Method of making electroluminescent phosphor using sonochemistry

Abstract

A method of making zinc sulfide based electroluminescent phosphors is described wherein a first-fired zinc sulfide material having a hexagonal β-ZnS crystal structure is at least partially converted to a distorted hexagonal β-ZnS crystal structure by ultrasonic irradiation. The first-fired material is then fired at a lower temperature to form an electroluminescent phosphor.

We claim:  
     
         1 . A method of making of zinc sulfide-based electroluminescent phosphors, comprising: 
 a) firing a mixture of zinc sulfide, at least one activator, and a flux to form a first-fired material having a hexagonal β-ZnS crystal structure;    b) suspending the first-fired material in a liquid medium;    c) at least partially converting the crystal structure of the first-fired material to a distorted hexagonal β-ZnS form by ultrasonic irradiation of the suspension; and    d) firing the at least partially converted first-fired material to form an electroluminescent phosphor.    
     
     
         2 . The method of  claim 1  wherein said mixture at a temperature from about 1050° to about 1400° C. for about 2 hours to about 8 hours.  
     
     
         3 . The method of  claim 1  wherein the suspension is ultrasonically irradiated from about 10 minutes to about 90 minutes.  
     
     
         4 . The method of  claim 2  wherein mixture contains copper and chlorine.  
     
     
         5 . The method of  claim 4  wherein the first-fired material is blended with a source of copper after the ultrasonic irradiation and prior to the second firing.  
     
     
         6 . The method of  claim 5  wherein the blended material is fired at a temperature from about 500° C. to about 1000° C. for about 1 to 5 hours.  
     
     
         7 . The method of  claim 2  wherein the at least partially converted first-fired material is fired at-a temperature from about 500° C. to about 1000° C. for about 1 to 5 hours.  
     
     
         8 . The method of  claim 1  wherein the first-fired material is suspended in water and the ultrasound has a frequency of 20 kHz.  
     
     
         9 . The method of  claim 1  wherein the suspension containing the first-fired material is circulated through a cell having an ultrasonic transducer.  
     
     
         10 . The method of  claim 9  wherein at least a portion of the suspension is recirculated through the cell.  
     
     
         11 . A method of making of zinc sulfide-based electroluminescent phosphors, comprising: 
 a) firing a mixture of zinc sulfide, at least one activator, and a flux at a temperature from about 10500 to about 1400° C. for about 2 hours to about 8 hours to form a first-fired material having a hexagonal β-ZnS crystal structure;    b) suspending the first-fired material in a liquid medium;    c) at least partially converting the crystal structure of the first-fired material to a distorted hexagonal β-ZnS form by ultrasonic irradiation of the suspension; and    d) firing the at least partially converted first-fired material at a temperature from about 500° C. to about 1000° C. for about 1 to 5 hours to form a zinc sulfide-based electroluminescent phosphor having a cubic α-ZnS crystal form.    
     
     
         12 . The method of  claim 11  wherein the phosphor is activated with copper.  
     
     
         13 . The method of  claim 12  wherein the first-fired material is blended with a source of copper after the ultrasonic irradiation and prior to the second firing.  
     
     
         14 . The method of  claim 11  the first-fired material is suspended in water and the ultrasound has a frequency of 20 kHz.