JP5062592B2 - Zinc oxide nanoparticles for ultraviolet light emitters and solutions in which the nanoparticles are dispersed - Google Patents

Description

The present invention relates to zinc oxide nanoparticles for ultraviolet light emitters that can be applied to an ultraviolet light source, an ultraviolet laser, and the like, and a solution in which the nanoparticles are dispersed.

  Zinc oxide has been used as an ultraviolet absorbing material, a photocatalytic material, and a fluorescent material for a fluorescent tube. Among them, zinc oxide, which has been used as a phosphor for a long time, has been used as a phosphor emitting green light, and these powders are obtained by firing ZnO powder in a reducing atmosphere and adding excess Zn and oxygen in the zinc oxide lattice. It has been prepared by introducing defects (see Non-Patent Document 1).

Zinc oxide has a band gap energy of 3.3 eV and has an exciton binding energy as high as 60 meV at room temperature. Therefore, zinc oxide is expected as a material that emits short wavelength light in the ultraviolet region at room temperature. Such ultraviolet light-emitting elements have been developed because they can be used not only for ultraviolet light sources but also for high-density optical memories, bio-applications, and environmental applications.
In recent years, light emission in the ultraviolet region and laser oscillation have been observed from a zinc oxide thin film composed of hexagonal columns of nanometer order, which is prepared at room temperature by a laser MBE (Molecular Beam Epitaxy) method.

As a result, development of zinc oxide particles as an ultraviolet light source has been actively promoted. In the case of such zinc oxide particles for ultraviolet light emission, when the particle size is on the order of nanometers, a large number of defects usually exist on the particle surface, and green light emission in which electron levels based on these defects are involved. There has been a problem that the intensity of ultraviolet light emission based on the transition between bands decreases as the intensity increases.
For these reasons, in order to increase the intensity of ultraviolet light emission, there has been a demand for zinc oxide nanoparticles for ultraviolet light emission that completely eliminate green light emission involving defect levels and a method for producing the same.

As a conventional technique, for example, in a method of producing zinc oxide fine particles, a step of introducing basic carbon carbonate by introducing carbon dioxide gas into a water slurry containing raw material zinc oxide, and drying the basic zinc carbonate obtained thereby And a method of producing fine zinc oxide particles comprising a step of thermally decomposing the dried basic zinc carbonate while pulverizing it into zinc oxide (see Patent Document 1).
Further, a predetermined amount of the zinc-containing liquid having a pH of 11 to 13 at the end of mixing and a predetermined amount of the alkaline aqueous solution are mixed with stirring for 0.1 second to 600 seconds, and then in the mixed liquid There is a production method characterized by aging a zinc oxide fine powder (see Patent Document 2). Furthermore, there is a production method in which a zinc oxide crystal production reaction is performed by heating a mixture containing a carboxylic acid zinc salt and an alcohol (see Patent Document 3).

With respect to Patent Document 3, ultraviolet light emitting zinc oxide fine particles containing no alkali metal element and / or halogen element can be produced, and these particles have a peak top of the emission spectrum in the wavelength range of 0.4 to 0.6 μm. It is thought that it is effective because it is said that it can produce ultra-violet light emitting zinc oxide fine particles.
However, all of these conventional methods are chemical wet synthesis methods, and the process is multi-stage and very complicated, requiring precise pH control or heat treatment. In other words, there is no technology capable of producing zinc oxide nanoparticles for ultraviolet light emission that eliminates green light emission, which has high crystallinity and eliminates green light emission, in a very simple process without requiring heat treatment or the like. There was a problem of inefficiency.
Fluorescent Material Society, edited by Ohmsha 1987, phosphor handbook, 157 pages JP 2001-342021 A JP 2002-284527 A JP2003-268368

The object of the present invention is to solve the above-mentioned problems of the prior art, and to apply a zinc oxide nanoparticle for an ultraviolet light emitter that can be applied to an ultraviolet light source, an ultraviolet laser, or the like having a high crystallinity and disappearing green light emission by a very simple process. It is to provide a solution in which fine particles and the nano fine particles are dispersed.

As a result of diligent research to achieve the object of the present invention, a strong energy was applied to the surface of zinc metal in a surfactant aqueous solution having various ionic properties excluding an anionic surfactant, so that zinc was contained in the aqueous solution. By releasing them as atoms, ions, and clusters and reacting them in the presence of a surfactant and water, they can be obtained in a very simple process without the need for heat treatment of zinc oxide nanoparticles. Obtained knowledge. In particular, zinc oxide nanoparticles for ultraviolet light emission that completely eliminate green light emission when pulse laser ablation is performed by applying energy by focused irradiation of pulsed laser light in a zwitterionic surfactant aqueous solution to a zinc metal target and It has been found that the dispersion can be obtained with high efficiency.

The present invention is based on this finding.
1. An ultraviolet light emitter characterized in that zinc oxide nanoparticles formed by laser ablation of metallic zinc in an aqueous surfactant solution excluding an unheated anionic surfactant have an average particle diameter of 2 nm to 100 nm Crystalline zinc oxide nanoparticles for use or a solution in which the nanoparticles are dispersed.
2. 2. The crystalline zinc oxide nanoparticle for ultraviolet light emitters according to 1 above, wherein the zinc oxide nanoparticle has an average particle diameter of 2 nm to 15 nm, or a solution in which the nanoparticle is dispersed.

Furthermore, the present invention provides
3. 3. The crystalline zinc oxide nanoparticles for ultraviolet light emitters according to 1 or 2 above, wherein the purity of metallic zinc is 98% or more, or a solution in which the nanoparticles are dispersed.
4). 4. The crystalline zinc oxide nanoparticle for ultraviolet light emitters or the nanoparticle according to any one of 1 to 3 above, wherein the surfactant is a cationic, amphoteric or nonionic surfactant Is a dispersed solution.
5. Ultraviolet light emitting according to any one of the above 1 to 4, characterized in that a ^- surfactant alkylbetaines a zwitterionic surfactant ^{_{(C n H 2n + 1 N}} + (CH 3) 2 CH 2 COO) A crystalline zinc oxide nanoparticle for body use or a solution in which the nanoparticle is dispersed is provided.

  The present invention provides a zinc oxide nanoparticle for ultraviolet light emitters and a solution in which the nanoparticle is dispersed, which can be applied to an ultraviolet light source or an ultraviolet laser that has high crystallinity and eliminates green light emission. In the process, it has an excellent effect that zinc oxide nanoparticles for ultraviolet light emitters can be produced.

Next, the present invention will be described with reference to the drawings. FIG. 1 shows a device for producing zinc oxide nanoparticles and a dispersion thereof (vertical cell manufacturing device (FIG. 1-1) and horizontal cell manufacturing device (FIG. 1-2)). Using these devices, the laser beam is irradiated from the laser device 2 to the zinc metal plate target 7 inserted in the quartz glass cell 5 through the laser light reflecting mirror 3 and the condenser lens 4.
A zinc metal plate having a purity of 98% or more is used for the zinc metal plate target 7, and the zinc metal plate target 7 is fixed to the bottom or the shaft 10 of the quartz glass cell 5. An appropriate amount of a surfactant aqueous solution, for example, an amphoteric surfactant aqueous solution 8 is added to the quartz glass cell 5. Reference numeral 9 denotes a table, reference numeral 11 denotes a gear box, and reference numeral 12 denotes a target rotation driving motor.

Any surfactant other than anionic surfactants, such as cationic, amphoteric, and nonionic surfactants, can be used as long as there is no strong light absorption with respect to the wavelength of the laser beam used. Can be used to produce zinc oxide nanoparticles.
For example, cationic surfactants such as alkyltrimethylammonium chloride and alkyltrimethylammonium bromide, amphoteric surfactants such as alkylbetaine and amidebetaine, and nonionic surfactants such as polyoxyethylene alkyl ether and polyol. Examples thereof include oxyethylene alkyl allyl ether.

Among these surfactants, amphoteric surfactants are particularly suitable for producing zinc oxide nanoparticles. Among these, alkyl betaines ^{_{(C n H 2n + 1 N}} + (CH 3) 2 CH 2 COO -) is particularly effective. In addition, the number n of carbon atoms in the alkyl chain in the alkylbetaine is preferably 6 to 22, particularly preferably n = 12.
The concentration of the zwitterionic surfactant may be 0.0001 mol / L or more, preferably at least the critical micelle concentration at 25 ° C. of the surfactant, more preferably at least 5 times the critical micelle concentration. Below the saturation concentration.

The laser beam wavelength of the usable laser device only needs to have no strong absorption with respect to the surfactant to be used. Third harmonics (wavelength: 355 nm) can be used.
As the energy of the laser beam, it is sufficient that the target zinc metal is released in the form of atoms, ions, and clusters in an aqueous solution. When a pulse laser is used as an energy source, the laser ablation phenomenon of zinc metal appears. It is enough if there is enough energy.

As energy per pulse, 50 mJ / pulse or more is sufficient. The energy density of the laser beam on the target surface may be 1 J / cm ² or more, preferably ² J / cm ² .
The size of the zinc oxide nanoparticles obtained in this way is obtained with an average particle size of 2 nm to 100 nm, and fine zinc oxide nanoparticles with an average particle size of 2 nm to 15 nm can be obtained. In addition, the zinc oxide nanoparticle obtained in this way is a nanoparticle with high crystallinity, and it is one of the major features of the present invention that it is crystallized without being subjected to heat treatment. Thus, since a heat treatment process is not required, it has the remarkable effect that manufacture is easy.

Next, an actually manufactured example will be described. FIG. 2 shows the preparation and analysis procedure. Table 1 shows representative surfactant names, chemical formulas, ionic types, and critical micelle concentrations at 25 ° C. used.
Thereafter, cetyltrimeryl ammonium bromide, a cationic surfactant, CTAB, lauryl dimethylaminoacetic acid betaine, an amphoteric surfactant, LDA, and octaethylene glycol monodecyl, a nonionic surfactant. Ether is denoted as OGM.
Further, the surfactants used are not limited to those listed in the table, and it goes without saying that various cationic, amphoteric and nonionic surfactants can be used except for anionic surfactants. Absent.

A surfactant aqueous solution was prepared, and the surfactant concentration was changed in the range of 0.0001 mol / L to 0.1 mol / L so that the critical micelle concentration was within the range of the aqueous solution used. .
A zinc plate of 99.9% purity (size 20 mm × 20 mm, thickness 5 mm) was mounted on the apparatus of FIG. 1, and a repetition frequency of 10 Hz was used with the third harmonic (wavelength: 355 nm) of a pulsed Nd: YAG laser. .
After adjusting the lens position so that the laser beam spot size on the target has a diameter of 1.4 mm with a pulse energy of 100 mJ / pulse, the target is rotated in the surfactant aqueous solution via the target rotation drive motor. The pulse laser beam was irradiated for 1 hour.

As a result, zinc is released into the aqueous solution as atoms, ions, and clusters, and immediately reacts in the presence of the surfactant and water to form crystalline zinc oxide nanoparticles in the aqueous solution. It was obtained very easily without the need for heat treatment and other steps.
The solution in which the obtained zinc oxide nanoparticles were dispersed was measured for the fluorescence spectrum as it was without any special treatment. Further, the obtained solid was washed after centrifugation, and washing and centrifugation were repeated several times to collect zinc oxide nanoparticles.
The obtained zinc oxide nanoparticles were dried at room temperature in dry air, and then subjected to structural analysis by X-ray diffraction analysis and scanning electron microscope observation.

FIG. 3 shows the X-ray diffraction patterns of the zinc oxide nanoparticles prepared in the aqueous solutions having the critical micelle concentrations and the ion-exchanged water of the surfactants shown in Table 1.
As shown in FIG. 3, a diffraction line based on zinc oxide was observed in any sample, and it was found that zinc oxide was formed.
FIG. 4 shows scanning electron micrographs of the zinc oxide nanoparticles prepared in the aqueous solutions having the critical micelle concentrations and the ion-exchanged water of the surfactants shown in Table 1. The particle size of the zinc oxide nanoparticle prepared in the LDA aqueous solution which is an amphoteric surfactant was the smallest and was in the range of 2 nm to 15 nm.

Thus, it became clear that the particle size of the zinc oxide fine particles prepared in an aqueous solution having a concentration equal to or higher than the critical micelle concentration at 25 ° C. of the amphoteric surfactant was smaller than that of other surfactants.
FIG. 5 shows the fluorescence spectrum of an aqueous solution in which zinc oxide nanoparticles prepared in an LDA aqueous solution having a concentration of 0.01 mol / L and ion-exchanged water are dispersed.
Here, 340 nm light was used as excitation light. It has been confirmed that there is no light emission from only the aqueous surfactant solution and ion-exchanged water, and all light emission is fluorescence emission from the zinc oxide nanoparticles contained in the dispersion of zinc oxide nanoparticles.

In the fluorescence spectra of the dispersions of zinc oxide nanoparticles prepared using various aqueous surfactant solutions excluding ion-exchanged water and anionic surfactants, the following characteristic peaks were observed.
1) an emission peak of ultraviolet light at 363 nm, 2) a Raman scattering peak from water molecules as a solvent observed at 385 nm, and 3) at least three peaks of a broad green light fluorescence peak having a peak at 540 nm.

The emission peak intensity of ultraviolet light at 363 nm and the fluorescence peak intensity of broad green light having a peak at 540 nm are strongly influenced by the type and concentration of the surfactant, and the absolute intensity is also influenced by the amount of zinc oxide particles. receive.
Therefore, these peak intensities are normalized by the amount of zinc oxide contained in the zinc oxide nanoparticles, and the ultraviolet light emission intensity at 363 nm and the green light emission intensity at 540 nm are plotted against the type and concentration of the surfactant. It was.

FIG. 6 shows the result. In the case of LDA which is an amphoteric surfactant, the green light emission intensity decreases and the ultraviolet light emission intensity increases as the concentration increases, and when the LDA concentration reaches 0.01 mol / L, The emission of green light disappeared, and only ultraviolet light was emitted.
This phenomenon was observed at a surfactant concentration of 0.01 mol / L or more, and the same phenomenon was observed with other amphoteric surfactants.

  Thus, when a metal zinc plate is laser ablated in an aqueous solution of a zwitterionic surfactant as a surfactant, 2-15 nm crystalline zinc oxide nanoparticles can be prepared very easily without the need for a heat treatment step or the like. If an aqueous solution having a concentration equal to or higher than the critical micelle concentration is used, the intensity of green fluorescence emitted from the fine particles can be reduced. Furthermore, it was revealed that zinc oxide nanoparticles for ultraviolet light emission without green fluorescence can be prepared by using a surfactant aqueous solution having a critical micelle concentration of 5 times or more.

As described above, by using liquid phase laser ablation in a cationic, amphoteric or nonionic surfactant aqueous solution, particularly in an aqueous solution of a zwitterionic surfactant, ultraviolet light without green light emission Zinc oxide nanoparticles for light emission can be produced and prepared in a very simple process. Such zinc oxide nanoparticles can emit ultraviolet short-wavelength light at room temperature, and can be used not only for ultraviolet light sources but also for high-density optical memory, biotechnology, and environmental applications.
Similarly, a solution in which zinc oxide nanoparticles obtained after ablation are dispersed can be applied to an ultraviolet light source, but it is extremely easy to apply to biomarkers such as intracellular markers using interactions with biomolecules. It can be used.
Furthermore, the dispersed solution can be used as a raw material for a nanocomposite material with a coating agent or a polymer, and its industrial application range is expected to be extremely wide.

It is a schematic explanatory drawing of the manufacturing apparatus of a zinc oxide nanoparticle and its dispersion solution (1-1 is a manufacturing apparatus of a vertical cell system, 1-2 is a manufacturing apparatus of a horizontal cell system). It is a figure which shows the preparation and analysis process of a zinc oxide nanoparticle. It is a figure which shows the X-ray-diffraction pattern of a zinc oxide nanoparticle. It is a figure which shows the scanning electron micrograph of a zinc oxide nanoparticle. It is a figure which shows the fluorescence spectrum of the aqueous solution in which the zinc oxide nanoparticle prepared in the LDA aqueous solution of the density | concentration of 0.01 mol / L was disperse | distributed. It is a figure which shows the change of the ultraviolet light emission intensity of 363 nm and the green light emission intensity of 540 nm when the kind and density | concentration of surfactant change.

Explanation of symbols

1-1 Vertical Cell System Manufacturing Device 1-2 Horizontal Cell System Manufacturing Device 2 Laser Device 3 Laser Light Reflecting Mirror 4 Condensing Lens 5 Quartz Glass Cell 6 Laser Light 7 Zinc Metal Plate Target 8 Surfactant Aqueous Solution 9 Unit 10 Axis 11 Gearbox 12 Target rotation drive motor

Claims (5)

An ultraviolet light emitter characterized in that zinc oxide nanoparticles formed by laser ablation of metallic zinc in an aqueous surfactant solution excluding an unheated anionic surfactant have an average particle diameter of 2 nm to 100 nm Crystalline zinc oxide nanoparticles for use or a solution in which the nanoparticles are dispersed.   The crystalline zinc oxide nanoparticles for ultraviolet light emitters or a solution in which the nanoparticles are dispersed, wherein the zinc oxide nanoparticles have an average particle diameter of 2 nm to 15 nm.   The crystalline zinc oxide nanoparticles for ultraviolet light emitters or a solution in which the nanoparticles are dispersed according to claim 1 or 2, wherein the purity of metallic zinc is 98% or more.   The crystalline zinc oxide nanoparticle for ultraviolet light emitters according to any one of claims 1 to 3, wherein the surfactant is a cationic, amphoteric or nonionic surfactant. A solution in which fine particles are dispersed. UV according to any one of claims 1 to 4, characterized in that a ^- surfactant alkylbetaines a zwitterionic surfactant ^{_{(C n H 2n + 1 N}} + (CH 3) 2 CH 2 COO) Crystalline zinc oxide nanoparticles for luminous bodies or a solution in which the nanoparticles are dispersed.