JP2012136567A - Phosphor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a new phosphor that has a relatively long emission life and yet a relatively high luminous efficiency.SOLUTION: The phosphor is provided with a substrate comprising a monolayered or multilayered graphene nanosheet, and a covering material covering the surface of the substrate. Preferably, the substrate has an average thickness of at least 0.3 nm and at most 50 nm and an average size of at least 1 nm and at most 1,000 nm. The substrate may further contain nitrogen. The phosphor is obtained by dispersing or dissolving the substrate and the covering material in a polar solvent and causing the polar solvent to volatilize.

Description

  The present invention relates to a light emitter, and more particularly to a novel light emitter that can be used for a probe, a light emitting element, an LED, a display, a fluorescent tag, and the like for detecting a biochemical reaction.

The light emitter in the present invention refers to a substance that emits light (fluorescence, phosphorescence) when electrons are excited by absorbing light of a specific wavelength and the excited electrons return to the ground state.
Among phosphors that emit fluorescence,
(1) An inorganic phosphor having an oxide, nitride, sulfide, or the like as a base material and doped with ions serving as a luminescent center;
(2) Organic phosphors such as rare earth complexes,
(3) Carbon phosphors such as carbon nanoparticles and graphene nanosheets,
Etc. are known.
Among these, carbon phosphors based on graphene have the characteristics of being excellent in electrical characteristics, thermal characteristics and mechanical characteristics, and being chemically stable.

Various proposals have been made regarding phosphors made of such graphene-based materials.
For example, in Non-Patent Document 1,
(1) As a starting material, micrometer-sized corrugated graphene nanosheets (GSs) obtained by thermal reduction of graphene oxide (GO) are used,
(2) By oxidizing GSs with high concentrations of H ₂ SO ₄ and HNO ₃ , oxygen-containing functional groups such as C═O / COOH, OH, and C—O—C are introduced on the edges and base surface. ,
(3) Hydrothermally treating the oxidized GSs at 200 ° C.,
(4) Graphene quantum dots (GQDs) obtained by filtering and dialyzing the obtained colloidal solution are disclosed.
In the same document,
(A) Deoxygenation occurs by hydrothermal treatment, and the (002) plane spacing of GQDs is close to that of bulk graphite.
(B) The size of GSs is remarkably reduced by hydrothermal treatment, and extremely fine GQDs (average diameter: 9.6 nm) can be separated by dialysis.
(C) Oxidized GSs do not exhibit photoluminescence (PL) behavior, whereas GQDs emit bright blue luminescence, even in neutral media,
(D) GQDs show a PL spectrum having a strong peak at 430 nm by excitation at 320 nm, and
(E) The PL quantum efficiency of GQDs is 6.9%, which is equivalent to luminescent carbon nanoparticles,
Is described.

Non-Patent Document 2 discloses a GO thin film reduced by hydrazine vapor.
In the same document,
(A) The PL characteristic of GO is derived from recombination of electron-hole (eh) pairs localized in small sp ² carbon clusters embedded in the sp ³ matrix,
(B) The absorbance of GO increases with hydrazine exposure time, consistent with the change in oxygen (from ~ 39 at% of the starting GO to 7-8 at% of the reduced GO),
(C) The PL peak position of the GO thin film is less changed by the reduction treatment, and has a center near 390 nm, and
(D) The PL strength of the GO thin film immediately after formation is weak, whereas exposure to hydrazine vapor for a short time results in a dramatic increase in PL strength,
Is described.

Further, Non-Patent Document 3 describes graphene quantum dots synthesized by solution chemistry, including 132 conjugated carbons, and three 2 ′, 4 ′, and 6 ′ that promote dissolution in three directions. -Disclosed by a trialkylphenyl group.
In the same document,
(A) The graphene is stable without aggregation in various organic solvents,
(B) When this graphene is dispersed in toluene and excited at 510 nm at room temperature, emission peaks appear at 670 nm and 740 nm,
(C) The emission at 740 nm is phosphorescence, and its time-dependent behavior is represented by a single exponential decay with a time constant of 4 μs at room temperature, and
(D) The emission at 670 nm is fluorescent and is compatible with bi-exponential decay with time constants of 5.4 ns and 1.7 ns,
Is described.

Carbon phosphors based on graphene nanosheets emit blue luminescence as described in Non-Patent Documents 1 and 2. In addition, some of the conventional phosphors containing harmful elements such as cadmium are known, but carbon phosphors do not require such harmful elements in order to obtain PL characteristics.
However, as described in Non-Patent Document 3, the carbon phosphor obtained by the conventional method has a very short emission lifetime. Further, as described in Non-Patent Document 1, the luminous efficiency of carbon phosphors reported so far is 6.9% at the maximum.

D. Pan et al., Adv. Mater. 2009, 21, 1-5 G.Eda et al., Adv.Mater. 2010, 22, 505-509 M.L.Mueller et al., Nano Lett. 2010, 10, 2679-2682

The problem to be solved by the present invention is to provide a novel light emitter that exhibits a relatively long light emission lifetime.
Another problem to be solved by the present invention is to provide a novel light emitter exhibiting relatively high light emission efficiency.

In order to solve the above problems, the light emitter according to the present invention is
A substrate comprising a single or multilayer graphene nanosheet;
And a covering material for covering the surface of the substrate.
The base material may further contain nitrogen.

When the surface of the base material including the graphene nanosheet is coated with a coating material, the light emission lifetime is increased. this is,
(1) Since the rotational movement and vibrational movement of the functional group in the coating material increase the spin-orbit interaction of the graphene nanosheet, and the intersystem crossing to the triplet state occurs, or
(2) The hydrogen bond formed between the coating material and the substrate suppresses quenching due to the reaction between the triplet state of the graphene nanosheet and dissolved oxygen,
it is conceivable that.
Further, when nitrogen is introduced into the graphene nanosheet, the light emission efficiency is further increased. This is presumably because the concentration of the emission center increases due to the introduction of nitrogen.

2 is an emission spectrum of the luminescent material synthesized in Example 1. FIG. 3 is a diagram showing a light emission lifetime of the light emitter synthesized in Example 1.

Hereinafter, an embodiment of the present invention will be described in detail.
[1. Luminous body]
The light emitter according to the present invention includes a base material and a covering material.
[1.1. Base material]
In the present invention, the “base material” refers to a material containing graphene nanosheets. The substrate may be composed only of graphene nanosheets, or may further contain nitrogen (nitrogen-containing graphene nanosheets). The substrate may be composed of only one kind of single-layer or multilayer graphene nanosheets, single-layer or multilayer nitrogen-containing graphene nanosheets, or may be a mixture of two or more kinds.

[1.1.1. Graphene nanosheet]
In the present invention, the “graphene nanosheet” has at least a part of a two-dimensional layered structure composed of carbon atoms. Further, the main part in the layer plane is a carbon ring structure and (sp ² bond). A) containing an aromatic ring and containing less than 0.5 wt% of nitrogen as an inevitable impurity.
In order to show the PL characteristics, graphene nanosheets are composed of fine clusters of carbon having sp ² type hybrid orbitals in an insulating matrix made of carbon having sp ³ type hybrid orbitals (sp ³ matrix). It is considered necessary to have a structure in which (sp ² clusters) are embedded. That is, in the graphene nanosheet exhibiting PL characteristics, the sp ² cluster is considered to function as a light emission center.

[1.1.2. Nitrogen-containing graphene nanosheet]
In the present invention, the “nitrogen-containing graphene nanosheet” refers to a graphene nanosheet in which nitrogen is intentionally introduced and the nitrogen content is 0.5 wt% or more.
"Nitrogen has been introduced"
(1) A part of carbon constituting the graphene nanosheet is substituted with nitrogen,
(2) a nitrogen-containing functional group is bonded to the edge and / or the base surface of the graphene nanosheet, or
(3) The nitrogen-containing compound is adsorbed on the surface of the graphene nanosheet or between the sheets,
Say.
Nitrogen introduced into the graphene nanosheet may exist in any one of substitution, bonding, and adsorption, or may exist in two or more forms.

In the present invention, the “nitrogen-containing functional group” refers to a functional group containing nitrogen as a constituent element. Examples of the nitrogen-containing functional group include an amino group, an imino group, an N-oxide group, an N-hydroxy group, a hydrazine group, a nitro group, a nitroso group, an azo group, a diazo group, and an azide group.
The nitrogen-containing graphene nanosheet may be bonded to any one of these nitrogen-containing functional groups, or may be bonded to two or more.

In the present invention, the “nitrogen-containing compound” refers to a compound containing nitrogen as a constituent element and capable of being dissolved or dispersed in water. Examples of nitrogen-containing compounds include:
(1) urea, ammonia, thiourea, hydrazine, nitrate ester, sodium nitrate, sodium nitrite, hydroxylamine, pyridine N-oxide, N-hydroxylalkylenimine, sodium azide, sodium amide, carboxylic acid azide,
(2) alkylamines such as methylamine, ethylamine, n-propylamine, isopropylamine, n-butylamine, tert-butylamine, n-pentylamine, n-hexylamine and their halogenated salts,
(3) Diamines such as ethylenediamine and propanediamine,
and so on.
The nitrogen-containing graphene nanosheet may be one in which any one of these nitrogen-containing compounds is adsorbed, or may be one in which two or more are adsorbed.

[1.1.3. Nitrogen content]
The nitrogen content contained in the substrate affects the light emission efficiency and the light emission wavelength.
In the present invention, the substrate does not necessarily contain nitrogen. However, as the nitrogen content increases, the light emission efficiency increases or the amount of change in the light emission wavelength increases. In order to obtain such an effect, the nitrogen content is preferably 0.5 wt% or more. The nitrogen content is more preferably 2 wt% or more, and further preferably 5 wt% or more.
On the other hand, if the nitrogen content is too high, the electronic state changes significantly and the PL characteristics cannot be obtained. Therefore, the nitrogen content is preferably 50 wt% or less. The nitrogen content is more preferably 20 wt% or less, and still more preferably 10 wt% or less.

[1.1.4. Average thickness]
The thickness of the substrate (that is, the number of laminated sheets) affects the light emission efficiency and the light emission wavelength.
Even if the substrate is a single-layer graphene nanosheet or a nitrogen-containing graphene nanosheet, it functions as a light emitter. The thickness of the monolayer (nitrogen-containing) graphene nanosheet is about 0.3 nm. That is, the average thickness of the substrate may be 0.3 nm or more. The average thickness is more preferably 1 nm or more, and further preferably 2 nm or more.

The greater the thickness of the substrate, the longer the emission wavelength. This is presumably because the π-π ^* energy gap is reduced by increasing the size of the sp ² cluster in the sheet stacking direction.
However, if the thickness of the substrate becomes too thick, the electronic structure approaches the bulk, and thus efficient light emission cannot be obtained. Therefore, the average thickness of the substrate is preferably 50 nm or less. The average thickness is more preferably 20 nm or less, and further preferably 10 nm or less.

Here, the “average thickness of the substrate” refers to an average value of the thicknesses of n (n ≧ 5) substrates selected at random.
As a method of measuring the thickness,
(1) A method of directly measuring the thickness of a sheet using an atomic force microscope (AFM),
(2) A method for obtaining a thickness in consideration of an ideal thickness (0.34 nm) from the number of layers of a sheet observed in a transmission electron microscope (TEM) photograph,
and so on. With either method, almost equivalent results are obtained.

[1.1.5. Average size]
The size of the substrate affects the light emission efficiency and the light emission wavelength.
In general, the smaller the substrate size, the greater the emission efficiency due to the quantum size effect, but the shorter the emission wavelength. In order to emit light in the visible light region, the average size of the substrate is preferably 1 nm or more. The average size is more preferably 2 nm or more, and further preferably 3 nm or more.
On the other hand, if the size of the substrate becomes too large, so-called “quenching” occurs in which the fluorescence emitted from the emission center is reabsorbed by the sheet, resulting in a decrease in luminous efficiency. Therefore, the average size of the substrate is preferably 1000 nm or less. The average size is more preferably 500 nm or less, and still more preferably 100 nm or less.

Here, the “average size of the base material” refers to an average value of the sizes of n (n ≧ 5) base materials selected at random.
The “base material size” refers to the major axis of the sheet plane (the length in the direction in which the length is maximum).

[1.2. Coating material]
The surface of the base material is coated with a coating material. The covering material may cover the entire surface of the substrate, or may cover a part of the surface of the substrate.
In the present invention, the “coating material” refers to a compound having a polar group and containing no π-conjugated bond. Graphene nanosheets are hydrophilic and disperse well in water. This also applies to the nitrogen-containing graphene nanosheet containing an appropriate amount of nitrogen. Since the covering material having a polar group and the hydrophilic sheet have an affinity for each other, when they are mixed in a polar solvent, they are easily combined and combined.

  The molecular weight of the coating material is not particularly limited, and may be any of a low molecular weight having a molecular weight of less than 1000, an oligomer having a molecular weight of 1,000 or more and less than 10,000, or a polymer having a molecular weight of 10,000 or more.

Specifically, as a covering material,
(1) epsilon caprolactam,
(2) Polyacrylic acid resin, cellulose resin, polyvinyl resin, polyurethane resin, methacrylic resin, polyester resin, silicone resin, polyethylene glycol, polyimide resin, polycarbonate, polyethylene oxide, polyamide resin,
(3) Silane, silane compound,
and so on.
Any one of these may be used as the covering material, or two or more may be used in combination.

[1.3. Amount of coating material]
The amount of the covering material affects the light emission lifetime.
In general, as the amount of the coating material increases, the light emission lifetime increases. On the other hand, the coating more than necessary with the coating material is saturated with no effect. The optimal amount of coating material is selected according to the type of substrate and the type of coating material. Usually, the amount of the covering material is 0.01 to 99.9 wt%.

[1.4. Luminous life]
The light emitter according to the present invention has a longer light emission lifetime than the conventional graphene-based phosphor. When the average thickness, average size, nitrogen content, etc. are optimized, the light emission lifetime is 10 ns or more, or 100 ns or more.
Here, “emission life”
(1) Wavelength: 320 nm light (excitation light) is irradiated on the sample,
(2) After blocking the excitation light irradiation, the afterglow intensity is 0.01% or less with respect to the emission intensity during the excitation light irradiation under the condition of the afterglow of wavelength: 430 nm and the measurement interval: 0.01 seconds. Measure to
(3) Coefficient when the relationship between the obtained time and the afterglow intensity is fitted with an exponential function (time to become 1 / e)
Say.

[1.5. Luminous efficiency]
The luminous body according to the present invention exhibits a luminous efficiency of 1% or more. When the average thickness, average size, nitrogen content, etc. of the substrate are optimized, the luminous efficiency is 7% or more, 10% or more, 15% or more, or 20% or more.
Here, “luminescence efficiency” refers to the ratio of the number of photons emitted as fluorescence to the number of absorbed photons.

[2. Method for producing nitrogen-containing graphene nanosheet]
Nitrogen-containing graphene nanosheets
Dispersing graphite oxide or graphene oxide in an aqueous solution in which a nitrogen-containing compound is dissolved (dispersing step),
The aqueous solution is heated at 60 ° C. or higher (heating step).
Can be manufactured.

[2.1. Dispersion process]
[2.1.1. Nitrogen-containing compounds]
“Nitrogen-containing compound” refers to a compound containing nitrogen as a constituent element and capable of being dissolved or dispersed in water. Since the specific example of a nitrogen-containing compound is as having mentioned above, description is abbreviate | omitted. As the starting material, any one of the nitrogen-containing compounds described above may be used, or two or more kinds may be used in combination.
Among these, urea is particularly suitable as a nitrogen-containing compound. This is because a peptide bond is easily formed with an oxygen functional group in graphite oxide or graphene oxide, and the reactivity is high.

  The nitrogen-containing compound is used in the state of an aqueous solution dissolved or dispersed in water. The concentration of the nitrogen-containing compound contained in the aqueous solution is not particularly limited, and an optimal concentration may be selected according to the type of starting material and required characteristics. The concentration of the nitrogen-containing compound is usually 0.1 to 10 mol / L.

[2.1.2. Graphite oxide and graphene oxide]
“Graphite oxide” means that an oxygen-containing functional group (for example, COOH-group, OH-group, —C—O—C-group, etc.) is bonded to the edge and / or basal plane of the graphene nanosheet constituting the graphite. Say what you are. Graphite oxide is obtained, for example, by oxidizing graphite using an oxidizing agent (potassium permanganate, potassium nitrate, etc.) in a strong acid (concentrated sulfuric acid).
“Graphene oxide” refers to a sheet-like substance obtained by peeling between layers of graphite oxide. The graphene oxide can be obtained, for example, by dispersing graphite oxide in an aqueous solution and irradiating with ultrasonic waves.
In the present invention, the starting material may be either graphite oxide before delamination or delaminated graphene oxide, or both.

  Graphite oxide and / or graphene oxide is added to an aqueous solution containing a nitrogen-containing compound. The amount of graphite oxide and / or graphene oxide contained in the aqueous solution is not particularly limited, and an optimal amount may be selected according to the type of starting material and required characteristics. The amount of graphite oxide and / or graphene oxide is usually 0.1 to 50 g / L.

[2.2. Heating process]
After dispersing graphite oxide and / or graphene oxide in an aqueous solution in which a nitrogen-containing compound is dispersed, the aqueous solution is heated. Heating is performed to increase the reaction rate. When the heating temperature exceeds the boiling point of the aqueous solution, the heating is performed in a sealed container.
If the heating temperature is too low, the reaction does not proceed sufficiently within a realistic time. Therefore, the heating temperature needs to be 60 ° C. or higher. The heating temperature is more preferably 70 ° C. or higher, more preferably 80 ° C. or higher.
On the other hand, if the heating temperature becomes too high, the substituted or bonded nitrogen may be desorbed. Further, an expensive pressure vessel is required, and the manufacturing cost increases. Therefore, the heating temperature is preferably 200 ° C. or less. The heating temperature is more preferably 180 ° C. or lower, and further preferably 160 ° C. or lower.

As the heating time, an optimum time is selected according to the heating temperature. In general, the higher the heating temperature, the shorter the reaction can proceed. The heating time is usually 1 to 20 hours.
When the heating conditions are optimized, the nitrogen content, average thickness, and average size of the nitrogen-containing graphene nanosheet can be controlled. In general, the higher the heating temperature and / or the longer the heating time, the lower the nitrogen content, the thinner the average thickness, or the smaller the average size.
The obtained nitrogen-containing graphene nanosheet may be used for various purposes as it is, or may be washed, filtered and / or dialyzed as necessary.

[3. Method for producing graphene nanosheet]
The graphene nanosheet can be produced by the same method as the nitrogen-containing graphene nanosheet except that water is used instead of the aqueous solution in which the nitrogen-containing compound is dissolved.

[4. Method for manufacturing illuminant]
The light emitter according to the present invention can be produced by dispersing or dissolving the base material and the coating material in a polar solvent and volatilizing the polar solvent.
The polar solvent should just be what can disperse | distribute or melt | dissolve a base material and a coating | covering material. Specific examples of the polar solvent include water, ethanol, methanol, butanol, and acetone. The volatilization conditions for the polar solvent are not particularly limited, and an optimum condition may be selected according to the type of the polar solvent.

[5. Action of luminous body]
Non-Patent Documents 1 to 3 describe phosphors based on graphene synthesized by various methods. However, as described in Non-Patent Document 3, the conventional phosphor has an extremely short light emission lifetime. Further, conventional phosphors have low luminous efficiency.

On the other hand, when the surface of the base material containing the graphene nanosheet is coated with a coating material, the light emission lifetime is remarkably increased. This is considered to be due to the following reason.
(1) When the base material surface is coated with a coating material having polarity, the rotational motion and vibration motion of the functional group in the coating material increase the spin-orbit interaction of the graphene nanosheet. As a result, intersystem crossing to the triplet state occurs, and the relaxation time of the excited electrons becomes long.
(2) When the substrate surface is coated with a coating material having polarity, hydrogen bonds are formed between the coating material and the substrate. This hydrogen bond extends the lifetime in order to suppress quenching due to the reaction between the triplet state of the graphene nanosheet and dissolved oxygen.

Further, when nitrogen is introduced into the graphene nanosheet, the light emission efficiency is further increased. This is considered to be due to the following reason.
That is, when graphite oxide and / or graphene oxide is dispersed in water and heated at a predetermined temperature, delamination of graphite oxide and nano-sizing of the exfoliated sheet-like graphene oxide occur. At the same time, a reduction reaction of an oxygen-containing functional group (for example, epoxide group) bonded to graphite oxide or graphene oxide occurs, and the concentration of sp ² clusters serving as a luminescence center increases.
At this time, when a nitrogen-containing compound is added to the aqueous solution, substitution, bonding and / or adsorption of nitrogen occurs simultaneously with the reduction of the oxygen-containing functional group bonded to the graphite oxide or graphene oxide. As a result, higher luminous efficiency can be obtained than when no nitrogen-containing compound is added. Further, the emission wavelength can be controlled relatively easily by controlling the nitrogen content, the thickness of the sheet, the number of laminated sheets, and the like.

The increase in luminous efficiency due to the introduction of nitrogen
(1) The carbon in the sp ³ matrix is substituted with nitrogen, so that the substitution region becomes a luminescent center similar to the sp ² cluster, and the concentration of the luminescent center increases, or
(2) Since the nitrogen-containing functional group is bonded to carbon in the sp ³ matrix, the bonding region becomes a luminescent center similar to the sp ² cluster region, and the concentration of the luminescent center increases.
it is conceivable that.
The emission wavelength is changed by the introduction of nitrogen because the carbon in the sp ² cluster is substituted with nitrogen, the nitrogen-containing functional group is bonded to the carbon in the sp ³ matrix, or the nitrogen-containing compound is in the vicinity of the sp ² cluster. This is thought to be due to the fact that the electrons move from the π ^* excited state, which is the electronically excited state of carbon, to the n ^* excited state of nitrogen, which has lower energy, due to the adsorption of.

Example 1
[1. Preparation of sample]
0.1 g of graphite oxide was dispersed in 5 mL of 0.2 mol / L urea aqueous solution. The obtained aqueous solution was heated in a sealed container at 150 ° C. for 10 hours. After heating, it was thoroughly washed to separate the nitrogen-containing graphene nanosheet.
Next, 10 mg of polyacrylic acid (coating material) was dissolved in 5 mL of an aqueous dispersion in which 0.1 mg of nitrogen-containing graphene nanosheets are dispersed. The obtained solution was dried to obtain a nitrogen-containing graphene nanosheet / polyacrylic acid composite.

[2. Test method]
[2.1. Emission spectrum]
The emission spectrum of the illuminant was measured using a spectrofluorometer (FP-6500, manufactured by JASCO Corporation).
[2.2. Luminous efficiency]
Luminous efficiency was measured using an absolute fluorescence quantum yield measuring device (C9920-02, manufactured by Hamamatsu Photonics Co., Ltd.).
[2.3. Luminous life]
Using a spectrofluorometer (FP-6500, manufactured by JASCO Corporation), the emission lifetime was measured at room temperature.

[3. result]
In FIG. 1, the emission spectrum of the light-emitting body obtained in Example 1 is shown. In the case of Example 1, the peak position of the spectrum was 424 nm, and the half width was 90 nm. In the case of Example 1, the luminous efficiency was 22%, which was a very high value compared to Non-Patent Document 1 (Table 1).
Further, FIG. 2 shows the light emission lifetime of the light-emitting body obtained in Example 1. In the case of Example 1, the light emission lifetime was 0.54 seconds (Table 1), which was found to be a very long value.

(Example 2)
[1. Preparation of sample]
A nitrogen-containing graphene nanosheet / carboxymethylcellulose composite was obtained in the same manner as in Example 1 except that carboxymethylcellulose was used as the coating material.
[2. Test method]
Under the same conditions as in Example 1, the emission spectrum, emission efficiency, and emission lifetime were measured.
[3. result]
Table 1 shows the results. In the case of Example 2, the peak position of the spectrum was 433 nm and the half width was 90 nm. Further, the luminous efficiency was 21%, which was a very high value as compared with Non-Patent Document 1. Furthermore, the light emission lifetime was 0.47 seconds, which was found to be a very long value.

Example 3
[1. Preparation of sample]
A nitrogen-containing graphene nanosheet / polyvinyl alcohol composite was obtained in the same manner as in Example 1 except that polyvinyl alcohol was used as the coating material.
[2. Test method]
Under the same conditions as in Example 1, the emission spectrum, emission efficiency, and emission lifetime were measured.
[3. result]
Table 1 shows the results. In the case of Example 3, the peak position of the spectrum was 430 nm, and the half width was 78 nm. Further, the luminous efficiency was 23%, which was a very high value compared with Non-Patent Document 1. Furthermore, it was found that the light emission lifetime was 0.38 seconds, which was a very long value.

(Comparative Example 1)
[1. Preparation of sample]
The nitrogen-containing graphene nanosheet obtained in Example 1 was used for the test as it was.
[2. Test method]
Under the same conditions as in Example 1, the emission spectrum, emission efficiency, and emission lifetime were measured.
[3. result]
Table 1 shows the results. In the case of Comparative Example 1, the peak position of the spectrum was 430 nm, and the half width was 67 nm. The luminous efficiency was 24%. However, it was found that the light emission lifetime was less than the analysis lower limit (0.01 seconds) of the measuring device.

  Although the embodiments of the present invention have been described in detail above, the present invention is not limited to the above embodiments, and various modifications can be made without departing from the scope of the present invention.

  The illuminant according to the present invention can be used in probes for detecting biochemical reactions, light emitting elements, LEDs, displays, fluorescent tags, and the like.

Claims (6)

A substrate comprising a single or multilayer graphene nanosheet;
A light-emitting body comprising a covering material that covers the surface of the substrate. The substrate is
The average thickness is 0.3 nm or more and 50 nm or less,
The light-emitting body according to claim 1, wherein the average size is 1 nm or more and 1000 nm or less.   The light emitter according to claim 1, wherein the base material further contains nitrogen.   The luminous body according to claim 3, wherein the luminous efficiency is 1% or more. The substrate is
The light emitter according to claim 3 or 4, which is obtained by dispersing graphite oxide and / or graphene oxide in an aqueous solution in which a nitrogen-containing compound is dissolved, and heating the aqueous solution at 60 ° C or higher.   The light emitting body according to any one of claims 1 to 5, wherein the coating material is made of any one or more selected from polyacrylic acid, carboxymethylcellulose, and polyvinyl alcohol.

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