JP6129649B2 - Upconversion phosphor and method for producing the same - Google Patents

Description

  The present invention relates to an up-conversion phosphor capable of emitting light having higher energy than excitation light and a method for manufacturing the same.

The up-conversion phosphor can emit light having higher energy than the excitation light.
Up-conversion phosphors are expected to be applied in various fields because light sources with low energy can be used. However, phosphors emit light with lower energy than excitation light (down-conversion). Usually, in order to cause the up-conversion phenomenon, it is necessary to participate in excited state absorption, multiphoton absorption, energy transfer, and the like.
For this reason, various materials have been studied, and various studies and proposals have been made to increase luminous efficiency.

  Conventionally, rare earth oxides, fluorides, silicates, titanates, nanoparticles, glass, and the like have been used as host crystals for upconversion phosphors.

Specifically, as an example using a rare earth oxide, (R _1-x , Er _x ) ₂ O ₃ (R is at least one of Y, La, Gd and Lu. 001 ≦ x ≦ 0.20.) Phosphor fine particles that emit up-conversion light with light having a wavelength in the range of 500 nm to 2000 nm (see Patent Document 1), Y ₂ O ₃ : Eu ³⁺ , Yb ³⁺ from visible up-conversion emission (see Non-Patent Document 1).
As an example using fluoride, there is a report on the up-conversion characteristics of Eu ³⁺ -Yb ³⁺ : NaYF ₄ including Yb ³⁺ having a wide concentration range (see Non-Patent Document 2).
As an example of using nanocrystals of silicate, nanocrystalline _{Y 2 Si 2 O 7: Er} 3+ and _{Y 2 Si 2 O 7: Yb} 3+, for up-conversion fluorescence from Er ³⁺ in Er ³⁺ There are reports (see Non-Patent Document 3).
As an example using glass, there is a report on up-conversion fluorescence from infrared to visible light in an Er ³⁺ / Yb ^{3 +} -added titanate glass prepared by a method without using a container (see Non-Patent Document 4). .
Examples of using nanoparticles include a technique for producing up-conversion nanoparticles by irradiating a target in liquid (made of a fluorescent material having up-conversion characteristics) with laser light (see Patent Document 2), colloidal BaYF ₅ , and the like. There are reports on blue upconversion from near infrared in nanocrystals: Tm ³⁺ and Yb ³⁺ (Non-patent Document 5).

JP 2004-292599 A JP 2013-14651 A

H. Wang et.al., J. Phys. Chem. C, 2008, 112 (42), pp 16651-16654. B.S.Cao et.al., J. Luminescence, 2013, 135 (3), pp 128-132. J. Sokolnicki, Materials Chemistry and Physics, 2011, 131 (1-2), pp 306-312. X. Pan et.al., J. Luminescence, 2012, 132, pp 1025-1029. F. Vetrone et.al., Chem. Mater., 2009, 21 (9), pp 1847-1851.

  However, conventional up-conversion phosphors are still insufficient in light emission characteristics or use unfavorable materials such as fluoride. There is a need to provide it.

  Accordingly, an object of the present invention is to provide a novel up-conversion phosphor excellent in emission characteristics and a method for producing the same.

  The inventors of the present invention have made extensive studies to solve the above problems, and as a result, when the base crystal is a complex oxide of a specific divalent metal and a specific tetravalent metal, these single crystals It has been found that it exhibits excellent light emission performance that cannot be obtained when an oxide is used as a base crystal, and the present invention has been completed.

That is, the up-conversion phosphor according to the present invention is an up-conversion phosphor containing a first rare earth metal as a photosensitive component and a second rare earth metal as an activating component in a base crystal . rare earth metal is Yb, the second rare earth metal is Er, Tm or Pr, the host crystal is I complex oxide der of Ti as Zn and tetravalent metal as divalent metal and, wherein the der Rukoto those containing TiO ₂ phase.

The method for producing an up-conversion phosphor according to the present invention includes a Zn compound, a Ti compound, and an Er compound, wherein a mixing molar ratio of the Zn compound and the Ti compound is Zn: Ti = 1: 1.0 to 2.0. The mixture is fired.

The up-conversion phosphor of the present invention exhibits excellent fluorescence characteristics.
In addition, the method for producing an up-conversion phosphor of the present invention can produce an up-conversion phosphor excellent in fluorescence characteristics.

3 is an XRD measured by changing the Ti / Zn ratio in Example 1 in various ways. 3 is an emission spectrum measured by changing the Ti / Zn ratio in Example 1 in various ways. It is the graph which described these emission spectra together in order to contrast the fluorescent substance of Example 1, and the conventional fluorescent substance. In Example 1, it is a graph which shows the relationship between x (= Ti / Zn) and the phase change of complex oxide. 4 is a graph showing the relationship between x (= Ti / Zn) and light emission intensity in Example 1. 3 is an XRD measured by changing various Si / Zn ratios in Example 2. FIG. It is the emission spectrum measured in Example 2 by changing Si / Zn ratio variously. 4 is an XRD measured by changing various firing temperatures in Example 2. FIG. 4 is an emission spectrum measured in Example 2 with various firing temperatures. 6 is a graph showing a relationship between a firing temperature and emission intensity in Example 2. 6 is a graph showing changes in emission intensity when the Er / Yb ratio is variously changed in Example 3. 6 is a graph showing changes in emission intensity when the Er / Yb ratio is variously changed in Example 3. 4 is an XRD measured using various M compounds in Example 4. It is a figure which shows an Er / Yb upconversion mechanism.

  Hereinafter, the up-conversion phosphor and the manufacturing method thereof according to the present invention will be described in detail. However, the scope of the present invention is not limited to these descriptions, and the spirit of the present invention is not impaired except for the following examples. Changes can be made as appropriate within the range.

(Matrix)
The up-conversion phosphor of the present invention uses a specific complex oxide as a base crystal.

Specifically, the host crystal in the present invention is a composite oxide of a divalent metal selected from Zn, Mg, Ca, Ba and Sr and a tetravalent metal selected from Ti, Si and Ge.
When the divalent metal is Zn, particularly excellent fluorescence characteristics are exhibited.

[First rare earth metal]
The first rare earth metal is contained in the upconversion phosphor as a photosensitive component.
Here, the photosensitive component is one in which electrons are excited by absorbing light in a long wavelength region, and energy generated at that time is immediately transferred to the activating component.

  Examples of the first rare earth metal functioning as such a photosensitive component include Yb.

[Second rare earth metal]
The second rare earth metal is contained in the upconversion phosphor as an activating component.
Here, the activating component is one in which electrons are excited in multiple stages by the energy transferred from the photosensitive component, and emits high energy when returning from the excited state to the ground state.

  Examples of the second rare earth metal that functions as an activating component include Er, Tm, and Pr.

[Up-conversion phosphor]
In the up-conversion phosphor of the present invention, the base crystal is a composite oxide of the predetermined divalent metal and the predetermined tetravalent metal, It exhibits excellent operational effects that cannot be obtained when an oxide is contained alone.

  Furthermore, it was found that there are several phases in the up-conversion phosphor, and each of these phases affects the light emission performance. Although it cannot be generally stated, an example is as follows.

That is, for example, when a complex oxide of Zn and Ti is used as a base crystal, excellent light emission performance is exhibited when a Zn ₂ TiO ₄ phase and a TiO ₂ phase coexist.

Further, for example, when a complex oxide of Zn and Si is used as a base crystal, excellent light emission performance is exhibited when a Zn ₂ SiO ₄ phase is included and a SiO ₂ phase is substantially not included.

[Method for producing up-conversion phosphor]
The up-conversion phosphor of the present invention can be produced by firing a mixture of compounds containing the above components.
Although it does not necessarily limit, for example, it is preferable to manufacture as follows.

Specifically, first, each compound (for example, oxide or carbonate) containing the first rare earth metal, second rare earth metal, divalent metal, or tetravalent metal is mixed.
The mixing method may be either dry mixing or wet mixing, and is not particularly limited, but preferred is wet mixing performed by adding ethanol or the like. In the case of wet mixing, drying is performed as appropriate after mixing.

  The mixing ratio of each component is not particularly limited, but for example, the following ratio is preferable.

That is, the mixing ratio of the first rare earth metal is preferably selected as appropriate within a range of 0.105 mol or less of the first rare earth metal with respect to 1 mol of (Zn or M), for example.
In particular, when a complex oxide of Zn and Ti is used as a base crystal, the molar ratio is preferably Zn: first rare earth metal = 1: 0.06, and a complex oxide of Zn and Si is used. In the case of forming a base crystal, it is preferable that Zn: first rare earth metal = 1: 0.09 in terms of molar ratio.
Next, the mixing ratio of the second rare earth metal is, for example, in the case where a complex oxide of Zn and Ti is used as a base crystal, the molar ratio is Zn: second rare earth metal = 1: 0.01-0. A range of 05 is preferable, and it is more preferable that Zn: second rare earth metal = 1: 0.03. In the case where a complex oxide of Zn and Si is used as a base crystal, the molar ratio is preferably Zn: second rare earth metal = 1: 0.015.

For example, when a complex oxide of Zn and Ti is used as a base crystal, the mixing ratio of the Zn compound and the Ti compound is preferably in a range of Zn: Ti = 1: 0.25 to 2: A range of 0.8 to 1.2 is more preferable. Within these ranges, a host crystal in which a Zn ₂ TiO ₄ phase and a TiO ₂ phase coexist can be formed, and as described above, the light emission performance is excellent.

Further, for example, when a composite oxide of Zn and Si is used as a base crystal, the mixing ratio of the Zn compound and the Si compound is preferably in the range of Zn: Si = 1: 0.5 to 2 in terms of molar ratio. 0.5 is more preferable. As described above, when the Zn ₂ SiO ₄ phase is included but the SiO ₂ phase is substantially not included, excellent light-emitting performance is exhibited, but in the mixing ratio, the preferable phase is present. It is presumed that the same tendency is obtained when Ge, which is a family element, is used instead of Si.

  Next, the mixture obtained as described above is fired. Firing is preferably performed in an air atmosphere at 1200 to 1350 ° C. for about 4 hours.

  The firing temperature differs depending on the type of composite oxide to be obtained, and is not particularly limited. For example, when obtaining a Ti-based composite oxide, it is preferably 1200 ° C. or higher. However, if the firing temperature is too high, the fluorescence characteristics tend to be reduced, and therefore it is preferably less than 1350 ° C.

  In addition, for example, when an Si-based or Ge-based composite oxide is to be obtained, the temperature is preferably 1200 ° C. or higher. In general, the higher the firing temperature, the more the fluorescent property tends to be improved. However, if the temperature is too high, the effect of improving the fluorescent property is hardly seen, and on the other hand, the composite compound may be melted. Preferably there is.

  Hereinafter, although the up-conversion fluorescent substance concerning this invention and its manufacturing method are demonstrated in detail using an Example, this invention is not limited to these Examples.

[Example 1]
Each powder of ZnO, TiO ₂ , Yb ₂ O ₃ , and Er ₂ O ₃ was mixed in a mortar, and then ethanol was added and further mixed.
As the mixing ratio, the total weight of each powder is 4 g, the amounts of Yb and Er are fixed to 3 mol% and 1 mol%, respectively, and the molar ratio of Ti and Zn (Ti / Zn = x) is 0.25 to 2 Varyed in range.
After mixing, the mixture was dried and pulverized with a pestle to obtain a mixed powder. Furthermore, the obtained mixed powder was heated and held at 1200 ° C. for 4 hours in an air atmosphere to obtain each sample according to Example 1.

[Example 2]
Each powder of ZnO, SiO ₂ , Yb ₂ O ₃ , and Er ₂ O ₃ was mixed in a mortar, and then ethanol was added and further mixed.
The mixing ratio was Zn: Si: Er: Yb = 1: (0.5-2): 0.06: 0.09 in terms of molar ratio.
After the above mixing, the sample was completely dried and then placed in an alumina boat and baked in an air atmosphere at 1200 to 1350 ° C. for 4 hours to obtain each sample according to Example 2.

Example 3
Each powder of ZnO, SiO ₂ , Yb ₂ O ₃ , and Er ₂ O ₃ was mixed in a mortar, and then ethanol was added and further mixed.
The mixing ratio was Zn: Si = 1: 0.5 in terms of molar ratio, and the amount of Yb and Er added was changed by changing the molar amount of either Yb or Er.
Specifically, Yb is changed in the range of Er: Yb = 0.03: 0.03-0.105, or Er is changed in the range of Er: Yb = 0.005-0.025: 0.06. And mixing.
After the above mixing, the sample was completely dried and then placed in an alumina boat and baked in an air atmosphere at 1200 to 1350 ° C. for 4 hours to obtain each sample according to Example 3.

Example 4
Each sample according to Example 4 was obtained in the same manner as Example 2 except that MCO ₃ (M = Mg, Ca, Ba, or Sr) was used instead of ZnO.
At that time, the mixing ratio was M: Si: Er: Yb = 2: 1: 0.03: 0.09 in terms of molar ratio. The firing temperature was fixed at 1300 ° C.

[Performance evaluation and results]
About each obtained sample, the crystal phase identification by XRD was performed. Moreover, the emission spectrum was measured using a near-infrared laser (980 mm), and the light-emitting property was visually observed as necessary. Specifically, it is as follows.

<About Example 1>
(1) XRD measurement was performed on each sample prepared by changing various Ti / Zn ratios. The results are shown in FIG. In FIG. 1, “Z2T1” means that Zn: Ti (molar ratio) is 1: 0.5, and “Z1T1” means that Zn: Ti (molar ratio) is 1: 1. "Z1T2" means that Zn: Ti (molar ratio) is 1: 2. In addition, “RE” in RE ₂ Ti ₂ O ₇ is Yb or Er (since both peaks cannot be distinguished from each other, they are described in an integrated manner).
(2) The emission spectrum was measured for each sample prepared by changing the Ti / Zn ratio. The results are shown in FIG. In FIG. 2, “Z2T1” means that Zn: Ti (molar ratio) is 1: 0.5, and “Z1T1” means that Zn: Ti (molar ratio) is 1: 1. "Z1T2" means that Zn: Ti (molar ratio) is 1: 2.
(3) Emission spectrum measurement is performed on a sample prepared with Ti / Zn = 1: 1, and a conventional up-conversion phosphor (Y ₂ O ₃ : Er ³⁺ , Yb ³⁺ , Li ⁺ , Zn ²⁺ ) The emission spectrum was measured to compare the two. The results are shown in FIG. In FIG. 3, “Z1T1” means that Zn: Ti (molar ratio) is 1: 1.
(4) About each sample produced by changing Ti / Zn ratio (= x) variously, the relationship with the phase change of complex oxide was investigated by XRD. The results are shown in FIG.
(5) About each sample produced by changing Ti / Zn ratio (= x) variously, the relationship with emission intensity was investigated by the emission spectrum measurement using the near infrared laser. The results are shown in FIG.

<About Example 2>
(1) XRD measurement was performed on each sample prepared with various Si / Zn ratios. The firing temperature was fixed at 1300 ° C. The results are shown in FIG. In FIG. 6, “Z2S1” means that Zn: Si (molar ratio) is 1: 0.5, and “Z1S1” means that Zn: Si (molar ratio) is 1: 1. "Z1S2" means that Zn: Si (molar ratio) is 1: 2.
(2) The emission spectrum was measured for each sample prepared by changing the Si / Zn ratio. The firing temperature was fixed at 1200 ° C. The results are shown in FIG. In FIG. 7, “Z2S1” means that Zn: Si (molar ratio) is 1: 0.5, and “Z1S1” means that Zn: Si (molar ratio) is 1: 1. "Z1S2" means that Zn: Si (molar ratio) is 1: 2.
(3) XRD measurement was performed on each sample prepared by varying the firing temperature. Zn: Si was fixed at 2: 1. The results are shown in FIG.
(4) An emission spectrum was measured for each sample prepared by changing the firing temperature. Zn: Si was fixed at 2: 1. The results are shown in FIG.
(5) An emission spectrum was measured for each sample prepared by changing the firing temperature. Zn: Si was fixed at 2: 1. The results are shown in FIG.

<About Example 3>
An emission spectrum was measured for each sample prepared by changing Er: Yb in various ways. The firing temperature was fixed at 1300 ° C. The results are shown in FIG. 11 (when the amount of Yb added is changed) and FIG. 12 (when the amount of Er added is changed). In FIG. 11, X on the horizontal axis is the value of X when Er: Yb = 1.5: X. Further, in FIG. 11, Yb is not added, that is, data including X = 0 is shown. FIG. 12 shows an emission spectrum of Er: Yb = (0.5 to 2.5): 6.

<About Example 4>
(1) XRD was measured about each sample produced using various M compounds. The results are shown in FIG.
(2) Each sample was irradiated with a near-infrared laser (980 mm), and its luminescent property was observed with the naked eye. As a result, the emission intensity was inferior to that of the sample of Example 2 (using Zn). Upconversion emission was observed.

[Discussion]
In consideration of the above results, first, the up-conversion mechanism in each sample will be described.
That is, in each of the above embodiments, Er is used as the photosensitive component and Yb is used as the activating component. In this case, the up-conversion mechanism is as shown in FIG.
Up-conversion emission is enabled by two-stage excitation from Yb ³⁺ to Er ³⁺ . Green light emission at 544 nm and 557 nm is emitted when the electron relaxes from the excited level to the ground level, and red light emission at 660 nm is further excited from the excited electron to a slightly lower level. And is released when this is alleviated. Depending on the ratio of these colors, green to orange light is emitted.

<About Example 1>
(1) From the results shown in FIG. 1, in “Z1T1” and “Z1T2”, the coexistence of the TiO ₂ phase in addition to the Zn ₂ TiO ₄ phase and the RE ₂ Ti ₂ O ₇ phase is observed, whereas in “Z2T1” It was found that the TiO ₂ phase did not coexist.
(2) From the results shown in FIG. 2, it was found that “Z1T1” and “Z1T2” (particularly “Z1T1”) had higher upconversion emission intensity than “Z2T1”.
(3) From the results shown in FIG. 3, it was found that the up-conversion phosphor of the present invention exhibits better light emission than conventional up-conversion phosphors.
(4) From the results shown in FIG. 4, it was found that TiO ₂ coexisted when x (= Ti / Zn) exceeded 0.75.
(5) From the results shown in FIG. 5, the emission intensity suddenly increases when x (= Ti / Zn) exceeds 0.75, and the emission intensity decreases when x exceeds 1.25. (Excellent light emission was observed at x = 0.8 to 1.2). 1-4 together, it can be seen that the upconversion emission intensity is improved by the coexistence of the TiO ₂ phase, but that the upconversion emission is inhibited when the TiO ₂ phase is too much.

<About Example 2>
(1) From the results shown in FIG. 6, “Z1S1” and “Z1S2” have a SiO ₂ phase in addition to the Zn ₂ SiO ₄ phase, whereas “Z2S1” has no SiO ₂ phase. I understood.
(2) From the results shown in FIG. 7, it was found that the higher the Zn ratio, the higher the upconversion emission intensity (emission intensity: “Z2S1”>“Z1S1”> “Z1S2”).
(3) From the results shown in FIG. 8, it was confirmed that Zn ₂ SiO ₄ was generated at a firing temperature of 1200 to 1350 ° C.
(4) From the results shown in FIG. 9, it was confirmed that upconversion light emission occurred at a firing temperature of 1200 to 1350 ° C. It was found that a particularly high emission intensity was obtained at a firing temperature of 1250 to 1300 ° C.
(5) From the results shown in FIG. 10, as in FIG. 9, upconversion emission occurs at a baking temperature of 1200 to 1350 ° C., and a particularly high emission intensity is obtained at a baking temperature of 1250 to 1300 ° C. I understood that.

<About Example 3>
From the results shown in FIG. 11, the emission intensity tends to increase as the amount of Yb added increases. However, it has also been found that the emission intensity decreases when the amount of Yb added is too large. From the results shown in FIG. 12, the emission intensity tends to increase as the amount of Er added increases. However, it has also been found that the emission intensity decreases when the amount of Er added is too large.

<About Example 4>
(1) From the results shown in FIG. 13, it was confirmed what phase was formed when each M compound was used.
(2) It was confirmed by visual observation of the luminescent property that even if the M compound was used, upconversion luminescence could be caused.

The up-conversion phosphor of the present invention can be applied to uses similar to those of conventional phosphors such as color displays, infrared sensors, optical recording data, and laser materials. In particular, since a low energy excitation light source can be used, it is suitable as a phosphor excellent in energy saving and stability, replacing the conventional down-conversion phosphor. The method for producing the up-conversion phosphor of the present invention can be suitably used as a method for producing the excellent up-conversion phosphor as described above.
In particular, since the up-conversion phosphor of the present invention can be manufactured by a solid phase method using Zn, Ti, or the like as a raw material, the raw material cost is higher than that of a conventional product manufactured by a solution method using fluorinated glass or nanocrystals. There is also an advantage that the manufacturing cost can be kept low.

Claims (3)

An upconversion phosphor containing a first rare earth metal as a photosensitive component and a second rare earth metal as an activating component in a base crystal,
The first rare earth metal is Yb and the second rare earth metal is Er, Tm or Pr;
The host crystal is I complex oxide der of Ti as Zn and tetravalent metal as divalent metal, and is characterized in der Rukoto those containing TiO ₂ phase, up-conversion phosphors.   The up-conversion phosphor according to claim 1, wherein the first rare earth metal is Yb and the second rare earth metal is Er. Upconversion fluorescence by firing a mixture of Zn compound, Ti compound, Er compound and Yb compound , wherein the mixture molar ratio of Zn compound and Ti compound is Zn: Ti = 1: 1.0 to 2.0 Body manufacturing method.

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