JP2003502251A - Lanthanum, lutetium, yttrium or gadolinium borates containing two dopants and their precursors and their use in plasma or X-ray systems - Google Patents

Abstract

The invention relates to lanthanum, lutetium, yttrium or gadolinium borates containing two dopants, the precursors of the borates and the use of the borates in plasma or X-ray systems. The rare earth borates of the invention correspond to the LnBO ₃ formula (where Ln represents one or more rare earths selected from lanthanum, lutetium, yttrium and gadolinium) and also transfer electrons such as europium, samarium, thulium and ytterbium. At least one first element selected from trivalent elements that can be collected is selected from europium II and trivalent elements that can collect vacancies such as cerium, terbium, praseodymium, bismuth, lead, antimony, chromium, and iron. It is characterized by including at least one selected second element.

Description

Detailed Description of the Invention

TECHNICAL FIELD The present invention relates to lanthanum, lutetium, yttrium or gadolinium borate and its precursors containing two doping agents and their use in plasma or X-ray systems.

[0002] Plasma systems (screens and lamps) are some of the new technologies for developing visualization and lighting. A specific example is the replacement of current television screens with flat screens, which are lighter and smaller in size, such replacements being attempted to be solved by using plasma panels. Is.

In a plasma system, the gas introduced into the chamber is ionized under the action of a discharge. During this process, high energy electromagnetic radiation is emitted. Photons are directed towards the luminescent material.

[0004]   Moreover, in X-ray based systems, photons excite the luminescent material.

To be effective, the substance must be a luminophore that absorbs in the emission range of plasma or X-rays and emits in good yield in the visible range.

Rare earth borates are known as suitable substances of this type. But,
It would be necessary to find products with further improved emission yields.

[0007]   Therefore, it is an object of the invention to obtain a substance with an improved emission yield.

DISCLOSURE OF THE INVENTION To this end, the rare earth borate of the invention is in accordance with the formula LnBO ₃ where Ln represents one or more rare earths selected from lanthanum, lutetium, yttrium and gadolinium. And at least one first element selected from trivalent elements capable of collecting electrons, and at least a second element selected from europium II and a trivalent element capable of collecting holes. It is characterized by including one kind.

The invention also relates to such a rare earth metal borohydride, characterized in that the rare earth and a carbonate or hydroxycarbonate of said element are reacted with boric acid, the reaction medium is in the form of an aqueous solution and the reaction product is calcined. It also relates to the process of producing the acid salt.

Description of the Preferred Embodiments Other features, details and advantages of the invention will be more fully apparent from a reading of the following description and various specific but non-limiting examples intended to be exemplified. I think it will be.

The borate of the invention is based on one or more rare earth Ln capable of forming a product matrix with boron. Ln represents at least one rare earth selected from lanthanum, lutetium, yttrium, and gadolinium, or a combination of at least two of these rare earths. In the case of combinations, the respective proportions of the various rare earths can be as desired. According to a particular embodiment of the invention, yttrium and gadolinium are present in combination.

The borate of the invention also comprises a first further element and a second further element, these elements being able to act as a doping agent.

As mentioned above, the first element is selected from trivalent elements capable of collecting electrons. The first element is the element whose effective electron collecting section is larger than the vacancy collecting section.

The first element may more particularly include europium, samarium, thulium and ytterbium, which elements may be present on their own or in combination.

The content of europium and / or samarium can preferably be 2 to 25%, more particularly 4 to 15%. This content is based on europium and / or the moles of the rare earth borate and all further elements or doping agents.
Alternatively, it is represented by the mole of samarium, that is, [D ₁ ] / [Σ (Ln + D ₁ + D ₂ )] ratio, and D ₁ is the first element or the total of the first elements (in this case, europium and / or
Or samarium) and D ₂ represents the sum of the second element or other second elements. Europium used as a doping agent in the present invention is Europium III
Is.

The content of thulium can be preferably 0.1 to 5%, and the content of ytterbium can be preferably 1 to 2.5%. The contents of thulium and ytterbium are expressed in the same manner as listed above for europium and samarium.

The borate of the invention comprises europium II and at least one second element selected from trivalent elements capable of collecting vacancies in combination with a first element or a doping agent. This is the element where the section of elements that is effective in collecting vacancies is larger than the section that is effective in collecting electrons.

This second element is especially cerium, terbium, praseodymium, bismuth, lead,
It can be chosen from antimony, chromium and iron, these elements can be present on their own or in combination.

According to a particular embodiment of the invention, the first element can be europium and the second element can be terbium. Mention may more particularly be made of borate salts of yttrium and gadolinium in combination, which may also include europium and terbium. According to another particular embodiment, mention may be made of lanthanum borate containing thulium as the first element and terbium as the second element. According to a third particular embodiment of the invention, the first element can be thulium and the second element can be cerium, in which case the borate is especially a gadolinium borate. It is possible to

The total content of the second element is preferably 5 to 1,000, expressed in moles of the second element.
It can be in ppm and this content is also expressed in terms of moles relative to the moles of the rare earth borate and of said elements, ie [D ₂ ] / [Σ (Ln + D ₁ + D ₂ )]. This content is more particularly 10-500 ppm, even more particularly 30-100.
It can be ppm.

In a third said embodiment, namely a borate containing thulium and cerium,
The content of cerium can preferably be 0.1 to 15%, in particular 0.5 to 10%, even more particularly 5 to 10%. The content of thulium is especially 5 to 5,000 pp
m, more particularly 50 to 5,000 ppm.

The borate can be in the form of particles in which the size of the particles can vary within wide ratios. However, the volume median diameter of particles is 10 μm at maximum.
It is usually m, more particularly the largest and 5 μm, and even more particularly the volume median diameter can be 0.5 to 5 μm.

Throughout the description, the values of median diameter and dispersion index (indexes will be described later) are values obtained by employing laser diffraction techniques using a Coulter LS 230 type granulometer. is there.

According to a particular embodiment of the invention, the inventive borate may have a particular morphology, ie in the form of cubes, parallelepipeds (platelets) or spherical particles. The shape of the particles depends on the nature of the rare earths that make up the borate. In the case of lanthanum and lutetium, the borate is rather in the parallelepiped or plate form, in the case of yttrium the borate is in the spherical form, and for the combination of yttrium and gadolinium rare earth is the cubic form. . Additionally, the borate can have a dispersion index of 0.8 or less. This index is more particularly 0.
It can be 7 or less, and more particularly 0.6 or less. In the context of the present invention, it is possible to obtain products with a dispersion index of 0.4 to 0.5.

The dispersion index is understood to mean the following ratio: σ / m = (d ₉₀ −d ₁₀ ) / 2d ₅₀ where d ₉₀ is the equivalent diameter of the substance passing through equal to 90%. D ₁₀ is the equivalent diameter of the material passing through equal to 10%; d ₅₀ is the median diameter of the particles.

The borate of the invention can be obtained by any known process. Mention may be made of processes which employ a solid / solid reaction by mixing and melting precursors of the elements contained in the borate composition, for example oxides or carbonates.

A more specific process will be described below. This process applies more particularly to the preparation of boric acid having the above-mentioned morphology (parallelepipeds or plates, spheres, cubes) and a dispersion index of 0.8 or less.

The process comprises using these rare earth or doping agent carbonates or hydroxycarbonates as the sole rare earth or rare earths or the sole doping element or precursors of the doping elements contained in the borate composition. use.

It is possible to start from carbonates or hydroxycarbonates of rare earths and various doping agents or mixed carbonates or hydroxycarbonates of rare earths and doping agents.

The rare earth carbonates or hydroxycarbonates are products known per se and can be obtained, for example, by precipitating one or more rare earths with ammonium carbonate or ammonium bicarbonate. These carbonates or hydroxycarbonates can be used directly after precipitation or after optional washing and / or drying.

The starting carbonate or hydroxycarbonate is reacted with boric acid. The reaction is preferably carried out under the action of heat, for example at a temperature of 40 ° to 90 ° C.

According to another characteristic of this process, the reaction medium is in the form of an aqueous solution. this is,
It is meant that the amount of water present in the reaction medium is such that the weight ratio of water / boric acid + carbonate is at least 300%, more particularly at least 600%. This ratio can even more particularly be at least 1,000%.

It is possible to work with excess boric acid. This excess can be, for example, 1 to 250 mol% (that is, [B] / [Σ (Ln + D ₁ + D ₂ )] = 1.01 to 5).

It may be advantageous to carry out the reaction by removing the CO ₂ formed in the course of the reaction. This removal can be carried out, for example, by purging the reaction medium with a neutral gas such as nitrogen. This variant makes it possible to obtain products with finer particle sizes.

[0035]   A precipitate is obtained at the end of the reaction.

According to a variant of the invention, the precipitate can be aged in the reaction medium, preferably by keeping the medium at the same temperature at which the reaction was carried out. During this aging it is also possible to keep the pH of the aging medium constant. This pH can be fixed at a given value, for example the pH which the reaction mixture has just at the end of the reaction, ie at the end of the introduction of boric acid. The pH can be maintained in this way by adding a base, for example by adding an ammoniacal solution. Aging can last 1 to 3 hours.

The precipitate is then separated from the reaction medium by any known means, for example by filtration. The separated precipitate is optionally washed and then dried. One of the advantages of the described process is that it makes it possible to obtain a precipitate which can be easily filtered and washed. After drying, it is also possible to carry out a further washing with a dilute acid, for example nitric acid, in order to remove possible traces of carbonate which have not reacted completely.

[0038]   The precipitate is then calcined.

This calcination makes it possible to obtain the borate. This calcination is usually at a temperature of 500
It is carried out at between ° C and 1,400 ° C, more particularly between 500 ° and 1,100 ° C. It is fully possible to carry out this calcination in air. Also, a reducing atmosphere (for example, hydrogen)
Or, of course, a neutral atmosphere (argon) or mixtures thereof can also be employed for this calcination.

Calcination can also develop the luminescent properties of the product. Calcination will be carried out at higher temperatures if increased luminescence properties are desired.

A variant of the calcination stage can be mentioned. This variant involves mixing the dried precipitate with boric acid in an amount of acid which can be for example of the order of 5 to 15%.
Calcination is then carried out at a temperature which can be, for example, 900 ° to 1100 ° C. This variant gives the borate good luminescence performance at relatively slightly elevated calcination temperatures.

The invention also relates to the borate precursor composition described below. The composition collects one or more rare earths selected from boron, lanthanum, lutetium, yttrium and gadolinium, at least one primary element selected from trivalent elements capable of collecting electrons and europium II and vacancies. Characterized by being based on at least one second element selected from the trivalent elements capable of
And, after calcination, a rare earth borate of the formula LnBO ₃ , wherein Ln represents a single rare earth or a plurality of rare earths, the borate also comprising at least one said first element and at least one said It is characterized in that a material containing a second element can be provided. The first element can be selected from europium, samarium, thulium and ytterbium, and the second element can be selected from cerium, terbium, praseodymium, bismuth, lead, antimony, chromium and iron.

The composition can be prepared by mixing compounds of boron, compounds of rare earths and compounds of other said elements, these compounds being able to obtain the required borate after calcination. Selected from compounds that enable These compounds of rare earths and these compounds of other elements can be, for example, oxides or carbonates.

The composition may also be prepared by a more specific process of the type described above for borates. The process comprises reacting at least one of the rare earth carbonates or hydroxycarbonates, at least one of the first element carbonates or hydroxycarbonates and at least one of the second element carbonates or hydroxycarbonates with boric acid to form a reaction medium. It is characterized in that it is in the form of an aqueous solution and the reaction product is optionally washed and / or dried.
All of the above for this process up to obtaining a precipitate, separating and optionally washing and / or drying also apply here. The obtained precipitate is LnB (O
H) ₄ CO _{3 The} rare earth hydroxyborocarbonates or one of the rare earth hydroxyborocarbonates, at least one of the first element hydroxyborocarbonates and at least one of the second element hydroxys. Based on borocarbonate.

This composition based on hydroxyborocarbonates has the same morphological properties (cubic, parallelepiped (platelet) or spherical particles) and particle size properties (particularly particle size and dispersion index) as described above for borate. 0.8 or less).

Calcination of the precursor composition is carried out at a temperature sufficient to convert the composition to the borate, eg at least 500 ° C. as described above.

The invention further relates to the use of the borate described above as a luminophore in any process for visualization and illumination employing plasma excitation. This means a process that employs conditions that are conditions of the plasma system, ie, using a gas that, after ionization, emits radiation that matches a suitable wavelength of at least about 100 to about 200 nm, more particularly between 140 and 200 nm. Then be understood.

The invention also relates to a system for this type of visualization and lighting which comprises a borate according to the invention as a luminophore.

Visualization and lighting systems of this type that may be mentioned are plasma screens and lamps.

The inventive borate salts can also be used in any system that employs X-rays. X-rays are photons whose energy is about 10 to about 100.
It is understood to mean what is composed of what is Kev.

The invention also relates to an X-ray visualization system, which may include an imaging system, in particular an imaging system for medical imaging.

Borate salts are used to produce plasma or X-ray systems according to well known techniques, for example by serigraphy, electrophoresis or precipitation.

[0053]   Now let's give an example.

Examples 1 to 4 Products whose final composition is as follows are prepared. The content of doping element is
_{Expressed in} the manner listed above: Example 1 (comparative): Y _0.726 Gd _0.218 Eu _0.056 BO ₃ Example 2: Same composition as Example 1, but with 70 ppm terbium. Example 3 (comparative): Y _0.79 Gd _0.15 Eu _0.06 BO ₃ Example 4: Same composition as Example 3, but with praseodymium 50 ppm.

Preparation: A suspension of all the rare earth (Ln) carbonates contained in the product composition,
In the course of 1 hour under the action of heat (80 ° C.), 1.31 liter of a 1.3 M / liter solution of ammonium bicarbonate was appropriately stirred to obtain a solution 1 of a mixture of rare earth nitrates having a concentration of 0.7 M / liter. It is prepared by adding to 50 liters in such a proportion that the CO ₃ / Ln molar ratio is equal to 1.6.

A 0.8 M / liter boric acid solution is then added to the same medium, while still stirring and under the action of heat, in the course of 30 minutes so that the molar ratio B / Ln is equal to 1.5. Add. The resulting suspension is then left to mature by keeping the temperature at 60 ° C. and keeping the pH at a minimum of 4.6 by adding 6N ammoniacal solution.

After this 3 hour aging step, a white precipitate is obtained, which is isolated by filtration and then washed with demineralized water.

The moist product is then dried at 60 ° C. overnight, followed by 1, in the presence of H ₃ BO ₃ in a muffle furnace (under air) to obtain a boric acid solution of the rare earth.
Bake at 100 ° C for 2 hours.

Particle size was determined for the product of Example 2 by the Coulter technique described above. Also,
For the measurement, an ultrasonic probe (a probe having a tip with a diameter of 12 mm,
It is also stated that it was carried out on a dispersion of the calcined product in a 0.1% by weight aqueous solution of sodium hexametaphosphate, which had been passed through 450 W) for 3 minutes. The product of Example 2 has a median diameter of 2.3 μm and a dispersion index of 0.48.

Properties: 597 under X-ray excitation (XR: 30 KV) in the form of a prepared borate powder.
The intensity of the emission peak in nm was measured as a function of the content of the second element (terbium or praseodymium). The results are shown in Table 1 below.

[0061]

[Table 1] Table 1

The intensity of the emission peak at 150 nm under plasma excitation in the form of a powder of the products of Examples 1 and 2 is measured by an XUV spectrometer. The results are listed in Table 2 below.

[0063]

[Table 2] Table 2

Examples 5 and 6 Two products of the composition given below are prepared by the method given in the previous example: Example 5 (comparative): Gd _0.98 Ce _0.02 BO ₃ Example 6: Gd _{0. 99} Ce _0.005 Tm _0.005 BO ₃

597 under X-ray excitation (XR: 30 KV) in the form of a prepared borate powder.
The intensity of the emission peak in nm is measured. The results are listed in Table 3 below.

[0066]

[Table 3] Table 3

It can be seen that the emission intensity of the compound doped with cerium 0.5% and thulium 0.5% is higher than that of the compound doped with cerium 2%.

Claims (20)

[Claims] 1. A rare earth borate of the formula LnBO ₃ , wherein Ln is lanthanum,
Collecting at least one primary element selected from trivalent elements capable of collecting electrons, and europium II and vacancies, characterized by representing one or more rare earths selected from lutetium, yttrium and gadolinium A rare earth borate containing at least one second element selected from the trivalent elements capable of 2. The boron according to claim 1, wherein the first element is selected from europium, samarium, thulium and ytterbium, and the second element is selected from cerium, terbium, praseodymium, bismuth, lead, antimony, chromium and iron. Acid salt. 3. The borate of claim 2, wherein the first element is thulium and the second element is cerium. 4. The content of europium or samarium of the first element is 2 to 2 europium or samarium with respect to the rare earth borate and the moles of all the elements.
It is 5 mol%, The borate of Claim 1 or 2 characterized by the above-mentioned. 5. The borate of claim 2, wherein the content of thulium is 0.1 to 5 mol% of thulium with respect to the moles of the rare earth borate and all the elements. 6. The borate of claim 2, wherein the ytterbium content is 1-2.5 mol% ytterbium with respect to the moles of the rare earth borate and all the elements. 7. The content of the second element is 5 to 1,000 ppm of the second element, more particularly 10 to 500 p, expressed in moles relative to the moles of all the rare earths and the elements.
The borate of any one of claims 1, 2 and 4-6, which is pm. 8. A borate as claimed in claim 1, wherein Ln is a combination of yttrium and gadolinium. 9. The borate of claim 1, wherein the first element is europium and the second element is terbium or praseodymium. 10. A borate as claimed in claim 1, wherein Ln represents lanthanum, the first element is thulium and the second element is terbium. 11. A borate according to claim 1, characterized in that it is in the form of cubic, parallelepiped or spherical particles, and also has a dispersion index of 0.8 or less. 12. Collecting one or more rare earths selected from boron, lanthanum, lutetium, yttrium and gadolinium, at least one primary element selected from trivalent elements capable of collecting electrons and europium II and vacancies. A rare earth borate of the formula LnBO ₃ after calcination, characterized in that it is based on at least one secondary element selected from the group consisting of
Represents a single rare earth or a plurality of rare earths, and the borate can also provide at least one said first element and at least one said second element. . 13. The precursor according to claim 12, wherein the first element is selected from europium, samarium, thulium and ytterbium, and the second element is selected from cerium, terbium, praseodymium, bismuth, lead, antimony, chromium and iron. Material composition. 14. Based on said rare earth hydroxyborocarbonate or one of said rare earth hydroxyborocarbonates, at least one said first element hydroxyborocarbonate and at least one said second element hydroxyborocarbonate. 14. The precursor composition according to claim 12 or 13, characterized in that 15. The method according to claim 1, wherein the rare earth and the carbonate or hydroxycarbonate of the element are reacted with boric acid, the reaction medium is in the form of an aqueous solution, and the reaction product is calcined. Method for producing rare earth borate of. 16. Process according to claim 15, characterized in that the reaction medium is formed with water in a weight ratio of water / boric acid + carbonate or hydroxycarbonate of at least 300%, more particularly at least 600%. 17. Process according to claim 15 or 16, characterized in that the reaction is carried out by removing the CO ₂ formed in the course of the reaction. 18. A reaction medium in which at least one carbonate or hydroxycarbonate of the rare earth, at least one carbonate or hydroxycarbonate of the first element and at least one carbonate or hydroxycarbonate of the second element is reacted with boric acid. Is in the form of an aqueous solution, and the reaction product is optionally washed and / or dried to produce a precursor composition according to claim 12 or 13. 19. A visualization method employing plasma excitation or X-rays, characterized in that the borate of one of claims 1 to 11 is used as a luminophore. 20. A visualization system employing plasma excitation or X-rays, characterized in that it comprises the borate of one of claims 1 to 11 as a luminophore.