Colloidal dispersion of particles of a rare earth vanadate or phosphovanadate

Abstract

The invention concerns a colloidal dispersion of a vanadate or a phosphovanadate of at least a rare earth characterized in that it comprises either a complex-forming agent having a pK (cologarithm of the dissociation constant of the complex formed by the complex-forming agent and said rare earth) higher than 2.5, or an anion of a monovalent acid, soluble-in water and having a pKa ranging between 2.5 and 5. In the case of a vanadate dispersion, the particles have an average size of not more than 6 nm. The inventive dispersion is obtained by a method which consists in contacting a colloidal dispersion or a dispersion of initial complexes comprising at least a rare earth compound and at least a complex-forming agent or an anion of said monovalent acid and whereof the pH has been adjusted to a value of at least 7, with vanadate ions and, if required, with phosphate ions, then in adjusting the pH of the resulting medium to a value of at least 9 and heating.

1 - 16 . (Canceled)  
     
     
         17 . A colloidal dispersion of particles of a vanadate of at least one rare earth, said particles having a mean size of at most 6 nm and comprising either a complexing agent having a pK, said pK being the cologarithm of the dissociation constant of the complex formed by said complexing agent and said rare earth, of greater than 2.5, or an anion of a monovalent acid, soluble in water and having a pKa of between 2.5 and 5.  
     
     
         18 . A colloidal dispersion of particles of a phosphor vanadate of at least one rare earth, comprising either a complexing agent having a pK, said pK being the cologarithm of the dissociation constant of the complex formed by said complexing agent and said rare earth, of greater than 2.5, or an anion of a monovalent acid, soluble in water and having a pKa of between 2.5 and 5.  
     
     
         19 . The dispersion as claimed in  claim 18 , wherein the particles have a mean size of at most 20 nm.  
     
     
         20 . The dispersion as claimed in  claim 19 , wherein the particles have a mean size of at most 6 nm.  
     
     
         21 . The dispersion as claimed in  claim 17 , wherein the particles have a degree of agglomeration of less than 40%.  
     
     
         22 . The dispersion as claimed in  claim 20 , wherein the particles have a degree of agglomeration of less than 40%.  
     
     
         23 . The dispersion as claimed in  claim 17 , wherein the first rare earth of the vanadate or phosphovanadate is europium, and of the second rare earth is yttrium or lanthanum.  
     
     
         24 . The dispersion as claimed in  claim 18 , wherein the first rare earth of the vanadate or phosphovanadate is europium, and of the second rare earth is yttrium or lanthanum.  
     
     
         25 . The dispersion as claimed in  claim 17 , wherein the complexing agent is an acid, a polyhydroxyacid, a aliphatic amino acid, a polyacrylic acid or a salt of these said acids.  
     
     
         26 . The dispersion as claimed in  claim 18 , wherein the complexing agent is an acid, a polyhydroxyacid, a aliphatic amino acid, a polyacrylic acid or a salt of these said acids.  
     
     
         27 . The dispersion as claimed in  claim 17 , wherein the monovalent acid is acetic acid.  
     
     
         28 . The dispersion as claimed in  claim 18 , wherein the monovalent acid is acetic acid.  
     
     
         29 . A method for the preparation of a colloidal dispersion as defined in  claim 17  wherein comprising the steps of: 
 a) bringing into contact either an initial colloidal dispersion of at least one rare-earth compound comprising at least one complexing agent or an anion of said monovalent acid, said dispersion having a pH which has been adjusted to a value of at least 7, or an initial dispersion of complexes, which is based on a rare-earth compound, a complexing agent or an anion of said monovalent acid, which dispersion furthermore contains OH −  anions and the pH of which has been adjusted to a value of at least 7, with vanadate ions, and, optionally, with phosphate ions in order to obtain a medium whose pH of the medium is being adjusted to a value of at least 9; and    b) heating said medium obtained in step a).    
     
     
         30 . A method for the preparation of a colloidal dispersion as defined in  claim 18  wherein comprising the steps of: 
 a) bringing into contact either an initial colloidal dispersion of at least one rare-earth compound comprising at least one complexing agent or an anion of said monovalent acid, said dispersion having a pH which has been adjusted to a value of at least 7, or an initial dispersion of complexes, which is based on a rare-earth compound, a complexing agent or an anion of said monovalent acid, which dispersion furthermore contains OH −  anions and the pH of which has been adjusted to a value of at least 7, with vanadate ions and, optionally, with phosphate ions in order to obtain a medium whose pH of the medium is being adjusted to a value of at least 9; and    b) heating said medium obtained in step a).    
     
     
         31 . The method as claimed in  claim 29 , wherein in step a) the pH of the initial colloidal dispersion or of the initial dispersion of complexes is adjusted to a value of between 7 and 9.5.  
     
     
         32 . The method as claimed in  claim 30 , wherein in step a) the pH of the initial colloidal dispersion or of the initial dispersion of complexes is adjusted to a value of between 7 and 9.5.  
     
     
         33 . The method as claimed in  claim 31 , wherein, in step b), the pH of the mixture is adjusted to a value of between 9 and 12.5.  
     
     
         34 . The method as claimed in  claim 32 , wherein, in step b), the pH of the mixture is adjusted to a value of between 9 and 12.5.  
     
     
         35 . The method as claimed in  claim 33 , further comprising the step of: 
 c) washing the dispersion obtained after step b), by ultrafiltration and further heating again the washed dispersion.    
     
     
         36 . The method as claimed in  claim 34 , further comprising the step of: 
 c) washing the dispersion obtained after step b), by ultrafiltration and further heating again the washed dispersion.    
     
     
         37 . A process for the preparation of luminescent devices comprising the step of using a colloidal dispersion as defined in  claim 17 .  
     
     
         38 . A process for depositing a transparent film on a glass or quartz substrate comprising the step of using a colloidal dispersion as defined in  claim 17 .  
     
     
         39 . A device comprising a glass or quartz substrate which is equipped with transparent electrodes and on which a transparent film obtained by depositing a dispersion as defined in  claim 17 , is placed.  
     
     
         40 . A process for the preparation of luminescent devices comprising the step of using a colloidal dispersion as defined in  claim 18 .  
     
     
         41 . A process for depositing a transparent film on a glass or quartz substrate comprising the step of using a colloidal dispersion as defined in  claim 18 .  
     
     
         42 . A device comprising a glass or quartz substrate which is equipped with transparent electrodes and on which a transparent film obtained by depositing a dispersion as defined in  claim 18 , is placed.