Process of preparing infrared-excitable sodium rare earth fluoride luminescent materials

Claim 1

A method for producing a luminescent material consisting essentially of a sodium rare earth fluoride having a hexagonal crystal structure and a composition expressed by the following general formula: NaLn.sub.1.sub.-y.sub.-z Yb.sub.y Er.sub.z F.sub.4 wherein Ln represents at least one element selected from the group consisting of yttrium, lanthanum, gadolinium and lutetium, and y and z are numerical values defined by the following relationship: 0.09 ≦ y ≦ 0.99, 0.01 ≦ z = 0.10, and Y + z ≦ 1, said method comprising the steps of a. preparing an acidic aqueous solution containing rare earth ions in a composition expressed by the following general formula: Ln.sub.1.sub.-y.sub.-z Yb.sub.y Er.sub.z wherein Ln represents at least one element selected from the group consisting of yttrium, lanthanum, gadolinium and y and z are numerical values defined by the following relationships: 0.09 ≦ y ≦ 0.99, 0.01 ≦ z ≦ 0.10, and y + z ≦ 1, b. adding a fluorine ion as a precipitant to said acidic aqueous solution and thereby coprecipitating said rare earth ions in the form of fluorides to form a first raw material consisting of a rare earth fluoride coprecipitate having a composition expressed by the following general formula: Ln.sub.1.sub.-y.sub.-z Yb.sub.y Er.sub.z F.sub.3 wherein Ln, y and z are as defined above, c. mixing the first raw material with sodium silicofluoride Na 2 SiF 6 as a second raw material, the molar ratio of said second raw material to said first raw material being in the range of from 0.4 to 1.5, and d. packing the resultant mixture in a crucible at the bottom of which powder of sodium silicofluoride Na 2 SiF 6 has been charged in advance, in a manner such that the mixture of the raw materials is placed above the powder of sodium silicofluoride, and firing the contents of the crucible at a temperature of from 600° to 950° C. for a period of time of at least 1 hour in an oxygen-free atmosphere.

Claim 2

A method for producing a luminescent material consisting essentially of a sodium rare earth fluoride having a hexagonal crystal structure and a composition expressed by the following general formula: NaLn.sub.1.sub.-y.sub.-z Yb.sub.y Er.sub.z F.sub.4 wherein Ln represents at least one element selected from the group consisting of yttrium, lanthanum, gadolinium and lutetium, and y and z are numerical values defined by the following relationship: 0.09 ≦ y ≦ 0.99, 0.01 ≦ z = 0.10, and Y + z ≦ 1, said method comprising the steps of a. preparing an acidic aqueous solution containing rare earth ions in a composition expressed by the following general formula: Ln.sub.1.sub.-y.sub.-z Yb.sub.y Er.sub.z wherein Ln represents at least one element selected from the group consisting of yttrium, lanthanum, gadolinium and y and z are numerical values defined by the following relationships: 0.09 ≦ y ≦ 0.99, 0.01 ≦ z ≦ 0.10, and y + z ≦ 1, b. adding a fluorine ion as a precipitant to said acidic aqueous solution and thereby coprecipitating said rare earth ions in the form of fluorides to form a first raw material consisting of a rare earth fluoride coprecipitate having a composition expressed by the following general formula: Ln.sub.1.sub.-y.sub.-z Yb.sub.y Er.sub.z F.sub.3 wherein Ln, y and z are as defined above, c. mixing the first raw material with sodium silicofluoride Na 2 SiF 6 as a second raw material, the molar ratio of said second raw material to said first raw material being in the range of from 0.4 to 1.5, and d. packing the resultant mixture in a crucible at the bottom of which powder of sodium silicofluoride Na 2 SiF 6 has been charged in advance, in a manner such that the mixture of the raw materials is placed above the powder of sodium silicofluoride, and firing the contents of the crucible at a temperature of from 600° to 950° C. for a period of time of at least 1 hour in an oxygen-free atmosphere.