DE1276847B - Process for the production of yttrium oxide phosphors activated with europium - Google Patents

Description

Process for the production of yttrium oxide phosphors activated with europium Yttrium oxide phosphors, which are activated with europium, emit red light, when excited by the electron beam of a cathode ray tube. A Method for manufacturing the phosphor screen of a cathode ray tube which is a phosphor of the aforementioned type is the known pulp process. Another process is the well-known pollination process.

These methods of manufacturing fluorescent screens for cathode ray tubes require fluorescent particles of a predetermined size in order to be economical to manufacture to ensure. Provided that the phosphor samples have the same particle density may have an average diameter in terms of weight, d ", as equivalent diameter of a particle of weight w, which latter is the same the mean particle weight of the sample, Wm, can be defined. That means, that the total weight of those particles of the sample which have a greater weight than have a particle of diameter dw, equal to the total weight of those particles of the sample, which is lighter than the particle with the diameter d " own.

The desired specific particle size distribution for yttrium oxide phosphors, activated with europium, which are incorporated into a cathode ray tube fluorescent screen by the known dusting process, is., D " = 15 ± 8 microns.

According to the present invention, a method for producing yttrium oxide phosphors activated with europium, which have a predetermined particle size distribution, is that yttrium oxide and europium oxide are mixed together. The process is characterized in that an alkaline earth metal halide is added to the mixture as a flux and the mixture is then fired, the temperature being between 1100 and 1500 ° C. and the firing time between 1 and 24 hours.

In particular, yttrium oxide phosphors activated with europium are produced by mixing about 90 to 99.5 mole percent yttrium oxide (Y2,0,) with about 0.5 to 10 mole percent europium oxide (Eu, 0,) and adding an amount of alkaline earth metal halide to this mixture added as a superplasticizer, which corresponds to between 25 and 400 percent by weight of the amount of Y203 plus EU203. The flux halide can be, for example, barium, strontium or calcium chloride. The mixture is fired in a covered crucible at temperatures between 1100 and 1500 ° C. The burning time is between 1 and 24 hours.

Example 1 A batch of yttrium oxide activated with europium of the composition (Y ", 5Eu", 5) 20 was prepared by dry mixing 27.75 g of Y203 (99.999 0 /, purity) and 2.25 g of Eu, 0, ( 99.9 0 /, purity) with 15 g BaC1, p. A. manufactured. This approach corresponds to up to 50 percent by weight of flux, based on the total weight of Y, 0, + Eu, O ,. The mixture was then fired in a covered, 50 ml quartz crucible in a muffle furnace at 1200.degree. C. for 16 hours. The calcined batch was washed eight times with boiling distilled water by decantation until the wash water was free of chloride ions. The material was then dried for about 12 hours at 110 to 120.degree. C. and finally passed through a sieve with a mesh size of 44 p. given to remove the larger particles. The particles obtained had an average diameter of about 8 #t; the diameter fluctuated between 2 and 20 V ..

For the purpose of comparison, the intensity of the cathode luminescence and the photoluminescence of the phosphor produced by this method was compared with that of a phosphor produced by firing the mixed oxalates of yttrium and europium. It was found that the phosphors made using the oxalates had a large amount of dust and flaky particles, while the particles made using fluxes were quite uniform and tended to be more spherical. Comparisons were also made with samples which had been prepared directly from the oxides, but without the addition of flux. In this case, there was no noticeable increase in particle size and the response to ultraviolet excitation (2537 Å) was poor.

The intensity of the cathode ray luminescence for the phosphor produced according to Example I was 430 0/0, based on the yttrium oxide activated with europium, which had been produced by burning the mixed oxides without addition of barium chloride for 3 hours at 1700 ° C. , and was at the same level the intensity of the luminescent substance produced by burning the mixed oxalates of yttrium and europium without flux. The intensity of the photoluminescence when excited with light of 2537 Å was 85 Ω, that of yttrium oxide activated with europium, which had been produced by firing the mixed oxalates without flux. Example II Example I was repeated with the exception that 3.0 g of BaC12 were mixed with 11.1 g of Y20, and 0.9 g of EU201, the resulting mixture being approximately 25 percent by weight of barium chloride, based on the total weight of Y20, + EuO ". After firing, washing and sieving according to the procedure of Example I, the obtained phosphor particles were found to have an average diameter of about 8 #t with a fairly large amount of dust. The photoluminescence and the cathode ray luminescence - Properties were similar to those obtained with the phosphor of Example I. Example 111 27.75 g Y, 0 " 2.25 g Eu" 0 "and 40.0 g BaC12 (133 0 /, of the total weight of Y20, + EU20,) of the same quality as in Example I were dry with 0.4 g of dried silica p. A. mixed. The mixture was placed in a 50 ml covered alumina crucible and calcined at 1200.degree. C. for 16 hours; it was then washed and sieved following the procedure of Example I.

The particles obtained had an average diameter of about 15 #t; the size of the particles varied between 5 and 30 #t. The intensity of the cathode ray luminescence was 105 ″ based on the value obtained when the mixed oxides were burned at 1700 ° C. The intensity of the photoluminescence was 90 ″ , that which was obtained from a phosphor produced by the oxalatin method.

Example IV Example f was repeated with the exception that 24.0 g (200 weight percent Y203 + Eup, 03) BaC12 was used. The procedure of Example III was followed, 48 g (400 percent by weight) of BaC12 being used. In each case the results were essentially the same as those obtained in Example IH, with the exception that when 400 0 / "BaCI" was used, more dust fell off and the luminescence properties of the phosphor were somewhat inferior. Example VI One Batch of yttrium oxide activated with europium was prepared according to Example I, with the exception that 27.5 percent by weight CaCl, based on Y201 + EU20., Was introduced into the mixture in place of the BaC12 and that an alumina crucible was used in place of a quartz crucible The average particle size ranged between 5 and 10 #t and the photoluminescence when excited with light of 2537 Å was 94 Ω, that obtained with a material made from oxalate.

Example VI Example V was repeated with the exception that this time 100 percent by weight CaCl2 was used as the flux and the mixture was fired in a quartz crucible. The average diameter of the particles obtained was approximately 15 #t; the particle sizes were between 10 and 25 #t. The photoluninescence value when irradiated with light of 2537 Å was about 71 "/, the value obtained from a material made from oxalate. Example VII Example V was repeated except that 100 % by weight of strontium chloride was used as the flux. The resulting fluorescent particles had an average diameter of 10 t; the particles were in a range between 2 and 20 p .. When excited with 2537 A , the intensity of the photoluminescence corresponded to that of a material which had been produced from the oxalates the effect of the change in the ratio between Y203 and EU20 on the cathode luminescence emission of the phosphor was determined for those phosphors which were fired for 16 hours in a Pt-Rh dish at 1200.degree. C. using 133 percent by weight BaC12 and 2 percent by weight SiO2 When excited by an electron beam with a current density of 0.5 mA / CM2 phosphor surface it was found that the strongest red emission was obtained using 5 mole percent Eu20.

With 2 mole percent Eup.03 the intensity of the red emission was 89 Ω / □, that of the 5 mole percent sample and with 95 mole percent the emission intensity fell to 64 Ω / ″ based on the intensity of the 5 mole percent sample.

Claims (1)

Claim: Process for producing yttrium oxide phosphors activated with europium by mixing a mixture of oxides of yttrium and oxides of europium with a flux and firing this mixture at predetermined temperatures for specific periods of time, characterized in that the flux is an alkaline earth metal halide and that the Temperature between 1100 and 1500'C and the burning time between 1 and 24 hours. Papers considered: Journal of the Eleetrochemical Society, Vol. 111, pp. 311-317.