GB1597306A - Luminescent materials - Google Patents

Description

(54) LUMINESCENT MATERIALS (71) We, SONY CORPORATION, a corporation organised and existing under the laws of Japan, of 7-35 Kitashinagawa-6, Shinagawa-ku, Tokyo, Japan, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to methods of manufacturing luminescent materials and to luminescent materials manufactured by such methods. Since luminescent materials may be used as a phosphor in a cathode ray tube, for example, a beam indexing colour cathode ray tube, or a flying spot scanner tube.

It is desirable for a phosphor used in a beam indexing colour cathode ray tube to have a high peak intensity of emission and a short decay time, in order to obtain satisfactory beam indexing signals. Similar considerations apply in a flying spot scanner tube. Generally speaking, the shorter the decay time of a phosphor the lower the peak intensity, and the higher the peak intensity the longer the decay time.

It is well known that cerium activated phosphors containing yttrium, for example Y3Al5O12: Ce have a relatively high peak intensity and a long life. The cerium activated phosphor having the following formula: Y3Al3Ga2012 : Ce has a relatively high peak intensity and a shorter decay time than the cerium activated phosphor containing no gallium.

According to the present invention there is provided a method of manufacturing a luminescent material excitable by an electron beam and formed of cerium activated yttrium aluminium gallium oxide crystals of the form Y3AlxGayol2: Ce when x + y = 5. x = 1 to 4 andy = 4 to 1 comprising the steps of: providing a mixture of yttrium oxide, aluminium oxide, gallium oxide, cerium oxide and barium fluoride which melts to liberate fluorine at a sintering temperature of said mixture, said said barium fluoride being present in an amount of 1 to 50 mol % of the remainder of said mixture; heating said mixture under sealed conditions to a sintering temperature; and sintering said mixture at a temperature of from 1400"C to 17000C for from 1 to 6 hours to produce a luminescent material having a higher ratio of peak intensity to decay time than results from the sintering of said mixture in the absence of said barium fluoride.

The invention will now be described by way of example with reference to the accompanying drawings in which: Figure 1 is a plot of the relative peak intensity of emission against the concentration of barium fluoride at various aluminium to gallium molecular ratios; Figure 2 is a plot of the decay time against the concentration of barium fluoride at various ratios of aluminium to gallium molar concentration; and Figure 3 is a plot of the relative ratio of peak intensity of emission to the decay time against the concentration of barium fluoride present at various aluminium to gallium molar ratios.

The method to be described involves the steps of mixing raw materials to produce a mixture having the following generic formula: Y3AlxGayO,2: Ce where x + y = 5 x= 1to4 y=4to1 The reaction mixture comprises yttrium oxide, aluminium oxide, gallium oxide and cerium oxide, together with barium fluoride. The barium fluoride is present in an amount of from 1 to 50 mols per 100 moles of the remainder of the mixture and preferably 2.5 to 40 mols per 100 mosofthe remaining mixture. The mixture is sintered under sealed conditions at a temperature in the range from 1400 to 1700"C for a time in the range from 1 to 6 hours. This treatment is effective to decrease the decay time.Where the peak intensity is to be increased and the decay time decreased, a treatment at 1500 to 1600"C for from 2 to 4 hours is preferred.

At the sintering temperature, the barium fluoride melts and reacts with aluminium oxide to produce barium aluminate and liberate some fluorine gas. The melt or vapour reacts on the mixture as a flux providing improved mobility for the atoms, and promoting the formation of phosphor crystals without defects which cause heat loss. The barium cations are sufficiently large for them not to appear in the crystal lattice of the final product.

The following specific example illustrates the preparation of an improved phosphor.

EXAMPLE A cerium activated phosphor having the formula: Y3Al3Oa2O12: Ce is made up of raw materials comprising yttrium oxide (3/2 x 0.98 mol), aluminium oxide (3/2 mol), gallium oxide (1 mol) and cerium oxide (3/2 x 0.02 mol). These raw materials are combined with 0.1 to 0.2 mol of barium fluoride and mixed in a ball mill using ethyl alcohol as a solvent. Next the mixture is dried at 80 C, and then heated in an alumina crucible with a sealed lid in place in air at 15500C for 2 to 4 hours.

The sintering produces some barium aluminate by the reaction of barium fluoride and aluminium oxide, along with some fluorine gas. The barium aluminate may be eliminated by washing with water or acid, and the fluorine gas is volatilised.

The peak intensity of the phosphor produced in this example was more than twice as high as was observed in the case of the cerium activated phosphor which had not been sintered in the presence of the fluoride. Moreover, the decay time, which is the time in which the intensity of emission decays to 0.1 of the peak intensity, was measured to be 110 nanoseconds in the case of the phosphor produced according to the example, whereas a phosphor which is prepared without the barium fluoride had a decay time of 120 nanoseconds. Thus, the peak intensity is increased and the decay time is decreased, so that the ratio of peak intensity to decay time is substantially increased.

The relationship between the relative peak intensity and the decay time to the concentration of barium fluoride is shown in Figures 1 and 2, in which the abscissae refer to the molar concentration of barium fluoride. As shown in these two figures, when the concentration of the barium fluoride is between 1 to 50 mol % preferably between 2.5 and 40 mol %, the relative peak intensity and the decay time are improved.

The ratio of the relative peak intensity to the decay time is plotted as a function of the concentration of barium fluoride in Figure 3. It is apparent from this figure that the phosphor has optimum properties when using a concentration of barium fluoride between 1 to 50 mol %. Since the phosphor produced has characteristics of higher peak intensity of emission and shorter decay time than those of the conventional phosphor, it can conveniently be used as a phosphor in a beam indexing colour cathode ray tube or in a flying spot scanner tube.

WHAT WE CLAIM IS: 1. A method of manufacturing a luminescent material excitable by an electron beam and formed of cerium activated yttrium aluminium gallium oxide crystals of the form Y3AlxGayol2: Ce whenx + y = 5 x = 1 to 4 andy = 4 to 1, comprising the steps of: providing a mixture of yttrium oxide, aluminium oxide, gallium oxide, cerium oxide and barium fluoride which melts to liberate fluorine at a sintering temperature of said mixture, said barium fluoride being present in an amount of 1 to 50 mol % of the remainder of said mixture; heating said mixture under sealed conditions to a sintering temperature; and sintering said mixture at a temperature of from 1400"C to 17000C for from 1 to 6 hours to produce a luminescent material having a higher ratio of peak intensity to decay time than results from the sintering of said mixture in the absence of said barium fluoride.

2. A method according to claim 1 wherein said barium fluoride is present in an amount of 2.5 to 40 mols % of the remainder of said mixture.

3. A method according to claim 1 or claim 2 wherein said mixture is sintered at a temperature of from 1500 to 1600"C for from 2 to 4 hours.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (5)

**WARNING** start of CLMS field may overlap end of DESC **. where x + y = 5 x= 1to4 y=4to1 The reaction mixture comprises yttrium oxide, aluminium oxide, gallium oxide and cerium oxide, together with barium fluoride. The barium fluoride is present in an amount of from 1 to 50 mols per 100 moles of the remainder of the mixture and preferably 2.5 to 40 mols per 100 mosofthe remaining mixture. The mixture is sintered under sealed conditions at a temperature in the range from 1400 to 1700"C for a time in the range from 1 to 6 hours. This treatment is effective to decrease the decay time. Where the peak intensity is to be increased and the decay time decreased, a treatment at 1500 to 1600"C for from 2 to 4 hours is preferred. At the sintering temperature, the barium fluoride melts and reacts with aluminium oxide to produce barium aluminate and liberate some fluorine gas. The melt or vapour reacts on the mixture as a flux providing improved mobility for the atoms, and promoting the formation of phosphor crystals without defects which cause heat loss. The barium cations are sufficiently large for them not to appear in the crystal lattice of the final product. The following specific example illustrates the preparation of an improved phosphor. EXAMPLE A cerium activated phosphor having the formula: Y3Al3Oa2O12: Ce is made up of raw materials comprising yttrium oxide (3/2 x 0.98 mol), aluminium oxide (3/2 mol), gallium oxide (1 mol) and cerium oxide (3/2 x 0.02 mol). These raw materials are combined with 0.1 to 0.2 mol of barium fluoride and mixed in a ball mill using ethyl alcohol as a solvent. Next the mixture is dried at 80 C, and then heated in an alumina crucible with a sealed lid in place in air at 15500C for 2 to 4 hours. The sintering produces some barium aluminate by the reaction of barium fluoride and aluminium oxide, along with some fluorine gas. The barium aluminate may be eliminated by washing with water or acid, and the fluorine gas is volatilised. The peak intensity of the phosphor produced in this example was more than twice as high as was observed in the case of the cerium activated phosphor which had not been sintered in the presence of the fluoride. Moreover, the decay time, which is the time in which the intensity of emission decays to 0.1 of the peak intensity, was measured to be 110 nanoseconds in the case of the phosphor produced according to the example, whereas a phosphor which is prepared without the barium fluoride had a decay time of 120 nanoseconds. Thus, the peak intensity is increased and the decay time is decreased, so that the ratio of peak intensity to decay time is substantially increased. The relationship between the relative peak intensity and the decay time to the concentration of barium fluoride is shown in Figures 1 and 2, in which the abscissae refer to the molar concentration of barium fluoride. As shown in these two figures, when the concentration of the barium fluoride is between 1 to 50 mol % preferably between 2.5 and 40 mol %, the relative peak intensity and the decay time are improved. The ratio of the relative peak intensity to the decay time is plotted as a function of the concentration of barium fluoride in Figure 3. It is apparent from this figure that the phosphor has optimum properties when using a concentration of barium fluoride between 1 to 50 mol %. Since the phosphor produced has characteristics of higher peak intensity of emission and shorter decay time than those of the conventional phosphor, it can conveniently be used as a phosphor in a beam indexing colour cathode ray tube or in a flying spot scanner tube. WHAT WE CLAIM IS:

1. A method of manufacturing a luminescent material excitable by an electron beam and formed of cerium activated yttrium aluminium gallium oxide crystals of the form Y3AlxGayol2: Ce whenx + y = 5 x = 1 to 4 andy = 4 to 1, comprising the steps of: providing a mixture of yttrium oxide, aluminium oxide, gallium oxide, cerium oxide and barium fluoride which melts to liberate fluorine at a sintering temperature of said mixture, said barium fluoride being present in an amount of 1 to 50 mol % of the remainder of said mixture; heating said mixture under sealed conditions to a sintering temperature; and sintering said mixture at a temperature of from 1400"C to 17000C for from 1 to 6 hours to produce a luminescent material having a higher ratio of peak intensity to decay time than results from the sintering of said mixture in the absence of said barium fluoride.

2. A method according to claim 1 wherein said barium fluoride is present in an amount of 2.5 to 40 mols % of the remainder of said mixture.

3. A method according to claim 1 or claim 2 wherein said mixture is sintered at a temperature of from 1500 to 1600"C for from 2 to 4 hours.

4. A method of manufacturing a luminescent material and substantially as hereinbefore

described in the Example.

5. A luminescent material made by a method according to any one of the preceding claims.