3,028,339 3 Exainple 2 1 kffogram of refined cadmium nitrate was dissolved in 10 litres of pure methanol. The solution was processed in the manner described in Example 1. The resulting sulfide phosphor material was yellowish orange and somewhat more reddish than that obtained when water was used as a solvent with other conditions identical. The yield was 98%. Cadmium sulfide thus obtained was admixed with a phosphor material of zinc sulfide prepared as described in Example 1 substantially in the same proportions, and then 10-2 mol percent of silver activator and potassium chloride flux was added to the mixture followed by firing at a temperature of 1000' C. for one hour. The resulting phosphor emitted a light of yellow color by the bombardment of cathode ray on the same. Example 3 A zinc sulfide phosphor material prepared according to Example 1 was admixed with 10-2 mol percent copper chloride and 10-3 mol percent of lead as activator and t,hen fired at 800' C. for one hour. The resulting phosphor emitted greenish blue light under the influence of an alternating electric field. Exainple 4 I kilogram of thoroughly purified crystalline zir@c chloride (ZnCI2) was dissolved in 5 litres of ethanol. Hydrogen sulfide was passed through the solution for about 20 minutes, and then the solution was filtered. Tle precipitate thus obtained consisted of uniform particles which were more loosely bound as compared with the case where water was used as a solvent. Ther-efore, the solution had a low viscosity resulting in facilitation of filtration. The deposit was washed with pure ethanol, and dried at from 70' C. to 901 C. to provide a zinc sulfide phosphor material. The yield was 93%. Zinc sulfide thus obtained was mixed with 10-3 mol percent of copper activator and sodium chloride flux followed by firing at 1000, C. The fired product emitted green light in response to ultraviolet radiation. Example 5 1 kilogram of thoroughly purified crystalline zinc nitrate (Zn(NO3)2-6H20) was dissolved in 5 litres of acetone. Hydrogen sulfide was passed throu.-h this solution for about 20 minutes, and then the solution was filtered. The precipitate thus obtained also consisted of uniform particles and the solution could be easily filtered Fis in Example 4. The filtered precipitate was washed with pure acetone and dried at from 70' C. to 90' C. to produce zinc sulfide phosphor material. The yield was 95%. 10-3 mol percent of silver activator and barium chloride flux were added to the material, and the mixture was fired at from 800' C. to 1200' C. There was obtained an excellent phosphor capable of emitting green ligbt under the inffuence of ultraviolet radiation. Example 6 1 kilogram of thoroughly purified, crystalline cadmium nitrate (Cd(NO3)2-4H20) was dissolved in 5 litres of pure isopropyl alcohol. The solution was treated in the manner described in Example 5 except that isopropyl alcohol was used as a wasbing agent. Thus a cadmium sulfide phospbor material was obtained with the yield of 95%. 10-3 mol percent of copper activator and magnesium chloride flux were mixed with the material thus obtained and the mixture was fired at from 800' C. to 1200' C. Thus an excellent phosphor capable of enitting green lig'iit in respons.- to ultraviolet radiation was produced. Example 7 I kilogram of thoroughly purified crystalline zinc chloride (ZnCI2) was dissolved in 5 litres of ether. The so4- lution was treated as in Example 6 excepting that the deposited zinc sulfide was washed with ether. The yield was 95%. The resulting phosphor emitted green light in response to ultraviolet radiation. 5 Example 8 1 kilopram of zinc nitrate was dissol-,,ed in 10 litres of methanol, and then 0.75 gram of copper nitrate and 0.85 gram of lead nitrate were added to the solution. Hydro10 gen sulfide was passed throu.-h the resulting solution. Zinc and lead nitrates were first converted into zinc and lead sulfides and zinc was almost simultaneously deposited as zinc sulfide resulting in a zinc sulfide phosphor material intimately mixed with activators. The mixture 15 w@s washed with methanol and then dried. The dried mixture was fired at 950' C. for one hour to produce an electroluminescent phosphor responsive to an alternating electric field. Example 9 20 540 grams of zinc nitrate and 460 grams of cadmium nitrate were dissolved in 10 litres of methanol. Hydrogen sulfide was passed through the solution to produce a mixture of zinc sulfide and cadmium sulfide. 10-2 Mol percent of silver activator and sodiurn chloride flux were 25 added to the mixti-ire and then fired at 950' C. for one hour. The final product was a phosphor capable of emitting yellow light in response to cathode rays. Example 10 30 Zinc sulfate was dissolved again into the filtrate (which was methanol solution including sulfuric acid produced by the decomposition of zinc sulfate) produced during the step of obtaining zinc sulfide described in Example 1. Hydrogen sulfide was again passed through the solution. 35 The sulfide particles were produced at a low rate and were of a larger size, whereby filtration and washing were particularly well performed. Erainple 11 40 1 kilogram of zinc sulfale was dissolved in 5 litres of methanol. 250 grams of ammonium acetate was separately dissolved in 5 litres of methanol. Hydrogen stilfide was passed through the mixture of the two solutioiis, whereby zi.,ic sulfide was produced with sulfuric 45 aoid produced by dissociation. ne latter was reacted with ammonium acetate, thereby to liberate acetic acid. Acetic acid served to coxitrol the co,.icentration of hydrogen ion and to facilitate the reactioi- s6 that the yield of zinc sulfide approarhed a theoretical value. Zinc sulfide 50 thus obtaired was washed, dried and mixed with 5 percent by weight of 10-5 mol copper actinator followed by firing at 1200' C. for two hours. The resulting phosphor had a long afterglow and could emit green light in response to ultraviolet radiation. 55 What we clai-.ii is: 1. A process of preparing zinc siilfide and cadmium sulfide phosphor whic@t comprises dissolvin@ at least one rp.ember of the groupcot-@sistilig of zinc and cadmium salts of stron.@ inorganic acids selected from the group coi60 sisting of sulfuric acid, nitric acid and hydrochloric acid in a solvent havin.- a dielectric constant of less than 50 together with at least one wat,-r-soluble activator salt, addir@g a member of the group consisting of sodium sulfide and ammonium sulfide to the solution at a temperature 65 below the boiling point of said solution to precipitate at least one corresponding sulfide intimately mixed with the corresponding activator sulfide, drying the precipitate thus obtained, and firing the dried precipitate. 2. A process of preparing zinc sulfide and cadmium 70 sulfide phosphor wliieh comprises dissolving at least one member of the group consisting of zinc and cadmium salts of strong inorganic acids selected from the group consisting of sulfuric acid, nitric acid and hydrochloric acid in a solvent havin,@ a dielectric co-@istatit of less than 50, 75 passing hydrogen sulfide through the resultant solution at

3,028,339 5 a temperature below the boiling poi-@it of said solution to prec@ipitate at least one corresponding sulfide, drying the precipitate thus produced, mixing the dried precipitate with at least one activator, and firing the mixture thus produced. 5 3. A process of preparing zinc sulfide and cadmium sulfide phosphor which comprises dissolving at least one member of the group consisting of zinc and cadmium salts of strong inorganic acids selected from the group consisting of sulfuric acid, nitric acid and hydrochloric acid 10 in a solvent having a dielectric constant of less than 50, adding to the resultant solution at a temperature below the boiling point of said solution at least one member of the group consisting of hydrogen sulfide, sodium sulfide and ammonium sulfide to precipitate at least one corres1,5 ponding sulfide, drying the precipitate thus produced, mixing the dried precipitate with at least one activator, and firing the mixture thus produced. 4. A process of preparing zinc sulfide and cadmium sulfide phosphor which comprises dissolving at least one 20 member of the group consisting of zinc and cadmium salts of strong inorganic acids selected from the groiip - consisting of sulfurir, acid, nitric acid and hydrochloric acid in a solvent having a dielectric ronstant of less than 50 together with at least one water-soluble activator salt, add25 ing a member of the group consisting of hydrogen - sulfide, sodium,sulfide and ammonium sulfide to the solution at a temperature below the boiling point of said solution to precipitate at least one corresponding sulfide intimately mixed with the corresponding activator sulfide, drying the 30 precipitate thus obtained, and firing the dried precipitate. 5. A process as defined in claim Z, wherein said solvent is selected from the group consisting of alcohols, polyhydric alcohols, ketones, ethers, esters, organic acids, chloroform, nitriles, -and liquefied inorganic compounds, 3 5 each having a dielectric constant of less than 50. 6. A process as defined in claim 3, wherein said solvent is selected from the group consistin- of alcohols, polyhydric alcohols, ketones, others, esters, organic acids, chloroform, nitriles, and liquefied inorganic compounds, 4 0 each having a dielectric constant of less than 50. 7. A process as defined in claim 4, wherein said solvent is selected from the group consisting of alcohols, poly6, hydric alcohols, ketones, ethers, esters, organic acids, chloroform, nitriles, and liquefied organic compounds, each having a dielectric r-onstant of less than 50@. 8. A process as defined in claim 2, wherein the activator used is at least one member of the group consisting of copper, manganese, gold, silver, bismuth, tin, antimony, arsenic, lead, aluminum and halogens. 9. A process as defined in claim 3, wherein the activators used involve at least one member selected from the group consisting of copper, manganese, gold, silver, bismuth, tin, antimony, arsenic, lead, aluminum aiid halogens. 10. A process as defined in claim 4, wherein the activator is at least one member of the group consisting of compounds of copper, silver,- manganese, lead, bismuth, tin, antimony, arsenic, aluminum, and halogen. 1 1. A process of preparing zinc sulfide and cadmium sulfide phosphor which comprises dissolving at least one member of the group consisting of zinc and cadmium salts of strong inorganic acids selected from the group consisting of sulfuric acid, nitric acid and hydrochloric acid in a solvent having a dielectric constant of less than 50 and selected from the group consisting of alcohols, polyhydric alcohols, ketones, ethers, esters, organic acids, chloroform, nitriles, and liquefied inorganic compounds, adding to the resultant solution at a temperature below the boiling point of said solution, at least one member of the group consisting of hydrogen sulfide, sodium sulfide and ammonium sulfide, and adding ammonium acetate as a pH controller, to form at least one corresponding sulfide, drying the precipitate thus obtained, mixing the dried precipitate with at least one activator selected from the group consisting of copper, manganese, gold, silver, bismuth, tin, antimony, arsenic, lead, aluminum and halogens, and firing the resultant mixture. References Cited in the file of this patent UNITED STATES PATENTS 2,734,872 Young ----------------- Feb.14,1956 2,782,168 Fetters ---------------- Feb. 19, 1957 2,805,9,17 Nitsche ---------------- Sept. 10, 1957

United States Patent Office 39028,339 3,028,339 PROCESS OF PREPARING SULFIDE PHOSPI-IORS Yeshiki Inoue, 41 Zenshoji-cho I-Chome, Sumaku, Kobe, Japan; NaoMko Fijkuolia, 1310-29 Shinzail@edoinouchi, Aboslii-Im, Hinieji, Japan;'and Seiji Matsu- 5 molo, 259 BefLcho-NishiwaFd, Kakogawa, Japan No Drawing. Filed Feb. 15, 1960, Ser. No. 8,526 11 Claims. (Cl. 252-301.6) This invention relates to a process of preparing sulfide 10 phosphors. The conventional processes of prepar.,n.a sulfide phosphors have used, as a solvent, water which has a dieleetric constant of 80. Each of stich processes, however, is disadva-@itageous in that it is difficult to separate impuri1-5 ties frem a produced precipitate and also to futer and wash the precipitate which, in turil comprises essentially a phosphor material be@-aus,- thp- solution used has a hi,@h dielectric constant resulting in a high solvation. Further, in order to prepare pure, uniforin products, the 20 practice of the conventional processes requires both rare technical skill and expensive equipnient. Nevertheless their yields are very low. For those reasons, the su',flde phosphors presently available are of high cost. The i-iiventors have found that the abovementioned 25 difficu',ties can be avoided by using a solvent having a dielectric constgnt of less tijan 50. This results also in the facilitation of prepariig sulfide phosphors with an :improved Tiierefore, an importaiit object of the invention is to 30 provide a new, @'niproved process ol preparing sulfide phosphors. Ti-le obj'ect is accon@ plished by the present invention directed to a Di-ocess of pr-.parin.- sulfide phosphors, which comprises dissolvin.- a witer-soiuble salt of an element 3,5 suc@. as zinc or cadmium or a mixture of such salts @@'n a solvent having a d;electric constant of less than 50, either passing through the solution hydrogen sulfide at atmospheric pressure or under pressutized condition, or reactin.- the same with a compound capable of reacting 40 with sa;d salt or salts to precipitate a sulfide or sulfides, there,ifter mixing the precipitate with an activator or activators, and firing the mix+ure. The i,@ivetition will be more clearly understood as the description proceeds. 45 According to one feattire of the inven,@ion, a highly purified water-soluble salt of zinc or cadrnium or a m;xture of such salts is dissolved in a solvent having a dielectric constart of less than 50. The salts suitable for the use in the invention include 5( iilorgani c salts of zinc or cadmium purified in any wellknown manner. Typical inorganic salts include sulfates, chloride s and nitrates. Example s of the solvents comprise alcohols, polyhydric alcohols, ketones, ethers, esters, organic acids, chloro- 55 forni, nitriles, liquefied solvents such as ammonia or other inorgani c material and the like. @lf desired, an anioii which is the same as that contained in the used salt i.e. a comnion anion may be added to the solution. Then purified hydrogen sulfide is passed 60 through the solution thus produced to precipitate ziiic sulfide or cqdmium sulfide when a zinc salt or a cadmium salt is initia@'ly used respectively. Alternatively, if the ini'Lially used salt is a mixture ol- zinc and cadmiurn salts tbe-ri a mixture of zinc and cadmium sulfides will be pre- 65 cipitated. instead of hydro,,Cn sulfide there may be used a solution of a sul'@ide such as sodium sulfide or a-nw.oni@,im sulfide dissolved in the solvent mentioned l,reN,iotisly. The sulfide thiis prod@,iced is a sulfide phosphor rnaterial. The term "sulfide phosphor material" 70 used herein means substrate of objective sulfide phosphors. Patented Apr. 3, 1962 2 The sulfide phosphor material is then rnixed wifh an activator or activators selected from the group of elements consisting of copper, manganese, gold, silver, bismuth, tin, arsenic, lead, aluminum, chloride and -mixtures thereof and a flux such as sodium chloride, potassium chloride, ammonium chloride, aluminum nitrate and potassium bromide, and then ftred to complete the prepa@ ration of a desired phosphor having a hi,-h luminescent response to ultraviolet radiation, cathode ray and electric field. The mechanism of reaction for producing the sulfide described above is not yet understood, but it has been found that the reaction of the invention is not greatly atected by the concentration of hydrogen ion present and rapidly proce,-ds with a high yield. It is well known that a reaction by which a sulfide is produced in an aqueo@,is solution is greatly affected by the conc.-ntration of hydrogen ion present. Besides, the resulting reaction product according to the invention is relatively free from impurities because of the low dielectric constant of the solvent used, a@id can be easily filtered and washed resulting in a uniform precipitate. Further, the practice of the invention does not always require rare-technical skill nor expensive equipment. According to another feature of the invention, a watersoluble salt or salts of the element or elements mentioned above inay be dissolved, as an activator, in the solvent described previously, together with the starting sulfide or sulfides. Al ter-,iotivel.y, the water-soluble salt or salts (f the element or eiements may be first dissolved in the said solvent and then added to the solution of the startipg sulfide or sulfides. In either case, the use of a solvent havitg a dielectric constant of less than 50 facilitates greatly the separation of impurities, 'iltering and washing. In addition, the activator in the form of sulfide is uniformly distributed in the sulfide phosphor material and in intimate contact wil@h the particles of the latter. Therefore, ,he fir-ng operation is eff.-eted stich that the activator wi'il be rapidly diffused in be phospbor material. This -makes it possible to eliminate the use of rare technical si@ill and expensive equipment required to uniformly riix an activator with a phosphor niaterial and also to redtice its loss during the mlxing operation. Accordingly it will be appreciated that the invention can provide inexpensive sulfide phosphors. The followin,@.examples illustrate the practice of the invention. Example I I kilogram of crystalline zinc sulfate crystals (ZnSO,-7H20) which had been highly purified, was dissolved in 5 litres of pure methanol. Hydrogen sulfide was then passed through the solution for abo,,it 20 minutes, and the solution was filtered. The resulting deposited, particles were substantially of a size and more loosely bound with the solvent as compared with the known case where water was used. Tberefore,. the solution was of low viscosity and it could be easily filtered. The filtered.product was washed with pure niethanol three or four times. The washed precipitate was drie.-I at a temperature from' 70' C. to 90' C. to obtain a zinc sulfide phosphor material. Th-- yield was as high as 95% In order to prepare a desi'red phosphor, the phosphor material thus obtair@ed was rnixed with 10-3 mol perce,nt of copper activator and sodium chloride flux and then fired at a temperature of 1200' C. for one hour. This yielded an excellent phosphor which can emit green ligh.t in response to ultraviolet @adiation.