Hydrothermal method of synthesis of rare-earth tantalates and niobates
A hydrothermal method of synthesis of a family of rare-earth Group 5 oxides, where the Group 5 oxide is a niobate or tantalate. The rare-earth Group 5 oxides can be doped with suitable emitter ions to form nanophosphors.
1. A method of forming a rare-earth Group 5 oxide, the method comprising:
preparing an aqueous solution of a complexed rare-earth ion, wherein a pH of the aqueous solution is suitable for retaining the complexed rare-earth ion in solution;
adding a Group 5 oxide ion to the aqueous solution to form a reaction solution; and
reacting the complexed rare-earth ion and the Group 5 oxide ion under hydrothermal reaction conditions to form a rare-earth Group 5 oxide,
wherein the rare-earth Group 5 oxide is a tantalate or a niobate.
2. The method of claim 1 , wherein the step of adding a Group 5 oxide ion comprises at least one of adding a solid salt of the Group 5 oxide ion and adding a solution comprising the Group 5 oxide ion.
3. The method of claim 2 , wherein a counter ion of the solid salt of the Group 5 oxide is selected from the group consisting of Li + , Na + , K + , Rb + , Cs + , and trimethylammonium ion.
4. The method of claim 2 , wherein the solid salt is a tantalate salt that is selected from the group consisting of a salt of [Ta(O 2 ) 4 ] 3− and a salt of [Ta 6 O 19 ] 8− and wherein a counterion of the tantalate salt is selected from the group consisting of Li + , Na + , K + , Rb + , Cs + , and trimethylammonium ion.
5. The method of claim 1 , wherein the Group 5 oxide ion is at least one of hexatantalate, peroxotantalate, hexaniobate, and peroxoniobate.
6. The method of claim 1 , wherein the pH suitable for retaining the complexed rare-earth ion in solution is obtained by adjusting the pH by addition of a base.
7. The method of claim 6 , wherein the base is selected from the group consisting of Group I hydroxides, ammonium hydroxide, and alkyl ammonium hydroxides.
8. The method of claim 1 , wherein the step of preparing the aqueous solution of the complexed rare-earth ion further comprises adding a chelating agent to a solution of a rare-earth ion to form a precipitated complexed rare-earth ion and adjusting a pH of the aqueous solution to dissolve the precipitated complexed rare-earth ion.
9. The method of claim 8 , wherein the chelating agent is selected from the group consisting of citrate and EDTA.
10. The method of claim 1 , wherein the complexed rare-earth ion is a complex of a rare-earth ion with a chelating ligand.
11. The method of claim 10 , where the chelating ligand is selected from the group consisting of citrate, ethylenediamine tetraacetic acid and salts thereof, ethanol triamine, a diamine, a diketonate, a dicarboxylate, and an amino acid.
12. The method of claim 1 , wherein the aqueous solution of the complexed rare-earth ion further comprises a dopant ion.
13. The method of claim 12 wherein the dopant ion is suitable for incorporation in a rare-earth site of the rare-earth Group 5 oxide.
14. The method of claim 13 , wherein the dopant ion is selected from the group consisting of Eu 3+ , Tm 3+ , Dy 3+ , Pr 3+ , Sm 3+ , Ce 3+ , Tb 3+ , Er 3+ , Ho 3+ , and Nd 3+ .
15. The method of claim 14 , wherein the dopant ion is incorporated in a Group 5 atom site of the rare-earth Group 5 oxide.
16. The method of claim 15 , wherein the dopant ion is selected from the group consisting of Mn 2+ , Cr 3+ , Mn 4+ , Bi 3+ , and Sb 3+ .
17. The method of claim 1 , wherein the hydrothermal reaction conditions comprise a closed-volume reaction vessel and a reaction temperature greater than 100° C.
18. The method of claim 1 , wherein the step of reacting the complexed rare-earth ion and the Group 5 oxide ion under hydrothermal reaction conditions comprises heating the reaction solution to a temperature between approximately 100° C. and approximately 250° C. to form the rare-earth Group 5 oxide.
19. The method of claim 18 , wherein a counter ion of the Group 5 oxide ion is selected from the group consisting of Li + , Na + , K + , Rb + , Cs + , and trimethylammonium ion.
20. The method of claim 1 , wherein the step of preparing the aqueous solution comprises:
dissolving a rare-earth ion source and a dopant ion source in water;
adding a complexing ion; and
adjusting the pH of the aqueous solution to dissolve precipitated particles.
21. The method of claim 20 , wherein the pH is adjusted by addition of a base.
22. The method of claim 1 , further comprising annealing the rare-earth Group 5 oxide.
23. The method of claim 22 , wherein the annealing is performed at least in part under a controlled atmosphere with sufficiently low oxygen concentration to generate oxygen vacancies.