PHOSPHORESCENT COMPOUNDS

Abstract

The phosphorescent compounds of the invention have a matrix with the general formula M2SiO4 wherein M represents an alkaline earth such as barium, strontium or calcium, and the matrix is doped with europium and co-doped with at least one other lanthanide such as praseodymium, samarium, dysprosium or holmium. In accordance with a method embodiment, the dopant compounds are introduced into the matrix in the form of fluorides by calcination in a reducing atmosphere. The invention may be applied in the field of horology.

Description

Claims

1. A phosphorescent compound comprising: a silicate based matrix with a formula M2SiO4 wherein M represents an alkaline earth selected from the group consisting of barium, strontium and calcium, wherein the matrix is doped with europium and co-doped with at least one other lanthanide in the form of a fluoride or an element creating disconformities in the structure of the matrix, or in the form of a fluoride and an element creating disconformities in the structure of the matrix.

2. The phosphorescent compound according to claim 1, wherein the other lanthanide for co-doping the matrix is selected from the group consisting of praseodymium, samarium, dysprosium, holmium and a mixture thereof.

3. The phosphorescent compound according to claim 1, having the formula M2-xSiO4:Eua,Lnb wherein x, a and b represent molar proportions such that x=a+b, and Ln is the other lanthanide for co-doping the matrix selected from the group consisting praseodymium, samarium, dysprosium, holmium and a mixture thereof.

4. The phosphorescent compound according to claim 3, wherein the percentage a of europium is between 0.1% and 0.5% by molar proportion.

5. The phosphorescent compound according to claim 3, wherein the percentage b of the other co-dopant lanthanide is between 0.1% and 2.0% by molar proportion.

6. The phosphorescent compound according to claim 4, wherein the values of a and b are close to 0.4% by molar proportion.

7. The phosphorescent compound according to claim 6, wherein the compound comprises a Ba2SiO4 matrix doped with europium and co-doped with praseodymium.

8. The phosphorescent compound according to claim 1, wherein the luminescence peak after illumination is between 254 nm and 366 nm.

9. A synthesis method for the phosphorescent compound according to claim 1, wherein the method includes the steps of: a) grinding and mixing rare earth carbonates or silicates and silicon dioxide;b) calcinating the mixture at a high temperature between 1100° C. and 1500° C.;c) adding dopants and co-dopants in the form of fluorides, and treated in a reducing atmosphere composed of a mixture of N2/H2 at a lower temperature between 900° C. and 1000° C.; andd) leaving the product obtained at the preceding step (c) to cool, and grinding the product and calibrating the product by sieving.

10. The method according to claim 9, wherein in step (c) a flux is added to lower the temperature and create disconformities in the matrix structure.

11. The method according to claim 9, wherein the dopants and co-dopants are also added in steps (a) and (b).

12. A composition including the phosphorescent compound according to claim 1 applied to a support in order to make the support visible at night

13. A timepiece wherein at least one component of the timepiece incorporates a composition according to claim 12.

14. The phosphorescent compound according to claim 2, having the formula M2-xSiO4:Eua,Lnb wherein x, a and b represent molar proportions such that x=a+b, and Ln is the lanthanide for co-doping the matrix selected from the group consisting of praseodymium, samarium, dysprosium, holmium and a mixture thereof.

15. The phosphorescent compound according to claim 4, wherein the percentage b of the other co-dopant lanthanide is between 0.1% and 2.0% by molar proportion.

16. The phosphorescent compound according to claim 15, wherein the values of a and b are close to 0.4% by molar proportion.

17. The phosphorescent compound according to claim 5, wherein the values of a and b are close to 0.4% by molar proportion.

18. The phosphorescent compound according to claim 6, wherein the compound comprises a Sr2SiO4 matrix doped with europium and co-doped with dysprosium.

19. The phosphorescent compound according to claim 6, wherein the compound comprises a Ca2SiO4 matrix doped with europium and co-doped with holmium.

20. The method according to claim 10, wherein in step (c) the added flux is B2O3.