Na3WO4F and derivatives thereof as a scintillation material and their methods of making

Abstract

Direct synthesis methods are generally provided that include reacting Na.sub.2(WO.sub.4).Math.2H.sub.2O (and/or Na.sub.2(GeO.sub.4).Math.2H.sub.2O) with NaF in an inert atmosphere at a reaction tion temperature of about 950 C. to about 1400 C., along with the resulting structures and compositions.

Claims

1. A direct synthesis method, comprising: reacting Na.sub.2(WO.sub.4).Math.2H.sub.2O with NaF in an inert atmosphere at a reaction temperature of about 950 C. to about 1400 C.

2. A direct synthesis method, comprising: reacting Na.sub.2(WO.sub.4).Math.2H.sub.2O with NaF and Na.sub.2[MO.sub.4].Math.H.sub.2O in an inert atmosphere at a reaction temperature of about 950 C. to about 1400 C. according to the reaction:
(1x)Na.sub.2[WO.sub.4].Math.2H.sub.2O+xNa.sub.2[MO.sub.4].Math.H.sub.2O+NaF.fwdarw.Na.sub.3W.sub.1xM.sub.xO.sub.4F where 0x0.2; and M is B, Al, Si, P, S, Cr, V, Nb, Ta, Zr, Hf, Sc, Y, La, Ga, Ge, In, Mo, or combinations thereof.

3. The method as in claim 2, wherein x is 0 such that Na.sub.3(WO.sub.4)F is formed.

4. The method as in claim 3, wherein Na.sub.3WO.sub.4F is formed into single crystals having an impurity concentration present at a concentration of less than about 500 ppb.

5. The method as in claim 2, wherein 0<x0.2.

6. The method as in claim 5, wherein M is Mo such that Na.sub.3W.sub.1xMo.sub.xO.sub.4F is formed.

7. A crystal structure comprising: Na.sub.3(WO.sub.4)F with impurities present in a concentration of less than about 500 ppb.

8. The crystal structure as in claim 7, wherein impurities are present in concentration of less than about 100 ppb.

9. A scintillator material comprising the crystal structure of claim 7.

10. A phosphor material comprising the crystal structure of claim 7.

11. A composition of matter having the formula:
Na.sup.+.sub.3a2b3cA.sup.+.sub.aB.sup.2+.sub.bC.sup.3+.sub.cW.sub.1xM.sub.xO.sub.4F where 0a2; A.sup.+ is an alkali metal ion; 0b1; B.sup.2+ is an alkaline earth metal ion selected from Be.sup.2+, Mg.sup.2+, Ca.sup.2+, Sr.sup.2+, and/or Ba.sup.2+, a rare earth divalent cation from the atomic numbers 57-71, an activator divalent cation of Cr, Mn, Re, Cu, Ag, Au, Zn, Cd, Hg, Sn, or any combinations thereof; 0c1; C.sup.3+ is a rare earth trivalent cation from the atomic numbers 57-71, an activator trivalent cation of Ac, U, Cr, Mn, As, Sb, Bi, In, Tl, or any combinations thereof; 0<x0.2; and M is B, Al, Si, P, S, Cr, V, Nb, Ta Zr, Hf, Sc, Y, La, Ga, Ge, In, Mo, or combinations thereof.

12. The composition of matter as in claim 11, where a=b=c=0 such that the composition of matter has the formula:
Na.sub.3(W.sub.1xM.sub.xO.sub.4)F, where 0<x0.2, and M is B, Al, SL P, S, Cr, V, Nb, Ta, Zr, Hf, Sc, Y, La, Ga, Ge, In, Mo, or combinations thereof.

13. The composition of matter as in claim 11, wherein M is Mo.

14. The composition of matter as in claim 11, wherein impurities are present in a concentration of less than 500 ppb.

15. A scintillator material comprising the composition of claim 11.

16. A phosphor material comprising the composition of claim 11.

17. A composition having the formula:
Na.sup.+.sub.3a2b3cA.sup.+.sub.aB.sup.2+.sub.bC.sup.3+.sub.cW.sub.1xM.sub.xO.sub.4F where a is 0; A.sup.+ is an alkali metal on; b is 0; B.sup.2+ is an alkaline earth metal ion selected from Be.sup.2+, Mg.sup.2+, Ca.sup.2+, Sr.sup.2+, and/or Ba.sup.2+, a rare earth divalent cation from the atomic numbers 57-71, an activator divalent cation of Cr, Mn, Re, Cu, Ag, Au, Zn, Cd, Hg, Sn, or any combinations thereof; 0<c0.1; C is Ce, Eu, or a combination thereof; 0x<0.2; and M is B, Al, Si, P, S, Cr, V, Nb, Ta, Zr, Hf, Sc, Y, La, Ga, Ge, In, Mo, or combinations thereof.

18. A crystal structure comprising: Na.sub.3(GeO.sub.4)F with impurities present in a concentration of less than about 500 ppb.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIGS. 1A and 1B show a diagram representation of the crystal structure of Na.sub.3(WO.sub.4)F,

(2) FIG. 2 shows the excitation and emission spectra for several compositions formed according to the formula Na.sub.3W.sub.1xMo.sub.xO.sub.4F, where x is 0, 0.25, 0.5, 0.75, and 1;

(3) FIG. 3 shows the excitation and emission spectra for several compositions formed according to the formula Na.sub.33cCe.sub.cW.sub.1xMo.sub.xO.sub.4F where c is 0.05 and where x is 0 and 1;

(4) FIG. 4 shows the excitation and emission spectra for several compositions formed according to the formula Na.sub.33cEu.sub.cW.sub.1xMo.sub.xO.sub.4F where c is 0.05 and where x is 0 and 1;

(5) FIG. 5A shows an ac-plane projection of Na.sub.3(GeO.sub.4)F, which is essentially the same structure as in FIGS. 1A and 1B except for containing GeO.sub.4 tetrahedra instead of WO.sub.4 tetrahedra; and

(6) FIG. 5B shows an ab plane projection of the Na.sub.3(GeO.sub.4)F structure shown in FIG. 5A.

DETAILED DESCRIPTION

(7) Reference now will be made to the embodiments of the invention, one or more examples of which are set forth below. Each example is provided by way of an explanation of the invention, not as a limitation of the invention. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made in the invention without departing from the scope or spirit of the invention. For instance, features illustrated or described as one embodiment can be used on another embodiment to yield still a further embodiment. Thus, it is intended that the present invention cover such modifications and variations as come within the scope of the appended claims and their equivalents. It is to be understood by one of ordinary skill in the art that the present discussion is a description of exemplary embodiments only, and is not intended as limiting the broader aspects of the present invention, which broader aspects are embodied exemplary constructions.

(8) Chemical elements are discussed in the present disclosure using their common chemical abbreviation, such as commonly found on a periodic table of elements. For example, hydrogen is represented by its common chemical abbreviation H, helium is represented by its common chemical abbreviation He; and so forth.

(9) Na.sub.3WO.sub.4F and its derivatives are generally provided as new scintillation materials for use in medical imaging and the detection of particles and energies including, y-rays, x-rays, neutrons, neutrinos and weakly interaction massive particles (WIMPS). For example, derivatives of Na.sub.3WO.sub.4F can include a substituted material(s) in a portion of the tungsten (W) locales (e.g., Na.sub.3(W.sub.1xM.sub.xO.sub.4)F, where 0x0.2 and M is B, Al, Si, P, S, Cr, V, Nb, Ta, Zr, Hf, Sc, Y, La, Ga, Ge, In, Mo, or combinations thereof).

1. Crystal Structure of Na3WO4F and its Derivatives

(10) As shown in FIG. 1A and 1B, the structure of Na.sub.3WO.sub.4F is best described as an anti-perovskite structure 10 (WO.sub.4)FNa.sub.3, where the F ions 20 are in the center of an FNa.sub.6 octahedron 24 formed with the Na cations 12, 14 and face-sharing FNa.sub.6 octahedra columns are stacked in a hexagonal closest packing parallel to the a-axis. The isolated WO.sub.4.sup.2 tetrahedra 22 are formed by the W ions 16 and the O ions 18, and occupy the pores between the FNa.sub.6 octahedron 24. As such, there are two distinct Na cation sites 12 and 14.

(11) These WO.sub.4 tetrahedra are, as outlines above, important structural units and necessary for scintillation and photoluminescence. As explained in greater detail below, the tungsten in these MO.sub.4.sup.n units can be partially substituted with B, Al, Si, P, S, Cr, V, Nb, Ta, Zr, Hf, Sc, Y, La, Ga, Ge, In, Mo, or combinations thereof. In certain embodiments, for example, the tungsten in these MO.sub.4.sup.n units can be partially substituted with Mo, In, Cr, Ge, Ga, and/or Al.

(12) In these MO.sub.4.sup.n subunits of members of the family of ordered oxyfluorides (MO.sub.4)FA.sub.nB.sub.m, where M is B, Al, Si, P, S, Cr, V, Nb, Ta, Zr, Hf, Sc, Y, La, Ga, Ge, W, In, Mo, or combinations thereof and A and B are independently alkali and/or alkaline earth metals, ligand-to-metal charge transfers are facilitated where an electron is transferred from an oxygen based molecular orbital (MO) to the metal-based one. Increasing the oxidation state of M effectively increases its electronegativity and thus lowers the energy of this HOMO-LUMO gap. As one reduces the charge on M.sup.n+ one increases the Lewis base character of the tetrahedral unit. As one moves down a d-transition metal group CrO.sub.4.sup.2.fwdarw.MoO.sub.4.sup.2.fwdarw.WO.sub.4.sup.2 one increases the gap energy (3.3, 5.3 and 6.2 eV respectively) since the relative sizes of the d-orbitals increase. Another way of describing this is that the Lewis base character increases. A strong Lewis base will impact the electronic environment of activators such as Eu.sup.3+ in its vicinity. With the chemical diversity of available MO.sub.4.sup.n tetrahedrons that can be accommodated in these materials an exquisite control of PL properties is within reach. (See also, U.S. Publication No. 2009/0302236 of Vogt, et al. and U.S. Publication No. 2009/0174310 of Vogt, et al.; both of which are incorporated by reference herein).

2. Derivatives of Na3(WO4)F

(13) Defects in the cation sublattice can be introduced into Na.sub.3WO.sub.4F by substitution of two sodium ions (Na.sup.+) with an alkali, an alkaline earth metal, a rare earth metal, and/or lanthanide activators such as Eu.sup.2+. Additionally, a partial substitution of W.sup.4+ by Ga.sup.3+ and In.sup.3+ subsequently allows the substitution of A.sup.2+ and A.sup.3+ ions on the A-site of this A.sub.nFMO.sub.4 family of materials within this host lattice.

(14) In one embodiment, for example, the composition can be represented according to the formula:
Na.sup.+.sub.3a2b3cA.sup.+.sub.aB.sup.2+.sub.bC.sup.3+.sub.cW.sub.1xM.sub.xO.sub.4F,
where A.sup.+ is an alkali metal ion (e.g., Li.sup.+, K.sup.+, and/or Rb.sup.+), 0a2; B.sup.2+ is cation having a +2 charge, such as an alkaline earth metal ion selected from Be.sup.2+, Mg.sup.2+, Ca.sup.2+, Sr.sup.2+, and/or Ba.sup.2+, a rare earth divalent cation from the atomic numbers 57-71 (i.e., the lanthanoid series including the fifteen elements with atomic numbers 57 through 71: La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu), an activator divalent cation of Cr, Mn, Re, Cu, Ag, Au, Zn, Cd, Hg, Sn, and/or any combinations thereof; 0b1; C is a is cation having a +3 charge, such as a rare earth trivalent cation from the atomic numbers 57-71 (i.e., the lanthanoid series including the fifteen elements with atomic numbers 57 through 71: La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu), an activator trivalent cation of Ac, U, Cr, Mn, As, Sb, Bi, In, Tl, and/or any combinations thereof; 0c1; M is B, Al, Si, P, S, Cr, V, Nb, Ta, Zr, Hf, Sc, Y, La, Ga, Ge, In, Mo, or combinations thereof; and 0x0.2.

(15) For example, the compound can be rare earth doped such as having the formula Na.sub.33cCe.sub.cW.sub.1xMo.sub.xO.sub.4F, where 0<c0.1 and 0x<0.2 (e.g., Na.sub.2.85Ce.sub.0.05WO.sub.4F) or Na.sub.33cEu.sub.cW.sub.1xMo.sub.xO.sub.4F, where 0<c0.1 and 0x<0.2 (e.g., Na.sub.2.85Eu.sub.0.05WO.sub.4F).

(16) As stated, dopants can also be included into the Na.sub.3WO.sub.4F. For example, in one embodiment, the tungsten atoms can be replaced by other metals in the structure, such as represented by the formula: Na.sub.3(W.sub.1xM.sub.xO.sub.4)F, where 0<x0.2 and M is B, Al, Si, P, S, Cr, V, Nb, Ta, Zr, Hf, Sc, Y, La, Ga, Ge, In, Mo, or combinations thereof.

(17) For example, the parent compound FA.sub.nB.sub.m(MO.sub.4) with A=B=Na, n is 1, m is 2, and M is W (i.e., FNa.sub.3(WO.sub.4)) can be modified by aliovalent substitution with A being Li, K, Rb, Cs or combinations thereof and/or with MO.sub.4.sup.2 entities such as M being Mo, W or combinations thereof. In addition or in the alternative, high-Z MO.sub.4.sup.3 (where M is Nb, Ta or combinations thereof) can be substituted where A is Li, Na, K, Rb, Cs or combinations thereof, n=2, B is Ca, Sr, Ba or combinations thereof, and m=1. If MO.sub.4.sup.4 entities are used (where M is Zr, Hf or combinations thereof), then A is Li, Na, K, Rb, Cs or combinations thereof, n=1, B is Ca, Sr, Ba, or combinations thereof, and m=2. If MO.sub.4.sup.5 units with M being Y, La or combinations thereof are used, then n=0, B is Ca, Sr, Ba or combinations thereof, and m is 3.

(18) As stated, this material is part of an even larger family of ordered oxyfluorides (MO.sub.4)FA.sub.nB.sub.m , where M is B, Al, Si, P, S, Cr, V, Nb, Ta, Zr, Hf, Sc, Y, La, Ga, Ge, W, In, Mo, or combinations thereof and A and B are independently alkali and/or alkaline earth metals, that are best described as anti-perovskites such as Sr.sub.3AlO.sub.4F and others, which have found applications in lighting and as optical host lattices. For example, U.S. Publication Nos. 2009/0302236 and 2009/0174310 of Vogt, et al. describe such structures and are incorporated by reference herein.

(19) FIGS. 5A and 5B show, respectively, the ac-plane and the ab plane projections of Na.sub.3(GeO.sub.4)F, which is essentially the same structure as in FIGS. 1A and 1B except for containing GeO.sub.4 tetrahedra instead of WO.sub.4 tetrahedra. Such a structure, along with its derivatives, can be prepared according to any discussion herein by substituting Ge for W.

3. Direct Synthesis Method

(20) A direct synthesis method can be utilized to form the materials (e.g., Na.sub.3(W.sub.1xM.sub.xO.sub.4)F, where 0x0.2 and M is B, Al, Si, P, S, Cr, V, Nb, Ta, Zr, Hf, Sc, Y, La, Ga, Ge, In, Mo, or combinations thereof. In one embodiment, the method can involve the following reaction in an inert atmosphere (e.g., argon) and at elevated temperatures (e.g., about 950 C. to about 1400 C.):
(1x)Na.sub.2[WO.sub.4].Math.2H.sub.2O+xNa.sub.2[MO.sub.4].Math.H.sub.2O+NaF.fwdarw.Na.sub.3W.sub.1xM.sub.xO.sub.4F
where 0>x0.2 and M is B, Al, Si, P, S, Cr, V, Nb, Ta, Zr, Hf, Sc, Y, La, Ga, Ge, In, Mo, or combinations thereof. In one particular embodiment, x is greater than 0 but less than or equal to 0.2 (i.e., 0<x0.2). One particularly suitable compounds that can be formed from this method is Na.sub.3W.sub.1xMo.sub.xO.sub.4F, where 0<x0.2 (i.e., where M is Mo).

(21) For example, direct synthesis methods of Na.sub.3(WO.sub.4)F (i.e., where x is 0 in the formula shown above) can be achieved by reacting Na.sub.2(WO.sub.4).Math.2H.sub.2O with NaF in an inert atmosphere (e.g., argon) and at elevated temperatures (e.g., about 950 C. to about 1400 C.). In one particular embodiment, the components of the material are added in stoichiometric amounts. Due to this direct synthesis method, the Na.sub.3WO.sub.4F material can be formed into single crystals having controllable purity, with impurity concentrations in the parts-per-billion (ppb) scale (e.g., impurities are present at a concentration of less than about 500 ppb, such as less than about 100 ppb).

Example 1

(22) Compounds were prepared via the direct synthesis method described above to have the formulas: Na.sub.3W.sub.1xMo.sub.xO.sub.4F, where x is 0, 0.25, 0.5, 0.75, and 1. FIG. 2 shows the excitation and emission spectra for these compounds.

Example 2

(23) Two compounds were prepared via the direct synthesis method described above to have the formulas: (1) Na.sub.2.85Eu.sub.0.05WO.sub.4F and (2) Na.sub.2.85Eu.sub.0.05MoO.sub.4F. FIG. 3 shows the excitation and emission spectra for these compounds.

Example 3

(24) Two compounds were prepared via the direct synthesis method described above to have the formulas: (1) Na.sub.2.85Eu.sub.0 05WO.sub.4F and (2) Na.sub.2.85Eu.sub.0.05MoO.sub.4F. FIG. 4 shows the excitation and emission spectra for these compounds.

(25) These and other modifications and variations to the present invention may be practiced by those of ordinary skill in the art, without departing from the spirit and scope of the present invention, which is more particularly set forth in the appended claims. In addition, it should be understood the aspects of the various embodiments may be interchanged both in whole or in part. Furthermore, those of ordinary skill in the art will appreciate that the foregoing description is by way of example only, and is not intended to limit the invention so further described in the appended claims.