JP2002507630A - Self-activating rare earth oxide nanoparticles - Google Patents

Abstract

(57) [Summary] A compound represented by the formula Z ₂ O ₃ : Z ^{X +} (where Z is a rare earth metal and x is 2 to 4), nanoparticles thereof, and a method for producing the same As well as its use.

Description

DETAILED DESCRIPTION OF THE INVENTION

TECHNICAL FIELD [0001] The present invention relates to rare earth activated phosphors. Such phosphors are known to have excellent light output and color rendering properties and have been successfully utilized in many display technologies. One in particular of successful materials, europium-activated yttrium oxide ^{_{(Y 2 O 3: Eu 3+}} ) is represents a particularly promising results in the field of field emission displays.

There is a need for low voltage phosphors for use in flat panel displays or FED type (charge emission) displays. Reducing the voltage reduces the cost of the drive power used to control image generation. This requires very small particle sizes on the order of a few nm. However, a reduction in the particle size of a phosphor such as europium-activated yttrium oxide results in reduced luminous efficiency. This is caused by radiationless recombination via surface defect states.
However, if certain steps are taken during the preparation of the particles, this surface state can be passivated, thereby producing efficient phosphor nanoparticle dimensions.
However, the specific steps required to prepare ordinary phosphor nanoparticles (ie, ≦ 100 nm), such as europium-activated yttrium oxide, are complicated due to the high manufacturing costs. . It is also difficult to produce such particles on a significant scale.

[0003] Therefore, there is a need for a method of producing a phosphor in the form of nanoparticles that avoids this production difficulty. Surprisingly, it has been found that according to the present invention, a new class of rare earth oxide nanoparticles is easily obtained. In this, the active ions are active ions of the same element as the oxide. Accordingly, the present invention has the formula ^{_{Z 2 O 3: Z X +}} ( wherein, Z is a rare earth element, x is 2-4, generally a 3.) To provide a compound represented by.

[0004] Preferred rare earth elements / metals include terbium, europium and cerium.

Preferably, the phosphor is in the form of nanoparticles, in particular 2-10 nm, especially 5n
m (for example, about 4 nm).

[0006] The phosphor of the present invention can be easily manufactured by a simple precipitation method. In this method, an alkali is added to a solution of a rare earth metal salt, especially a chloride, in the presence of a metal complex surfactant molecule.

As mentioned above, the preferred salt is chloride, and the presence of chloride enhances display technology, but also luminescent nanoparticles that are completely free of chlorine from soluble salts (eg, from nitrates). It can be manufactured.

[0008] Surfactant molecules bind and activate rare earth ions and passivate a surface state that can undergo non-radiative recombination. That is, it has a surface capping effect. This binding activity is also beneficial to the optical properties as it reduces the likelihood of recombination via surface dangling bond states. Suitable surface-active molecules which can be used preferably also include trioctylphosphine oxide (TOPO), as well as sodium hexametaphosphate, crown ethers and amines. Generally, it is better to use pure organic molecules that do not contain metals.

[0009] The nature of the alkali used is not particularly important as long as it is soluble in the solvent used. Typical alkalis include ammonium hydroxide and sodium hydroxide.

[0010] Typically, this method involves combining the salt and the surface-active molecule in a common solvent, eg, about 15
This is done by mixing for one minute and then adding the alkali to the solvent to form a colloidal precipitate over several minutes.

[0011] The two solvents must be, but need not be, compatible with each other to form a single phase. In general, it is desirable to use slightly reducing or dehydrating solvents, such as thiols and alcohols (which must, of course, be able to dissolve the salt), glycols (eg, ethylene glycol) and aliphatic alcohols (ethanol, Propanol, and very preferably methanol).

This method is preferred to be performed with little or no water, since it facilitates the formation of hydroxides. The pH should generally be between 5 and 9 (measured in methanol; 5.7 corresponds to about 8 in water).

The reaction is usually performed at room temperature. Increasing the temperature tends to increase or conversely decrease the particle size. Thus, a typical temperature range is between 20C and 40C.

The relative molar amounts of the rare earth salt and the surface-active molecule generally range from a minimum of 0.3 to 2.0, although no significant excess is necessary. Preferably, the molar ratio of the surface active molecule to the rare earth salt is from about 1: 1 to 2: 1. Particle sizes in the range of 50 nm or less can be varied by varying this ratio, with preferred ratios providing particles in the range of 5 nm or less. FIG. 3 of the accompanying drawings shows how the luminescence efficiency changes with particle size for Eu ₂ O ₃ nanoparticles, the number in parentheses is the ratio of rare earth salt: surface active molecule (TOPO). .

Typically, the concentration of the rare earth metal salt in the solution is between 0.0001 and 0.5 molar (eg, 0.000
5 to 0.1 mol). At higher concentrations, aggregation tends to occur.

The precipitate and the solvent obtained can be thickened by evaporation, and the particles obtained can be separated and dried. If desired or necessary, the particular particle size can be selected using various methods known in the art.

It has been found that particles having good dimensional uniformity and good crystal structure can be obtained using this method. This is not the case when trying to reduce the larger particles produced by previous procedures involving firing, milling / ball milling, and the like.

A preferred compound of the present invention is Tb_TwoO_Three: Tb³⁺, Ce_TwoO_Three: Ce³⁺And Eu _Two O_Three: Eu³⁺Is included. The properties of the various rare earth oxides obtained are the same.
Typically, they emit light (some in the ultraviolet range, but mostly in the visible range).
The resulting absorption spectrum has a strong peak. For example, (average particle size 4n
m) Tb_TwoO_Three: Tb³⁺In the case of, as shown in the attached FIG.
At 0 nm. The photoluminescence spectrum of this material is shown in FIG. This can be seen to provide peaks at 500 nm and 540 nm which result in green light emission.
Call Typical quantum efficiencies of the resulting particles are in the range of 10-40%. Corresponding
Lium and europium particles emit light in the blue / UV and red regions, respectively. Business
By using suitable rare earth precursor materials, all
It will be appreciated that a gamut of colors can be achieved. That is, corresponding
(Dy) compound emits white light, and samarium (Sm) compound
The compound emits orange light, the holmium (Ho) compound emits blue light, and
(Er) compounds or neodymium (Nd) compounds provide near-infrared light emission
You. Corresponding Eu²⁺Compounds can also be prepared.

The nanoparticles of the present invention are suitable for use in FED type displays. For this purpose, the particles can be fixed in a suitable plastics material by various methods, including dip coating, spin coating and meniscus coating, or by using an air gun spray. Accordingly, the present invention also provides a plastic material incorporating the nanoparticles of the present invention.

Suitable polymers that can be used include polyacrylic acid, polystyrene and polymethyl methacrylate. Such plastic materials can also be used for photoluminescence applications and for electroluminescence applications using AC current. If a DC current is used, conductive polymers such as polyvinylcarbazole, polyphenylenevinylidene and polymethylphenylsilane can be used. Poly 2- (4-biphenylyl) -5- (4-tert-arylbutylphenyl) -1,3,4-oxydiazole (butyl-PBD) can also be used. Desirably, the polymer must be compatible with the solvent (typically methanol) used to apply the particles to the plastic material.

Typically, the particles are applied to a thin layer of plastic material, typically 0.5 to 15 μm thick.

The maximum concentration of the particles is generally about 35% by weight and comprises 65% by weight of polymer. If the concentration exceeds this value, cracks tend to occur in the polymer. A typical minimum concentration is about 2% by weight (98% polymer by weight). If the concentration falls below this value, "pores" are likely to be formed in the plastic material.

The following procedure illustrates a typical synthetic method of the present invention. 5 mL of 5 × 10 ⁻³ M TbCl ₃ .6H ₂ O in HPLC grade methanol was mixed with 5 mL of 5 × 10 ⁻³ M TOPO in methanol for 10 minutes. To this, 1.3 mL of 5 × 10 ⁻³ M NaOH in methanol was added dropwise to precipitate the nanoparticles. The solution was mixed for another 10 minutes. FIG. 4 shows the particle size distribution of a representative sample of 180 terbium oxide nanoparticles. One drop of the particles in the solution was dropped on a lace-like carbon film, and methanol was evaporated. Particle size was determined using a high resolution transmission electron microscope. FIG. 5 is a transmission electron micrograph of europia nanoparticles obtained by the same method.

[Brief description of the drawings]

FIG. 1 shows an absorption spectrum of Tb ₂ O ₃ : Tb ³⁺ .

FIG. 2 shows a photoluminescence spectrum of Tb ₂ O ₃ : Tb ³⁺ .

FIG. 3 is a graph showing how luminous efficiency changes depending on the particle size of Eu ₂ O ₃ nanoparticles.

FIG. 4 is a graph showing the particle size distribution of 180 terbium oxide nanoparticles.

FIG. 5 is a transmission electron micrograph of europia nanoparticles.

[Procedural Amendment] Submission of translation of Article 34 Amendment of the Patent Cooperation Treaty

[Submission date] April 4, 2000 (200.4.4)

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] Claims

[Correction method] Change

[Correction contents]

[Claims]

[Procedure amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0006

[Correction method] Change

[Correction contents]

[0006] The phosphor of the present invention can be easily manufactured by a simple precipitation method. In this method, an alkali is added to a solution of a rare earth metal salt, especially a chloride, in the presence of a metal complex surface active molecule having a surface capping effect.

────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Gareth Wakefield UK, Ox 1.3 PJ, Oxford, Parks Road, Department of Engineering Sciences, University of Oxford F term (reference) 4G076 AA02 AB04 BA13 BB03 BC02 CA02 CA26 DA11 DA30 4H001 CA02 CA04 CF01 XA00 XA08 XA21 XA39 XA58 XA63 XA65 YA00 YA21 YA39 YA58 YA63 YA65 4J002 AA001 BC021 BG011 BG051BJ01 CP011B0101

Claims (18)

[Claims] 1. A compound represented by the formula Z ₂ O ₃ : Z ^{X +} (wherein Z is a rare earth metal and x is 2 to 4). 2. The compound according to claim 1, wherein x is 3. 3. The compound according to claim 1, wherein Z is europium, terbium or cerium. 4. The compound according to claim 1, which is in the form of particles having a size of less than 100 nm. 5. The compound according to claim 4, in the form of particles having a size of 2 to 10 nm. 6. The compound according to claim 5, in the form of particles having a size of about 4 nm. 7. The compound according to claim 1, particularly identified herein. 8. A method according to claim 1, comprising adding an alkali to the solution of the rare earth metal salt to precipitate the rare earth oxide in the presence of the metal-extracting surface-active molecule. how to. 9. The method according to claim 8, wherein a solution of the salt and the surface active molecule is prepared, and an alkaline solution is added thereto. 10. The method according to claim 8, wherein the solvent is an aliphatic alcohol. 11. The method according to claim 8, wherein the molar concentration of the surface active molecule relative to the molar concentration of the rare earth metal salt is at least 0.3. 12. The molar ratio of the surface active molecule to the rare earth metal salt is from 1: 1 to 2
The method of claim 11, wherein the ratio is 1: 1. 13. The method according to claim 8, wherein the rare earth metal salt is chloride. 14. The particles according to claim 4 or claims 8 to 1.
A plastic material containing particles prepared by the method according to any one of the preceding claims. 15. The material according to claim 14, which has a thickness of 0.5 to 15 μm. 16. The material according to claim 14, which contains 2 to 35% by weight of particles based on the weight of the material. 17. The material according to claim 14, which is manufactured from a conductive polymer. 18. The material according to claim 14, which is produced from polyacrylic acid, polymethyl methacrylate or polystyrene.