KR20010073118A - Lanthanum, Lutetium, Yttrium or Gadolinium Borate Comprising Two Doping Agents and Its Precursor, Use in Plasma or X-ray Systems - Google Patents

Abstract

The present invention relates to lanthanum, ruthetium, yttrium or gadolinium borate, precursors thereof and their use in plasma or X-ray systems comprising two dopants. The rare earth borate corresponds to the formula LnBO ₃ where Ln represents at least one rare earth element selected from lanthanum, lutetium, yttrium and gadolinium, and at least one selected from trivalent elements capable of trapping electrons, such as europium, samarium, thulium and ytterbium. Further comprising one or more second elements selected from trivalent elements and europium II capable of capturing flawed electrons such as cerium, terbium, praseodymium, bismuth, lead, antimony, chromium and iron do.

Description

Lanthanum, Lutetium, Yttrium or Gadolinium Borate and Its Precursors Containing Two Doping Agents and Its Precursor, Use in Plasma or X-ray Systems}

The present invention relates to borates of lanthanum, lutetium, yttrium or gadolinium, precursors thereof and their use in plasma or X-ray systems comprising two dopants.

Plasma systems (screens and lamps) belong to novel techniques of advanced visualization and lighting. A specific example is the replacement of current television screens with flat screens having less weight and smaller dimensions, which is solved by the use of plasma panels.

In a plasma system, gas introduced into the chamber is ionized under discharge. High energy electromagnetic radiation is emitted during this process. Photons are directed at the luminescent material.

Also, in systems using X-rays, photons excite the luminescent material.

To be effective, this material must be a luminophore absorbed within the emission range of plasma or X-rays emitted in the visible range with good yield.

Borates of rare earth elements are known as suitable materials of this type. However, it is considered necessary to find products with further improved luminous yields.

Accordingly, it is an object of the present invention to obtain a material having improved luminescence yield.

To achieve this object, the rare earth borate of the present invention corresponds to the formula LnBO ₃ , which Ln represents at least one rare earth element selected from lanthanum, ruthetium, yttrium and gadolinium and is selected from trivalent elements capable of trapping electrons. At least one first element and at least one second element selected from trivalent elements capable of trapping holes and europium II.

The present invention also relates to a process for producing the rare earth metal borate, wherein the carbonate or hydroxycarbonate of the element and rare earth element is reacted with boric acid, the reaction medium is in the form of an aqueous solution, and the reaction product is calcined. will be.

Other features, details and advantages of the invention will become more fully apparent upon reading the following detailed description as well as various specific embodiments which are intended to be illustrative and not limiting.

The borate of the present invention is based on at least one rare earth element Ln capable of forming a product matrix with boron. Ln represents one or more rare earth elements selected from lanthanum, lutetium, yttrium and gadolinium, or a combination of two or more of these rare earth elements. In the case of combinations, various proportions of various rare earth elements are possible. According to certain embodiments of the present invention, yttrium and gadolinium are present in combination.

The borate of the present invention is also characterized by including first and second additional elements that can serve as dopants.

As described above, the first element is selected from trivalent elements capable of trapping electrons. This is an element larger than the compartment effective for trapping electrons, which is effective for trapping electrons.

As the first element, more particularly mention may be made of europium, samarium, thulium and ytterbium, in which the elements may exist by themselves or in combination.

The content of europium and / or samarium may preferably be 2% to 25%, more particularly 4% to 15%. This content is expressed as the ratio of moles of europium and / or samarium to all the rare earth elements and additional elements of the borate or to the moles of the dopant, ie [D ₁ ] / [∑ (Ln + D ₁ + D ₂ )] Wherein D ₁ refers to the first element or all of the first elements (in this case europium and / or samarium), and D ₂ refers to the second element or all of the second elements. The europium used as the dopant herein is europium III.

The content of thulium may be preferably 0.1% to 5%, and the content of ytterbium may be preferably 1% to 2.5%. The content of thulium and ytterbium is shown in the same manner as given above for europium and samarium.

The borate of the present invention is characterized in that it comprises at least one second element selected from a trivalent element capable of trapping holes and europium II in combination with a first element or a dopant. This is an element larger than the compartment effective for trapping electrons, which is effective for trapping holes.

This second element may in particular be selected from cerium, terbium, praseodymium, bismuth, lead, antimony, chromium and iron which may be present by themselves or in combination.

According to a particular embodiment of the invention, the first element may be europium and the second element may be terbium. More particularly mention may be made of combinations of borate of yttrium and gadolinium further comprising europium and terbium. According to another particular embodiment, mention may be made of borate of lanthanum comprising thulium as the first element and terbium as the second element. According to a third specific embodiment of the invention, the first element is thulium and the second element may be cerium, in which case the borate may in particular be a borate of gadolinium.

The total content of the second element may preferably be from 5 ppm to 1,000 ppm in the moles of the second element, which content is also the moles of rare earths of all borates and the moles of the elements, ie [D ₂ ] / [∑ (Ln + D ₁ + D ₂ )]. This content may be more particularly 10 ppm to 500 ppm, even more particularly 30 ppm to 100 ppm.

In the third embodiment, namely borate comprising thulium and cerium, the content of cerium may preferably vary from 0.1% to 15%, in particular from 0.5% to 10%, more particularly from 5 to 10%. The content of thulium may in particular be from 5 ppm to 5,000 ppm, more particularly from 50 to 5,000 ppm.

The borate may be in the form of particles, which may vary within wide proportions. However, the volume median particle diameter of the particles can usually be 10 μm or less, more particularly 5 μm or less, even more particularly 0.5 to 5 μm.

In all the descriptions, the median particle size value and the dispersion index value to be mentioned later are values obtained using a laser diffraction technique using a granulometer of Coulter LS 230 type.

According to certain embodiments of the present invention, the borate of the present invention may take the form of a particular form, ie cuboidal, parallel hexagonal (small plate) or spherical particles. The shape of the particles depends on the intrinsic properties of the rare earth elements that make up the borate. In the case of lanthanum and lutetium, the borate is parallel hexagonal or plate-shaped, and in the case of yttrium, it is cubic, in the case of the combination of yttrium and gadolinium, the rare earth elements. In addition, the borate may have a dispersion index of 0.8 or less. This index may be more particularly 0.7 or less, even more particularly 0.6 or less. In the present invention, a product having a dispersion index of 0.4 or 0.5 can be obtained.

Dispersion index is understood to mean ratio.

σ / m = (d ₉₀ -d ₁₀ ) / 2d ₅₀

In the formula,

-d ₉₀ is the equivalent diameter of 90% of the material passing through.

-d ₁₀ is the equivalent diameter of 10% of the material passing through.

-d ₅₀ is the particle size of the particle.

The borate of the present invention can be obtained by any known method. Mention may be made of methods of using solid / solid reactions by mixing and fusing precursors of elements contained in borate compositions, such as oxides or carbonates.

More particular methods will be described below. This method is applied to the preparation of the above-described form (parallel hexahedron or plate, sphere, cube) and borate with a dispersion index of 0.8 or less.

This method uses a rare earth element or carbonates or hydroxycarbonates or dopants of rare earth elements as precursors of the rare earth elements or elements or doping elements or elements included in the borate composition.

It is possible to start with carbonates or hydroxycarbonates of rare earth elements and mixtures of various dopants, or mixtures of mixed carbonates or hydroxycarbonates and dopants of rare earth elements.

Carbonates or hydroxycarbonates of rare earth elements are products known per se, for example obtained by precipitation of one or more rare earth salts with ammonium carbonate or ammonium bicarbonate. These carbonates or hydroxycarbonates can be used immediately after precipitation or after any washing and / or drying.

Starting carbonates or hydroxycarbonates react with boric acid. The reaction is preferably carried out under the influence of heat, for example at a temperature between 40 ° C. and 90 ° C.

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

It is possible to carry out with excess boric acid. This excess can be for example from 1 mol% to 250 mol% (ie [B] / [∑ (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 this process. This removal can be done, for example, by purifying the reaction medium with neutral gas, for example nitrogen. This modification makes it possible to obtain products of finer particle size.

A precipitate is obtained at the end of the reaction.

According to one variant of the invention, the precipitate can be aged in the reaction medium, preferably by maintaining the medium at the same temperature at which the reaction takes place. During this ripening, the pH of the ripening medium may be kept constant. This pH may be fixed at a given value, for example, which may be the pH the reaction mixture has only at the end of the reaction, ie at the end of boric acid introduction. The pH can be maintained by adding a base in this manner, for example by adding a solution comprising ammonia. Aging can last for 1 to 3 hours.

The precipitate is then separated from the reaction medium by any known method, for example by filtration. The separated precipitate is optionally washed and then dried. One of the advantages of the described method is that the precipitate can be obtained by easy filtration and washing. After drying, traces of unreacted trace carbonate can be removed if present with further washing with dilute acid, for example nitric acid.

The precipitate is then calcined.

Borate can be obtained by this baking. This is usually done at a temperature of 500 to 1,400 ° C., more particularly 500 to 1,100 ° C. It is entirely possible to carry out this firing in air. Reducing atmospheres (for example hydrogen) or neutral atmospheres (argon) or mixed atmospheres thereof can of course also be used for this firing.

Firing may also improve the luminescent properties of the product. Firing will be performed at higher temperatures if increased luminescence properties are required.

One variant of the firing step may be mentioned. This variant involves mixing the dried precipitate with boric acid in an amount that can be approximately 5% to 15%, for example. Firing is then carried out at a temperature which can be, for example, 900 ° C to 1,100 ° C. This deformation provides good luminescence performance for the borate at firing temperatures that are relatively rarely elevated.

The invention also relates to a precursor composition of borate, which will be described below. The composition is selected from one or more rare earth elements selected from boron, lanthanum, lutetium, yttrium and gadolinium, one or more first elements selected from trivalent elements capable of trapping electrons and trivalent elements capable of trapping holes and europium II Based on one or more second elements, a rare earth borate of the formula LnBO ₃ , where Ln represents the rare earth element or elements after firing, can be obtained, and the borate can also contain one or more of said first element and one or more said second element It is characterized by including. The first element may be selected from europium, samarium, thulium and ytterbium, and the second element may be selected from cerium, terbium, praseodymium, bismuth, lead, antimony, chromium and iron.

The composition can be prepared by mixing boron, rare earth elements and other compounds of the above elements, these compounds being selected from those which allow to obtain the required borate after firing. The rare earth element and the compound of the other elements can be, for example, oxides or carbonates.

The compositions may also be prepared by more specific methods of the type described above for the borate. The process reacts at least one of the rare earth elements, at least one of the first elements and at least one of the second elements with a carbonate or hydroxycarbonate with boric acid, the reaction medium is in the form of an aqueous solution and optionally washes the reaction product. And / or drying. All of the above described also apply here for this method of obtaining a precipitate, separating it and optionally washing and / or drying it. The precipitate obtained is a hydroxyborocarbonate of at least one of said rare earth elements, represented by the formula LnB (OH) ₄ CO ₃ , at least one of hydroxyborocarbonates of at least said first element and at least one of said second elements. Based on hydroxyborocarbonates.

This composition, based on hydroxyborocarbonate, has the same morphological characteristics (cubical, equilateral hexahedral (small plate) or spherical particles) and particle size characteristics (particle size and especially up to 0.8) as described above for borate Dispersion index).

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

The present invention relates to the use of the above-described borate as luminophore in any method for visualization and illumination using plasma excitation. This is understood as meaning a method of using a state of using a gas which emits light corresponding to the conditions of the plasma system, ie at least about 100 nm to about 200 nm, more particularly 140 nm to 200 nm after ionization.

The invention also relates to a system for visualization and illumination of this type comprising the borate according to the invention as luminophore.

These types of visualization and lighting systems mentioned above are plasma screens and lamps.

The borate of the present invention can also be used in any system using X-rays. X-rays are understood as meaning those that consist of photons with an energy of about 10 to about 100 Kev.

The present invention relates to X-ray visualization systems and imaging systems, in particular medical imaging systems, which may be mentioned.

Borate is used in the manufacture of plasma or X-ray systems according to well known techniques such as silkscreen printing, electrophoresis or sedimentation.

Examples are now described below.

Examples 1-4

A product was prepared in which the final composition was as follows and the content of the dopant was given in the manner given above.

Example 1 (comparative): Y _0.726 Gd _0.218 Eu _0.056 BO ₃

Example 2 The product of a composition as in Example 1 but having 70 ppm of terbium.

Example 3 (comparative): Y _0.79 Gd _0.15 Eu _0.06 BO ₃

Example 4 The product of the composition as in Example 3, but having 50 ppm of praseodymium.

Manufacturing :

A carbonate suspension of all rare earth elements (Ln) included in the composition of the product was added to 1.50 L of a mixture solution of 1.3 M / L ammonium bicarbonate solution suitably stirred for 1 hour under the influence of heat (80 ° C.). It was added to prepare a concentration of 0.7 M / L at a rate of 1.6 mole ratio of CO ₃ / Ln.

Subsequently, 0.8 M / l boric acid solution was added to the same medium under the influence of heat for 30 minutes while the stirring was continued, so that the molar ratio of B / Ln was 1.5. The suspension obtained was then aged to maintain a temperature of 60 ° C. and a pH of at least 4.6 by addition of a solution containing 6 N ammonia.

After this 3 hours of aging, a white precipitate was obtained, which was separated by filtration and then washed with demineralized water.

The moist product was then dried overnight at 60 ° C. and then calcined in the presence of 15% H ₃ BO ₃ in a muffle furnace (in air) at 1,100 ° C. to obtain rare earth borate.

Particle size was measured for the product of Example 2 by the Coulter technique. This measurement was also carried out on a dispersion of the calcined product in 0.1% by weight aqueous solution of sodium hexametaphosphate which had been passed through an ultrasonic probe for 3 minutes (probe 12 mm in diameter, 450 W). The product of Example 2 has a median diameter of 2.3 μm and a dispersion index of 0.48.

Characteristics :

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

TABLE 1

Example Content of second element (ppm) Emission intensity at 597 nm (arbitrary unit) One 0 100 2 70 130 3 0 100 4 50 125

The intensity of the emission peak at 150 nm under plasma excitation of the products of Examples 1 and 2 in powder form was measured with a VUV spectrometer. The results are shown in Table 2 below.

TABLE 2

Example Content of second element (ppm) Emission intensity at 150 nm (arbitrary unit) One 0 4,200 2 70 5,100

Examples 5 and 6

Two products of the composition given below were prepared in the manner shown in the examples above:

Example 5 (comparative): Gd _0.98 Ce _0.02 BO ₃

Example 6: Gd _0.99 Ce _0.005 Tm _0.005 BO ₃

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

TABLE 3

Example burglar 5 0.186 6 0.196

It was found that the emission intensity of the compound doped with 0.5% cerium and 0.5% tulium is greater than that of the compound comprising 2% cerium.

Claims (20)

Ln represents at least one rare earth element selected from lanthanum, lutetium, yttrium and gadolinium, at least one first element selected from trivalent elements capable of trapping electrons, and selected from trivalent elements and europium II capable of trapping holes Rare earth borate of formula LnBO ₃ , comprising at least one second element. The borate 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. 3. The borate of claim 2, wherein the first element is thulium and the second element is cerium. The borate according to claim 1 or 2, wherein the content of the first element europium or samarium is 2 mol% to 25 mol% with respect to all the rare earth elements of the borate and the number of moles of the elements. The borate according to claim 2, wherein the content of thulium is 0.1 mol% to 5 mol% with respect to all the rare earth elements of the borate and the number of moles of the elements. The borate according to claim 2, wherein the content of ytterbium is 1 mol% to 2.5 mol% with respect to all the rare earth elements of the borate and the moles of the elements. The method according to any one of claims 1, 2 and 4 to 6, wherein the content of the second element is from 5 ppm to 1,000 ppm, more particularly from 10 ppm to all the rare earth elements and the moles of the elements. 500 ppm borate. 8. The borate according to any one of claims 1 to 7, wherein Ln represents a combination of yttrium and gadolinium. The borate according to any one of claims 1 to 8, wherein said first element is europium and said second element is terbium or praseodymium. The borate according to any one of claims 1 to 9, wherein Ln represents lanthanum, wherein the first element is thulium and the second element is terbium. The borate according to any one of claims 1 to 10, wherein the borate is a cubic, equilateral hexahedral or spherical particle, and has a dispersion index of 0.8 or less. boron; One or more rare earth elements selected from lanthanum, lutetium, yttrium and gadolinium; At least one first element selected from trivalent elements capable of trapping electrons; And at least one second element selected from trivalent elements capable of capturing holes and europium II, wherein after calcination Ln is represented by the formula LnBO ₃ representing the rare earth element or the earth element and also at least one of the first A rare earth borate comprising an element and at least one second element can be obtained. 13. The precursor composition of 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. The hydroxyborocarbonate of at least one of the above rare earth elements, the hydroxyborocarbonate of at least one of the first elements and the hydroxyborocarbonate of at least one of the second elements. Precursor composition based on. A rare earth element and carbonate or hydroxycarbonate of the elements according to any one of claims 1 to 11 are reacted with boric acid, the reaction medium is an aqueous solution, and the reaction product is fired. A process for producing the rare earth borate according to claim 11. Process according to claim 15, wherein the reaction medium is formed using water having a weight ratio of water / boric acid + carbonate or hydroxycarbonate of at least 300%, more particularly at least 600%. The process according to claim 15 or 16, wherein the reaction is carried out by removing the CO ₂ formed during the reaction. A carbonate or hydroxycarbonate of at least one rare earth element, at least one first element and at least one second element, as described in claim 12 or 13, is reacted with boric acid, the reaction medium is in the form of an aqueous solution, and Process for preparing the precursor composition according to claim 12 or 13, characterized in that the product is optionally washed and / or dried. 12. A visualization method using plasma excitation or X-rays, wherein the borate according to any one of claims 1 to 11 is used as a luminophore. 12. A visualization system using plasma excitation or X-rays as a luminophore comprising the borate according to any one of claims 1-11.