts of [ZnS:Ag] containing silver in the activating amount of 10 4 g/g were fully mixed by using a mortar. A fluorescent display device was prepared in the same manner as in Example 23 except that the thus obtained fluorescent composition was employed. This fluorescent display I device displayed blue emission having a luminance of 4.0 ft-L
¦ under an anodic plate potential of 80V, a cathode potential of ¦ 0.6~ and a cathode current of 40mA.
Example 37 1 20 Reagent ZnO (Sazex 2000 manufactured by Sakai Chemicals) ¦ was placed in an alumina crucible and fired at 700C for one ~ hour in air. The resulting heat treated ZnO was well-ground ¦ to a fine powder by means of a ball-mill. One weight part of ~, the thus obtained heat treated ZnO and one weight part of ~ZnS:Ag] containing silver in the activating amount of 10 g/g were fully mixed by using a mortar. A fluorescent display ~ device was prepared in the same manner as in Example 23 except ,~ ~- that the thus obtained fluorescent composition was employed.
:
~ ~ ' ; ~

. ~: .

,: . , . , ~ , , ,: -- -. .. : . , ~ ,. , ~ ,., ,, :

, . . . , . : , . . .

108;~445 This fluoresc~nt display device displayed blue emission having a luminance of 5.3 ft-L under an anodic plate potential of 80V, a cathode potential of 0.6V and a cathode current of 40mA.
Example 38 B Reagent ZnO (Sazex 2000 manufactured by Sakai Chemicals) was placed in an alumina crucible and fired at 1000C for one ~ hour in air. The resulting heat treated ZnO was well-ground ; to a fine powder by means of a ball-mill. 7 weight parts of the thus obtained heat treated ZnO and 3 weight parts of ~ZnS:Ag]
containing silver in the activating amount of 10 4 g/g were fully I mixed by using a mortar. A fluorescent display device was prepared in the same manner as in Example 23 except that the thus obtained fluorescent composition was employed. This fluorescent display device displayed blue emission having 1 15 a luminance of 6.0 ft-L under an anodic plate potential of 80V, s ¦ a cathode potential of 0.6V and a cathode current of 40mA.
Example 39 Zinc oxalate (ZnC2O4) was placed in an alumina crucible and fired at 1000C for one hour in air. The resulting heat treated ZnO was well-ground to a fine powder by means of a ball-mill. 7 weight parts of the thus obtained heat treated ZnO
and 3 weight parts of IZnS:Ag] containing silver in the activating amount of 10 4 g/g were fully mixed by using a mortar.
, A fluorescent display device was prepared in the same manner J 25 as in Example 23 except that the thus obtained fluorescent composition was employed. This fluorescent display device ,.. ~
displayed blue emission havinq a luminance of 5.5 ft-L under , an anodic plate potential of 80V, a cathode potential of 0.6V
~ :
and a cathode current of 4On~.

1.~-- - . . , ........... --, , -, . . . ~ ,.. ,. , ,, , ~ , 1~8;~45 Example 40 Zinc carbonate (ZnCO3) was placed in an alumina crucible and fired at 1000C for one hour in air. The resulting heat treated ZnO was w~ ground to a fine powder by means of a ball-mi]l. 7 weight parts of the thus obtained heat treated ZnO
and 3 weight parts of [ZnS:Ag] containing silver in the activatinq amount of 10 4 g/g were fully mixed by using a mortar.
A fluorescent display device was prepared in the same manner as in Example 23 except that the thus obtained fluorescent composition was employed. This fluorescent display device displayed blue emission having a luminance of 5.7 ft-L under an anodic plate potential of 80V, a cathode potential of 0.6V
I and a cathode current of 4OmA.
I Example 41 ¦ ~ ~eagent ZnO ~Sazex 2000 manufactured by Sakai Chemicals) and IY2O2S:EU3 containing europium in the activating amount of 5 x 10 2 g/g were mixed thoroughly in equivalent weight parts l by using a mortar. A fluorescent display device was prepared 1 in the same manner as in Example 23 except that the thus obtained fluorescent composition was employed. This fluorescent display device displayed red emission having a luminance of 1.5 ft-L
under an anodic plate potential of 80V, a cathode potential of O.6V and a cathode current of 40mA.
¦ Example 42 ¦ 25 Reagent ZnO (Sazex 2000 manufactured by Sakai Chemicals) ~¦ was placed in an alumina crucible and fired at 1000C for one ~- ¦ hour in air. The resulting heat treated ZnO was well-ground to a fine powder by means of a ball-mill. 7 weight parts of 1: :
,.~

!-`,''',"'` ''''"`, ''" '' ''`~` '' '~'''. " "" ' ''' ' ' " "'. `',''''' ' ` . `

108A~445the thus obtained heat treated ZnO and 3 weight parts of [Y2O2S:Eu]
containing europium in the activating amount of 5 x 10 2 g/g were fully mixed by using a mortar. A fluorescent display device was prepared in the same manner as in Example 23 except that the thus obtained fluorescent composition was employed. This fluorescent display device displayed red emission having a luminance of 3.0 ft-L under an anodic plate potential of 80V, a cathode potential of 0.6V and a cathode current of 4OmA.
Example 43 10Zinc oxalate (ZnC2O4) was placed in an alumina crucible ; and fired at 1000C for one hour in air. The resulting heat treated ZnO was well-ground to a fine powder by means of a ball-mill. 7 weight parts of the thus obtained heat treated ZnO
and 3 weight parts of [Y2O2S:Eu] containing europium in the activating amount of 5 x 10 2 g/g were fully mixed by using a mortar. A fluorescent display device was prepared in the same manner as in Example 23 except that the thus obtained fluorescent ¦ composition was employed. This fluorescent display device displayed red emission having a luminance of 3.1 ft-L under ¦ 20 an anodic plate potential of 80V, a cathode potential of 0.6V
and a cathode current of 4OmA.
¦ Example 44 Zinc oxalate (ZnC2O4) was placed in an alumina crucible and fired at 1000C for one hour in air. The resulting heat treated ZnO was well-ground to a fine powder by means of a ball-¦ mill. 7 weight parts of the thus obtained heat treated ZnO
, , and 3 weight parts of [Y2O2S:Eu] containing europium in the ~;~ , activating amount of 5 x 10 2 g/g were fully mixed by using ~,' j ` - 46 .~1 .,, .. 1 - :.

~, . . . .:: . - . . ,., : .
. ~ .: : , :
, .. . . .. .. . .

~08;~445 a mortar. A fluorescent display device was prcpared in the same manncr as in Example 23 exccpt that the thus obtained fluorescent composition was employed. This fluorescent display device displaycd rcd emission having a luminance of 2.7 ft-L
under an anodic platc pote~ntial of %OV, a cathod~ potential of 0.6V and a cathode current of 4OmA.

:`t'~

~ I - 47 ~ !
,.. ~. . .. . - .... . . ... .. . ~. ~ .. . . . - . . .

, - . . . . .. . . ... . .. . . .
~,` . . . ' . ~ . . . . ... . . ..
... .. .. .. .. .. . . . . .

Claims (17)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE PROPERTY
OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A fluorescent composition for low velocity electron excitation which contains a mechanical mixture consisting of zinc oxide and a phosphor selected from the group consisting of a copper and aluminium activated zinc cadmium sulfide phosphor [(Zn1-x' Cdx)S:Cu, Al, wherein the value x is within the range of 0?x?0.1], a cerium activated yttrium aluminium gallium oxide phos-phor [Y3(Al1-y, Gay)5O12:Ce, wherein the value y is within the range of 0?y?0.5], a manganese activated zinc silicate phosphor [Zn2SiO4:Mn], a terbium activated yttrium lanthanum oxysulfide phosphor [(Y1-z, Laz)2O2S:Tb, wherein the value z is within the range of 0?z?1], a europium activated strontium gallium sulfide phosphor [SrGa2S4:Eu2+], a silver activated zinc sulfide phosphor [Zns:Ag] and a europium activated yttrium oxysulfide phosphor [Y2O2S:Eu], said two components being present in a mixing weight ratio ranging from 1:9 to 9:1.

2. A fluorescent composition as defined in claim 1 wherein said phosphor is a copper and aluminium activated zinc cadmium sulfide phosphor [(Zn1-x' Cdx)S:Cu, Al, wherein the value x is within the range of 0?x?0.1].

3. A fluorescent composition as defined in claim 1 wherein said phosphor is a cerium activated yttrium aluminium gallium oxide phosphor [Y3(Al1-y, Gay)5O12:Ce, wherein the value is within the range of 0?y?0.5].

4. A fluorescent composition as defined in claim 1 wherein said phosphor is a manganese activated zinc silicate phosphor [Zn2SiO4:Mn].

5. A fluorescent composition as defined in Claim 1 wherein said phosphor is a terbium activated yttrium lanthanum oxysulfide phosphor [(Y1-z, Laz)2O2S:Tb, wherein the value z is within the range of 0?z?1].

6. A fluorescent composition as defined in Claim 1 wherein said phosphor is a europium activated strontium gallium sulfide phosphor [SrGa2S4:Eu2+].

7. A fluorescent composition as defined in Claim 1 wherein said phosphor is a silver activated zinc sulfide phosphor [ZnS:Ag].

8. A fluorescent composition as defined in Claim 1 wherein said phosphor is a europium activated yttrium oxysulfide phosphor [Y2)2S:Eu].

9. A low-velocity electron excited fluorescent display device having a fluorescent screen which is comprised of a fluorescent composition which contains a mechanical mixture con-sisting of a zinc oxide and a phosphor selected from the group consisting of a copper and aluminium activated zinc cadmium sulfide phosphor [(Zn1-x, Cdx)S:Cu, Al, wherein the value x is within the range of 0?x?0.1], a cerium activated yttrium alumi-nium gallium oxide phosphor [Y3(Al1-y, Gay)5O12:Ce, wherein the value y is within the range of 0?y?0.5], a manganese activated zinc silicate phosphor [Zn2SiO4:Mn], a terbium activated yttrium lanthanum oxysulfide phosphor [(Y1-z, Laz)2O2S:Tb, wherein the value z is within the range of 0?z?1], a europium activated strontium gallium sulfide phosphor [SrGa2S4:Eu2+], a silver activated zinc sulfide phosphor [ZnS:Ag] and a europium activated yttrium oxysulfide phosphor [Y2O2S:Eu], said two components being present in a mixing weight ratio ranging from 1:9 to 9:1.

10. A low-velocity electron excited fluorescent dis-play device as defined in Claim 9 wherein said phosphor is a copper and aluminium activated zinc cadmium sulfide phosphor [(Zn1-x' Cdx)S:Cu, Al, wherein the value x is within the range of 0?x?0.1].

11. A low-velocity electron excited fluorescent display device as defined in Claim 9 wherein said phosphor is a cerium activated yttrium aluminium gallium oxide phosphor [Y3(Al1-y, Gay)5O12:Ce, wherein the value y is within the range of 0?y?0.5].

12. A low-velocity electron excited fluorescent display device as defined in Claim 9 wherein said phosphor is a manganese activated zinc silicate phosphor [Zn2SiO4:Mn].

13. A low-velocity electron excited fluorescent display device as defined in Claim 9 wherein said phosphor is a terbium activated yttrium lanthanum oxysulfide phosphor [(Y1-z, Laz)2O2S:Tb, wherein the value z is within the range of 0?z?1].

14. A low-velocity electron excited fluorescent display device as defined in Claim 9 wherein said phosphor is a europium activated strontium gallium sulfide phosphor [SrGa2S4:Eu2+].

15. A low-velocity electron excited fluorescent display device as defined in Claim 9 wherein said phosphor is a silver activated zinc sulfide phosphor [ZnS:Ag].

16. A low-velocity electron excited fluorescent display device as defined in Claim 9 wherein said phosphor is a europium activated yttrium oxysulfide phosphor [Y2O2S:Eu].

17. A low-velocity electron excited fluorescent display device as defined in Claim 9 wherein said fluorescent display device is constructed with an anodic plate having the fluorescent screen on one side thereof and a cathode, the cathode standing face to face with the fluorescent screen within an evacuated tube.