Luminophores and core-shell luminophore precursors

Patent metadata

Field	Value
Publication number	US-9611424-B2
Application number	US-201314063930-A
Country	US
Kind code	B2
Filing date	Oct 25, 2013
Priority date	Jul 28, 2006
Publication date	Apr 4, 2017
Grant date	Apr 4, 2017

Abstract

A novel type of green luminophore containing mixed rare-earth phosphates is produced from precursor particles having a mean diameter ranging from 1.5 to 15 microns; such particles have an inorganic core and a shell of a mixed lanthanum and/or cerium phosphate, optionally doped with terbium, evenly covering the inorganic core with a thickness greater than or equal to 300 nm.

First claim

The invention claimed is:

1. A phosphor precursor (P) comprising particles having an average diameter ranging from 1.5 to 15 microns, the particles comprising:
a mineral core based on a non-phosphor mineral material a comprising a yttrium, gadolinium or cerium oxide; and
a shell based on a mixed phosphate of lanthanum and/or cerium, optionally doped with terbium, homogeneously covering the mineral core over a thickness greater than or equal to 300 nm.

2. The phosphor precursor as defined by claim 1 , wherein the shell has a thickness from 0.3 to 1 micron.

3. The phosphor precursor as defined by claim 1 , wherein the mixed phosphate of the shell has the formula (I) below:
La (1-x-y) Ce x Tb y PO 4   (I)

in which:
x ranges from 0 to 0.95, inclusive;
y ranges from 0.05 to 0.3, inclusive; and
the sum (x+y) is less than or equal to 1.

4. The phosphor precursor as defined by claim 3 , wherein the mixed phosphate of the shell has the formula (Ia) below:
La (1-x-y) Ce x Tb y PO 4   (Ia)

in which:
x ranges from 0.1 to 0.5, inclusive;
y ranges from 0.1 to 0.3, inclusive; and
the sum (x+y) ranges from 0.4 to 0.6.

5. The phosphor precursor as defined by claim 1 , wherein the mixed phosphate of the shell has the formula (Ib) below:
La (1-y) Tb y PO 4   (Ib)

in which:
y ranges from 0.05 to 0.3, inclusive;
or has the following formula (Ic):
La (1-y) Ce y PO 4   (Ic)

in which:
y ranges from 0.01 to 0.3, inclusive.

6. The phosphor precursor as defined by claim 1 , wherein the particles have a dispersion index of less than 0.6.

7. The phosphor precursor as defined by claim 1 , wherein the mineral core has a specific surface area of at most 1 m 2 /g.

8. The phosphor precursor as defined by claim 1 wherein the mineral core of the particles has been densified by using the technique of molten salts.

9. A phosphor (L) comprising particles having an average diameter ranging from 1.5 to 15 microns, these particles comprising:
a mineral core based on a non-phosphor mineral material comprising a yttrium, gadolinium or cerium oxide; and
a shell based on a mixed phosphate of lanthanum and/or cerium, with the structure of lanthanum phosphate, optionally doped with terbium (LAP), homogeneously covering the mineral core, over a thickness greater than or equal to 300 nm.
wherein the phosphor has a substantially identical or greater photoluminescence yield and a Tb content at least 5 wt % lower than a mixed phosphate of La and/or Ce doped with Tb having a composition, expressed by weight, of 55% La oxide, 30% Ce oxide and 15% Tb oxide.

10. A phosphor (L) as defined by claim 9 , wherein the mixed phosphate of the shell has the general formula (Ia) below:
La (1-x-y) Ce x Tb y PO 4   (Ia)

in which:
x ranges from 0.1 to 0.5, inclusive;
y ranges from 0.1 to 0.3, inclusive; and
the sum (x+y) ranges from 0.4 to 0.6.

11. A phosphor (L) as defined by claim 9 , wherein the mixed phosphate of the shell has the general formula (Ib) or (Ic) below:
La (1-y) Tb y PO 4   (Ib)

in which:
y ranges from 0.05 to 0.3, inclusive; or
La (1-y) Ce y PO 4   (Ic)

in which:
y ranges from 0.01 to 0.3, inclusive.

12. A phosphor (L) as defined by claim 9 , wherein the mineral core has a specific surface area of at most 1 m 2 /g.

13. A plasma system, a display screen or a lighting system having a green luminescence provided by a phosphor as defined by claim 9 .

14. A UV excitation device, trichromatic lamp, mercury vapor trichromatic lamp, lamp for backlighting liquid crystal systems, plasma screen, xenon excitation lamp, device for excitation by light-emitting diodes or UV excitation marking system, comprising a phosphor as defined by claim 9 .

15. A luminescent device having a green luminescence comprising a phosphor (L) as defined by claim 9 .

16. A luminescent device as defined by claim 15 , comprising a UV excitation device, trichromatic lamp, mercury vapor trichromatic lamp, lamp for backlighting liquid crystal systems, plasma screen, xenon excitation lamp, device for excitation by light-emitting diodes or UV excitation marking system.

17. A process for preparing a phosphor precursor (P) as defined by claim 1 , comprising:
adding, continuously and gradually with stirring, an aqueous solution (s) of soluble lanthanum and/or cerium, and optionally terbium, salts to an aqueous medium (m) having an initial pH (pH 0 ) of 1 to 5 and initially comprising:
particles (p 0 ) based on a mineral material, in the dispersed state; and
phosphate ions,

maintaining the pH of the reaction medium at an approximately constant value during precipitation of the mixed phosphate, with variations in the pH of at most 0.5 pH units, whereby particles are obtained that comprise a core based on a non-phosphor mineral material, comprising a tyyrium, gadolinium or cerium oxide, deposited at the of which is a mixed phosphate of lanthanum and/or cerium, and optionally terbium, and
(B) separating from the particles obtained from the reaction medium, and heat treating then at a temperature of 400° to 900° C.

18. The process as defined by claim 17 , wherein the particles (p 0 ) are particles of isotropic morphology.

19. The process as defined by claim 17 , wherein the particles (p 0 ) have an average diameter ranging from 0.5 to 14 microns.

20. The process as defined by claim 17 , wherein the particles (p 0 ) have a dispersion index of less than 0.6.

21. The process as defined by claim 18 , wherein the particles (p 0 ) are approximately spherical.

22. The process as defined by claim 17 , wherein, the phosphate ions are initially present in the aqueous medium (m) in the form of ammonium phosphates.

23. The process as defined by claim 17 , wherein, the phosphate ions are introduced in a stoichiometric excess into the aqueous medium (m), with an initial phosphate/(La+Ce+Tb) molar ratio greater than 1.

24. The process as defined by claim 17 , further comprising maturing the reaction medium after the addition of all of the solution(s) and prior separating the particles.

25. The process as defined by claim 17 , wherein the particles (p 0 ) have a specific surface area of at most 1 m 2 /g.

26. A process for preparing a phosphor (L) from a precursor (P) as defined by claim 1 , which comprises a step (C) in which:
(C) said precursor (P) is heat-treated at a temperature above 900° C.

Assignees

• Rhodia Operations

Inventors

• Le-Mercier Thierry
• Buissette Valerie

Classifications

• H01J61/44

  Devices characterised by the luminescent material · CPC title

• C09K11/7777

  Phosphates · CPC title

• B01J14/00

  Chemical processes in general for reacting liquids with liquids; Apparatus specially adapted therefor (B01J8/00, B01J19/08 take precedence) · CPC title

• C09K11/025 Primary

  non-luminescent particle coatings or suspension media · CPC title

• H01K1/04 Primary

  characterised by the material thereof · CPC title