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Cerium and/or terbium phosphate, optionally with lanthanum, phosphor resulting from said phosphate, and methods for making same

A light-emitting material, phosphate technology

Inactive Publication Date: 2011-10-12
RHODIA OPERATIONS SAS
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Problems solved by technology

The described method more particularly uses nitrates as rare earth metal salts and proposes the use of ammonia as a base, which has the disadvantage of emitting nitrogen-containing products
Thus, while this method does produce a high performance product, it may complicate its implementation in order to meet increasingly stringent ecological legislation that prohibits or limits such emissions
[0007] It cannot be denied that, in particular, strong bases other than ammonia (e.g. alkali metal hydroxides) can be used, but the latter lead to the presence of alkali metals in the LAP, which is believed to enable the use of phosphors. Medium (especially in mercury vapor lamps) reduces its luminous properties

Method used

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  • Cerium and/or terbium phosphate, optionally with lanthanum, phosphor resulting from said phosphate, and methods for making same
  • Cerium and/or terbium phosphate, optionally with lanthanum, phosphor resulting from said phosphate, and methods for making same
  • Cerium and/or terbium phosphate, optionally with lanthanum, phosphor resulting from said phosphate, and methods for making same

Examples

Experimental program
Comparison scheme
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no. 1 approach

[0071] For the first embodiment, a minimum lithium content is not necessary and it may correspond to the lowest value detectable by the analytical technique used to measure this content. However, this minimum lithium content is generally at least 10 ppm, more particularly at least 90 ppm.

[0072] Phosphates of the monazite crystal structure consist of microparticles which themselves consist of aggregates of crystallites with a size measured in the plane (012) of at least 70 nm, more particularly of at least 80 nm, which size may also vary with the precursor in It varies with the calcination temperature experienced during its preparation. Here again, as before, it can be observed that the phosphates according to the invention have better crystallinity than the phosphates of the prior art with the same structure.

[0073] For those phosphates that have been subjected to calcination or heat treatment at temperatures generally above 600°C, advantageously 800 to 900°C, although t...

Embodiment 2

[0154] This example relates to the preparation of lanthanum, cerium and terbium phosphates according to the invention.

[0155] Within 1 h, to 1 L containing 1.5 mol / L analytical grade phosphoric acid H previously adjusted to pH 1.6 by addition of LiOH and adjusted to 60 °C 3 PO 4 Add 1 liter of rare earth metal chloride solution of 4N purity to the solution, the solution of rare earth metal chloride has an overall concentration of 1.3 mol / liter, and can be subdivided as follows: 0.57 mol / liter of lanthanum chloride, 0.56 mol / liter of Cerium chloride and terbium chloride at 0.17 mol / l. The pH was adjusted to 1.6 by adding LiOH during the precipitation.

[0156] At the end of the precipitation step, the mixture was maintained at 60°C for an additional 15 minutes. The resulting precipitate was then recovered by filtration, washed with water, then dried in air at 60°C, and then subjected to heat treatment in air at 840°C for 2 hours. At the end of the calcination, the product...

Embodiment 4

[0165] This example relates to the preparation according to the invention of a phosphor obtained from the phosphate of Example 2.

[0166] The precursor phosphate obtained in Example 2 was reprocessed under the same conditions as in Example 3.

[0167] The characteristics of the products of Examples 3 and 4 are listed in Table 2 below.

[0168] Table 2

[0169]

[0170] The luminescence yield of product 4 according to the invention is given relative to comparative product 3.

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Abstract

The invention relates to a rare earth element phosphate (Ln), where Ln is either at least one rare earth element selected from cerium and terbium, or lanthanum in combination with at least one of the above two rare earth elements, having a crystalline structure of the rhabdophane type or of the monazite type with a lithium content of 300 ppm at most. The phosphate is obtained by the precipitation of a rare earth element chloride at a constant pH lower than 2, and then calcining and redispersing the same in hot water. The invention also relates to a phosphor obtained by calcining the phosphate at at least 1000 DEG C.

Description

technical field [0001] The present invention relates to phosphates of cerium and / or terbium, optionally with lanthanum, to phosphors produced from such phosphates, and to processes for their preparation. Background technique [0002] Mixed phosphates of lanthanum, terbium, and cerium, and mixed phosphates of lanthanum and terbium (hereinafter generally denoted LAP) are well known in the art for their luminescent properties. For example, when containing cerium and terbium, they emit bright green light when illuminated by certain high-energy radiations (UV or VUV radiation used in lighting or display systems) having wavelengths below the visible range. Phosphors utilizing this property are generally used on an industrial scale, for example, in three-color fluorescent lamps, in backlighting systems for liquid crystal displays or in plasma systems. [0003] Several methods of preparing LAP are known. These methods are of two types. Firstly, there are "dry" processes in which ...

Claims

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Application Information

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IPC IPC(8): C01B25/45C09K11/81C09K11/77
CPCC01B25/37C01B25/45C09K11/7778Y10T428/2982C09K11/77
Inventor V·比塞特T·勒-梅西耶尔
Owner RHODIA OPERATIONS SAS
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