JP2012144400A - Layered rare earth hydroxide, method for producing the same and application thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a layered rare earth hydroxide, a method for producing the same and application thereof.SOLUTION: The layered rare earth hydroxide is represented by the general formula: Ln(OH)SOnHO (1<n<3), wherein Ln includes at least one trivalent rare earth ion. The layered rare earth hydroxide has a pillar structure comprising host layers of Ln hydroxy polyhedrons and sulfate ion located between the host layers, wherein oxygen atoms in the sulfate ion bond directly to Ln in the adjacent host layers.

Description

  The present invention relates to a layered rare earth hydroxide, a method for producing the same, and a use thereof.

In recent years, the general formula Ln ₂ (OH) _6-m (A ^x− ) _{m / x} · nH ₂ O (1)
(Here, Ln is a trivalent rare earth ion, A is an anion, m satisfies 0.5 ≦ m ≦ 2.0, x is the valence of A, and n is 0 <n <4. Studies of various layered rare earth hydroxides represented by

  In the formula (1), a layered rare earth hydroxide having m = 1 has been successfully produced (see, for example, Patent Documents 1 to 3). In addition, in the formula (1), structural analysis of a layered rare earth hydroxide in which m = 2 is reported (see, for example, Non-Patent Document 1).

Patent Documents 1 to 3 disclose layered rare earth hydroxides in which m = 1 and A is a halogen ion or a nitrate ion. Specifically, the layered rare earth hydroxides described in Patent Documents 1 to 3 are (R) (OH) _2.5 Z _0.5 · 0.125XH ₂ O ((R) is a rare earth element or a rare earth element). It is a combination with a trivalent element, Z is a halogen ion or nitrate ion, and X is 6 <X <8), has a highly symmetric crystal structure, and has high crystallinity. Have. Furthermore, since Z does not coordinate directly to (R), it exhibits an anion exchange ability at room temperature. In addition, (R) shows fluorescence based on rare earth elements, or when (R) is a solid solution, various material designs are possible depending on the balance of the solid solution elements.

On the other hand, according to Non-Patent Document 1, production of a single crystal of Nd (OH) ₂ NO ₃ .H ₂ O as a layered rare earth hydroxide in which m = 2, Ln is Nd, and A is nitrate ion And has succeeded in structural analysis.

  If another layered rare earth hydroxide is obtained in addition to the layered rare earth hydroxide described above, the degree of freedom in material design is increased, which is advantageous. In addition, development of applications of layered rare earth hydroxides other than those described above is desired.

  As described above, an object of the present invention is to provide a layered rare earth hydroxide, a method for producing the layered rare earth hydroxide, and a use thereof.

The layered rare earth hydroxide according to the present invention is represented by the general formula Ln ₂ (OH) ₄ SO ₄ .nH ₂ O (1 <n <3), and the Ln includes at least one trivalent rare earth ion, A host layer composed of the Ln hydroxy polyhedron and a sulfate ion located between the host layers, and having a pillar structure in which oxygen atoms in the sulfate ion are directly bonded to the Ln in the adjacent host layer, This solves the above problem.
The Ln may be a rare earth ion selected from at least one selected from the group consisting of Pr ³⁺ , Nd ³⁺ , Sm ³⁺ , Eu ³⁺ , Gd ³⁺ and Tb ³⁺ .
The layered hydroxide may have an A-bottom monoclinic lattice.
The method for producing the layered rare earth hydroxide according to the present invention comprises the steps of preparing a mixed aqueous solution containing a sulfate of Ln and a pH adjuster, decomposing the pH adjuster, and Hydrolyzing, thereby solving the above problems.
The pH adjuster may be hexamethylenetetramine or urea.
The mixed aqueous solution may further contain an alkali metal sulfate.
The phosphor according to the present invention is composed of the above-mentioned layered rare earth hydroxide, and the Ln contains at least one trivalent rare earth ion serving as an emission center, thereby solving the above-mentioned problems.
The porous body according to the present invention comprises the layered rare earth hydroxide and has pores between the sulfate ions located between the layers, thereby solving the above-mentioned problems.

The layered rare earth hydroxide according to the present invention is represented by the general formula Ln ₂ (OH) ₄ SO ₄ .nH ₂ O (1 <n <3), and Ln contains at least one trivalent rare earth ion. Further, the layered rare earth hydroxide according to the present invention comprises a host layer composed of an Ln hydroxy polyhedron and sulfate ions located between the host layers, and oxygen atoms of the sulfate ions are adjacent to the rare earth ions (Ln) in the adjacent host layer. Since it has a directly coupled pillar structure, it has rigidity in the stacking direction in addition to the plane direction.

  In addition, when Ln contains at least one trivalent rare earth ion serving as an emission center, the layered rare earth hydroxide of the present invention can be a phosphor. Moreover, since it has a space between sulfate ions between layers, the layered rare earth hydroxide of the present invention can be a porous body.

  The layered rare earth hydroxide according to the present invention includes a step of preparing a mixed aqueous solution containing a sulfate of Ln and a pH adjuster, and a step of decomposing the pH adjuster and hydrolyzing the sulfate of Ln. Produced by a homogeneous precipitation method. This eliminates the need for a dedicated high-pressure device such as an autoclave, and can provide a high-quality layered rare earth hydroxide simply, inexpensively and in large quantities.

The figure which shows the schematic diagram of the layered rare earth hydroxide of this invention The flowchart which shows the step which manufactures the layered rare earth hydroxide of this invention Schematic diagram of light-emitting diode device using phosphor of the present invention The figure which shows the relationship between pore cross-sectional area and the ionic radius of Ln The figure which shows the SEM image of Tb-LREH of Example 1. The figure which shows the TEM image of Tb-LREH of Example 1. The figure which shows the SEM image of Ln-LREH (Example Ln = Gd, Eu, Sm, Nd, and Pr) of Examples 2-6. It shows an SEM image of _Tb 0.5 _Gd 0.5 -LREH Example 7 It shows an SEM image of _Tb 0.25 _Gd 0.75 -LREH Example 8 The figure which shows the synchrotron radiation X-ray-diffraction pattern of Tb-LRHE of Example 1. The figure which shows the powder X-ray-diffraction pattern of Tb-LRHE of Example 1. The figure which shows the powder X-ray-diffraction pattern of Ln-LREH (Ln = Gd, Eu, Sm, Nd, and Pr) of Examples 2-6. The figure which shows the ion size dependence of Ln of a lattice constant Shows a powder X-ray diffraction pattern of _Tb 0.25 _Gd 0.75 LREH of _Tb 0.5 _Gd 0.5 -LREH and Example 8 Example 7 Diagram showing the relationship between the embodiment according to the 1, 2, 6 and _{7 (Tb x Gd 1-x} ) 2 (OH) 4 SO 4 · nH x value at ₂ O and a-axis length and b-axis length FT-IR spectrum a of Tb-LREH of Example 1, FT-IR spectrum b of Tb ₂ (OH) ₅ (SO ₄ ) _1/2 · nH ₂ O, and FT-IR of Tb ₂ O ₂ SO ₄ Diagram showing spectrum c The figure which shows FT-IR spectrum of Ln-LREH (Ln = Gd, Eu, Sm, Nd, and Pr) of Examples 2-6. The figure which shows Ln dependence of the fundamental mode of an FT-IR spectrum The figure which shows TG profile of Tb-LREH of Example 1. The figure which shows the Kissinger plot of Tb-LREH of Example 1. The figure which shows TG profile of Ln-LREH (Ln = Gd, Eu, Sm, Nd, and Pr) of Examples 2-6. The figure which shows the heating temperature dependence of the powder X-ray-diffraction pattern of Tb-LREH of Example 1. The figure which shows the powder X-ray-diffraction pattern of Ln-LREH (Ln = Gd, Eu, Sm, Nd, and Pr) of Examples 2-6 after heating at 1000 degreeC. The figure which shows the SEM image of Tb-LREH of Example 1 after heating at 1000 degreeC. The figure which shows the excitation spectrum (A) and emission spectrum (B) of Tb-LRHE of Example 1. The figure which shows the excitation spectrum (A) and emission spectrum (B) of Eu-LRHE of Example 3.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In addition, the same reference number is attached | subjected to the same component and the description is abbreviate | omitted.

The inventors of the present application focused on m = 2 and A = SO ₄ ²⁻ in the above formula (1), proceeded with experiments and research, and formed a layered rare earth having a structure and characteristics different from those of existing layered rare earth hydroxides. Successful production and development of hydroxides.

(Embodiment 1)
FIG. 1 is a diagram showing a schematic diagram of a layered rare earth hydroxide of the present invention.

  1A and 1B are schematic views of the layered rare earth hydroxide of the present invention as seen from the b-axis direction and the a-axis direction, respectively.

The layered rare earth hydroxide 100 of the present invention (sometimes simply referred to as Ln-LREH) has a general formula Ln ₂ (OH) ₄ SO ₄ .nH ₂ O (1 <n <3) (2)
It is represented by Here, Ln contains at least one trivalent rare earth ion and is not limited to one kind. In this specification, trivalent rare earth ions are lanthanoids from lanthanum (La) having an atomic number of 57 to lutetium (Lu) having an atomic number of 71, scandium (Sc) having an atomic number of 21, and atoms. A rare earth element ion composed of No. 39 yttrium (Y) is intended.

  In the formula (2), n is in the range of 1 to 3. When n is in the range of 1 to 3, a stable layered rare earth hydroxide is obtained. When n is less than 1 or greater than 3, the crystal structure becomes unstable, and the layered rare earth hydroxide of the present invention is obtained. It may not be obtained.

As shown in FIGS. 1A and 1B, in the layered rare earth hydroxide 100 of the present invention, the cation of Ln (sometimes referred to as Ln ion or Ln ³⁺ ) 110 is a hydroxyl group, It combines with water molecules and oxygen atoms from sulfate ion 120 to form Ln hydroxy polyhedron 130. More specifically, the coordination number of the cation 110 of Ln is 9, and one hydroxyl group is shared by the three cation 110 of Ln and binds the Ln hydroxy polyhedron 130 to each other. As a result, the layered rare earth hydroxide 100 of the present invention includes a host layer 140 formed by linking Ln hydroxy polyhedrons 130 along the a axis and the b axis, and sulfate ions 120 positioned between the host layers 140. Become.

  Furthermore, the layered rare earth hydroxide 100 of the present invention has a pillar structure in which oxygen atoms in the sulfate ions 120 are directly bonded (150) to the Ln cations 110 in the adjacent host layer 140. Thus, the host layers 140 are firmly connected in the stacking direction 160.

  Moreover, as schematically shown in FIGS. 1A and 1B, the layered rare earth hydroxide 100 of the present invention has a monoclinic system, more specifically, an A bottom-centered monoclinic lattice. As shown in the region 180, the host layer 140 has a structure in which the host layers 140 are laminated with a ½ period slip in the b-axis direction with respect to each other.

Here, the existing layered rare earth hydroxide of m = 2 in formula (1) (Nd (OH) ₂ NO ₃ .H ₂ O described in Non-Patent Document 1) and the layered rare earth hydroxide 100 of the present invention are used. The difference is described. Nd (OH) ₂ NO ₃ .H ₂ O is monoclinic like the layered rare earth hydroxide 100 of the present invention and has C2 / m (No. 12). Different from the layered rare earth hydroxide 100. Specifically, nitrate ions in Nd (OH) ₂ NO ₃ .H ₂ O only coordinate with Nd ions in one host layer, and do not have a pillar structure. Therefore, it does not have rigidity in the stacking direction. On the other hand, in the layered rare earth hydroxide 100 of the present invention, the oxygen atom in the sulfate ion 120 is bonded to any of the Ln cations 110 in the host layer 140 composed of the adjacent Ln hydroxy polyhedron 130, and is in a trans-bidentate coordination. It becomes. As a result, the layered rare earth hydroxide 100 of the present invention has the above-described pillar structure and has rigidity in the stacking direction in addition to the in-plane direction.

  It should be noted that such a structural difference is not easily conceived even if sulfate ion is simply applied as A (anion) in the above formula (1), and is not a characteristic characteristic of sulfate ion. .

Reference is again made to equation (2). Ln contains at least one trivalent rare earth ion as described above, but is preferably selected from at least one rare earth selected from the group consisting of Pr ³⁺ , Nd ³⁺ , Sm ³⁺ , Eu ³⁺ , Gd ³⁺ and Tb ³⁺ Ion. With these rare earth ions, the layered rare earth hydroxide 100 of the present invention can be reliably obtained.

  Moreover, the lattice constant of the layered rare earth hydroxide 100 of the present invention obtained can be controlled by the rare earth ions to be selected. For example, the larger the ion radius of the rare earth ions, the larger the lattice constant, and the smaller the ion radius of the rare earth ions, the smaller the lattice constant. Such control of the lattice constant is advantageous, for example, when the layered rare earth hydroxide 100 of the present invention, which will be described later, is used as a porous body, for precise fine pore size adjustment.

Ln is not limited to one kind of trivalent rare earth ion, but when Ln is composed of two or more kinds of rare earth ions (that is, when Ln is composed of a solid solution of a plurality of rare earth ions), depending on the combination of rare earth ions Since various functions (emission characteristics, magnetism, ferroelectricity, etc.) are manifested, material design according to the application is possible. Examples of the combination of two or more of Ln include, but are not limited to, a combination of Gd ³⁺ and Tb ³⁺ .

  In addition, when Ln consists of two or more kinds of rare earth elements, whether or not these two or more kinds of rare earth elements are dissolved can be confirmed by whether or not the second phase is present in the X-ray diffraction pattern. Further, by examining whether or not the lattice constant obtained from the X-ray diffraction pattern complies with the Vegard law, the solid solution state and the solid solution ratio can be known. Thereby, the layered rare earth hydroxide 100 of the present invention in which the solid solution ratio is controlled can be obtained.

  The layered rare earth hydroxide 100 according to the present invention reflects a monoclinic system and is a plate crystal. The size of the plate crystal is a rectangle of several μm, and its thickness is about 100 nm or less.

  The layered rare earth hydroxide 100 of the present invention has rigidity in the stacking direction 160 and has heat resistance up to about 200 ° C. Therefore, the layered rare earth hydroxide 100 of the present invention is stable under a normal use environment.

  Next, a uniform precipitation method will be described in detail as an exemplary method for producing the layered rare earth hydroxide 100 of the present invention.

  FIG. 2 is a flowchart showing steps for producing the layered rare earth hydroxide of the present invention.

  Step S210: A mixed aqueous solution containing a sulfate of rare earth element Ln (Ln is the same as Ln described with reference to FIG. 1 and description thereof is omitted) and a pH adjuster is prepared. In the aqueous solution, water (for example, ultrapure water, Milli-Q water) alone may be used as a solvent, or a nonaqueous solvent such as ethanol may be used in addition to water, but at least water is contained. This is because the reaction is promoted by hydration of rare earth ions with water. Since at least water should be contained in the aqueous solution, a sulfate hydrate of Ln may be used.

The pH adjuster is any pH adjuster that functions to raise the pH of the mixed aqueous solution after decomposition, but is more preferably hexamethylenetetramine (HMT) or urea. Since these can surely increase the pH of the mixed aqueous solution after decomposition and slowly increase the pH, they are advantageous for producing a high-quality layered rare earth hydroxide. More preferably, the molar ratio of the pH adjusting agent (HMT) to the sulfate of Ln is in the range of 25 mol% to 70 mol%. If this ratio is not satisfied, impurities such as Ln (OH) ₃ may be generated.

  In step S210, an alkali metal sulfate may be further mixed into the mixed aqueous solution. This promotes synthesis even under conditions where the concentration of Ln sulfate is low. As a result, the morphology or crystallinity of the obtained layered rare earth hydroxide can be improved.

  Step S220: The pH adjuster in the mixed aqueous solution obtained in Step S210 is decomposed to hydrolyze Ln sulfate.

  When HMT or urea is selected as the pH adjuster, they are decomposed to produce ammonia. Thereby, pH of mixed aqueous solution rises and it becomes alkaline. As a result, the sulfate of Ln is hydrolyzed, and precipitation of the layered rare earth hydroxide occurs. In particular, when the pH adjusting agents are HMT and urea, these produce ammonia slowly at a controlled rate, so there is no bias in nucleation and crystallization, and high quality layered rare earths with uniform grain size and high crystallinity. It is preferable because a hydroxide is obtained.

  The pH adjuster is decomposed, for example, by stirring the mixed aqueous solution obtained in step S210 at room temperature for a long time. From the viewpoint of efficiency, it is preferable to heat at a temperature of at least 70 ° C. while stirring. . Thereby, since decomposition | disassembly of HMT and urea is accelerated | stimulated, a synthesis | combination advances efficiently. Crystal formation can be visually confirmed by heating for 30 minutes to 1 hour, but typically heating is performed for 6 hours to 10 hours. Moreover, although the upper limit of heating temperature changes with solvents to be used, it is the temperature which does not exceed 100 degreeC. More preferably, the pH adjuster is decomposed by refluxing under a nitrogen atmosphere. If reflux is used, decomposition can be promoted while maintaining the mixed aqueous solution at a constant temperature without measuring the temperature.

  Subsequent to step S220, the obtained layered rare earth hydroxide may be washed and dried at room temperature. This makes it possible to obtain a powdery layered rare earth hydroxide that is easy to handle. Washing is repeated several times with water and ethanol.

  As described above, according to the exemplary method of the present invention, a dedicated high-pressure device such as an autoclave is not necessary. Therefore, since a glass container such as a flask can be used, a high-quality layered rare earth hydroxide can be provided easily and inexpensively. Furthermore, since an existing apparatus can be used, the capacity is not particularly limited, and the layered rare earth hydroxide of the present invention can be produced in large quantities.

  The method for producing the layered rare earth hydroxide of the present invention by the uniform precipitation method has been described in detail with reference to FIG. 2, but the method for producing the layered rare earth hydroxide of the present invention is not limited to the uniform precipitation method. For example, the layered rare earth hydroxide of the present invention may be produced by a hydrothermal synthesis method, or more simply by mixing Ln sulfate with ammonia or NaOH.

(Embodiment 2)
Next, the use of the layered rare earth hydroxide of the present invention described in detail in Embodiment 1 will be described.

(1) Raw material for oxygen storage material Rare earth oxysulfate Ln ₂ O ₂ SO ₄ (Ln is a trivalent rare earth ion) is known as an oxygen storage material. Ln ₂ O ₂ SO ₄ is reduced to Ln ₂ O ₂ S by H ₂ , CO, etc. (ie, oxygen release). On the other hand, the reduced Ln ₂ O ₂ S is reoxidized reversibly by O ₂ or the like (that is, oxygen storage).

Known methods for producing rare earth oxysulfates include heating of Ln ₂ (SO ₄ ) · 8H ₂ O salt, thermal decomposition of hydroxide intercalated with dodecacil sulfate, or oxidation of Ln ₂ S _3. It has been. However, both methods are economically undesirable because they require high temperature heating exceeding 800 ° C. Furthermore, part of SO ₂ is released during production by high-temperature heating, which is not preferable for the environment.

  The layered rare earth hydroxide of the present invention can be used as a raw material for such a rare earth oxysulfate. If the layered rare earth hydroxide of the present invention is used, it can be dehydrated by heating at a temperature exceeding at least 350 ° C., and a rare earth oxysulfate can be easily obtained.

More specifically, when the layered rare earth hydroxide of the present invention is heated at a temperature exceeding at least 350 ° C., the following two-stage dehydration occurs.
Ln ₂ (OH) ₄ SO ₄ .nH ₂ O → Ln ₂ (OH) ₄ SO ₄ + nH ₂ O (3)
Ln ₂ (OH) ₄ SO ₄ → Ln ₂ O ₂ SO ₄ + 2H ₂ O (4)

  The dehydration represented by the formula (3) occurs in a temperature range of about 200 ° C. to 275 ° C. and is dehydration of hydrated water in the hydrate. The dehydration represented by the formula (4) occurs in a temperature range of about 320 ° C. to 350 ° C. and is dehydration from the host layer (140 in FIG. 1) made of the Ln hydroxy polyhedron (130 in FIG. 1). The heating temperature is preferably 450 ° C. or higher. This enables reliable dehydration and promotes dehydration, so that rare earth oxysulfate can be obtained efficiently.

  In this way, the layered rare earth hydroxide of the present invention can be easily dehydrated by heating at a mild temperature. Therefore, by using the layered rare earth hydroxide of the present invention, it is economically and environmentally friendly. Rare earth oxysulfate can be produced.

(2) Phosphor The layered rare earth hydroxide of the present invention can be used as a phosphor. More specifically, the phosphor is composed of the layered rare earth hydroxide of the present invention containing at least one trivalent rare earth ion serving as an emission center as Ln.

For example, when the phosphor of the present invention is composed of a layered rare earth hydroxide containing at least Eu ³⁺ as Ln, the phosphor of the present invention is excited by ultraviolet light, visible light, or an electron beam, and is red based on the emission center Eu. Light (for example, emission peak wavelength 617 nm) is emitted. The phosphor of the present invention is more preferably composed of a layered rare earth hydroxide containing Gd ³⁺ or Y ³⁺ and Eu ³⁺ as Ln. In this case, the phosphor of the present invention is represented by the general formula ((Gd or Y), Eu) ₂ (OH) ₄ SO ₄ .nH ₂ O (1 <n <3), and (Gd or Y) ₂ ( OH) ₄ SO ₄ .nH ₂ O is used as a base crystal, and this is a phosphor that emits red light activated by Eu. In such a system in which Ln is dissolved, the solid solution amount (solid solution amount) of Eu can be controlled, so that it is possible to suppress a decrease in light emission efficiency and light emission intensity due to concentration quenching.

For example, when the phosphor of the present invention is composed of a layered rare earth hydroxide containing at least Tb ³⁺ as Ln, the phosphor of the present invention is excited by ultraviolet light, visible light, or an electron beam and is green based on the emission center Tb. Emits light (for example, emission peak wavelength 545 nm). The phosphor of the present invention is more preferably composed of a layered rare earth hydroxide containing Gd ³⁺ or Y ³⁺ and Tb ³⁺ as Ln. In this case, the phosphor of the present invention is represented by the general formula ((Gd or Y), Tb) ₂ (OH) ₄ SO ₄ .nH ₂ O (1 <n <3), and (Gd or Y) ₂ ( OH) ₄ SO ₄ .nH ₂ O is used as a base crystal, and this becomes a phosphor emitting green light activated by Tb. In such a system in which Ln is dissolved, the activation amount of Tb can be controlled, so that a decrease in emission intensity due to concentration quenching can be suppressed.

For example, the phosphor of the present invention may be a layered rare earth hydroxide composed of Gd ³⁺ or Y ³⁺ , Tb ³⁺ , and Eu ³⁺ as Ln. In this case, the phosphor of the present invention is represented by ((Gd or Y), Eu, Tb) ₂ (OH) ₄ SO ₄ .nH ₂ O (1 <n <3), and (Gd or Y) ₂ ( OH) ₄ SO ₄ .nH ₂ O is used as a base crystal, and this is a phosphor activated with Eu and Tb. Either Eu or Tb functions as a co-activator, and the emission color and / or emission spectrum may change depending on the activation amount. For example, when the solid solution amount of Eu is larger than that of Tb, the red component increases, so that a broad emission spectrum can be obtained.

  Note that these specific combinations are merely examples, and combinations for obtaining a desired emission color are not limited to these.

  The activation amount (solid solution amount) of the luminescent center is not particularly limited, but is preferably 20 mol% or less. If it exceeds 20 mol%, the light emission efficiency is reduced by concentration quenching. Moreover, although the activation amount should just be not 0, 1 mol% or more is preferable. If it is less than 1 mol%, sufficient light emission may not be obtained. The activation amount is more preferably 10 mol% or less. Within this range, higher emission intensity can be obtained.

  FIG. 3 is a schematic view of a light-emitting diode element using the phosphor of the present invention.

  The light emitting diode element 300 includes lead wires 310 and 320 which are electrode terminals, a semiconductor light emitting element 330 placed on the lead wire 310 via a conductive paste, and bonding for connecting the semiconductor light emitting element 330 and the lead wire 320. It includes a wire 340, a phosphor 350 made of the layered rare earth hydroxide of the present invention as a phosphor, a resin 360 in which the phosphor 350 of the present invention is dispersed, and a resin 370 that seals the entire light emitting diode element 300. .

The operation of the light emitting diode element 300 will be described. Here, the semiconductor light emitting device 330 is a semiconductor light emitting device that emits ultraviolet rays (main wavelength: 380 nm), and the phosphor 350 of the present invention is made of a layered rare earth hydroxide containing Eu ³⁺ as a light emission center as Ln, and red. Suppose that it emits light.

  When conducting to the lead wires 310 and 320, the semiconductor light emitting device 330 emits ultraviolet rays. The emitted ultraviolet light irradiates the phosphor 350 of the present invention, and the phosphor 350 of the present invention is excited. As a result, the phosphor 350 emits red light. The emitted red light passes through the light projecting resins 360 and 370 and becomes a red light emitting diode element.

  The semiconductor light emitting device 330, the phosphor 350 of the present invention, and the combination thereof can be appropriately changed according to the desired emission color of the light emitting diode device 300. For example, when a blue light emitting diode is used as the semiconductor light emitting element 330 and a phosphor made of a layered rare earth hydroxide that emits yellow light is used as the phosphor 350 of the present invention, the light emitting diode element 300 has blue light and yellow light. And a white light emitting diode element.

  The phosphor of the present invention can be excited by ultraviolet light, visible light or electron beam to emit visible light. Therefore, the phosphor of the present invention is mixed with a resin or the like and added to the light emitting diode illustrated with reference to FIG. The present invention can be applied to fluorescent display tubes, field emission displays, plasma display panels, cathode ray tubes, white light emitting diodes, and the like.

(3) Porous body The layered rare earth hydroxide of the present invention can be used as a porous body. Here, FIG. 1 will be referred to again. The layered rare earth hydroxide 100 of the present invention shown in FIG. 1 has pores 170 made of a space between sulfate ions 120. A porous body made of the layered rare earth hydroxide of the present invention using the pores 170 can be provided. In addition, such pores 170 are extremely regular and uniform because of the crystal structure (pillar structure) of the layered rare earth hydroxide of the present invention.

  FIG. 4 is a diagram showing the relationship between the pore cross-sectional area and the ionic radius of Ln.

4 (A) and 4 (B) show a simplified model of layered rare earth hydroxide for calculating the pore cross section. Here, the pore cross-sectional area is the area of a parallelogram (dotted line 410) defined by four oxygen atoms of SO ₄ (sulfate ions) that serve as an index of the pore size. For simplicity, FIGS. 4A and 4B show the outline of the pores as a solid line 420 in a space-filling mode model that leaves only atoms in the space. Specifically, FIGS. 4A and 4B show simplified pores of sulfate ions located in the same direction as the a-axis. The pore cross-sectional area was calculated using a parallelogram 410 shown in FIG. For example, in the case of Pr, it was (6.358−1.36 × 2) × (2.467 + 1.36 × 2) × sin115.447 = 17.039 ² .

  According to FIG. 4C, the pore cross-sectional area tends to increase as the ionic radius of Ln increases, and the pore cross-sectional area tends to decrease as the ionic radius of Ln decreases. This suggests that fine pore cross-sectional area (that is, pore size and pore volume) can be controlled by selecting Ln.

  The present invention will now be described in detail using specific examples, but it should be noted that the present invention is not limited to these examples.

A layered rare earth hydroxide was produced using a homogeneous precipitation method. Tb ₂ (SO ₄ ) ₃ · 8H ₂ O (purity 99.9%) as a sulfate of Ln, hexamethylenetetramine (HMT) (purity 99.5% or more) as a pH adjuster, and an alkali metal sulfate Na ₂ SO ₄ (purity 99.5% or more) was used. Tb ₂ (SO ₄ ) ₃ · 8H ₂ O, and HMT and Na ₂ SO ₄ were obtained from Sigma Aldrich Japan Co., Ltd. and Wako Pure Chemical Industries, Ltd., respectively. These reagents were used in the synthesis without further purification. For the synthesis, Milli-Q water having a specific resistance exceeding 18 MΩ · cm was used as ultrapure water.

Prepare a mixed solution by dissolving predetermined amounts of Tb ₂ (SO ₄ ) ₃ · 8H ₂ O, Na ₂ SO ₄ and HMT in water (1 dm ³ ) so that the respective concentrations are 5 mM, 25 mM and 1.8 mM. (Step S210 in FIG. 2). Each of the mixed solutions was refluxed for 6 hours under a nitrogen atmosphere (step S220 in FIG. 2). After reflux, a white precipitate (product) was confirmed in the mixed solution. The product was collected by filtration and washed sequentially with a large amount of water and ethanol. The washed product was dried in a container whose relative humidity was controlled at about 75% until the weight was constant.

  The amount of rare earth ions and sulfate ions in the obtained product was determined by dissolving a precisely weighed sample (product) in an aqueous HCl solution, then inductively coupled plasma (ICP) emission spectroscopy (Seiko SPS1700HVR) and ion chromatography, respectively. It was measured by (Toso LC-8020).

The amount of OH ^{− in} the obtained product was measured by dissolving the weighed product (about 0.1 g) in 25 cm ³ of standard HCl solution (0.1 M), and then back titrated with standard NaOH solution (0.1 M). And decided. By monitoring with a pH meter, the pH value of the solution was plotted against the amount of NaOH solution added to determine the end point.

  The amount of carbon (impurities) and hydrogen in the obtained product was measured with a LECO CS-412 analyzer. Further, the amount of water in the obtained product was calculated by subtracting the amount of hydrogen in the hydroxyl group from the total amount of hydrogen measured.

As a result of these chemical analyses, the composition of the obtained product was Tb _2.00 (OH) _4.02 (SO ₄ ) _0.99 · 2.20H ₂ O (theoretical value (%): Tb; 61. 0, SO ₄ ; 18.2, OH; 13.1, H ₂ O; 7.6, found (%): Tb; 60.4, SO ₄ ; 18.1, OH; 13.0, H ₂ O; 7.5). Furthermore, a trace amount of carbon (0.1 to 0.2%) was detected. This is due to the carbon in the HMT used for the sample. It is known that trace amounts of carbon impurities are detected in hydroxides produced using HMT. It should be noted that this level of impurity carbon can be ignored because it has no effect in practical use and is not the essence of the layered rare earth hydroxide of the present invention. From the above, the product obtained in Example 1 can be simplified as Tb ₂ (OH) ₄ SO ₄ .2.2H ₂ O. Therefore, it is shown that a layered rare earth hydroxide in which Ln is Tb ³⁺ and n is 2.2 in the general formula Ln ₂ (OH) ₄ SO ₄ .nH ₂ O (1 <n <3) is obtained. It was.

  Next, various characteristics of the layered rare earth hydroxide produced in Example 1 (referred to as Tb-LREH for simplicity) were measured.

  A Keyence VE8800 scanning electron microscope (SEM) was used for the observation of Tb-LREH. The observation results are shown in FIG.

  For further observation of Tb-LREH, a JEOL-1010 transmission electron microscope (TEM) was used. The observation condition was an acceleration voltage of 100 kV. As a sample for TEM observation, Tb-LRHE, which was poured into ethanol, was dispersed by ultrasonic treatment and dropped onto a carbon grid having holes. The observation results are shown in FIG.

  X-ray diffraction pattern of Tb-LREH, synchrotron radiation X-ray diffraction using Spring 8 BL15, and powder using Rigaku Rint-2200 diffractometer using monochromated CuKα ray (λ = 0.15405 nm) It was measured by X-ray diffraction. X-ray diffraction patterns are shown in FIGS. Based on the synchrotron radiation X-ray diffraction pattern, fitting by Rietveld method and structural refinement of Tb-LREH were performed. The results are shown in FIG.

  Furthermore, lattice constants (a-axis, b-axis, c-axis and β angle) were determined from the obtained diffraction pattern by synchrotron radiation X-ray diffraction. The results are shown in Table 3, FIG. 13 and FIG.

  The FT-IR spectrum of Tb-LREH was measured by the KBr pellet method using a Varian 7000e Fourier Transform Infrared (FT-IR) spectrophotometer equipped with a liquid nitrogen cooled MCT detector. The results are shown in FIGS.

  The differential thermal and thermogravimetric simultaneous measurement (TG-DTA) was performed on Tb-LREH using a Rigaku TGA-8120 apparatus. The temperature was scanned from 25 ° C to 1000 ° C. The heating temperature was changed from 3 ° C./min to 13 ° C./min to create a Kissinger plot. The results are shown in FIGS. 19 to 21 and Table 4.

  Next, in order to confirm the effectiveness of Tb-LREH as a raw material for rare earth oxysulfate, Tb-LREH was heated at 150 ° C., 300 ° C., 450 ° C., and 1000 ° C. in the air for 1 hour, respectively.

  X-ray diffraction patterns of Tb-LREH heated at 150 ° C., 300 ° C., 450 ° C. and 1000 ° C. were measured by powder X-ray diffraction. The results are shown in FIG. 22 and FIG.

  SEM was used for observation of Tb-LREH heated at 1000 ° C. The observation results are shown in FIG.

  The FT-IR spectrum of Tb-LREH heated at 1000 ° C. was measured using an FT-IR spectrophotometer. The results are shown in FIG.

  Next, in order to confirm the effectiveness of Tb-LREH as a phosphor, an excitation / emission PL spectrum at room temperature was measured using a Hitachi F-4500 fluorescence spectrophotometer. The results are shown in FIG.

Instead of Tb ₂ (SO ₄ ) ₃ · 8H ₂ O (purity 99.9%) of Example 1 as a sulfate of Ln, Gd ₂ (SO ₄ ) ₃ · 8H ₂ O (purity 99.9%) was used. Since it is the same as that of Example 1 except having used, description is abbreviate | omitted.

Similar to Example 1, a white precipitate (product) was produced. As a result of conducting a chemical analysis on the product in the same manner as in Example 1, it was found that the product obtained in Example 2 was Gd ₂ (OH) ₄ SO ₄ · 2.16H ₂ O. Therefore, it is shown that a layered rare earth hydroxide in which Ln is Gd ³⁺ and n is 2.16 in the general formula Ln ₂ (OH) ₄ SO ₄ .nH ₂ O (1 <n <3) is obtained. It was.

  Similar to Example 1, the layered rare earth hydroxide of Example 2 (referred to as Gd-LRHE for simplicity) observation by SEM, synchrotron X-ray diffraction, powder X-ray diffraction, synchrotron X-ray diffraction and Calculation of lattice constant by powder X-ray diffraction, measurement of FT-IR spectrum, and TG-DTA measurement were performed. These results are shown in FIGS. 7, 12 to 15, 17, 18, 21, and Table 3.

  In the same manner as in Example 1, Gd-LREH was heated at 1000 ° C. in the atmosphere for 1 hour. The powder X-ray diffraction of the heated Gd-LREH was measured. The results are shown in FIG.

Instead of Tb ₂ (SO ₄ ) ₃ · 8H ₂ O (purity 99.9%) of Example 1 as a sulfate of Ln, Eu ₂ (SO ₄ ) ₃ · 8H ₂ O (purity 99.9%) was used. Since it is the same as that of Example 1 except having used, description is abbreviate | omitted.

Similar to Example 1, a white precipitate (product) was produced. As a result of conducting a chemical analysis on the product in the same manner as in Example 1, it was found that the product obtained in Example 3 was Eu ₂ (OH) ₄ SO ₄ .2.1H ₂ O. Therefore, it is shown that a layered rare earth hydroxide in which Ln is Eu ³⁺ and n is 2.1 in the general formula Ln ₂ (OH) ₄ SO ₄ .nH ₂ O (1 <n <3) is obtained. It was.

  Similar to Example 1, the layered rare earth hydroxide of Example 3 (referred to as Eu-LRHE for simplicity) by SEM observation, synchrotron X-ray diffraction, powder X-ray diffraction, synchrotron X-ray diffraction Lattice constant calculation, FT-IR spectrum measurement, TG-DTA measurement, and excitation / emission PL spectrum measurement were performed. These results are shown in FIGS. 7, 12, 13, 17, 18, 21, 26 and Table 3.

  Similarly to Example 1, Eu-LRHE was heated at 1000 ° C. in the air for 1 hour. The powder X-ray diffraction of the heated Eu-LREH was measured. The results are shown in FIG.

Instead of Tb ₂ (SO ₄ ) ₃ · 8H ₂ O (purity 99.9%) of Example 1 as the sulfate of Ln, Sm ₂ (SO ₄ ) ₃ · 8H ₂ O (purity 99.9%) was used. Since it is the same as that of Example 1 except having used, description is abbreviate | omitted.

A pale yellow precipitate (product) was formed in the mixed solution. As a result of conducting a chemical analysis on the product in the same manner as in Example 1, it was found that the product obtained in Example 4 was Sm ₂ (OH) ₄ SO ₄ .2.04H ₂ O. Therefore, it is shown that in the general formula Ln ₂ (OH) ₄ SO ₄ .nH ₂ O (1 <n <3), a layered rare earth hydroxide in which Ln is Sm ³⁺ and n is 2.04 is obtained. It was.

  Similar to Example 1, the layered rare earth hydroxide of Example 4 (referred to as Sm-LRHE for simplicity) by SEM observation, synchrotron X-ray diffraction, powder X-ray diffraction, synchrotron X-ray diffraction Calculation of lattice constant, measurement of FT-IR spectrum, and TG-DTA measurement were performed. These results are shown in FIGS. 7, 12, 13, 17, 18, 21 and Table 3.

  In the same manner as in Example 1, Sm-LREH was heated at 1000 ° C. in the air for 1 hour. The powder X-ray diffraction of the heated Sm-LREH was measured. The results are shown in FIG.

Instead of Tb ₂ (SO ₄ ) ₃ · 8H ₂ O (purity 99.9%) of Example 1 as the sulfate of Ln, Nd ₂ (SO ₄ ) ₃ · 8H ₂ O (purity 99.9%) was used. Since it is the same as that of Example 1 except having used, description is abbreviate | omitted.

A pale purple precipitate (product) was formed in the mixed solution. As a result of conducting a chemical analysis on the product in the same manner as in Example 1, it was found that the product obtained in Example 5 was Nd ₂ (OH) ₄ SO ₄ .2.2H ₂ O. Therefore, it is shown that a layered rare earth hydroxide in which Ln is Nd ³⁺ and n is 2.2 in the general formula Ln ₂ (OH) ₄ SO ₄ .nH ₂ O (1 <n <3) is obtained. It was.

  Similar to Example 1, the layered rare earth hydroxide of Example 5 (referred to as Nd-LRHE for simplicity) by SEM observation, synchrotron X-ray diffraction, powder X-ray diffraction, synchrotron X-ray diffraction Calculation of lattice constant, measurement of FT-IR spectrum, and TG-DTA measurement were performed. These results are shown in FIGS. 7, 12, 13, 17, 18, 21 and Table 3.

  In the same manner as in Example 1, Nd-LRHE was heated at 1000 ° C. in the air for 1 hour. The powder X-ray diffraction of the heated Nd-LREH was measured. The results are shown in FIG.

Instead of Tb ₂ (SO ₄ ) ₃ · 8H ₂ O (purity 99.9%) of Example 1 as a sulfate of Ln, Pr ₂ (SO ₄ ) ₃ · 8H ₂ O (purity 99.9%) was used. Since it is the same as that of Example 1 except having used, description is abbreviate | omitted.

A green precipitate (product) was formed in the mixed solution. As a result of conducting a chemical analysis on the product in the same manner as in Example 1, it was found that the product obtained in Example 6 was Pr ₂ (OH) ₄ SO ₄ .16H ₂ O. Therefore, it is shown that a layered rare earth hydroxide in which Ln is Pr ³⁺ and n is 2.16 in the general formula Ln ₂ (OH) ₄ SO ₄ .nH ₂ O (1 <n <3) is obtained. It was.

  Similar to Example 1, the layered rare earth hydroxide of Example 6 (referred to as Pr-LRHE for simplicity) by SEM observation, synchrotron X-ray diffraction, powder X-ray diffraction, synchrotron X-ray diffraction Calculation of lattice constant, measurement of FT-IR spectrum, and TG-DTA measurement were performed. These results are shown in FIGS. 7, 12, 13, 17, 18, 21 and Table 3.

  In the same manner as in Example 1, Pr-LRHE was heated at 1000 ° C. in the air for 1 hour. The powder X-ray diffraction of the heated Pr-LREH was measured. The results are shown in FIG.

In addition to Tb ₂ (SO ₄ ) ₃ · 8H ₂ O (purity 99.9%, 2.5 mM) of Example 1 as sulfate of Ln, Gd ₂ (SO ₄ ) ₃ · 8H ₂ O (purity 99. Except for using 9%, 2.5 mM), it is the same as Example 1, and thus the description is omitted.

Similar to Example 1, a white precipitate (product) was produced. As a result of performing chemical analysis on the product in the same manner as in Example 1, the product obtained in Example 7 is (Tb _0.5 Gd _0.5 ) ₂ (OH) ₄ SO ₄ .2H ₂ O. I understood. Accordingly, a layered rare earth hydroxide in which Ln is a combination (solid solution) of Tb ³⁺ and Gd ^{3+ in} the general formula Ln ₂ (OH) ₄ SO ₄ .nH ₂ O (1 <n <3), and n is 2. Was shown to be obtained.

Similar to Example 1, the layered rare earth hydroxide of Example 7 (referred to as Tb _0.5 Gd _0.5 -LRHE for simplicity) observation by SEM, powder X-ray diffraction, and synchrotron radiation X The lattice constant was calculated by line diffraction. These results are shown in FIG. 8, FIG. 14 and FIG.

In addition to Tb ₂ (SO ₄ ) ₃ · 8H ₂ O (purity 99.9%, 1.25 mM) of Example 1 as sulfate of Ln, Gd ₂ (SO ₄ ) ₃ · 8H ₂ O (purity 99. Except for using 9% and 3.75 mM), the description is omitted because it is the same as Example 1.

Similar to Example 1, a white precipitate (product) was produced. As a result of performing chemical analysis on the product in the same manner as in Example 1, the product obtained in Example 8 is (Tb _0.25 Gd _0.75 ) ₂ (OH) ₄ SO ₄ .2H ₂ O. I understood. Accordingly, a layered rare earth hydroxide in which Ln is a combination (solid solution) of Tb ³⁺ and Gd ^{3+ in} the general formula Ln ₂ (OH) ₄ SO ₄ .nH ₂ O (1 <n <3), and n is 2. Was shown to be obtained.

Similar to Example 1, the layered rare earth hydroxide of Example 8 (referred to as Tb _0.25 Gd _0.75 -LREH for simplicity) observation by SEM, powder X-ray diffraction, and synchrotron radiation X The lattice constant was calculated by line diffraction. These results are shown in FIG. 9, FIG. 14 and FIG.

Table 1 summarizes the chemical analysis results and general formulas of Examples 1-8.

  In addition, the layered rare earth hydroxide of the whole Example or the layered rare earth hydroxide of the present invention may be collectively referred to as Ln-LREH.

FIG. 5 is a view showing an SEM image of Tb-LREH in Example 1.
FIG. 6 is a diagram showing a TEM image of Tb-LREH of Example 1. FIG.

  According to FIGS. 5 and 6, Tb-LRHE is shown to be an elongated plate crystal having an edge length of several micrometers. Further, the thickness of the plate crystal was several tens of nanometers.

  FIG. 7 is a diagram showing SEM images of Ln-LREH (Ln = Gd, Eu, Sm, Nd and Pr) in Examples 2 to 6.

  According to FIG. 7, it is shown that all Ln-LRHE are flake-like plate crystals, and these plate crystals are aggregated. Although not shown, according to Sm-LREH TEM observation, the plate-like crystals had well-developed edges and were hexagonal.

  From FIG. 5 and FIG. 7, when a rare earth ion having an atomic number larger than Tb is selected as Tn with Tb and Gd as a boundary, the layered rare earth hydroxide of the present invention becomes an elongated plate crystal. When a rare earth ion having an atomic number smaller than Gd is selected, it is suggested that the layered rare earth hydroxide of the present invention can be a flake-like plate crystal.

8 is a SEM image of Tb _0.5 Gd _0.5 -LREH in Example 7. FIG.
9 is a view showing an SEM image of Tb _0.25 Gd _0.75 -LREH in Example 8. FIG.

According to FIG. 8, Tb _0.5 Gd _0.5 -LREH was an elongated plate-like crystal similar to Tb-LREH (Example 1). On the other hand, according to FIG. 9, Tb _0.25 Gd _0.75 -LREH was a flake-like plate-like crystal similar to Gd-LREH (Example 2). From this, when Ln consists of 2 or more types of combinations, it was found that the shape of the layered rare earth hydroxide crystal of the present invention can be controlled according to the selected rare earth ion of Ln.

  FIG. 10 is a diagram showing a synchrotron radiation X-ray diffraction pattern of Tb-LRHE of Example 1.

  FIG. 10 shows a sharp diffraction peak, and all diffraction peaks could be indexed to the monoclinic system. When the unit cell length was calculated, the a-axis length (nm), b-axis length (nm), c-axis length (nm) and β angle (°) were 0.624528 (2) and 0.371268 (1), respectively. ), 1.66330 (1) and 90.072. Both the bottom reflection peak and the non-bottom reflection peak were very sharp, and no asymmetrical spread was observed in the profile.

  FIG. 10 shows that Tb-LREH has high crystallinity, and the uniform precipitation method used in Example 1 is preferable for the production of the layered rare earth hydroxide of the present invention.

  Further, in FIG. 10, it was found that Tb-LREH has an A-bottom monoclinic lattice from the regular disappearance of diffraction peaks satisfying k + 1 = 2n + 1 of hkl. This indicates that Tb-LRHE causes the host layer (140 in FIG. 1) composed of adjacent Tb hydroxy polyhedrons (130 in FIG. 1) to slip by ½b in the b-axis direction with respect to each other. As a result, the c-axis length is twice the base interval (region 180 in FIG. 1).

  Further, the fact that the a-axis length (0.624528 (2) nm) of Tb-LREH is comparable to √3 of the b-axis length (0.371268 (1) nm) is that the host layer of Tb-LRHE (FIG. 1). 140) has a quasi-two-dimensional hexagonal structure. Here, referring to FIG. 6, the edge angle of the Tb-LRHE plate crystal is 120 °, which is considered to be a result of reflecting this structural feature.

  FIG. 11 is a diagram showing a result of fitting the synchrotron radiation X-ray diffraction pattern of FIG. 10 by the Rietveld method.

  A profile a indicated by a red dot in the upper stage indicates an actual measurement pattern, and a profile b indicated by a green line indicates a calculation pattern. The pattern c indicated by the lower blue line indicates the difference between the measured pattern and the calculated pattern, and the green vertical bar d indicates the diffraction peak position that appears due to the crystal structure of the layered rare earth hydroxide of the present invention.

With reference to the symmetry estimated by the lattice constant and the extinction rule, and the crystal structures of Tb ₂ (OH) ₅ Cl · nH ₂ O (n≈1.6) and Tb (OH) ₃ which are similar compounds A structural model was derived, and based on this, a synchrotron radiation powder X-ray diffraction pattern was fitted by the Rietveld method. Based on space group A2 / m (No. 12), the reliability factor was calculated | required. Table 2 shows the results of the structural refinement.

Confidence factors R _wp = 5.92%, R _p = 4.42%, R _I = 2.01% and R _F = 1.23% were obtained, and satisfactory fitting was possible.

  From the results of the structural refinement shown in Table 2, the Tb-LRHE host layer (140 in FIG. 1) has a 9-coordinate Tb hydroxy polyhedron (130 in FIG. 1) as a basic structural unit, as schematically shown in FIG. ). The Tb cation (110 in FIG. 1) is coordinated with water molecules, sulfate ions, and hydroxyl groups. As a result, the obtained Tb hydroxy polyhedron is bonded to each other, and a pseudo hexagonal two-dimensional plate crystal and I can understand.

  FIG. 12 is a diagram showing a powder X-ray diffraction pattern of Ln-LRHE (Ln = Gd, Eu, Sm, Nd and Pr) of Examples 2 to 6.

  FIG. 12 also shows the powder X-ray diffraction pattern of Tb-LRHE of Example 1. According to FIG. 12, all the X-ray diffraction patterns of Ln-LREH of Examples 2 to 6 corresponded to those of Example 1. From this, it was confirmed that the layered rare earth hydroxides of Examples 2 to 6 also have a monoclinic system and high crystallinity. In addition, FIG. 12 shows the interplanar spacing (d value) of Examples 1 to 6. As in Example 1, it was confirmed that the layered rare earth hydroxides of Examples 2 to 6 also showed a layered structure. . The d value was almost constant between 0.830 nm and 0.840 nm. This supports that the layered rare earth hydroxide of the present invention has a rigid pillar structure.

Table 3 is a table | surface which shows the list of the lattice constant computed from the synchrotron radiation X-ray-diffraction pattern of Examples 1-6.

  FIG. 13 is a diagram showing the dependence of the lattice constant on the ion size of Ln.

FIG. 13 visualizes the results of Table 3 for ease of understanding. The ion size (ion radius) of Ln was determined by Shannon et al. Acta Crystallogr. , Sect. B, 1969, 25, 925 based on 9-coordinate ion radius. As shown in FIG. 13 and Table 3, the layered rare earth hydroxide of the present invention has any Ln ₂ (OH) ₄ SO ₄ .nH ₂ O as the ion size of Ln increases (the atomic number of Ln decreases). It was found that the lattice constant and β also increased almost linearly. From this, it was shown that the layered rare earth hydroxide having a desired lattice constant and the layered rare earth hydroxide having a fine pore volume controlled can be designed by selecting Ln.

14 is a graph showing the powder X-ray diffraction patterns of Tb _0.5 Gd _0.5 -LREH of Example 7 and Tb _0.25 Gd _0.75 LREH of Example 8. FIG.

FIG. 14 also shows the powder X-ray diffraction patterns of Tb-LREH of Example 1 and Gd-LREH of Example 2 for reference. None of the X-ray diffraction patterns of Tb _0.5 Gd _0.5 -LREH of Example 7 and Tb _0.25 Gd _0.75 LREH of Example 8 showed a peak corresponding to the formation of the second phase. Consistent with that of Examples 1 and 2. From this, it was confirmed that the layered rare earth hydroxides of Examples 7 and 8 also have a monoclinic system and high crystallinity.

FIG. 15 is a diagram illustrating the relationship between the x value, the a-axis length, and the b-axis length in (Tb _x Gd _1-x ) ₂ (OH) ₄ SO ₄ .nH ₂ O according to Examples 1, 2, 7, and 8. It is.

  From FIG. 15, the a-axis length and the b-axis length are both as the Ln of the layered rare earth hydroxide Ln-LRHE of the present invention changes from a Tb simple substance to a solid solution of Tb and Gd, and a Gd simple substance. It was found to increase linearly. From the linear change of the lattice constant, that is, the establishment of the Vegard rule, it is shown that Tb and Gd are completely dissolved between Tb-LREH and Gd-LRHE.

From FIG. 14 and FIG. 15 above, in the layered rare earth hydroxide (Ln ₂ (OH) ₄ SO ₄ .nH ₂ O) of the present invention, Ln contains at least one kind of rare earth element and a combination of two or more kinds Has also been shown to be possible.

FIG. 16 shows the FT-IR spectrum a of Tb-LREH of Example 1, the FT-IR spectrum b of Tb ₂ (OH) ₅ (SO ₄ ) _1/2 · nH ₂ O, and Tb ₂ O ₂ SO _4. It is a figure which shows FT-IR spectrum c of.

The FT-IR spectrum b is Tb ₂ (OH) ₅ (SO ₄ ) _1/2 · nH produced by anion exchange on the synthesized Tb ₂ (OH) ₅ Cl · nH ₂ O (n≈1.6). It is an FT-IR spectrum of ₂ O (n≈1.6). The FT-IR spectrum c is an FT-IR spectrum of Tb ₂ O ₂ SO ₄ (described later with reference to FIG. 22) produced by heating the Tb-LREH of Example 1 at 1000 ° C.

Based on the FT-IR spectra a to c, the bonding state of the hydroxyl group and sulfate ion in Tb-LREH was examined. In FT-IR spectra a, 2 two sharp peaks of 3613cm ^-1 and 3477cm ^-1 are hydrogen bond is equivalent to stretching modes of OH groups free not involved.

In the FT-IR spectrum a, the broad split peaks near 3261 cm ⁻¹ and 3198 cm ⁻¹ are comparable to the broad peaks seen in the FT-IR spectrum b from 3200 to 3700 cm ⁻¹ , and hydrogen bonding is Due to the OH groups involved. Such broadening of the peak is caused by the interaction between the hydroxyl group and the water molecule / interlayer anion, and Tb ₂ (OH) ₅ (SO ₄ ) _1/2 · nH in the FT-IR spectrum b. It is known as a feature commonly seen in ₂ O (a layered rare earth hydroxide with m = 1 in the formula (1)) and a layered double hydroxide.

In FT-IR spectra ^a, 1647cm ^-1, 812cm -1 and 592cm ^-1 near the peak is due to the bending mode of water molecules coordinated to the metal ion.

In the FT-IR spectrum a, all fundamental modes (ν ₁ , ν ₂ , ν ₃ and ν ₄ ) of sulfate ions were observed. The ν ₁ and ν ₂ modes are inherently IR-inactive modes of sulfate ions (T _d point group) in an ideal shape, and their appearance is caused by distortion of the sulfate ions in the structure, and the point group becomes C _2v . This suggests that it is decreasing. It should be noted that the ν ₃ mode is split into three independent peaks, clearly different from the 1109 cm ⁻¹ broad single peak (ν ₃ mode) in the FT-IR spectrum b. Three similar peaks are observed in the peak (ν ₃ mode) of the FT-IR spectrum c. Such splitting of the ν ₃ mode into three peaks indicates that the sulfate chelate has a trans-bidentate coordination. More importantly, these fundamental modes ν _{1 to} ν ₃ , among them, the fundamental mode ν ₃ indicated by three peak splits were also observed in the FT-IR spectrum c. That is, it was found that the fundamental mode ν ₃ observed with Tb-LRHE corresponds to that of Tb ₂ O ₂ SO ₄ .

Tb ₂ O ₂ SO ₄ has a structure in which TbO ₂ ²⁺ layers and sulfate ions are alternately repeated, and sulfate ions are directly coordinated to Tb ³⁺ cations to connect adjacent TbO ₂ ²⁺ layers. From this, it was found that the sulfate ion in Tb-LREH was co-coordinated to the Tb ³⁺ cation.

  The above results agree with the schematic diagram of the layered rare earth hydroxide of the present invention shown in FIG.

  FIG. 17 is a diagram showing an FT-IR spectrum of Ln-LREH (Ln = Gd, Eu, Sm, Nd and Pr) in Examples 2 to 6.

  FIG. 18 is a diagram illustrating the Ln dependence of the fundamental mode of the FT-IR spectrum.

  The FT-IR spectrum Tb shown in FIG. 17 is the same as the FT-IR spectrum a of Tb-LREH of Example 1 shown in FIG. According to FIG. 17, the FT-IR spectra of Examples 2 to 6 also showed the same spectrum as that of Example 1, and it was confirmed that a layered rare earth hydroxide was obtained.

However, according to FIGS. 17 and 18, as the ion size of Ln increases (atomic number decreases), free OH group stretching modes and characteristic modes such as sulfate ion fundamental mode ν _3, etc. Shifted to the lower wavenumber side. This is because, in the layered rare earth hydroxide of the present invention, the larger the ion size of Ln, the weaker the bonds between the hydroxyl groups and the atoms in the sulfate ions, and Ln is a rare earth element with a small ion size. The more it shows, the stronger the bond within the hydroxyl group and sulfate ion.

Furthermore, if attention to the shape of the fundamental mode [nu ₃ were split into three peaks, as the ion size of Ln increases, the peak of the fundamental mode [nu ₃ became asymmetric. This indicates that in the layered rare earth hydroxide of the present invention, the strain of sulfate ions is larger as Ln is a rare earth element having a larger ion size. Therefore, Ln may be appropriately selected according to the required / allowed degree of distortion of Ln-LREH, and the material may be designed.

  FIG. 19 is a diagram showing a TG profile of Tb-LREH of Example 1.

As shown in FIG. 19, Tb-LRHE showed a two-stage weight loss with heating. The first weight loss was 7.8% in the temperature range of 200 ° C. to 275 ° C. This weight loss indicates that hydrated water in Tb-LREH (corresponding to 2.2H ₂ O in Tb ₂ (OH) ₄ SO ₄ .2.2H ₂ O) has been removed. In addition, compared with the layered rare earth hydroxide (Ln ₂ (OH) ₅ A · nH ₂ O, A = Cl, NO ₃ , n = 1.6) represented by Patent Documents 1 to ₃ The dehydration of the hydrate of Tb-LREH occurred at higher temperatures and was steeper. This indicates that the water molecules in Tb-LREH are tightly bound by the structure.

  The second weight loss was 7.2% at a temperature of about 350 ° C. The second weight loss was even steeper than the first weight loss. This weight loss indicates dehydration from the host layer (140 in FIG. 1) consisting of a Tb hydroxy polyhedron (130 in FIG. 1). The weight loss 7.2% was almost equal to the value calculated from the chemical formula shown in Table 1 (6.9%).

From the above, dehydration in Tb-LRHE is
Tb ₂ (OH) ₄ SO ₄ .2.2H ₂ O → Tb ₂ (OH) ₄ SO ₄ + 2.2H ₂ O (200 ° C. to 275 ° C.) .... (3 ')
Tb ₂ (OH) ₄ SO ₄ → Ln ₂ O ₂ SO ₄ + 2H ₂ O (about 350 ° C.) (4 ′)
It was confirmed that From this, it was found that the layered rare earth hydroxide of the present invention was dehydrated by heating at a temperature exceeding at least 350 ° C. to become a rare earth oxysulfate.

Next, the reaction rate of the formula (4 ′) was examined by the Kissinger approach.
20 is a diagram showing a Kissinger plot of Tb-LREH of Example 1. FIG.

Table 4 shows a data list of the Kissinger plot.

In Table 4, C (° C./min) is the temperature increase rate of the DTA curve shown in FIG. 20, and T _m (K) is the endothermic peak temperature. According to Kissinger's approach, the apparent activation energy (E _a ) is E _a / R = d [−ln (C / T _m ² )] / d (1 / T) (where R is 8. 314 (gas constant) and T _m is the endothermic peak temperature). Then, plot the -ln (C _{/ T} ^{m 2)} against 1000 / T, it was determined activation energy _{(E a)} from the slope of the resulting straight line.

According to the DTA curve in FIG. 20, the endothermic peak temperature shifted to the high temperature side as the temperature increase rate increased. As shown in Table 4 and FIG. 20, the apparent activation energy (E _a ) obtained is about 240 ± 8 KJ / mol, that of UCl ₃ type rare earth hydroxide La (OH) ₃ (240 ± 10 KJ / mol). This indicates that the hydroxyl group in Tb-LREH is similar to that of UCl ₃ type rare earth hydroxide in both the binding and dehydration kinetics.

  FIG. 21 is a diagram showing a TG profile of Ln-LREH (Ln = Gd, Eu, Sm, Nd and Pr) in Examples 2 to 6.

  The TG profile Tb shown in FIG. 21 is the same as the Tb-LREH TG profile of the first embodiment shown in FIG. According to FIG. 21, the TG profiles of Examples 2 to 6 also show the same TG profile as that of Example 1, and two stages of weight loss (dehydration of hydrate and dehydration from the host layer) with heating. )showed that.

However, according to FIG. 21, as the ion size of Ln increases (atomic number decreases), the temperature at which the second dehydration occurs shifts to the low temperature side. On the other hand, the temperature at which the first dehydration occurs did not show Ln dependence. This is based on the fact that the second dehydration is dehydration from the host layer and requires the breaking of the Ln ³⁺ —OH ⁻ bond. In the layered rare earth hydroxide of the present invention, Ln has an ion size. It shows that the larger the rare earth element, the lower the stability of the host layer (140 in FIG. 1) made of the hydroxy polyhedron of Ln, and the higher the stability of the host layer, the more the rare earth element having a smaller ion size. When such subtle stability is required, Ln may be appropriately selected to design a desired layered rare earth hydroxide.

  The above results are consistent with the FT-IR spectra shown in FIGS. 16 to 18 and the changes in the lattice constants shown in Table 3 and FIG.

  FIG. 22 is a graph showing the heating temperature dependence of the powder X-ray diffraction pattern of Tb-LRHE of Example 1.

  In FIG. 22, the X-ray diffraction pattern a is the same as the X-ray diffraction pattern Tb-LREH in FIG. X-ray diffraction patterns b, c, d and e are X-ray diffraction patterns of Tb-LREH heated at 150 ° C., 300 ° C., 450 ° C. and 1000 ° C., respectively.

  When the X-ray diffraction patterns a and b were compared, there was no change in the X-ray diffraction pattern. On the other hand, when the X-ray diffraction patterns a and c were compared, a clear change was made to the X-ray diffraction pattern, and many peaks were observed even after heating. This indicates that Tb-LREH is crystalline even after the first weight loss (hydrate dehydration) described with reference to FIG.

When the X-ray diffraction patterns a and d were compared, the X-ray diffraction pattern d was completely different from the X-ray diffraction pattern a. Comparing the X-ray diffraction patterns d and e, the X-ray diffraction pattern e showed a sharper peak than the X-ray diffraction pattern d, but the X-ray diffraction patterns were substantially the same. In addition, all diffraction peaks of the X-ray diffraction pattern e were indexed to the X-ray diffraction pattern (JCPDS No. 41-0684) of Tb ₂ O ₂ SO ₄ . From the above, it was confirmed that Tb-LREH heated at 450 ° C. and 1000 ° C. became rare earth oxysulfate (Tb ₂ O ₂ SO _{4 in} Example 1) by dehydration.

  FIG. 23 is a diagram showing a powder X-ray diffraction pattern of Ln-LREH (Ln = Gd, Eu, Sm, Nd and Pr) of Examples 2 to 6 after heating at 1000 ° C.

The X-ray diffraction pattern Tb shown in FIG. 23 is the same as the X-ray diffraction pattern e in FIG. According to FIG. 23, the X-ray diffraction patterns of Examples 2 to 6 also show the same X-ray diffraction pattern as that of Example 1, and the layered rare earth hydroxides of Examples 2 to 6 are heated by 1000 ° C. It was confirmed that the rare earth oxysulfate (Ln ₂ O ₂ SO ₄ , Ln = Gd, Eu, Sm, Nd, Pr) was obtained.

  FIG. 24 is a diagram showing an SEM image of Tb-LREH of Example 1 after heating at 1000 ° C. FIG.

Referring to FIG. 5 (SEM image of Tb-LREH before heating), the Tb-LREH after heating shown in FIG. 24 (ie, Tb ₂ O ₂ SO ₄ ) maintains the morphology of Tb-LREH before heating. It was an elongated plate-like crystal. From this, it was found that the layered rare earth hydroxide of the present invention can maintain its state even after being heated to 1000 ° C. and changed to a rare earth oxysulfate.

  As described above, FIG. 22 to FIG. 24 show that the layered rare earth hydroxide of the present invention is effective as a raw material for the rare earth oxysulfate.

  25 is a diagram showing an excitation spectrum (A) and an emission spectrum (B) of Tb-LRHE of Example 1. FIG.

The excitation spectrum (A) has an emission wavelength λ _em. It is a plot of emission intensity of ^- (7 _{F 5} line ^545nm, 5 _D 4). The emission spectrum (B) shows the excitation wavelength λ _ex. It is a plot of the emitted light intensity of each light emission wavelength in (212 nm).

The excitation spectrum (A) showed a peak of 4b-5d transition of Tb ³⁺ with spin tolerance (low spin, LS) and spin forbidden (high spin, HS). Moreover, the peak of LS transition is much stronger than the peak of HS transition, and Tb (OH) _2.5 Cl _0.5 · nH ₂ O, Tb (OH) _2.5 (NO ₃ ) _0.5 · nH _The excitation band was different from that of the layered rare earth hydroxide of m = 1 that can exchange anions such as ₂ O.

According to the emission spectrum (B), a sharp green emission of 545 nm of Tb ³⁺ was exhibited by UV excitation of 212 nm.

  FIG. 26 is a diagram showing an excitation spectrum (A) and an emission spectrum (B) of Eu-LRHE of Example 3.

The excitation spectrum (A) has an emission wavelength λ _em. It is a plot of emission intensity of ^- (7 _{F 2} lines ^617nm, 5 _D 0). The emission spectrum (B) shows the excitation wavelength λ _ex. It is a plot of the emitted light intensity of each light emission wavelength in (394 nm).

According to the excitation spectrum (A), a series of sharp peaks due to the Eu ³⁺ ff transition and a high broad peak of 270 nm or less were shown. The broad peak is due to charge transfer between O ²⁻ and Eu ³⁺ , typically known as Eu ³⁺ doped YVO ₃ and (Eu _1−Z Gd _Z ) ₂ O ₃ . It has been.

According to the emission spectrum (B), 580.6nm, 589.4nm, 617.6nm, typical ⁵ D ₀ to 652.2nm and 697.8nm - indicates ⁷ F _{J (J} = 0-4) peak, Red light was emitted. These ⁵ D ₀ - the emergence of ⁷ F _J peaks suggest that ^{the Eu 3+} occupies the grid point having no inversion symmetry.

^Furthermore, 5 _D 0 ^- 7 _{F 2} prominent peak (617.6nm) _{is, Eu (OH) 2.5 Cl 0.5} · nH 2 O, Eu (OH) 2.5 (NO 3) 0.5 A slight red shift compared to that of the layered rare earth hydroxide with m = 1, such as nH ₂ O (all 620 nm). This red shift is attributed to the fact that the sulfate ion in Eu-LRHE of the present invention is coordinated to Eu ³⁺ unlike Cl ⁻ and NO ₃ ⁻ .

  As described above, FIG. 25 and FIG. 26 show that the layered rare earth hydroxide of the present invention functions as a phosphor when it contains at least one trivalent rare earth ion serving as an emission center.

The layered rare earth hydroxide of the present invention is represented by the general formula Ln ₂ (OH) ₄ SO ₄ .nH ₂ O (1 <n <3, Ln includes at least one trivalent rare earth ion). The layered rare earth hydroxide of the present invention comprises a host layer composed of an Ln hydroxy polyhedron and sulfate ions located between the host layers, and further has a pillar structure. Such a layered rare earth hydroxide of the present invention has rigidity in the laminating direction in addition to the in-plane direction. Further, the layered rare earth hydroxide of the present invention functions as a phosphor by selecting a trivalent rare earth ion serving as a light emission center for Ln. Such phosphors are applied to light emitting diodes, fluorescent display tubes, field emission displays, plasma display panels, cathode ray tubes and the like. Furthermore, the layered rare earth hydroxide of the present invention has uniform pores formed by the Ln hydroxy polyhedron and sulfate ions, and thus functions as a porous body.

100 Layered rare earth hydroxide of the present invention 110 Ln cation 120 Sulfate ion 130 Ln hydroxy polyhedron 140 Host layer 150 Bonding 160 Stacking direction 170 Pore 300 Light emitting diode element 310, 320 Lead wire 330 Semiconductor light emitting element 340 Bonding wire 350 The present invention Phosphor of 360, 370 resin

JP 2009-184868 A JP 2009-184890 A JP 2010-229007 A

Louer et al. Solid. State. Chem. , 1987, 68, 292

Claims (8)

Represented by the general formula Ln ₂ (OH) ₄ SO ₄ .nH ₂ O (1 <n <3),
Ln includes at least one trivalent rare earth ion;
A host layer made of the Ln hydroxy polyhedron, and sulfate ions located between the host layers,
A layered rare earth hydroxide having a pillar structure in which an oxygen atom in the sulfate ion is directly bonded to the Ln in the adjacent host layer. 2. The layered rare earth hydroxide according to claim 1, wherein the Ln is a rare earth ion selected from at least one selected from the group consisting of Pr ³⁺ , Nd ³⁺ , Sm ³⁺ , Eu ³⁺ , Gd ³⁺ and Tb ³⁺ .   The layered rare earth hydroxide according to claim 1, wherein the layered hydroxide has an A-centered monoclinic lattice. A method for producing the layered rare earth hydroxide according to any one of claims 1 to 3,
Preparing a mixed aqueous solution containing a sulfate of Ln and a pH adjuster;
Decomposing the pH adjuster and hydrolyzing the Ln sulfate.   The method according to claim 4, wherein the pH adjuster is hexamethylenetetramine or urea.   The method according to claim 4, wherein the mixed aqueous solution further contains an alkali metal sulfate. A phosphor comprising a layered rare earth hydroxide,
The layered rare earth hydroxide is
The layered rare earth hydroxide according to any one of claims 1 to 3,
Ln is a phosphor containing at least one trivalent rare earth ion serving as an emission center. A porous body made of layered rare earth hydroxide,
The layered rare earth hydroxide is
The layered rare earth hydroxide according to any one of claims 1 to 3,
A porous body having pores between the sulfate ions located between layers.