JPH11293241A - Phosphor and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a nano-crystalline phosphor which can be excited at a low voltage and fluoresces a green or red color. SOLUTION: There is provided a nano-crystalline phosphor comprising a nano-structure crystal comprising a fluorine-charge-compensated terbium or europium-activated zinc sulfide and having a particle diameter of 2-5 nm. To produce the nano-crystalline phosphor, zinc acetate and sodium sulfide, terbium nitrate (or europium nitrate), and sodium fluoride are mixed in such amounts that the terbium (or europium) is present in an amount of 0.5-5 mol.% based on the zinc, and the fluorine is present in an amount of 1.5-15 mol.%, and the mixture is subjected to a liquid-phase reaction to coprecipitate nano-structure crystals of zinc sulfide doped with a fluorine-charge-compensated terbium (or europium). By compensating the difference between the charges of terbium or europium and zinc by introducing fluoride ions, the luminance characteristics can be markedly improved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a phosphor and a method for producing the same, and more particularly, to a so-called nanocrystal phosphor and a method for producing the same.

[0002]

2. Description of the Related Art In recent years, it has been noted that nanostructure crystals of II-VI group semiconductors such as ultrafine particles represented by Si and Ge, porous silicon and the like exhibit specific optical characteristics. Here, the nanostructure crystal is a few nm
It refers to a crystal grain having a particle size of a certain degree, and is generally called a nanocrystal.

[0003] Comparing the case of having the above-mentioned nano-structured crystal and the case of having a bulk-shaped structural crystal in the II-VI group semiconductor, it is found that good light absorption characteristics and emission characteristics are obtained in the case of having the nano-structured crystal. Show. This is probably because the II-VI group semiconductor having the nanostructured crystal has a larger band gap than that of the bulk crystal structure because the quantum size effect is exhibited. That is, it is considered that the band gap of the II-VI group semiconductor having the nanostructure crystal may be widened by the quantum size effect.

[0004] Various phosphors are used in displays such as televisions, and the phosphors used in this type of display have been synthesized by firing raw materials at a high temperature. The particle size of the synthesized phosphor is about several μm (3 to 10 μm).

On the other hand, in recent years, in the field of televisions and the like, it has been desired to reduce the thickness of displays.
It is called PDP. ), A field emission display (hereinafter, referred to as FED), and an electroluminescent display (hereinafter, referred to as ELD).

[0006]

By the way, for example, in the above-mentioned FED, which has received special attention, an electron emission source (cathode) for emitting an electron beam is made finer and thinner. Miniaturization greatly reduces the voltage of the electron beam.

In a display in which the voltage of the electron beam is reduced due to the reduction in thickness, if a phosphor having a particle diameter of about several μm is used as described above, it will not emit light sufficiently because the voltage of the electron beam is low. There's a problem.

It is considered that this is because the irradiated electron beam cannot reach the light emitting portion of the phosphor due to the large size of the conventional phosphor crystal.

Therefore, in order to realize the above-mentioned FED, a phosphor which can be excited at a low voltage is required.

[0010] In the field of CRTs as well, higher definition is being promoted, and finer phosphors are required. Also in the field of ELD, a phosphor having higher luminous efficiency is required.

[0011] As a phosphor satisfying such conditions,
Expectations are high for II-VI semiconductors having nanostructured crystals as described above.

At present, only about ZnO: Zn has been practically used as a light-emitting material which can be excited at a low voltage.

The above-mentioned ZnO: Zn emits green-blue color. Therefore, a II-VI group semiconductor having a nanocrystalline structure which develops another color is required. A method for manufacturing a VI group semiconductor has not been sufficiently studied, and a phosphor having sufficient characteristics has not always been obtained.

The present invention has been proposed in view of such conventional circumstances, and has as its object to provide a phosphor having a nanocrystal structure which can be excited at a low voltage and emits green or red light. Further, it is an object of the present invention to provide a manufacturing method thereof.

[0015]

The present inventors have conducted various studies on nanocrystal phosphors and found that phosphors that emit green and red light can be obtained by activating zinc sulfide with terbium or europium. The luminescence efficiency is dramatically improved by charge compensation with fluorine at the time of activation, and by using a liquid phase reaction using coprecipitation instead of a normal solid phase reaction, these nanocrystals Were found to be able to be manufactured stably, and the present invention was completed.

That is, the phosphor of the present invention is made of zinc sulfide activated by terbium or europium charge-compensated by fluorine, and has a particle diameter of 2 nm or more and 5 n
m or less of nanostructured crystals.

Further, according to the production method of the present invention, zinc acetate and sodium sulfide and terbium nitrate (or europium nitrate) and sodium fluoride are mixed in a solvent in an amount of 0.5 to 5 mol% terbium (or europium) with respect to zinc. Mixing at a ratio of 1.5 to 15 mol% of fluorine to cause a liquid phase reaction to coprecipitate a nanostructured crystal of zinc sulfide doped with terbium (or europium) which is charge-compensated with fluorine. It is characterized by the following.

Zinc sulfide nanocrystals activated with terbium emit green light and afterglow, and zinc sulfide nanocrystals activated with europium emit red light and afterglow. At this time, by introducing F ^- ions,
The difference in charge between terbium or europium and zinc is compensated, and the light emission characteristics are greatly improved.

At the time of production, nano-particles having a particle size of about 3 nm and having excellent light-emitting characteristics are obtained by using a liquid phase reaction utilizing coprecipitation instead of a conventional high-temperature firing of raw materials, that is, a solid phase reaction. You can get a crystal.

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION The phosphor of the present invention is made of zinc sulfide activated by terbium or europium, and is made of a nanostructure crystal (nanocrystal) having a particle size of 2 nm to 5 nm.

As an activator, terbium (Tb), europium (Eu), and fluorine (F) are used, and when these are doped into zinc sulfide, they have intrinsic light emitting properties. For example, zinc sulfide activated with Tb or TbF ₃ emits green light and afterglow. Zinc sulfide activated with Eu or EuF ₃ emits red light and afterglow. In the following description, for example, zinc sulfide doped with Tb is referred to as “ZnS: Tb”.

The activator-doped zinc sulfide nanocrystal phosphor has a wide band gap as a result of generating a quantum size effect capable of confining exciton, electron and hole pairs within a range of several nm. It will be.

In the present invention, not only terbium and europium but also F ^- ions are introduced at the time of activation.
This is from the viewpoint of charge compensation. In other words, when doping zinc sulfide with terbium or europium, zinc is divalent (2+), whereas terbium or europium is trivalent (3+), and the matching cannot be obtained. Therefore, fluorine, which is a negative ion, is introduced to perform charge compensation. As a result, the emission characteristics are improved by a factor of two or more as compared with the case where no F ^- ions are introduced.

To prepare the above zinc sulfide nanocrystal phosphor, a liquid phase reaction utilizing coprecipitation is used when doping the above-mentioned activator into zinc sulfide.

The liquid phase reaction utilizing this coprecipitation is a reaction in which a salt having an atom serving as an activator coexists in a reaction system when synthesizing zinc sulfide in a predetermined solvent. In addition,
At this time, the activator to be doped does not need to be one kind of atom, and may be composed of a plurality of kinds of atoms.

Specifically, when producing ZnS: Tb, the following liquid phase reaction occurs.

Zn (CH ₃ COO) ₂ + Tb (NO ₃ ) ₃ +
Na ₂ S → ZnS: Tb + 2CH ₃ COONa When producing ZnS: TbF ₃ , the following liquid phase reaction occurs.

Zn (CH ₃ COO) ₂ + Tb (NO ₃ ) ₃ +
3NaF + Na ₂ S → ZnS: TbF ₃ + 2CH ₃ COO
When producing NaZnS: Eu, the following liquid phase reaction occurs.

Zn (CH ₃ COO) ₂ + Eu (NO ₃ ) ₃ +
Na ₂ S → ZnS: Eu + 2CH ₃ COONa When producing ZnS: EuF ₃ , the following liquid phase reaction occurs.

Zn (CH ₃ COO) ₂ + Eu (NO ₃ ) ₃ +
3NaF + Na ₂ S → ZnS: EuF ₃ + 2CH ₃ COO
Na In this method, the activator is added as a salt during the liquid phase reaction, as described above. At this time, examples of the salt having an atom serving as an activator include an acetate, a nitrate, a sulfate and the like depending on the type of the atom.

Specifically, for example, in a solvent, zinc acetate and sodium sulfide and terbium nitrate (or europium nitrate), and sodium fluoride are mixed with 0.5 to 5 mol% of terbium (or europium) and fluorine of zinc. According to the present invention, a nanostructure crystal of zinc sulfide doped with terbium (or europium), which is charge-compensated with fluorine, is mixed and mixed in a ratio of 1.5 to 15 mol% to cause a liquid phase reaction. In the method for producing a phosphor, an activator-doped zinc sulfide having a particle size of about several nm can be produced by using a liquid phase reaction utilizing such coprecipitation. Zinc sulfide doped with an activator has a wide band gap as a result of generating a quantum size effect capable of confining exciton, electron, and hole pairs within a range of several nm. Therefore, according to the present invention, it is possible to manufacture a phosphor having improved light absorption and emission characteristics.

The reason why F ions are introduced using NaF is from the viewpoint of charge compensation. As will be described later, it is possible to improve the light emission characteristics by introducing the F ^- ion more than twice as much as the case where no F ^- ion is introduced.

[0033]

EXAMPLES Specific examples to which the present invention is applied will be described below based on experimental results.

ZnS: TbF ₃ First, a case where Tb is used as an activator will be described. Below Z
The manufacturing process of nS: Tb is shown.

A methanol solution of zinc acetate (0.133 m
(ol / l) 150 ml and 75 ml of a terbium nitrate methanol solution (0.008 mol / l) were mixed and stirred with a magnetic stirrer for 10 minutes to obtain a mixed solution.

Next, an aqueous solution of sodium sulfide (0.4 mol) was stirred using a magnetic stirrer.
(l / l) The above mixed solution was added to 60 ml. Then, the mixture was further vigorously stirred for 20 minutes.

Next, using a centrifuge, 4000 rpm
and centrifugation at 20 m for 20 minutes. Thereafter, the precipitate separated by centrifugation was blow-dried at 50 ° C. for 24 hours. Then, ZnS: Tb was produced by pulverizing the air-dried solid.

Here, the methanol solution of terbium nitrate is preferably added in the range of 12.5 ml to 125 ml. That is, Tb is 0.1 to 1 mol of Zn.
It is preferably added at a ratio of 5 mol% to 5 mol%, and 3 mol% is optimal.

The above nanocrystal phosphor ZnS: Tb
FIG. 1 shows the emission spectrum of the photoexcitation. Of Tb ^{3+ 5} D ₄
Green light emission of the → ⁷ F ₅ can be observed in the 543nm. The excitation spectrum is shown in FIG. It has peaks at 380 nm and 490 nm.

Similarly, green light emission was successfully achieved by electron beam excitation. FIG. 3 shows an emission spectrum of electron beam excitation under the conditions of 5 kV and 20 nA. Green emission _⁵ D ₄ → ⁷ F ⁵ of as in the case of photoexcitation Tb ³⁺ can be observed in the 543 nm.

From the above, it has been found that a nanocrystal phosphor that emits green light can be obtained by using Tb as an activator. Next, the case where Tb and F are used as activators will be described. The manufacturing process of ZnS: TbF ₃ is shown below.

First, a zinc acetate methanol solution (0.1
A mixture of 150 ml of 33 mol / l), 75 ml of a methanol solution of terbium nitrate (0.008 mol / l), and 75 ml of an aqueous solution of sodium fluoride (0.024 mol / l) was stirred with a magnetic stirrer for 10 minutes, and then mixed. I got

Next, an aqueous solution of sodium sulfide (0.4 mol) was stirred with a magnetic stirrer.
(l / l) The above mixed solution was added to 60 ml. Then, the mixture was further vigorously stirred for 20 minutes.

Next, using a centrifuge, 4000 rpm
and centrifugation at 20 m for 20 minutes. Thereafter, the precipitate separated by centrifugation was blow-dried at 50 ° C. for 24 hours. Then, the solid that has been blown and dried is pulverized to obtain ZnS: TbF _3.
Was manufactured.

Here, the methanol solution of terbium nitrate is preferably added in the range of 12.5 ml to 125 ml, and the aqueous solution of sodium fluoride is preferably added in the range of 12.5 ml to 125 ml. That is, Tb is 1 mo of Zn.
Preferably, F is added at a ratio of 0.5 mol% to 5 mol%, and F is added at a ratio of 1.5 mol% to 15 mol%, and Tb is most preferably 3 mol%, and F is most preferably 9 mol%.

The above nanocrystal phosphor ZnS: Tb
The emission spectrum of excitation of F ₃ shown in FIG. also,
⁵ green emission D ₄ → ⁷ F ₅ of Tb ³⁺ can be observed in the 543 nm. In addition, the introduction of F ^- ions from the viewpoint of charge compensation improved the light emission characteristics by about 2.5 times.

[0047] ZnS: EuF ₃ will now be described the case of using Eu as an activator. The manufacturing process of ZnS: Eu is described below.

A solution of zinc acetate in methanol (0.133 m
ol / l) 150 ml and 75 ml of a methanol solution of europium nitrate (0.008 mol / l) were mixed and stirred for 10 minutes using a magnetic stirrer to obtain a mixed solution.

Next, an aqueous solution of sodium sulfide (0.4 mol) was stirred using a magnetic stirrer.
(l / l) The above mixed solution was added to 60 ml. Then, the mixture was further vigorously stirred for 20 minutes.

Next, using a centrifuge, 4000 rpm
and centrifugation at 20 m for 20 minutes. Thereafter, the precipitate separated by centrifugation was blow-dried at 50 ° C. for 24 hours. Then, ZnS: Eu was produced by pulverizing the air-dried solid.

Here, the methanol solution of europium nitrate is preferably added in the range of 12.5 ml to 125 ml. That is, Eu is preferably added at a ratio of 0.5 mol% to 5 mol% with respect to 1 mol of Zn, and 3 mol% is optimal.

The above nanocrystal phosphor ZnS: Eu
5 shows the emission spectrum of the photoexcitation. Eu ^{3+ 5} D ₀
→ Red emission of ⁷ F ₂ can be observed at 616 nm. The excitation spectrum is shown in FIG. It has peaks at 397 nm and 466 nm.

Similarly, red emission was also successfully achieved by electron beam excitation. FIG. 7 shows an emission spectrum of electron beam excitation under the conditions of 5 kV and 20 nA. Red light ⁵ D ₀ → ⁷ F ₂ of as in the case of photoexcitation Eu ³⁺ can be observed in the 616 nm.

From the above, it has been found that a nanocrystal phosphor that emits red light can be obtained by using Eu as an activator. Next, the case where Eu and F are used as activators will be described. Hereinafter, a manufacturing process of ZnS: EuF ₃ will be described.

First, a zinc acetate methanol solution (0.1
33 mol / l) 150 ml, methanol solution of europium nitrate (0.008 mol / l) 75 ml, aqueous solution of sodium fluoride (0.024 mol / l) 75 ml
And stirred with a magnetic stirrer for 10 minutes to obtain a mixed solution.

Then, an aqueous solution of sodium sulfide (0.4 mol) was stirred using a magnetic stirrer.
(l / l) The above mixed solution was added to 60 ml. Then, the mixture was further vigorously stirred for 20 minutes.

Next, using a centrifuge, 4000 rpm
and centrifugation at 20 m for 20 minutes. Thereafter, the precipitate separated by centrifugation was blow-dried at 50 ° C. for 24 hours. Then, the solid matter blown and dried is pulverized to obtain ZnS: EuF _3.
Was manufactured.

Here, it is preferable that the methanol solution of europium nitrate is added in the range of 12.5 ml to 125 ml, and the aqueous solution of sodium fluoride is also added in the range of 12.5 ml to 125 ml. That is, Eu is 1 m of Zn
ol at a rate of 0.5 mol% to 5 mol%,
Is preferably added at a ratio of 1.5 mol% to 15 mol%, and optimally, Eu is 3 mol% and F is 9 mol%.

The above nanocrystal phosphor ZnS: Eu
The emission spectrum of excitation of F ₃ shown in FIG. also,
Red light emission of Eu ^{3+ 5} D ₀ → ⁷ F ₂ can be observed at 616 nm. Moreover, the introduction of F ^- ions from the viewpoint of charge compensation improved the light emission characteristics by about 2.2 times.

The ZnS: Tb manufactured as described above
And ZnS: TbF ₃ , ZnS: Eu, ZnS: EuF ₃
Was analyzed on the basis of the transmission electron microscope and the spread of the X-ray diffraction peak.

In particular, ZnS: TbF ₃ and ZnS: EuF
₃ is a thin flat panel display that can excite and emit light at a low voltage and has a low voltage electron beam, for example, an FED
It is suitable for use as a phosphor. Of course, high definition CRT
Needless to say, it is also effective for ELD.

[0062]

As is clear from the above description, according to the present invention, it is possible to provide a nanocrystal phosphor that emits green or red light.

In particular, by introducing F ^- ions from the viewpoint of charge compensation, the luminous efficiency can be greatly improved, and the fluorescent particles are ultrafine particles of nano size and can emit and emit light even at a low voltage. Body can be provided.

The phosphor of the present invention can be used for FED or high-definition CR.
It can be used for T, ELD, etc., and is effective for improving the performance of these displays.

[Brief description of the drawings]

FIG. 1 is a characteristic diagram showing an emission spectrum of ZnS: Tb.

FIG. 2 is a characteristic diagram showing an excitation spectrum of ZnS: Tb.

FIG. 3 is a characteristic diagram showing an emission spectrum when ZnS: Tb is excited by an electron beam.

FIG. 4 is a characteristic diagram showing a comparison between emission spectra of ZnS: Tb and ZnS: TbF ₃ .

FIG. 5 is a characteristic diagram showing an emission spectrum of ZnS: Eu.

FIG. 6 is a characteristic diagram showing an excitation spectrum of ZnS: Eu.

FIG. 7 is a characteristic diagram showing an emission spectrum of ZnS: Eu upon electron beam excitation.

FIG. 8 is a characteristic diagram showing a comparison between emission spectra of ZnS: Eu and ZnS: EuF ₃ .

Claims (6)

[Claims] 1. A phosphor comprising a nanostructure crystal having a particle size of 2 nm or more and 5 nm or less, comprising zinc sulfide activated by terbium charge-compensated by fluorine. 2. The phosphor according to claim 1, wherein the phosphor is activated by TbF ₃ . 3. A phosphor comprising zinc sulfide activated by europium charge-compensated by fluorine and a nanostructured crystal having a particle size of 2 nm or more and 5 nm or less. 4. The phosphor according to claim 1, wherein the phosphor is activated by EuF ₃ . 5. In a solvent, zinc acetate and sodium sulfide are mixed with terbium nitrate and sodium fluoride at a ratio such that terbium is 0.5 to 5 mol% and fluorine is 1.5 to 15 mol% based on zinc. A method for producing a phosphor, comprising mixing and performing a liquid phase reaction to co-precipitate a nanostructured crystal of zinc sulfide doped with terbium whose charge is compensated by fluorine. 6. A solvent in which zinc acetate and sodium sulfide are mixed with europium nitrate and sodium fluoride with 0.5 to 5 mol% of europium and 1.5 to 15 mol% of fluorine based on zinc.
A method for producing a phosphor, comprising mixing at a molar ratio to cause a liquid phase reaction, and coprecipitating terbium-doped zinc sulfide nanostructured crystals charge-compensated with fluorine.