JP2013060568A - Upconversion phosphor - Google Patents

Abstract

An up-conversion type phosphor, which is a ceramic having practical luminance, and more particularly, an up-conversion type phosphor, which is a cerium oxide-based ceramic.
A cerium oxide (CeO ₂ ) as a base material is doped with silicon atoms (Si) and at least one rare earth atom, and the total number of the silicon atoms (Si), cerium atoms (Ce), and all rare earth atoms. An up-conversion phosphor, which is a ceramic containing 0.1 to 50 atomic percent of the silicon atom (Si) when the content is 100 atomic percent.
[Selection] Figure 2

Description

  The present invention relates to a phosphor expected to be used in various fields, and more particularly to an up-conversion phosphor expected to be used in a biomedical field.

A phosphor is a substance that converts external energy taken into visible light, such as a fluorescent lamp, a white LED (light-emitting diode), a CRT (cathode-ray tube) display, a plasma display, a backlight for a liquid crystal display, etc. Widely used and used for lighting and displays.
The fluorescence phenomenon that occurs in the phosphor is a phenomenon in which, in an atom serving as an activator, when electrons excited by absorbing external energy of electromagnetic waves return to the ground state, fluorescence having a wavelength in the visible light region is emitted. The conversion of external energy into visible light that occurs in such a phosphor is roughly classified into the following two.

One is known as down-conversion, which refers to a phenomenon in which a phosphor emits energy as fluorescence that is lower than the absorbed external energy.
More specifically, external energy having energy higher than that in the visible light region, such as normal ultraviolet light, electron beam, or X-ray, is absorbed by the down-conversion phosphor, and energy lower than the absorbed external energy. This is a method for converting energy by emitting visible light from a down-conversion type phosphor.

As substances that perform such conversion, for example, red phosphor YVO ₄ : Eu, blue phosphor BaMgAl ₁₀ O ₁₇ : Eu, and green phosphor Zn ₂ SiO ₄ : Mn are known. .

The other is known as up-conversion, which is a method of converting energy by emitting a higher energy than the absorbed external energy as fluorescence, contrary to the down-conversion.
More specifically, normally, external energy, which is an energy line having a wavelength lower than that of visible light, such as infrared light, is absorbed by the up-conversion phosphor and has higher energy than the absorbed infrared light. This is a method of converting energy by emitting visible light having a shorter wavelength than infrared light.

For example, NaYF ₄ : Er, Yb, Y ₂ O ₃ : Er, Yb, Gd ₂ O ₃ : Er, Yb are known as up-conversion phosphors.
Of these phosphors, up-conversion phosphors, unlike down-conversion phosphors, do not require the use of ultraviolet light, which tends to affect the irradiated object, as external energy. Therefore, even if the object to be irradiated is, for example, a living tissue, infrared light that transmits the object to be irradiated with little damage, particularly near infrared light can be used as external energy.・ It is highly expected to be applied to the medical field.

Conventionally, in the biomedical field, fluorescent proteins, nano-down conversion phosphors, and quantum dots have been used for bioimaging. However, since there is a concern about the chemical stability and safety of these substances, up-conversion phosphors are attracting attention instead.
As an example of such a substance that becomes an up-conversion type phosphor, a fluoride ceramic such as NaYF ₄ : Er, Yb in which a halide as a base material is doped with a rare earth atom, or an oxide as a base material is used. Oxide ceramics such as CeO ₂ : Er, Yb doped with rare earth atoms are known (Patent Document 1 and Patent Document 2).

  The former fluoride-based ceramics doped with rare earth atoms in such a special metal fluoride show high brightness, but the latter oxide-based ceramics doped with rare earth atoms in oxides still have sufficient practical brightness. Not achieved.

JP 2006-117864 A JP 2004-107612 A

An object of the present invention is to provide an up-conversion type phosphor that is a ceramic having practical luminance, in particular, an up-conversion type phosphor that is a cerium oxide-based ceramic.
Another object of the present invention is to provide an up-conversion phosphor that exhibits high chemical stability and is easy to manufacture.
A further object of the present invention is to provide an upconversion phosphor capable of emitting high-luminance visible light fluorescence having a peak in the visible light region using infrared light having a peak in the infrared light region. Yes.
Another object of the present invention is to provide an up-conversion type phosphor that can be used for a wide range of applications.
In the present specification, “high luminance” means higher luminance than the luminance of conventional oxide ceramics such as CeO ₂ : Er, Yb.

In the present invention, the base material cerium oxide (CeO ₂ ) is doped with silicon atoms (Si) and at least one rare earth atom, and the total number of silicon atoms (Si), cerium atoms (Ce) and all rare earth atoms Is an up-conversion type phosphor that is a ceramic containing 0.1 to 50 atomic percent of the silicon atom (Si) when the atomic percentage is 100 atomic percent.

Here, the rare earth atoms are preferably erbium atoms (Er) and / or ytterbium atoms (Yb).
The ceramic of the present invention is preferably composed of a group of fine particles having a number average particle diameter determined by measurement using an electron microscope in the range of 1 to 200 nm.
The up-conversion phosphor of the present invention is preferably a ceramic phosphor that absorbs near infrared light of 960 to 1000 nm and emits visible light of 450 to 750 nm.

According to the present invention, the brightness is higher than that of CeO ₂ : Er, Yb, which has been considered to have a high brightness among the conventional oxide ceramic phosphors, and the resistance to the load caused by the environment such as water resistance. Thus, it is possible to provide an up-conversion type phosphor that is a cerium oxide ceramic having high chemical stability.

In this up-conversion type phosphor, silicon atoms (Si) are doped together with rare earth atoms in the base material, cerium oxide (CeO ₂ ).
Therefore, it is composed of smaller primary particle groups than the ceramic phosphor in which the base material cerium oxide (CeO ₂ ) is not doped with silicon atoms (Si), and the standard deviation of the particle size distribution of the primary particle groups Is a state in which the average particle size is uniform, for example, a fine particle group having an average particle size of 1 to 200 nm is formed.

  According to the present invention as described above, for example, particles of a size that can be used in the biomedical field can be easily provided.

The calculated values (simulation pattern) of CeO _{2 and} the results of X-ray diffraction analysis of ceramics obtained in 3 to 7, Reference Example 1 and Comparative Example 1, and the relationship between angle (2θ) and strength (au) (“CeO ₂ Cubic ICSD # 29046” is “calculated value of CeO ₂ ” and “%” is “atomic%”). It is a figure which shows the relationship between the wavelength of emitted light, and intensity | strength (au) when 980 nm near-infrared light is irradiated to the ceramics obtained in Example 1 and Comparative Example 1. FIG. The scanning electron micrograph (SEM) of the ceramics obtained in Example 1 and Comparative Example 1 is shown. When the ceramics obtained in Examples 1, 2, 4 and Comparative Example 1 were irradiated with electromagnetic waves of 980 nm, the amount (%) of silicon atoms (Si) in the ceramics and the fluorescence intensity (au) at 560 nm. ("%" Is "atomic%"). It is a figure which shows the relationship between the wavelength of emitted light, and intensity | strength (au) when 980 nm near-infrared light is irradiated to the ceramics obtained in Example 8 and Comparative Example 2. FIG.

[Definition]
In this specification, the following terms are defined as follows.
“Visible light” refers to an electromagnetic wave having a wavelength of 380 to 750 nm, and is also referred to as visible light.
“Ultraviolet light” refers to an electromagnetic wave having a wavelength of 10 nm or more and less than 380 nm, and is also referred to as ultraviolet light.
“Infrared light” refers to electromagnetic waves having a wavelength of more than 750 nm and less than or equal to 1000000 nm, and are also referred to as infrared rays.
“Near-infrared light” refers to an electromagnetic wave having a wavelength exceeding 750 nm and not more than 2500 nm among infrared light, and is also referred to as near-infrared light.

When the ceramic composition is expressed by a composition formula, colon (:), element symbol and number (all displayed for each element), for example, “Ce _0.84 O _1.98 : Er _0.035 Yb _0.0044 Si _0.12 ”, the colon The composition formula on the left side of the ceramics represents the composition formula of the basic skeleton structure of the ceramic, the element symbol on the right side of the colon represents the type of atoms doped in the base material, and the subscript numbers are silicon atoms (Si), cerium atoms (Ce) ) And the total number of all rare earth atoms is 1, respectively. This notation indicates the actual composition of ceramics determined by, for example, elemental analysis measurement. Note that the colon may be omitted.

On the other hand, for example, when no number is written on the right side of the colon as in “CeO ₂ : Er, Yb”, the left side of the colon represents the base material, and the right side of the colon represents the type of dopant. This notation does not indicate the actual composition of ceramics (composition ratio of each atom). Note that the colon may be omitted.

“Base material” refers to a material constituting a doped body (doped body) doped with a dopant such as silicon atoms (Si) and rare earth atoms. The composition of the “base material” does not indicate the actual composition in the ceramic. When the actual composition in ceramics is indicated, it is separately indicated as “basic structure skeleton”. For example, in a ceramic having a composition of “Ce _0.84 O _1.98 : Er _0.035 Yb _0.0044 Si _0.12 ” to be described later, the composition of the base material is “cerium oxide (CeO ₂ )” and the basic structural skeleton is “Ce _0.84 O _1.98 ”. It is. However, in the X-ray diffraction measurement, even if the basic structural skeleton is different from CeO ₂ , the peak value coincides with “CeO ₂ ”.
Although Y ₂ O ₃ and Gd ₂ O ₃ and the like may be used as a base material, a CeO ₂ as compared with the embodiment in which a base material, since the emission fluorescence intensity of ceramics is inferior, in the present invention CeO ₂ Is the base material.

“Cerium oxide” refers to tetravalent cerium oxide represented by the chemical formula “CeO ₂ ” unless otherwise specified. In addition, the tetravalent cerium oxide represented by the chemical formula “CeO ₂ ” is extremely brighter than the trivalent cerium oxide represented by the chemical formula “Ce ₂ O ₃ ”. It is an advantage.

“Doping” or “doping” refers to adding a small amount of impurities (dopant) to a base material. Dopant has only to be present in some form of cerium oxide (CeO ₂₎ as the base material, it may be substituted with the crystal lattice of atoms of oxide cerium (CeO _2), oxide of cerium (CeO ₂ ) A mixed state in which the crystal lattice and the dopant are mixed may be used.

“Crystal lattice of cerium oxide (CeO ₂ )” means that not only the crystal lattice of cerium oxide (CeO ₂ ) but also at least a part of atoms of cerium oxide (CeO ₂ ) are substituted by atoms derived from a dopant. This includes the crystal lattice. The same applies to “the crystal structure of cerium oxide (CeO ₂ )”.

The “doping amount” refers to an amount doped in the base material (amount of dopant contained in the base material).
“Atom%” refers to the ratio (percentage) of the number of target atoms when the total number of specific atomic groups is 100 atomic%.
“Au” is an abbreviation for “arbitrary unit” and indicates an arbitrary unit.
The present invention will be described below.
1. Up-conversion type phosphor The up-conversion type phosphor according to the present invention is a ceramic in which a specific amount of silicon atoms (Si) and at least one rare earth atom is doped into a base material, cerium oxide (CeO ₂ ). The silicon atoms (Si), which are dopants, and at least one rare earth atom are uniformly distributed in the upconversion phosphor.

1-1. Configuration of up-conversion phosphor
<Base material: Cerium oxide (CeO ₂ )>
The cerium oxide (CeO ₂ ), which is the base material of the upconversion phosphor, has rare earth atoms supported in its crystal structure, for example, in a state capable of upconversion emission, or incorporated by atomic substitution or the like. It is rare. In this way, rare earth atoms are doped.
The cerium oxide as the base material is not particularly limited as long as it is transparent to excitation light as long as it is tetravalent cerium oxide. Here, “having transparency with respect to the excitation light” means that the excitation light is not absorbed or does not cause scattering due to interaction with the excitation light.

<Rare earth atoms>
In the up-conversion type phosphor of the present invention, rare earth atoms are doped in cerium oxide (CeO ₂ ) as a base material.
The rare earth atoms doped in the cerium oxide include erbium atoms (Er), holmium atoms (Ho), praseodymium atoms (Pr), thulium atoms (Tm), neodymium atoms (Nd), gadolinium atoms (Gd), europium atoms. (Eu), ytterbium atom (Yd), and samarium atom (Sm).
These may be doped singly into the cerium oxide (CeO ₂ ), or two or more may be combined and doped into the cerium oxide (CeO ₂ ). From the viewpoint of width and brightness (fluorescence), the cerium oxide is preferably doped in combination of two or more.

  These rare earth atoms can be appropriately selected in consideration of the wavelength and luminance (fluorescence) of the emission color. In particular, erbium atoms (Er) and / or ytterbium atoms (Yd) can be selected or combined. From the viewpoint of providing a high-brightness up-conversion phosphor. Especially, the combination which uses an erbium atom (Er) as an activator and another rare earth atom as a coactivator is preferable, and when a combination of erbium atom (Er) and ytterbium atom (Yd) is used, one kind of rare earth atom is used. Compared to the mode of using alone or other rare earth atoms in combination, the upconversion type phosphor has higher reproducibility of the fluorescence behavior, and the upconversion type phosphor emits fluorescence with higher brightness. There is a tendency.

<Silicon atom (Si)>
In the upconversion phosphor of the present invention, cerium oxide (CeO ₂ ) as a base material is doped with silicon atoms (Si) in addition to the rare earth atoms.
Since the up-conversion phosphor is doped with silicon (Si), it emits fluorescence with higher brightness than an up-conversion phosphor not doped with silicon (Si).

<Other ingredients>
In the up-conversion type phosphor of the present invention, in addition to cerium oxide (CeO ₂ ) as a base material, rare earth atoms and silicon atoms (Si) as dopants, the scope of the present invention is not impaired. Other components such as aluminum (Al) may be included as necessary.
However, from the viewpoint that the luminance of the phosphor obtained by adding other component atoms tends to decrease, the up-conversion phosphor of the present invention is composed of cerium oxide (CeO ₂ ), which is the base material, and a dopant. In general, the other components other than rare earth atoms and silicon atoms (Si) are preferably 0.1% by weight or less.

1-2. Composition of Upconversion Phosphor The composition of the upconversion phosphor of the present invention can be represented by the following formula (1).
_{Ce m O n: R x Si} y A z ··· (1)
In formula (1), R represents a rare earth atom (one or more), and A represents the above-mentioned other components. m, n, x, y, and z are, respectively, the number of cerium atoms (Ce), the number of oxygen atoms (O), the number of all rare earth atoms (R), the number of silicon atoms (Si), and the other component (A) atoms. Represents a number.
Each of the atoms is preferably contained in the upconversion phosphor in the following amounts from the viewpoint that the upconversion phosphor emits light with high luminance.

<When the total number of silicon atoms (Si), cerium atoms (Ce) and all rare earth atoms is 100 atomic% (m + x + y = 1)>
When the total number of silicon atoms (Si), cerium atoms (Ce) and all rare earth atoms in the upconversion phosphor is 100 atomic% (m + x + y = 1):
The cerium atom (Ce) is usually 50 to 99.9 atomic% (m = 0.50 to 0.999), preferably 70 to 89 atomic% (m = 0.70 to 0.89), more preferably 79. -89 atomic% (m = 0.79-0.86);
Rare earth atoms are Er and / or Yb (R _x = Er _x1 , Yb _x2 , or Er _x1 Yb _x2 , x1 and x2 represent the number of erbium atoms (Er) and the number of ytterbium atoms (Yb), respectively) When
Er is usually 0.1 to 20 atomic% (x1 = 0.001 to 0.2), preferably 1 to 10 atomic% (x1 = 0.01 to 0.1), more preferably 3 to 5 atomic%. (X1 = 0.03-0.05),
Yb is 0.05 to 30 atomic% (x2 = 0.005 to 0.3), preferably 0.1 to 20 atomic% (x2 = 0.001 to 0.2), more preferably 0.3 to 3 atomic% (x2 = 0.003 to 0.03);
The addition amount (doping amount) of silicon atoms (Si) is usually 0.1 to 0.1 (although it varies depending on the kind of rare earth atoms doped in cerium oxide (CeO ₂ ) and the desired brightness level (fluorescence intensity)). 50 atomic% (y = 0.001 to 0.5), preferably 1 to 20 atomic% (y = 0.01 to 0.2), more preferably 10 to 20 atomic% (y = 0.10 to 0) 20), more preferably 11-13 atomic% (y = 0.1-10.13);
The other component (A) is preferably 1 atomic% or less, (z ≦ 1), more preferably 0.1 atomic% or less (z ≦ 0.1), and 0 atomic% (z = 0). Is particularly preferred. The amount of oxygen atom (O) is naturally determined by the relationship with the oxidation number of other atoms.

<When the number of cerium atoms (Ce) is 1 (m = 1)>
When the number of cerium atoms (Ce) in the upconversion phosphor is 1 (m = 1):
The rare earth atom (Er) number (x) is usually 0.0012 to 0.2395, preferably 0.012 to 0.12, more preferably 0.036 to 0.06;
When the rare earth atom is Er and / or Yb,
The rare earth atom (Yb) number (x ′) is usually 0.0006 to 0.36, preferably 0.0012 to 0.24, more preferably 0.0036 to 0.036;
The number of silicon atoms (Si) (y) depends on the kind of rare earth atoms doped in cerium oxide (CeO ₂ ) and the desired brightness level (fluorescence intensity), but is usually 0.0012 to 0.6, Preferably it is 0.012-0.24, More preferably, it is 0.12-0.24, More preferably, it is 0.13-0.16;
The number of atoms (z) of the other component (A) is preferably 0.1 or less, and more preferably 0. The amount of oxygen atom (O) is naturally determined by the relationship with the oxidation number of other atoms.

In particular, in the case where cerium oxide is doped with erbium atoms (Er) and ytterbium atoms (Yb) as the rare earth atoms, as an example, an upconversion phosphor represented by the following formula (2) is exemplified.
_{Ce m O n: Er x1 Yb} x2 Si y ··· (2)
(In the formula (2), m, n, and y are the same as the definitions in the above formula (1). X1 and x2 are as described above.),
When the amount of cerium atoms (Ce) in the upconversion phosphor is 1 (m = 1), the number (x1) of erbium atoms (Er) is preferably 0.001 to 0.2. Preferably it is 0.01-0.1, 0.03-0.05, and the ytterbium atom (Yb) number (x2) is preferably 0.0005-0.2, more preferably 0.001-0. .1, particularly preferably 0.003 to 0.03.

<Others>
The number of silicon atoms (Si) (y) is preferably 0.1 to 23, more preferably 1 to 6, and further preferably 2.5 to 5 when the total number of all rare earth atoms is 1 (x = 1). .6, particularly preferably 2.5 to 4.0.

1-3. The above-mentioned up-conversion phosphor such as the properties of the up-conversion phosphor preferably has a number average particle diameter determined as follows using a field emission scanning electron microscope (hereinafter also referred to as FE-SEM), preferably 1 to It is desirable to be composed of fine particle groups in the range of 200 nm, more preferably 10 to 150 nm, particularly preferably 20 to 80 nm.

How to find the number average particle size:
In an electron micrograph of a magnification of 100,000, which was taken using an FE-SEM, arbitrary 30 particles were selected within an arbitrary 1220 nm × 910 nm region, and the major axis (nm) and minor axis ( nm).
Here, since each particle is not necessarily spherical, the length of the longest diameter is taken as the major axis, and the perpendicular second etc. intersecting the perpendicular direction (minor axis) inside the particle shape with respect to the major axis direction (major axis) The length of the branch line is the minor axis. In the case of a sphere, the major axis is the minor axis.
Next, about each particle | grain, the average diameter of a major axis and a minor axis is calculated | required from following formula (1).
Average diameter of major axis and minor axis (nm) = {major axis (nm) + minor axis (nm)} / 2 (1)
Next, a number average particle diameter is calculated | required from following formula (2).
Number average particle diameter (nm) = {total of major diameter and minor diameter of 30 particles (nm)
/ 30} (2)

In addition, the up-conversion phosphor is preferably composed of a group of fine particles having the same number average particle diameter and particle shape from the viewpoint of high brightness.
Specifically, the number average particle diameter of the fine particle group constituting the upconversion phosphor is in the above range, and the standard deviation of the particle size distribution obtained as follows using the FE-SEM is 0 to 25. Preferably there is.

How to find the standard deviation of particle size distribution:
The average diameter (nm) and the number average particle diameter (nm) of the major axis and minor axis of each of the 30 particles are determined by the method described in the item for determining the average particle diameter.
Next, for each particle, a square value of “average diameter of major axis and minor axis (nm) −number average particle diameter (nm)” is obtained, and the total is divided by 30 to obtain a dispersion value.
Next, the square root of the variance value is obtained and set as the standard deviation.

  This up-conversion phosphor is taken into a living body, and near-infrared light is irradiated from outside the living body to emit visible light in the body, so that it is used in the so-called biomedical field, particularly in the field of bioimaging. In this case, it is desirable that the average particle diameter of the primary particles of the fine particle group constituting the upconversion phosphor is adjusted to a range of 20 to 80 nm in order to ensure high dispersibility. Control of the average particle diameter of the primary particles of the fine particle group constituting the up-conversion phosphor can be easily performed by a liquid phase method described later.

  The external energy, which is the excitation light that irradiates the up-conversion phosphor to cause up-conversion emission, can be applied to an irradiated object such as a living tissue that is exposed to the excitation light when the up-conversion phosphor is irradiated with the excitation light. From the viewpoint of not damaging, light (electromagnetic wave) having a wavelength in the range of 500 to 2000 nm is preferable, light in the range of 700 to 1600 nm is more preferable, light in the range of 800 to 1100 nm is particularly preferable, and light in the range of 960 to 1000 nm is preferable. A range of light is most preferred.

  When irradiation is performed using light having such a wavelength as excitation light, visible light is generated from the upconversion phosphor, but the wavelength is 400 nm depending on the type of rare earth atoms doped in the ceramic base material cerium oxide. Blue light in the region of 500 nm or less, green light in the wavelength region of 500 nm or more and less than 600 nm, and / or red light in the region of wavelength of 600 nm or more and less than 800 nm are generated.

  Specifically, when both Tm and Yb are used as dopants (Tm and Yb co-doping), blue light emission in the region of 400 nm or more and less than 500 nm occurs, and Er and, if necessary, more excitation light. When Yb for efficient absorption is used as a dopant, green light emission in a wavelength region of 500 nm or more and less than 600 nm and red light emission in a region of 600 nm or more and less than 800 nm are generated, and only Ho or Ho When Yb and Yb are used as dopants, green light emission in a region having a wavelength of 500 nm or more and less than 600 nm occurs. In addition, among the above, when the colored light of a phosphor that emits light of a plurality of colors is viewed (without spectroscopy), it is observed as a mixed color of the plurality of colored light, so the type and amount of dopant By appropriately adjusting the ratio, it is possible to emit light of a desired color in addition to the above color.

  Among these aspects, the up-conversion phosphor that emits visible light of 450 to 750 nm when absorbing near-infrared light of 960 to 1000 nm does not damage the irradiated object such as the above-described living tissue. And is preferable from the viewpoint of easy detection of emitted light.

<Specific examples of up-conversion phosphors>
Hereinafter, the up-conversion phosphor of the present invention will be described in more detail with reference to a ceramic phosphor using erbium (Er) and ytterbium (Yd) as rare earth atoms.

  In an up-conversion phosphor using erbium atoms (Er) and ytterbium atoms (Yd) as rare earth atoms, silicon atoms (Si) with a constant addition amount (doping amount) of erbium atoms (Er) and ytterbium atoms (Yd) are used. ) Addition amount (doping amount), the doping amount of silicon atoms (Si) when the total number of silicon atoms (Si), cerium atoms (Ce) and all rare earth atoms is 100 atomic% is 12 atomic% In this case, the maximum luminance is shown, and the luminance at the doping amount before and after that is lower than the maximum luminance (see FIG. 4).

As an example, the total composition of the up-conversion phosphor in which the silicon (Si) addition amount is 12 atomic% when the total number of silicon atoms (Si), cerium atoms (Ce) and all rare earth atoms is 100 atomic% can be cited. If
Ce _0.84 O _1.98 Er _0.035 Yb _0.0044 Si _0.12
It is.
The detailed structure of such an up-conversion phosphor has not yet been clearly analyzed.

  However, according to the X-ray diffraction analysis of the up-conversion phosphor using erbium atoms (Er) and ytterbium atoms (Yd) as the rare earth atoms shown in FIG. 1, the silicon atoms (Si), cerium atoms (Ce) and Even when the Si atom content (doping amount) is increased to 67 atom% when the total number of all rare earth atoms is 100 atom%, the X-ray diffraction intensity does not increase and no peak shift occurs. I understand that.

Therefore, a structure in which a rare earth atom and a silicon atom (Si) coexist in the cerium oxide (CeO ₂ ) crystal lattice, that is, a structure in which the cerium atom (Ce) of cerium oxide (CeO ₂ ) is replaced by a silicon atom (Si). rather, the cerium atoms (Ce) cerium oxide substituted with a rare earth atom (CeO ₂₎ crystal structure enters rare earth atom of cerium oxide (CeO ₂₎ to cerium oxide (CeO ₂₎ in the crystal lattice, silicon described later It is presumed that the SiO ₄ tetrahedron produced by the oxidation of the compound approaches and causes some kind of interaction (interaction) with each other.

In any case, by doping rare earth atoms and silicon atoms (Si) into the base material cerium oxide (CeO ₂ ), the luminance is higher than that of a ceramic phosphor having a composition of CeO ₂ : Er, Yb. There is an effect that a further improved up-conversion type phosphor can be provided.

2. Production method of up-conversion type phosphor The up-conversion type phosphor composed of fine particles of the cerium oxide ceramics according to the present invention comprises an appropriate amount of rare earth metal salt and silicon compound (other components as required) added to the cerium compound. To produce a ceramic (up-conversion type phosphor) precursor (hereinafter also referred to as “ceramic precursor”), and then subject the resulting ceramic precursor to high-temperature firing for an appropriate time. In accordance with this, the obtained fired product is pulverized to produce fine particles.

More specific description will be given below.
Unless otherwise noted, the pressure condition in the production method is substantially normal pressure.
2-1. The manufacturing method of the up-conversion type phosphor of the present invention such as manufacturing conditions includes at least a ceramic precursor preparation step and a ceramic precursor firing step. Moreover, the manufacturing method of the up-conversion type | mold phosphor of this invention may also include other processes, such as a grinding | pulverization process of a baked material, as needed.

Hereinafter, it demonstrates in order.
<Preparation process of ceramic precursor>
In the ceramic precursor preparation step, an unfired ceramic precursor, which is a precursor of the upconversion phosphor (ceramics) of the present invention, is prepared.

Examples of the method for producing the unfired ceramic precursor include a solid phase method, a liquid phase method, and a gas phase method.
The solid phase method has a simple work process, can be mass-produced at low cost, and has high productivity. Therefore, for example, it is generally often used when manufacturing on a factory scale. On the other hand, the diffusion rate of ions in the solid is very slow, and it tends to be difficult to obtain desirable fine particles.
The liquid phase method has an advantage that a homogeneous reaction easily proceeds, an ion diffusion rate in the liquid is high, and fine particles with high purity can be easily obtained.
The gas phase method is not suitable for mass production, but has the advantage that the reaction proceeds according to the stoichiometric ratio with high purity, and ultrafine particles can be synthesized.

  Since any method can be used to produce an unfired ceramic precursor, a method to be appropriately employed may be selected in consideration of productivity and desired physical properties, but the liquid phase method has high brightness and From the viewpoint of the advantage that an unfired ceramic precursor composed of fine particles having a uniform particle diameter is easily obtained, it is more convenient.

[Liquid phase method]
Hereinafter, the liquid phase method will be described in more detail.
The liquid phase method is a method of preparing an unfired ceramic precursor by mixing at least raw materials once in a solution state and then thoroughly mixing them. The unsintered ceramic precursor is subjected to a firing process.
Therefore, the liquid phase method tends to require a longer manufacturing process as compared with the solid phase method or the gas phase method. However, on the other hand, it is easy to proceed a predetermined reaction by constructing a reaction system in which raw materials are uniformly distributed at the ion level, and the unfired ceramic precursor obtained by the liquid phase method is crystallized by firing. Ceramics with high crystallinity can be easily manufactured.

As a result, the unfired ceramic precursor obtained by the liquid phase method is a high-purity unfired ceramic, and has a high fluorescence extraction efficiency, which is a conversion rate of excitation light energy to fluorescence energy. It is easy to produce ceramics composed of a group of fine particles with uniform particle morphology.
Therefore, when importance is attached to the properties of the ceramics to be manufactured as a phosphor, the liquid phase method is a more preferable manufacturing method than the solid phase method or the gas phase method.
Specific means of the liquid phase method include a precipitation method, a coprecipitation method, a complex polymerization method, etc. Among them, the adoption of the complex polymerization method can produce an unfired ceramic precursor in which raw materials are uniformly distributed. To preferred.

(Complex polymerization method)
Hereinafter, the complex polymerization method will be described in detail.
By the complex polymerization method, an unfired ceramic precursor for use in the firing step can be produced.
In the complex polymerization method, for example, a cerium compound, a rare earth metal salt, and a silicon compound are uniformly dispersed in a polymer such as polyester.
Next, a metal-carboxylic acid complex (where “metal” constituting the “metal-carboxylic acid complex” is cerium and a rare earth metal, the same shall apply hereinafter) is once synthesized and then heated at a high temperature to form a polymer. An unfired ceramic precursor is produced by thermal decomposition.
The unsintered ceramic precursor obtained in this ceramic precursor preparation step undergoes other steps as necessary, and then, in the firing step, the precursor is fired at a high temperature by a normal method using, for example, a heating furnace.

  Thus, the target ceramic phosphor can be produced from the unfired ceramic precursor containing the silicon compound and the metal-carboxylic acid complex obtained in the ceramic precursor preparation step. The green ceramic precursor obtained here is a ceramic phosphor in which rare earth atoms and silicon atoms are uniformly distributed in cerium oxide and has a desired composition.

(Specific example of liquid phase method using complex polymerization method)
The preparation process of the ceramic precursor will be described in more detail with an example as follows.

For example, a cerium compound such as cerium nitrate and a nitrate of the rare earth metal salt are dissolved in water to prepare an aqueous solution. The temperature condition at this time is usually 20 to 90 ° C.
Next, by adding a water-soluble silicon compound and a carboxylic acid compound such as citric acid to the obtained aqueous solution, a complex in which the carboxylic acid compound is coordinated to cerium and a rare earth metal (a complex having a multidentate ligand) and silicon A mixture containing the compound is formed.

  Next, a polyol such as ethylene glycol or propylene glycol is added to the obtained mixture, and when the obtained mixture is heated at 120 to 150 ° C. for 300 to 600 minutes, a dehydration condensation reaction between the carboxylic acid compound and the polyol proceeds and polyester is obtained. A polyester in which a complex in which a carboxylic acid compound is coordinated to the cerium and rare earth metal and a silicon compound are uniformly dispersed is obtained. When the carboxylic acid and / or polyol has three or more reactive functional groups, a gel product is obtained.

  Subsequently, the product is heated at a temperature within a specific range by a normal method using a heating furnace to produce a ceramic precursor. The heating temperature depends on the type of polymer obtained above, but when heated to about 400 to 500 ° C., the decomposition reaction of the polymer in the product proceeds.

<Baking process>
The firing step is performed after at least the preparation step of the ceramic precursor.
The firing of the ceramic precursor may be performed for 60 to 600 minutes under a temperature condition of usually 800 to 1500 ° C., preferably 1000 to 1200 ° C. according to a conventional method using a heating furnace.
The ceramics thus obtained (up-conversion type phosphor) can obtain a group of crystalline fine particles having a small average particle size of primary particles and a uniform shape and average particle size. Showing gender.

<Other processes>
The method for producing the up-conversion phosphor may include steps other than the ceramic precursor preparation step and the firing step.
For example, the residual raw material may be removed from the mixture containing the ceramic precursor obtained in the ceramic precursor preparation step before the firing step.
In addition, for example, after the firing step, the obtained ceramic is subjected to pulverization using a pulverizer such as a ball mill or a bead mill, so that the up-conversion type fluorescence having an average particle diameter of 1 to 200 nm and a particle size distribution in the above-described range. The body may be manufactured.
In the step of preparing the ceramic precursor, materials other than the above materials may be added and mixed. Examples of such a material include boron for increasing crystallinity.

[material]
<Cerium compound>
In producing the up-conversion type phosphor of the present invention, a cerium compound is used as a raw material as a cerium atom source of cerium oxide (CeO ₂ ) as a base material.

The cerium compound should just be oxidized by the time the baking process mentioned later is complete | finished, and comprises the cerium oxide which is a base material. Examples of such a cerium compound include cerium nitrate, cerium chloride, cerium acetate, and cerium carbonate.
Among these, cerium nitrate is preferable from the viewpoint of solubility in water.
The purity of the cerium compound is preferably 98.0% or more from the viewpoint of obtaining a stable composition.

The cerium compound is usually 50 in terms of the number of cerium atoms (Ce) when the total number of silicon atoms (Si) of the silicon compound, cerium atoms (Ce) of the cerium compound and all rare earth atoms of the rare earth metal salt is 100 atomic%. It is used in an amount of ˜99.85 atomic%, preferably 70 to 98.9 atomic%, more preferably 92 to 96.7 atomic%.
When the cerium compound is used in such an amount, an upconversion phosphor having the above composition can be produced.

<Rare earth metal salt>
In order to dope the rare earth atoms into cerium oxide, rare earth metal salts are used in the production of upconversion phosphors.
Examples of rare earth metal salts include nitrates, chlorides, acetates and carbonates of rare earth atoms doped into cerium oxide. These may be hydrates containing crystal water.
Specifically, erbium nitrate _{(Er (NO 3) 3)} , ytterbium nitrate _{(Yb (NO 3) 3)} , erbium chloride (ErCl _3), ytterbium chloride (YbCl _3), and the like.

The purity of the rare earth metal salt is preferably 99.98% or more from the viewpoint of obtaining a stable composition.
The rare earth metal salt is preferably from 0.010 to 0.60 mmol, more preferably from 0.15 to 0.40 mmol, particularly preferably from 0.04 to 0, in terms of rare earth metal atoms, per 1 mmol of cerium atom of the cerium compound. Used in an amount of 10 mmol.
Moreover, when the total number of silicon atoms (Si) of the silicon compound, cerium atoms (Ce) of the cerium compound and the total rare earth atoms of the rare earth metal salt is 100 atomic%, the rare earth metal salt is converted into the number of rare earth metals, Usually, it is used in an amount of 0.1 to 50 atomic%, preferably 1 to 30 atomic%, more preferably 10 to 20 atomic%, and still more preferably 11 to 13 atomic%.

In particular, when an erbium salt and an ytterbium salt are used as the rare earth metal salt, the erbium salt is preferably 0.0012 to 0.24 mmol in terms of erbium atom (Er) relative to 1 mmol of cerium atom of the cerium compound, More preferably, it is used in an amount of 0.012-0.12 mmol, particularly preferably 0.036-0.060 mmol. The ytterbium salt is preferably 0.00060-0.36 mmol in terms of ytterbium atom (Yb), more preferably It is preferably used in an amount of 0.0012 to 0.24 mmol, particularly preferably 0.0036 to 0.036 mmol.
When the rare earth metal salt is used in such an amount, an up-conversion phosphor in which rare earth atoms are doped in the above amount in cerium oxide as a base material can be produced.

<Silicon compound>
In order to dope silicon atoms into cerium oxide, silicon compounds are used in the production of upconversion phosphors.
Examples of the silicon compound include silane compounds, silicon dioxide, silicon fluoride, tetraethoxysilane, and tetra (2-hydroxypropoxy) silane.
Among these, water-soluble silicon compounds such as tetra (2-hydroxypropoxy) silane are preferable from the viewpoint of water solubility and non-volatility, and among them, tetra (2-hydroxypropoxy) silane (Si (OCH ₂ CH (OH) —CH ₃ ) ₄ ) is convenient.

The purity of the silicon compound is preferably 90% or more from the viewpoint of suppressing a decrease in luminance due to impurity atoms. When the total number of silicon atoms in the silicon compound, cerium atoms in the cerium compound, and all rare earth atoms in the all rare earth metal salt is 100 atomic%, the silicon compound is converted to the number of atoms, and usually 0.1 to It is used in an amount of 50 atomic%, preferably 1 to 20 atomic%, preferably 10 to 20 atomic%, more preferably 11 to 13 atomic%.
In addition, the silicon compound is preferably 0.01 to 1 mmol, more preferably 0.11 to 0.25 mmol, and particularly preferably, in terms of silicon atom, with respect to 1 mmol of all rare earth atoms of the cerium compound and dopant atoms of the cerium compound. Used in an amount of 0.12-0.15 mmol.
When a silicon compound is used in such an amount, a ceramic phosphor in which silicon atoms are doped in the above amount in cerium oxide as a base material can be produced.

<Carboxylic acid compound>
The carboxylic acid compound is not particularly limited, and examples thereof include citric acid, lactic acid, glycolic acid, and tartaric acid. Among these, a carboxylic acid compound having three or more carboxyl groups is preferable from the viewpoint of complex forming ability, and citric acid ((CH ₂ COOH) ₂ C (OH) (COOH)) is particularly advantageous from the same viewpoint.

The carboxylic acid compound is preferably 1 to 10 times equivalent, more preferably 2 to 8 times equivalent to the total of the cerium atom in the cerium compound and the total rare earth atom of the all rare earth metal salt and silicon in the silicon compound. Preferably it is used in an amount of 2.5 to 5 times equivalent.
When the carboxylic acid compound is used in such an amount, an upconversion phosphor having the above composition can be produced. When the complex polymerization method is employed, a polymer in which the above raw materials are uniformly distributed is obtained. Can be manufactured.

<Polyol compound>
Although a polyol is not specifically limited, For example, the alkylene glycol containing ethylene glycol and propylene glycol etc. are mentioned. Among these, ethylene glycol and propylene glycol are advantageous from the viewpoint of low toxicity.

The polyol is preferably 5 to 50 times equivalent, more preferably 8 to 30 times equivalent, particularly preferably 10 to 20 times equivalent to the total of cerium atoms in the cerium compound and all rare earth atoms of all rare earth metal salts. Is used in an amount.
When the complex polymerization method is employed, when such an amount of polyol is used, a polymer in which the raw materials are uniformly distributed can be produced.

3. Applications of up-conversion phosphors The up-conversion phosphors of the present invention are expected to be applied to, for example, the biomedical field, chemical analysis field (for fluorescence analysis and environmental test analysis), photodynamic therapy, and the like. From the above viewpoint, it can be suitably used particularly in the biomedical field including bioimaging.
Examples of the mode used in the biomedical field include imaging of living cells using an IR laser and an optical microscope.

EXAMPLES Hereinafter, although an Example and a comparative example demonstrate this invention further in detail, this invention is not limited to an Example.
In the following Examples and Comparative Examples, all operations were performed under normal pressure unless otherwise specified.

[Raw materials]
The raw materials used in the following examples and comparative examples are as follows.
Cerium nitrate: Ce (NO ₃ ) ₃ · 6H ₂ O, manufactured by Wako Pure Chemical Industries, purity 98.0%,
Erbium nitrate: Er (NO ₃ ) ₃ , made of Japanese yttrium, purity 99.9%,
Ytterbium nitrate: Yb (NO ₃ ) ₃ , made of Japanese yttrium, purity 99.9%,
Citric acid: (CH ₂ COOH) ₂ C (OH) (COOH), manufactured by Wako Pure Chemical Industries, purity 98%,
Propylene glycol: Wako Pure Chemical Industries, purity 99%,
Tetra (2-hydroxypropoxy) silane: tetra (2-hydroxyethyl) silane and propylene glycol in a molar ratio of 1: 4 (propylene glycol 0.4 mol, tetra (2-hydroxyethyl) silane 0.1 mol) After mixing, add a few drops of hydrochloric acid (corresponding to 0.1 ml), stir at 80 ° C. for 30 minutes, then add distilled water to the resulting reaction solution to a molar concentration of silicon of 1 mol / L. Adjusted,
Tantalum pentachloride: TaCl ₅ , high purity chemical company, purity 99.90%,
Niobium pentachloride: NbCl ₅ , manufactured by Furuuchi Chemical Co., Ltd., purity 99.9%
Ammonium vanadate: NH ₄ VO ₃ , Wako Pure Chemical Industries, 99% purity
Zirconium oxynitrate: ZrO (NO ₃ ) ₂ , Wako Pure Chemical Industries, 99% purity
Yttrium nitrate: Y (NO ₃ ) ₃ , manufactured by Japan Yttrium, purity 99.9%,
Aluminum nitrate: Al (NO ₃ ) ₃ , manufactured by Kanto Chemical Co., Inc., purity 99%,
Ammonium molybdate: (NH ₄ ) ₆ Mo ₇ O ₂₄ · 4H ₂ O, manufactured by Kanto Chemical Co., Inc., purity 99%.

Example 1
Cerium nitrate 0.84 mmol, erbium nitrate 0.035 mmol and ytterbium nitrate 0.0044 mmol were dissolved in 10 mL of distilled water.
Next, 0.12 mL of an aqueous solution containing 0.12 mmol of tetra (2-hydroxypropoxy) silane was added.
An amount (2.5 mmol) of citric acid corresponding to about 2.5 times mol of the total amount of all metals and silicon of the compound used previously was added to the obtained liquid.
Furthermore, propylene glycol in an amount (10 mmol) corresponding to about 10 times mol of the total amount of all metals and silicon was added to the resulting liquid, and the mixture was allowed to stand at 70 ° C. for 12 hours.
Next, the obtained liquid was heated under a temperature condition of 120 to 150 ° C. to evaporate the water and proceed the esterification reaction to obtain a polymer gel.
Next, the obtained polymer gel was heated on a sand bath set at 450 ° C. to thermally decompose the polyester in the polymer gel. Furthermore, the residue obtained after the thermal decomposition of the polyester was baked by heating for 300 minutes in an electric furnace set at 1200 ° C.
In this way, a fired product (ceramics) was obtained.

[Elemental analysis]
When the elemental analysis of the obtained fired product was performed using an energy dispersive X-ray analyzer (EDX) (manufactured by Horiba, EMAX-2770), the fired product had the following composition and was a silicon atom. When the total number of (Si), cerium atoms (Ce) and all rare earth atoms was 100 atomic%, the ceramic contained Si in an amount of 12 atomic%.
Ce _0.84 O _1.98 Er _0.035 Yb _0.0044 Si _0.12
Next, the obtained fired product was subjected to X-ray diffraction analysis, measurement of luminance of fluorescence generated when a semiconductor laser having a wavelength of 980 nm was irradiated as excitation light, and photographing of an electron micrograph as follows.

[X-ray diffraction analysis]
X-ray diffraction analysis was performed using an X-ray source (CuKα) using a powder X-ray diffraction analyzer (manufactured by Rigaku Corporation, GeigerFlex RAD-2X).
The X-ray diffraction pattern of the obtained fired product coincided with the X-ray diffraction pattern of CeO ₂ which is a standard substance.
The result is shown in the uppermost part of FIG. 1 (CeO ₂ calculated value).

[Measurement of fluorescence intensity (evaluation of luminance)]
The fluorescence intensity was measured using a 980 nm semiconductor laser (500 mA, THORLABS, TCLD-M9) as a light source, and the generated fluorescence was detected by a multichannel spectrophotometer.
The obtained fired product emitted green fluorescence around 550 nm and red fluorescence around 660 nm in the above measurement.
The result of scanning the fluorescence intensity of 500 nm to 700 nm is shown in FIG. 2 (solid line), and the measurement result of the fluorescence intensity at 560 nm is shown in FIG. 4 (Si (%) = 12). In both cases, the horizontal axis represents wavelength (nm) and the vertical axis represents intensity (au).

[Measurement of electron micrograph]
Electron micrographs were taken according to the method described above.
An electron micrograph (magnification: × 100,000) of the obtained fired product is shown in FIG. 3 (right figure).
As a result, a group of fine particles having a particle size in the range of 30 to 200 nm was observed.
The number average particle size determined according to the method described above was 74.9 nm, and the standard deviation of the particle size distribution was 23.1.

  In addition, the emission intensity at 560 nm (hereinafter also referred to as “emission intensity (980, 560)”) of the fired product obtained in Example 1 when irradiated with near-infrared radiation of 980 nm is the emission of Comparative Example 1 described later. When the strength (980, 560) was 1, it was 1.9.

(Examples 2-8, Reference Example 1, Comparative Examples 1-9)
In Example 1, the baked goods were obtained similarly to Example 1 except having set the compounding quantity of the compound described in Tables 1-5 as Tables 1-5. The obtained fired product was subjected to X-ray diffraction analysis, fluorescence intensity measurement, and electron micrograph photography in the same manner as in Example 1.

Tables 1 to 5 show preparation amounts of raw materials and the like and compositions of the obtained fired products in each example.
Further, the results of X-ray diffraction analysis are shown in FIG. 1 (data in which atomic% of Si in each example matches) for Examples 3 to 7, Reference Example 1 and Comparative Example 1.
The result of measuring the fluorescence intensity in the wavelength region of 500 to 700 nm when irradiated with near infrared rays of 980 nm is shown in FIG. 2 (broken line) for Comparative Example 1, and for Example 8 and Comparative Example 2, FIG. (Solid line, broken line)
The results of measuring the emission intensity at 560 nm when irradiated with near infrared rays of 980 nm are shown in FIG. 4 for Comparative Example 1, Example 2 and Example 5 (data in which the atomic percentage of Si in each example matches). Shown in
The result of taking an electron micrograph is shown in FIG.

  The light emission intensity (980, 560) of the fired product obtained in Example 2 is 1.5 when the light emission intensity (980, 560) of the fired product of Comparative Example 1 is 1. The light emission intensity (980, 560) of the fired product obtained in 4 was 1.7 when the light emission intensity (980, 560) of the fired product of Comparative Example 1 was 1.

* In Tables 1 to 5, “-” in the column of “raw material etc.” indicates that the corresponding compound was not blended.

  The upconversion phosphor obtained in the present invention can be used as a phosphor for fluorescence analysis or environmental test analysis. It can also be used in the biomedical field, for example, image diagnosis using bioimaging, and novel treatment and diagnosis methods for cancer using near infrared light that does not damage living tissue as excitation light Furthermore, it can be expected to be applied to the provision of devices and drugs for them.

Claims (4)

The base material cerium oxide (CeO ₂ ) is doped with silicon atoms (Si) and at least one rare earth atom,
It is a ceramic containing the silicon atom (Si) in an amount of 0.1 to 50 atomic% when the total number of the silicon atoms (Si), cerium atoms (Ce) and all rare earth atoms is 100 atomic%. Up-conversion type phosphor characterized by   The up-conversion phosphor according to claim 1, wherein the rare earth atom is erbium (Er) and / or ytterbium (Yb).   The up-conversion phosphor according to claim 1 or 2, wherein the up-conversion type phosphor is composed of a group of fine particles having a number average particle diameter of 1 to 200 nm determined by measuring the ceramics with an electron microscope.   The up-conversion type phosphor according to any one of claims 1 to 3, wherein the up-conversion type phosphor emits visible light of 450 to 750 nm when absorbing near-infrared light of 960 to 1000 nm. Phosphor.