JP5810442B2 - Layered cerium compound phosphor and method for producing the same - Google Patents

Description

The present invention relates to a phosphor exhibiting ultraviolet emission with high quantum yield, a layered organic-inorganic hybrid phosphor in which a dodecyl sulfate anion layer is inserted between Ce (OH) _x layers, and a dodecyl sulfate anion layer is CeO. _{The present} invention relates to a layered organic-inorganic hybrid phosphor inserted between _2-y layers and a method for producing the same.

  Phosphors that emit ultraviolet light are mainly used for sterilization and deodorization, and are also used in devices such as LEDs by combining with phosphors that emit light in the visible region.

For such phosphors, luminous efficiency is one of the most important characteristics. However, there are very few solid organic phosphor materials that exhibit ultraviolet light emission with a high quantum yield of, for example, about 90%.
In the field of ultraviolet light-emitting EL devices, nitride phosphors such as GaN are mainly used. However, in order to produce a nitride thin film, it is necessary to react at a high temperature and to control the reaction atmosphere, and the synthesis thereof has a disadvantage that the cost is generally high. In addition, there is a restriction that a substrate that can withstand high-temperature processing must be selected.

  On the other hand, a liquid phase synthesis method using sodium dodecyl sulfate is known as a method for forming a metal oxide or metal hydroxide nanosheet. The present inventors disclosed in Chemical Communication 2010, 46, 877-879 (Non-Patent Document 1) a liquid phase synthesis method of a layered compound comprising europium oxide or europium hydroxide and dodecyl sulfate anion, and Chemistry of Materials. 2010, 22, 3158-3164 (Non-patent Document 2) discloses a liquid phase synthesis method of a layered compound composed of zinc oxide or zinc hydroxide and dodecyl sulfate anion.

  Further, Fogg et al., In Chemistry of Materials 2008, 20, 335-340 (Non-patent Document 3) discloses a method for synthesizing a layered body using lanthanum hydroxide.

  However, none of the oxide and hydroxide layered compounds formed by these synthesis methods exhibited ultraviolet light emission with a high quantum yield.

Matsumoto et al., Chemical Communication 2010, 46, 877-879. Matsumoto et al., Chemistry of Materials 2010, 22, 3158-3164 Fogg et al., Chemistry of Materials 2008, 20, 335-340

  There is a demand for the development of a phosphor that can be synthesized by a simple process and exhibits ultraviolet emission with a high quantum yield.

The present invention relates to a phosphor exhibiting ultraviolet emission with high quantum yield, a layered organic-inorganic hybrid phosphor in which a dodecyl sulfate anion layer is inserted between Ce (OH) _x layers, and a dodecyl sulfate anion layer is CeO. A layered organic-inorganic hybrid phosphor inserted between _2-y layers and a synthesis method thereof are provided.

The phosphor of the present invention has a layered structure in which dodecyl sulfate anion layers and Ce (OH) _x layers or CeO _2-y layers are alternately stacked. In the Ce (OH) _x layer, x is x = 2 to 3, and in the CeO _2-y layer, y is y = 0 to 0.5.

In the phosphor of the present invention, the dodecyl sulfate anion layer is a bimolecular layer of dodecyl sulfate anion, and a sulfate group having a negative charge is made to face the surface of the Ce (OH) _x layer or CeO _2-y layer. A vesicle is formed.

In the phosphor of the present invention, the dodecyl sulfate anion has a length of 1.9 nm per molecule in the extending direction of the carbon chain, and the thickness of the dodecyl sulfate anion layer is 1.9 to 2.5 nm.
In the phosphor of the present invention, the CeO _2-y layer has a thickness of 1 nm to ₂ nm, and the Ce (OH) _x layer has a thickness of 1 nm to 3 nm.

The phosphor of the present invention is a plate-like body having a surface area constituting each layer of the layered structure of about 1 to 1000 μm ^2. On the other hand, the film thickness in the stacking direction of the layered structure is 50 regardless of the area of each layer. About 100 nm.

The phosphor of the present invention has a peak wavelength of light emission in the ultraviolet region in the range of about 320 to 380 nm and a high quantum yield of about 60% to 90%.
Hereinafter, a method for obtaining the phosphor of the present invention will be described.

First, a method for synthesizing a layered organic-inorganic hybrid phosphor in which a dodecyl sulfate anion layer is inserted between Ce (OH) _x layers will be described.
First, a cerium nitrate aqueous solution is added to an aqueous solution of sodium dodecyl sulfate to form a precipitate. It is preferable to add 5 to 20 ml of 0.5 mol / l cerium nitrate aqueous solution to 5 to 20 ml of 0.01 mol / l to 0.1 mol / l aqueous sodium dodecyl sulfate. By adding an aqueous solution of cerium nitrate to an aqueous solution of sodium dodecyl sulfate, a precipitate is immediately formed. Therefore, the solid precipitate is separated by centrifugation. Centrifugation is preferably performed at 3000 rpm for about 10 minutes.

Finally, the solid precipitate is washed and vacuum dried at a temperature of 0 to 100 ° C. to obtain a layered organic-inorganic hybrid phosphor in which a dodecyl sulfate anion layer is inserted between Ce (OH) _x layers.

Next, a method for synthesizing a layered organic-inorganic hybrid phosphor in which a dodecyl sulfate anion layer is inserted between CeO _2-y layers will be described.
First, an aqueous cerium nitrate solution is added to an aqueous solution containing sodium dodecyl sulfate and a base for oxidizing cerium to form a precipitate. 5 to 20 ml of 0.5 mol / l cerium nitrate aqueous solution is added to 5 to 20 ml of 0.01 mol / l to 0.1 mol / l sodium dodecyl sulfate aqueous solution to which a base has been added.

  As the base for oxidizing cerium, various bases such as Na (OH), K (OH), and ammonia can be used, but hexamethylenediamine (HMDA) or hexamethylenetetramine (HMTA) is preferable. Most preferred is hexamethylenetetramine. When the base is mixed, it is necessary to adjust the amount of the base so that the pH of the aqueous solution is in the range of 7 to 14, preferably 8 to 9. When HMTA is used as the base, sodium dodecyl sulfate is used. 1-5 ml of 2 mol / l HMTA aqueous solution is added to the aqueous solution.

  By adding an aqueous solution of cerium nitrate to an aqueous solution containing sodium dodecyl sulfate and a base, a precipitate is immediately formed. The aqueous solution in which the precipitate is formed is heated to a certain reaction temperature and maintained at the reaction temperature for a certain time. At this time, the reaction temperature for synthesizing the phosphor is preferably 40 ° C to 100 ° C, and more preferably 80 to 90 ° C. When the reaction temperature exceeds 90 ° C., the layered structure of the resulting phosphor is destroyed, and the light emission characteristics deteriorate, which is not preferable. The time for maintaining the aqueous solution at the reaction temperature is preferably 1 to 24 hours.

The aqueous solution is then centrifuged to separate the solid precipitate.
Finally, the solid precipitate is washed and vacuum dried to obtain a layered organic-inorganic hybrid phosphor in which a dodecyl sulfate anion layer is inserted between CeO _2-y layers.

INDUSTRIAL APPLICABILITY According to the present invention, a novel phosphor exhibiting ultraviolet emission with a high quantum yield and a simple and less toxic aqueous solution process for synthesizing the novel phosphor are provided.
The method of the present invention provides a novel layered compound phosphor having an extremely high quantum yield of 90% to 60%.

Since the phosphor obtained by the method of the present invention is a plate-shaped body having a surface area constituting each layer of the layered structure having a size of about 1 to 1000 μm ² , the phosphor of the present invention is spin coated on the substrate. By applying by a low temperature wet process such as dip coating, a relatively dense and smooth phosphor film can be formed on the substrate. Therefore, a heat-sensitive material such as a polymer or paper can be used as a substrate, and it is expected to be applied to an organic EL element.

FIG. 1 shows the X-ray diffraction results of Example 1 and Example 2 of the present invention together with the X-ray diffraction results of CeO nanoparticles as a comparative example. FIG. 2 shows a TEM photograph of the resultant product of Example 1. FIG. 3 shows the results of UV-visible absorption and photoluminescence spectroscopy of Examples 1 and 2 of the present invention. FIG. 4 shows SEM photographs of the results of Example 1 and Example 2 of the present invention. FIG. 5: shows the result of the X-ray photoelectron spectroscopy (XPS) of the result in Example 1 of this invention with the result of the CeO nanoparticle as a comparative example. FIG. 6 shows the results of thermogravimetry (TG) of the resultant product in Example 2 of the present invention.

  Examples of the present invention are specifically shown below, but the present invention is not limited thereto.

<CeO _2-y / Synthesis of Dodecyl Sulfate (DS) Anion Layered Compound (1)>
Under atmospheric pressure and atmospheric pressure, in a 50 ml beaker, 10 ml of 0.1 mol / l sodium dodecyl sulfate (SDS: CH ₃ (CH ₂ ) ₁₁ SO ₄ Na) aqueous solution (solvent: distilled water) and 2 mol / l hexa 1 ml of an aqueous solution of methylenetetramine (HMTA) was added, and 20 ml of an aqueous solution of 0.5 mol / l cerium nitrate (CeNO ₃ ) was added. Since a precipitate was formed as soon as it was added, the precipitate was dissolved by thoroughly stirring using a magnetic stirrer (manufactured by AS ONE: RS-6DR).

Next, this aqueous solution was heated to 80 ° C. using a hot water bath (manufactured by SANSYO: SSB-103) and maintained at 80 ° C. as it was overnight.
Next, the aqueous solution was cooled to room temperature to form a precipitate, and then the precipitate was separated using a centrifuge (manufactured by Kubota: 2410). The precipitate was thoroughly washed with distilled water and ethanol, and vacuum-dried at room temperature for 24 hours using a vacuum dryer (manufactured by AS ONE: AVO-200NS).

  The obtained product was subjected to X-ray diffraction (XRD) (manufactured by RIGAKU: INT-2500VHF), X-ray photoelectron spectroscopy (XPS) (manufactured by Sigma Probe: Thermo Scientific), transmission electron microscope (TEM) (manufactured by Hitachi, HF) -2000), Raman spectroscopy (Raman) (manufactured by Jasco: NRS-3100), and scanning electron microscope (SEM) (manufactured by Hitachi: SU-8000).

FIG. 1 shows the XRD pattern of the resulting product. On the low angle side, a sharp peak corresponding to the (00 l) reflection of the layered compound was present, while a peak corresponding to the CeO _2−x layer was hardly observed. This is considered to indicate that the CeO _2-y layer is a very thin layer of about 1 to 3 molecules. The interlayer distance of the resultant product calculated from the (001) peak, that is, the thickness of the layer including one CeO _2-y layer and one dodecyl sulfate anion layer was 3.3 nm.

The result of Raman spectroscopy of the obtained CeO _2-y / DS layered compound shows a peak corresponding to the F _2g band at 470 cm ⁻¹ , suggesting that a CeO _2-y layer is formed.
From the results of TEM observation, it was found that the CeO _2-y layer had a cubic fluorite structure in the obtained CeO _2-y / DS anion layered compound. Moreover, the obtained CeO _2-y / DS layered compound is a layered structure having a flat plate-like shape, and the average major axis in the direction parallel to the surface constituting each layer is 20 μm to 100 μm. The minor axis was 1 μm to 10 μm.

FIG. 2 shows a high-resolution TEM image of the resultant product. It can be seen that a layered structure in which CeO _2-y layers and dodecyl sulfate anion layers are alternately laminated is formed. The thickness of the CeO _2-y layer is about 1 to ₂ nm, and the thickness of the dodecyl sulfate anion layer is estimated to be about 1.9 to 2.5 nm. From this, as shown in the schematic diagram at the lower right of FIG. 2, the dodecyl sulfate anion forms a bimolecular layer with a part of it overlapping, and the sulfate group having a negative charge is converted to CeO _2-y. It is considered that the vesicle is formed so as to face the surface of the layer.

FIG. 3 shows an excitation spectrum and an emission spectrum of the obtained CeO _2-y / DS layered compound. The layered compound has an emission peak wavelength at 380 nm, which is in the ultraviolet or near ultraviolet region. When the ratio between the number of photons emitted and the number of photons absorbed in the excitation light is defined as the quantum yield, it can be seen that the layered compound exhibits a very high emission quantum yield of about 60% at an excitation wavelength of 275 nm. The light emission characteristics of the CeO _2-y / DS layered compound of the present invention are obtained by ionic bonding of Ce ³⁺ ions and dodecyl sulfate anions present on the surface of CeO _2-y . Since the CeO _2-y / DS anionic layered compound of the present invention has a thin layer structure, it is possible to form an interface between Ce ³⁺ and dodecylsulfuric acid at a higher density than the particulate compound. As a result, a high quantum yield is obtained. One of the reasons why the CeO _2-y / DS layered compound of the present invention having a thin layer structure can form an interface between Ce ³⁺ and dodecyl sulfate at a higher density than in the case of particles is the layered structure. This is considered to be because Ce ³⁺ adsorbed with dodecylsulfuric acid in the process of forming the structure is not easily oxidized and remains as Ce ³⁺ without being oxidized by the base. On the other hand, in the case of CeO nanoparticles, for example, the relative density of Ce ³⁺ ions present in CeO _{2-y with} respect to Ce ⁴⁺ ions is low, and the amount of dodecyl sulfate to be bound is small. Thus, sufficient light emission cannot be obtained.

In FIG. 4, the SEM observation result of the obtained CeO2 _-y / DS layered compound is shown. It can be seen that the obtained CeO2 _-y / DS layered compound is a plate-like body having a thickness of submicron (about 50 nm-100 nm) and a width of about 1-5 μm.

In FIG. 5, the XPS observation result of the obtained CeO2 _-y / DS layered compound is shown. These peaks shown in the range of 870-930 eV correspond to the 3d electron orbit of Ce. Calculating the molar ratio of ^{Ce 3+} and ^{Ce 4+} from the peak, it was found ^{that the Ce 3+} and ^{Ce 4+} are present in a ratio of 1: 1. From this, when it is considered that the charges of Ce ³⁺ and Ce ⁴⁺ and O ²⁻ are balanced as a whole, in the CeO _2-y layer, 2-y is a value of 1.75, that is, y is 0.25. It turns out that it is the value of.

<Synthesis of Ce (OH) _x / dodecylsulfuric acid (DS) anionic layered compound>
10 ml of 0.1 mol / l aqueous sodium dodecyl sulfate (SDS: CH ₃ (CH ₂ ) ₁₁ SO ₄ Na) (solvent: distilled water) was placed in a 50 ml beaker under atmospheric pressure at atmospheric pressure, and 0.5 mol / l 1 ml of an aqueous cerium nitrate (CeNO ₃ ) solution was added. Since a precipitate was formed as soon as it was added, the precipitate was dissolved by thoroughly stirring using a magnetic stirrer (manufactured by AS ONE: RS-6DR).

  Next, the dissolved precipitate was again settled and separated using a centrifuge (manufactured by Kubota: 2410). The precipitate was thoroughly washed with distilled water and ethanol, and vacuum-dried at room temperature for 24 hours using a vacuum dryer (manufactured by AS ONE: AVO-200NS).

FIG. 1 shows the XRD pattern of the resulting product. As in the case of the CeO _2-y / DS anion layered compound (Example 1), a sharp peak corresponding to the (00 l) reflection of the layered compound exists on the low angle side, and the peak corresponding to the Ce (OH) _x layer Was hardly observed. The interlayer distance of the resultant product calculated from this (001) peak is 3.74 nm, and it can be seen that the interlayer distance is slightly longer than 3.3 nm of CeO2 _-y / DS layered compound (Example 1). As in Example 1, a layered compound obtained by laminating Ce (OH) _x / dodecylsulfuric acid (DS) anions was obtained.

FIG. 3 shows an excitation spectrum and an emission spectrum of the obtained Ce (OH) _x / DS layered compound. It can be seen that the layered compound has an emission peak wavelength at 320 nm and an emission quantum yield of about 90% at an excitation wavelength of 290 nm.

As is clear from the above, when a layered cerium compound phosphor is synthesized by the synthesis method of the present invention, the layered cerium compound phosphor has a peak wavelength of light emission in the range of 320 to 380 nm and an extremely high quantum yield of 60% to 90%. Compound phosphors can be synthesized. This is due to the d → f transition of Ce ³⁺ 5d orbital electrons. Normally, when oxygen or a hydroxyl group is present on the cerium surface, the excited electrons of cerium are thermally relaxed, but the dodecyl sulfate anion is adsorbed on the cerium surface, so that the excited electrons of cerium follow the emission relaxation process, and quantum The yield is thought to increase.

Claims (9)

A dodecyl sulfate anion layer consisting of a bimolecular layer of dodecyl sulfate anion and a thickness of the bimolecular layer of 1.9 to 2.5 nm, and CeO _2-y (y represents a value of 0 to 0.5) A layered cerium compound phosphor having a layered structure in which layers are alternately stacked.   The layered cerium compound phosphor according to claim 1, wherein the layered cerium compound phosphor exhibits an emission quantum yield of 60% at an excitation wavelength of 275 nm and has an emission wavelength peak at 380 nm. A dodecyl sulfate anion layer comprising a bimolecular layer of dodecyl sulfate anion and a thickness of the bimolecular layer of 1.9 to 2.5 nm, and a Ce (OH) _x (x represents a value of 2 to 3) layer A layered cerium compound phosphor having a layered structure in which and are alternately stacked.   The layered cerium compound phosphor according to claim 3, which exhibits a light emission quantum yield of 90% at an excitation wavelength of 290 nm and has a peak of the light emission wavelength at 320 nm. The layered cerium compound phosphor according to claim 1, wherein the CeO _2-y layer has a thickness of 1 to 2 nm. The layered cerium compound phosphor according to claim 3, wherein the Ce (OH) _x layer has a thickness of 1 to 3 nm. Adding 5 to 20 ml of an aqueous solution of 0.5 mol / l cerium nitrate to 5 to 20 ml of 0.01 to 0.1 mol / l aqueous sodium dodecyl sulfate solution to form a precipitate, and precipitation in the aqueous solution Collecting things,
A dodecyl sulfate anion layer having a thickness of 1.9 to 2.5 nm and a Ce (OH) _x layer alternately laminated. A method for producing a cerium compound phosphor. Adding a base to 5-20 ml of 0.01-0.1 mol / l sodium dodecyl sulfate aqueous solution and adding 5-20 ml of 0.5 mol / l aqueous solution of cerium nitrate to produce a precipitate;
Heating the aqueous solution in which the precipitate is dissolved to a temperature of 40 to 100 ° C., maintaining the temperature at the temperature for 1 to 24 hours, and precipitating again; and
Collecting the precipitate in the aqueous solution,
A layered cerium comprising a dodecyl sulfate anion layer having a thickness of 1.9 to 2.5 nm and a CeO _2-y layer alternately laminated. A method for producing a compound phosphor. The method for producing a layered cerium compound phosphor according to claim 8 , wherein the base is an aqueous solution containing hexamethylenediamine or hexamethylenetetramine at a concentration of 2 mol / l, and the addition amount thereof is 1 to 5 ml.