KR20210090516A - Composition for UC fluorescent particle, UC fluorescent particle made from the same composition, method of making the same particle, security luminescent ink including the same particle - Google Patents

Abstract

The present invention relates to an upconversion phosphor composition, a method for manufacturing the same, and security luminescent ink including the same, and more specifically, to an upconversion phosphor particle having high luminance and excellent stability in various usage environments, a method for manufacturing the same at low costs, and security luminescent ink that is difficult to counterfeit by including the same.

Description

An upconversion phosphor composition, upconversion phosphor particles prepared therefrom, a method for preparing the same, and a security luminescent ink comprising the same ink including the same particle}

The present invention relates to an upconversion phosphor composition, a method for manufacturing the same, and a security light emitting ink comprising the same, and more particularly, to upconversion phosphor particles having high luminance and excellent stability in various use environments, and a method for manufacturing the same at a low cost And it relates to a security light emitting ink that can make it difficult to counterfeit products including the same.

With the growth of the global economy, counterfeiting products or counterfeiting documents is increasing as a global problem, not just occurring in some countries. Distribution of counterfeit products not only threatens the economic interests of intellectual property owners, but also threatens public health and safety. The increase in such crimes related to counterfeiting means an increase in demand for advanced technologies to prevent related crimes. Therefore, global companies are paying much attention to the development of anti-counterfeiting technology to protect their products, and legal, institutional and technical devices are required to block various types of counterfeit products. Conventional anti-counterfeiting technologies include a method of attaching an ID to a product, a method using secret ink or invisible printing, a hologram method with the unique characteristics and marks of the manufacturer and product, an authentication method using a barcode, and product information There is an RFID method that utilizes an RF tag in which is stored. 1 illustrates conventional anti-counterfeiting techniques.

In addition to these various anti-counterfeiting techniques, there is a technique using a fluorescent pigment. Fluorescent pigments are pigments that emit fluorescence conspicuously with long-wavelength light by receiving ultraviolet rays of sunlight and purple, blue, and green rays of visible light. Counterfeit goods can be easily distinguished from counterfeit products by making a specific pattern with a luminescent material and allowing the fluorescent pigment in the specific pattern to be emitted by ultraviolet (UV) or near-infrared (NIR) light. Fluorescent pigments include organic fluorescent pigments and inorganic fluorescent pigments. Organic and inorganic luminescent materials based on downconversion (DC) luminescence are used as luminescent inks. It absorbs short-wavelength light, such as ultraviolet, and emits long-wavelength visible light. However, UV downconversion materials and UV light sources have the disadvantage of being easy to access and easy to replicate.

In contrast, near-infrared (NIR) luminescent materials based on upconversion (UC) luminescence are difficult to replicate compared to UV luminescent materials, and NIR light sources are also difficult to access. In addition, the upconversion luminescent material has the advantage of being difficult to replicate because it can be formulated to produce a designed emission color only under the designed emission lifetime.

A phosphor is a light-emitting material that absorbs low-energy light such as electron beams or X-rays and emits high-energy visible light. The phosphor is largely composed of a host, an activator, and a co-activator. The matrix is a material constituting most of the phosphor, which fixes the activator in the matrix grid, absorbs excitation energy and transfers it to the activator. The activator is mainly substituted at the cation site, receives the activator from the parent, is excited, and then releases energy while falling to the ground state. It determines the energy involved in the luminescence process and affects the luminous color and luminous efficiency. The characteristic luminescent properties are obtained by adding a relatively small amount of the active agent to the parent material. The deactivator is added to increase the luminous efficiency, and it is excited by receiving energy and then falls to the ground state and transfers energy to the activator. 2 is a diagram showing a schematic diagram of a phosphor containing an activator. When the parent body of the phosphor absorbs energy from the outside, the activator takes over the energy from the parent body and creates a center that converts it into visible light and emits light.

Phosphor is used as a good security material because it has excellent hiding power and can easily observe light emission by an external light source. It is also applied to various fields such as light energy conversion technology, display devices, lasers, radiation detectors, and biolabels. Rare earth-based oxides, fluorine compounds, and chlorine compounds are mainly used as the matrix for these UC phosphors. In order to manufacture a more competitive UC phosphor, it must be inexpensive in terms of price and must be a material that can have stability in various use environments. Therefore, it is necessary to develop UC phosphors based on non-rare earth oxides.

Registered Patent Publication No. 10-1957927 (2019.03.07.)

The present invention has been devised to solve the above problems, and the first problem to be solved by the present invention relates to a method of manufacturing UC phosphor particles having excellent luminance and stability in various use environments.

A second problem to be solved by the present invention is to provide a composition for preparing the above-described UC phosphor particles and UC phosphor particles prepared therefrom.

The third problem to be solved by the present invention is to provide a security light emitting ink having excellent light emitting luminance to which the above-described UC phosphor is applied.

In order to solve the first problem described above, the present invention provides (1) an activator precursor comprising at least one metal selected from among holmium (Holmium, Ho), thulium (Tm) and erbium (Erbium, Er); a co-activator precursor comprising a ytterbium (Yb) metal; and zirconium (Zr) as a first metal and lanthanum (La), cerium (Cerium, Ce), gadolinium (Gd), yttrium (Y) and lutetium (Lutetium, Lu) as the second metal ) preparing a UC phosphor composition comprising a host precursor including at least one selected from among rare earth metals;

(2) forming droplets by spraying the UC phosphor composition; and

(3) pyrolyzing and drying the droplets to form a precursor powder; provides a method for producing UC phosphor particles comprising a.

In the manufacturing method according to a preferred embodiment of the present invention, the mole fraction of the first metal may be greater than the mole fraction of the second metal.

The manufacturing method according to a preferred embodiment of the present invention may further include; after step (3), (4) post-heating the precursor powder at a temperature of 700°C to 1,300°C.

In the manufacturing method according to a preferred embodiment of the present invention, in step (1), the second metal may be added in a molar fraction of 5 mol% to 20 mol%.

According to a preferred embodiment of the present invention, the activator and the deactivator may be added to the upconversion phosphor particle composition in an amount of 0.1 mol% to 0.5 mol% and 1 mol% to 20 mol%, respectively.

According to a preferred embodiment of the present invention, the thermal decomposition in step (3) may be performed at a temperature in the range of 700 ℃ to 1,100 ℃.

According to a preferred embodiment of the present invention, the first metal may be included in the form of a nitrate or sulfate of zirconium.

According to a preferred embodiment of the present invention, a UC phosphor composition may be prepared by further adding a flux to the active solution in step (1).

The flux _{may be at least one selected from Li 2} CO ₃ , LiCl, LiNO ₃ , Na ₂ CO ₃ , NaHCO ₃ and KCl, and in step (1), the flux is preferably added to the UC phosphor particle composition by 0.5 wt. % to 5 wt% may be added.

In addition, in order to solve the second problem described above, the present invention provides a mother precursor comprising at least one rare earth metal selected from zirconium as a first metal and lanthanum, cerium, gadolinium, yttrium and lutetium as a second metal; an active agent comprising at least one metal selected from holmium, thulium and erbium; and a deactivator including a ytterbium metal; provides a UC phosphor composition comprising.

According to a preferred embodiment of the present invention, the second metal may be included in a mole fraction of 5 mol% to 20 mol%.

UC phosphor particles are prepared by spray pyrolysis of the phosphor composition of the present invention as described above, and the UC phosphor particles include a compound represented by the following formula (1).

[Formula 1]

(Zr _1-xyz A _x Yb _y M _z )O ₂

In Formula 1, A is an activator comprising at least one metal selected from holmium, thulium, and erbium, M is a second metal comprising at least one rare earth metal selected from lanthanum, cerium, gadolinium, yttrium and lutetium, and 0.001≤ x≤0.005, 0.01≤y≤0.2, and 0.05≤z≤0.2.

In the upconversion phosphor particles according to a preferred embodiment of the present invention, the crystal structure of the matrix may be tetragonal at a temperature of 900°C to 1,300°C.

In order to solve the fourth problem described above, the present invention provides a security light emitting ink comprising the above-described UC phosphor particles.

The up-conversion phosphor particles according to the present invention have excellent luminescence luminance, and compared to down-conversion phosphor particles, it is easy to use as an anti-counterfeiting technology because it is difficult for the general public to access the light source and material. It has the advantage of excellent stability.

The light emitting ink according to the present invention exhibits excellent light emission luminance regardless of temperature, and can be used as an anti-counterfeiting and tampering ink.

1 shows (a) invisible ink, (b) hologram, and (c) RFID as examples of conventional anti-counterfeiting technology.
2 is a diagram showing a schematic diagram of a phosphor including an activator.
3 is a diagram schematically illustrating a light emitting mechanism of an upconversion phosphor according to an embodiment of the present invention.
4 is a view schematically illustrating a method of manufacturing upconverted phosphor particles according to an embodiment of the present invention.
5 is a view showing the crystal structures of the parent body of the upconverted phosphor particle according to an embodiment of the present invention according to a change in temperature.
6 is a view showing (a) photoluminescence (PL) spectrum and (b) XRD pattern graphs measured at different post-heat treatment temperatures of an upconversion phosphor containing _{ZrO 2 .}
7 is a view showing a PL spectrum (left) and an XRD pattern graph (right) of an upconverted phosphor particle according to an embodiment of the present invention having a matrix having a different content of cerium.
FIG. 8 shows a comparison of PL spectra of upconverted _{phosphor particles and ZrO 2} upconverted phosphor particles to which cerium is not added according to an embodiment of the present invention.
9 is a view showing a PL spectrum (left) and an XRD pattern graph (right) of an upconverted phosphor particle according to an embodiment of the present invention prepared by changing the post-heat treatment temperature.
FIG. 10 is a graph showing the comparison of luminescence characteristics according to the treatment temperature of _{ZrO 2 upconversion phosphor particles with and without cerium.}
11 is a PL spectrum graph showing the luminescence characteristics of _{ZrO 2} upconversion phosphor particles according to the ^{Yb 3+ ion content when the Ho 3+} ion content is fixed at 0.2 mol%.
FIG. 12 is a PL spectrum graph comparing the emission characteristics of _{ZrO 2} upconversion phosphor particles according to the content of ^{Ho 3+ ions when the content of Yb 3+} ions is fixed at 2 mol%.
13 is a view showing a PL spectrum (left) and an XRD pattern (right) showing a difference in emission luminance according to a content of _{Li 2} CO _{3 in ZrO 1.87} cubic upconversion phosphor particles.
14 is a photograph of upconverted phosphor particles according to the present invention, (a) (Zr, Ce)O ₂ :Ho ³⁺ /Yb ³⁺ , (b) (Zr, Ce)O ₂ :Ho ³⁺ /Yb ³⁺ and Li ₂ CO ₃ , respectively.
15 is a PL spectrum graph showing luminescence characteristics of upconverted phosphor particles according to an embodiment of the present invention having different Li2CO3 contents.
16 is a view illustrating a case of (a) irradiating a 980 nm IR laser after (a) irradiating a 980 nm IR laser (b) irradiating a 980 nm IR laser after applying a luminescent ink to which an upconversion phosphor particle according to an embodiment of the present invention is applied to a product Each was photographed.

In the present invention, the term “mol fraction” means the mole fraction between metal atoms excluding oxygen (O) in the compound represented by the following formula (1).

[Formula 1]

(Zr _1-xyz A _x Yb _y M _z )O ₂

In Formula 1, A is at least one selected from Ho, Tm, and Er, M is at least one selected from La, Ce, Gd, Y and Lu, and 0.001≤x≤0.005, 0.01≤y≤0.2, 0.05≤z≤ is 0.2.

In the present invention, "spray solution" is a solution for producing a UC phosphor through spray pyrolysis, and is the same as the UC phosphor composition.

In the present invention, "precursor powder" is a powder prepared through spray pyrolysis of the UC phosphor composition, and means a phosphor powder before crystal growth through post-heat treatment.

Hereinafter, the present invention will be described in more detail.

As described above, the conventional phosphor is a down-conversion (DC) phosphor, or has a problem in that manufacturing cost is high by using a rare earth as a matrix, or the light emitting characteristic is weakened according to temperature. Accordingly, the present invention provides an activator precursor comprising at least one metal selected from holmium (Holmium, Ho), thulium (Tm) and erbium (Erbium, Er); a co-activator precursor comprising a ytterbium (Yb) metal; and zirconium (Zr) as a first metal and lanthanum (La), cerium (Cerium, Ce), gadolinium (Gd), yttrium (Y) and lutetium (Lutetium, Lu) as the second metal ) preparing an up-conversion (UC) phosphor particle composition comprising a host precursor including at least one selected from among rare earth metals; (2) spraying the UC phosphor particle composition to form droplets; and (3) thermally decomposing and drying the droplets to form a precursor powder.

Preferably, step (1) comprises the following two steps:

(1-1) preparing an activator solution comprising the activator precursor and the deactivator precursor; (1-2) adding the parent precursor to the active solution to prepare the UC phosphor particle composition;

Hereinafter, each step will be described.

4 is a schematic diagram illustrating a method of manufacturing UC phosphor particles according to an embodiment of the present invention step by step.

Referring to FIG. 4 , preparing a UC phosphor composition (spray solution) including a parent precursor (parent), a flux, and an activator precursor (activator precursor and deactivator precursor); spray pyrolyzing the UC phosphor composition; and post-heat treatment (heat treatment) of the precursor powder obtained by spray pyrolysis; it can be seen that UC phosphor particles can be prepared.

In step (1), first, an active solution including a parent precursor, an activator precursor, and a deactivator precursor is prepared. Preferably, step (1) includes the following two steps.

(1-1) preparing an activator solution comprising an active agent and the sub-active agent; and

(1-2) preparing the upconverted phosphor particle composition by adding the parent precursor to the active solution.

The parent precursor is a first metal of zirconium and a second metal of lanthanum (Lanthanum, La), cerium (Cerium, Ce), gadolinium (Gadolinium, Gd), yttrium (Yttrium, Y) and lutetium (lutetium, Lu) one or more selected rare earth metals. Here preferably the mole fraction of the first metal is greater than the mole fraction of the second metal. That is, since the molar fraction of zirconium, which is the first metal, is the largest among metals included in the UC phosphor composition, there is an advantage in that it can be produced at a lower price than conventional upconversion phosphor particles based on rare earth metals.

The first metal may be preferably included in the form of a nitrate or sulfate of zirconium. That is, the first metal is Zr(NO ₃ ) ₄ Or Zr(SO ₄ ) _{2 It} may be included in the form of. More preferably, it may include a hydrate of the zirconium sulfate. That is, Zr(SO ₄ ) ₂ ·4H ₂ O may be used.

The second metal may preferably be cerium. Cerium is preferably used in the form of nitrate or a hydrate of nitrate. That is, Ce(NO ₃ ) ₃ ·6H ₂ O may be added in the form.

In addition, by using the above-described second metal together with the first metal, it is possible to improve the stability of the zirconium-based UC phosphor particles at a high temperature. For example, when cerium is included in zirconium oxide, which changes to a crystal structure without upconversion light-emitting properties at high temperatures, the crystal structure does not change even at a high temperature of about 1,100°C to 1,300°C, so the upconversion light-emitting efficiency at high temperature is maintained can be

According to an embodiment of the present invention, the second metal may have a mole fraction of 5 mol% to 20 mol%. When the mole fraction of the second metal is less than 5 mol%, the crystal structure of the zirconium oxide matrix changes at a high temperature, and thus the UC light-emitting properties are lost.

5 is a diagram illustrating a crystal structure that _{ZrO 2 may have depending on temperature.} Among them, UC light emission may occur in cubic and tetragonal crystal structures, but when ZrO ₂ is at a high temperature of about 1,200° C. or higher, a phase transformation into a monoclinic structure occurs. , there is no UC emission characteristic in the monoclinic structure.

As described above, when the mole fraction of the second metal is less than 5 mol%, the crystal structure of the parent undergoes a phase transformation from a tetragonal to a monoclinic at a high temperature of 1,200° C., and the UC emission characteristics are lost.

Conversely, when the mole fraction of the second metal exceeds 20 mol%, the production cost is high due to an increase in the amount of rare earth metal used.

The activator precursor may include one or more metal oxides selected from holmium, thulium, and erbium. Preferably, it may include an oxide of holmium. As an oxide of holmium, Ho ₂ O ₃ is have. Holmium is substituted for Zr in the crystal lattice _{of ZrO 2} in the cation form of ^{Ho 3+} in the UC phosphor particles and functions as an activator.

The activator is substituted at the cation site in the host, which is the material that constitutes most of the phosphor particles, receives energy from the parent, is excited, and then falls to the ground state and emits energy. It affects the luminous efficiency.

The sub-activator is a material added together with the activator to improve the luminous efficiency of the phosphor particles. Like the activator, the sub-activator is excited by receiving energy and then falls to the ground state and transfers energy to the activator. The precursor of the deactivator may preferably include an oxide of ytterbium. As an oxide of ytterbium, there is Yb ₂ O ₃ . Ytterbium functions as a deactivator in the cation form of ^{Yb 3+} in the matrix of UC phosphor particles.

2 is a diagram schematically showing a lattice structure of phosphor particles containing an activator. In FIG. 2, H represents the host, and A represents the activator. Referring to FIG. 2 , it can be seen that the activator in the parent lattice is excited and then emits light.

3 is a view showing the energy flow in which the activator and the deactivator are excited by obtaining photons in the UC phosphor particles according to a preferred embodiment of the present invention, and then fall to the ground state and emit light. Referring to Figure 3, a Yb ³⁺ ion was in the ground state to the ² F _7/2 state to receive energy from the light source was here ² F _5/2 state to deliver the energy to Ho ³⁺ ions, ⁵ I ₈ ^{Ho 3+} ions in the ground state are ^{excited to energy levels such as 5} I ₆ , ⁵ F ₅ , ⁵ F ₄ ⁵ S ₂ , and then stabilize again and emit light of wavelengths such as green and red. .

In step (1-1), an activator is prepared by dissolving an activator and a subactive agent in a solvent.

Preferably, the active solution may be an aqueous solution in which the active agent and the sub-active agent are dissolved in an acid. For example, the active solution may be an aqueous solution in which an active agent and a sub-active agent are dissolved in nitric acid. However, the acid is not necessarily limited to nitric acid.

For example, when using Ho ₂ O ₃ as an activator and Yb ₂ O ₃ as a sub-activator, when an activator aqueous solution is prepared by dissolving an activator and a sub-active agent in nitric acid, the reaction formulas are the following Reaction Schemes 1 and 2-2 same.

[Scheme 1]

Ho ₂ O ₃ + 6HNO ₃ → 2Ho(NO ₃ ) ₃ + 3H ₂ O

[Scheme 2]

Yb ₂ O ₃ + 6HNO ₃ → 2Yb(NO ₃ ) ₃ + 3H ₂ O

Since the reactions of Schemes 1 and 2 are both exothermic reactions, it is preferable to dissolve them while cooling by adding distilled water together.

Next, in step (1-2), an upconversion phosphor particle composition is prepared by further adding other additives such as a parent precursor and a flux to the active solution prepared in step (1-1) above. The composition may preferably be an aqueous solution.

In this case, the active agent and the sub-active agent in the composition may be included so as to have a mole fraction of 0.1 mol% to 0.5 mol%, 1 mol% to 20 mol%, respectively.

When the molar fraction of the active agent is less than 0.1 mol%, all the energy transmitted by the deactivator is not received, and the luminescence luminance of the UC phosphor particles is lowered. When the molar fraction of the active agent is excessively high than 0.5 mol%, the ratio between active agents There is a problem in that the luminance is lowered due to the occurrence of a concentration decay phenomenon due to the transfer of luminescent energy.

Also, the molar fraction of the deactivator When the concentration is less than 5 mol%, energy cannot be sufficiently transferred to the activator and the luminance is lowered. Conversely, when the concentration exceeds 20 mol% and the concentration is too high, the concentration decreases (non-luminescence between sub-activators rather than transfer of absorbed light to the active agent) There is a problem in that the luminance of light is lowered due to the energy transfer) phenomenon.

The molar fraction of the active agent may preferably be between 0.15 mol% and 0.25 mol%, and the concentration of the co-active agent may preferably be between 10 mol% and 15 mol%.

According to a preferred embodiment of the present invention, a flux (flux) may be further added to the UC phosphor composition. Flux lowers the melting points of the parent, active and deactivator materials, helping pyrolysis and positioning of the active and deactivator within the matrix lattice.

The flux may be preferably _{at least one selected from Li 2} CO ₃ , LiCl, LiNO ₃ , Na ₂ CO ₃ , NaHCO ₃ and KCl, and more preferably Li ₂ CO ₃ .

The flux may be preferably added to the UC phosphor composition in an amount of 0.5 wt% to 5 wt%. If the content of the flux is less than 0.5 wt%, the effect of improving luminance of light emission may be low. However, when the content of the flux exceeds 5 wt%, excessive particle growth may be induced in the post-heat treatment process, thereby degrading powder properties and luminescence luminance.

The thus-prepared UC phosphor composition can be prepared into UC phosphor particles through a spray pyrolysis process, the process comprising the steps of (2) spraying the UC phosphor composition to form droplets; and (3) thermally decomposing and drying the droplets to form a precursor powder.

The spray pyrolysis apparatus preferably includes a droplet generating unit that generates droplets using an ultrasonic vibrator, a kiln in which thermal decomposition occurs with high-temperature energy, and a collecting unit in which dried particles are collected.

Since the device is maintained at a high temperature during the pyrolysis process, it is preferable to continuously flow the cooling water around the vibrator of the droplet generator. For smooth flow of the droplets generated in the droplet generator, air at about 30 L/min to 100 L/min can spill

Preferably, the thermal decomposition may be performed at a temperature in the range of 700 °C to 1,100 °C.

The manufacturing method according to a preferred embodiment of the present invention may further include; after step (3), (4) post-heating the precursor powder at a temperature of 700°C to 1,300°C. The crystal size of the UC phosphor particles grows through such a post-heat treatment step, which affects the luminance of light emission.

When the post-heat treatment temperature is less than 700°C, crystal growth of the UC phosphor particles does not occur sufficiently, resulting in low luminance, and when the post-heat treatment temperature exceeds 1,300°C, a crystal structure with low luminance or an impurity phase is formed to form a UC phosphor The emission luminance of the particles may decrease.

Preferably, the post-heat treatment temperature may be 900 to 1,300 °C.

Hereinafter, the UC phosphor composition used in the above-described manufacturing method will be described.

The present invention relates to a mother precursor comprising zirconium as a first metal and at least one rare earth metal selected from among lanthanum, cerium, gadolinium, yttrium and lutetium as a second metal; an activator precursor comprising at least one metal selected from holmium, thulium and erbium; and a deactivator precursor including ytterbium; provides a UC phosphor particle composition comprising.

Here, the first metal is included in the UC phosphor composition in the form of nitrate, sulfate, or sulfate in the form of a hydrate is the same as that described above, so the description is omitted, and the second metal is preferably cerium, and the description of cerium also As described above, detailed descriptions are omitted, and descriptions of the functions and mole fractions of the active agent and the sub-active agent are also omitted.

In addition, since the description of the composition between each component of the UC phosphor composition is also the same as that described above, a description thereof will be omitted.

Hereinafter, UC phosphor particles prepared by the above-described method using the UC phosphor composition will be described.

The present invention is prepared by spray pyrolysis of the above-described phosphor composition of the present invention. The phosphor composition constitutes each particle of the precursor powder prepared by thermally decomposing and drying the droplets in step (3) of the above-described manufacturing method, and preferably, the precursor powder obtained in step (3) is post-heat-treated to grow crystals. It may be a made-up particle.

The UC phosphor particles according to the present invention include a compound represented by the following formula (1).

[Formula 1]

(Zr _1-xyz A _x Yb _y M _z )O ₂

In Formula 1, A is an activator comprising at least one metal selected from holmium, thulium, and erbium, M is a second metal comprising at least one rare earth metal selected from lanthanum, cerium, gadolinium, yttrium and lutetium, and 0.06 ?x+y+z?0.45.

According to a preferred embodiment of the present invention, at least one of the following conditions 1) to 3) for x, y, and z in Formula 1 may be satisfied.

1) 0.001≤x≤0.005

2) 0.01≤y≤0.2

3) 0.05≤z≤0.2.

Here, x, y and z are the molar fraction of the active agent, the molar fraction of the deactivator, and the mole fraction of the second metal, respectively, and the effects according to the molar fraction ranges are the same as described above, and thus descriptions thereof will be omitted below.

In the UC phosphor particles according to a preferred embodiment of the present invention, the crystal structure of the matrix may be tetragonal at a temperature of 900°C to 1,300°C. Originally, ZrO _{2 changes} its crystal structure from tetragonal to monoclinic at a high temperature exceeding 1,100 ° C. When the mole fraction z of the second metal is within the above range, this phase transformation is suppressed to improve upconversion luminescent properties. It can be maintained while reducing manufacturing costs. _{When z is less than 0.05, the crystal structure of ZrO 2} may change to a monoclinic system in the post-heat treatment process, and thus the UC luminescence performance may be lost. In the UC phosphor particles according to the present invention, even at a temperature of 1,100° C. to 1,300° C., the crystal structure of the parent maintains a tetragonal system, thereby maintaining upconversion emission performance and increasing emission luminance. Accordingly, it is used as a luminescent ink and is easy to use as a counterfeit prevention technology.

According to a preferred embodiment of the present invention, the phosphor particles may have an average particle diameter (D50) of 0.6 μm to 1.5 μm. When the size of the phosphor particles is the same as above, it is preferable because the maximum emission luminance can be achieved.

The present invention also provides a secure luminescent ink comprising the above-described upconverted phosphor particles. The light emitting ink has a characteristic of emitting visible light by receiving energy from an infrared light source, and thus can be used as an anti-counterfeiting ink for detecting counterfeiting or tampering of a product.

Hereinafter, the present invention will be described in more detail with reference to the following examples, but the following examples are not intended to limit the scope of the present invention, which should be construed to aid understanding of the present invention.

<Example>

Example 1: Preparation of Upconverted Phosphor Particles

Ho ₂ O _{3 as an activator and Yb 2} O ₃ as a sub-activator were dissolved in a 60% aqueous nitric acid solution to make an active aqueous solution.

For Ho2O3, 99.9% purity of HANKYUNG was used, and for Yb2O3, 99.9% purity of Alfa Aesar's was used.

1 g and 10 g of holmium oxide and ytterbium oxide were used, respectively, and about 15.06 ml of nitric acid was used to dissolve them. In the active solution generation reaction, a small amount of distilled water was added to cool the heat due to an exothermic reaction, and when all the oxides were dissolved and the solution became transparent, distilled water was added to adjust the amount of the active agent aqueous solution to a total of 400 g.

The thus-prepared active solution and the following reagent were put into a 1L beaker, and distilled water was filled to the 500 ml scale, and then stirred until all the solute was dissolved and the solution became transparent. A spray solution (upconversion phosphor particle composition) was prepared by fixing the total volume to 500 ml and the total moles of the parent precursor to 0.2 M.

Parent: Zr(SO ₄ ) ₂ ·4H ₂ O (purity 98%, Alfa Aesar Company) 27.85 g and Ce(NO ₃ ) ₃ ·6H ₂ O (purity 99%, Sigma Aldrich Company) 4.39 g

Activator solution: 15.13 g of 400 g of aqueous solution in which 1 g of Ho ₂ O _{3 is dissolved}

Sub-activator solution: 102.56 g of an aqueous solution of 400 g dissolved in _{10 g Yb 2} O ₃

Flux: Li ₂ CO ₃ (purity 99.99%, High Purity Chemicals) 0.11 g

Organic additive: Citric acid (purity 99.5%, Alfa Aesar) and ethylene glycol (purity 99.8%, Sigma Aldrich) 50 mol% based on the parent molar concentration

Drying control agent: Dimethylformamide (purity 94.4%, Daejung Corporation) 0.1 M

The molar fractions of Zr, Ce, Ho and Yb in the finally prepared spray solution were 76.8%, 10%, 0.2% and 13%, respectively.

The spray solution was put into a spray pyrolysis device to perform spray pyrolysis and post-heat treatment.

The spray pyrolysis device is composed of a droplet generating unit using six ultrasonic vibrators of 1.7 MHz, a kiln where thermal decomposition occurs with high-temperature energy, and a collecting unit in which dried and generated particles are collected. For smooth flow, 50 L/min of air was flowed, and the spray solution was thermally decomposed at a temperature of 900° C. in the kiln.

After thermal decomposition, the resultant was dried and the obtained precursor powder was collected in a collecting unit.

Post-heat treatment was performed by maintaining the precursor powder in a box furnace maintained at 1,100° C. for 3 hours to obtain upconverted phosphor particles.

Examples 2 to 24 and Comparative Examples 1 to 5: Preparation of upconversion phosphor particles

Upconversion phosphor particles were prepared in the same manner as in Example 1, except that the post-heat treatment temperature, cerium molar ratio, activator/deactivator concentration, and flux addition concentration were adjusted as shown in Table 1 below.

division (Zr _1-y Ce _y )O ₂
in y Ho ³⁺ concentration
(mol%) Yb ³⁺ concentration
(mol%) Li ₂ CO ₃ concentration
(wt%) Post heat treatment temperature Example 2 0.1 0.2 13 2 1,300 Example 3 0.1 0.2 13 2 1,100 Example 4 0.1 0.2 13 2 1,000 Example 5 0.1 0.2 13 2 900 Example 6 0.027 0.2 13 2 1,200 Example 7 0.077 0.2 13 2 1,200 Example 8 0.127 0.2 13 2 1,200 Example 9 0.177 0.2 13 2 1,200 Example 10 0.277 0.2 13 2 1,200 Example 11 0.477 0.2 13 2 1,200 Example 12 0.1 0.1 2 2 1,200 Example 13 0.1 0.2 2 2 1,200 Example 14 0.1 0.3 2 2 1,200 Example 15 0.1 0.4 2 2 1,200 Example 16 0.1 0.5 2 2 1,200 Example 17 0.1 0.2 One 2 1,200 Example 18 0.1 0.2 3 2 1,200 Example 19 0.1 0.2 5 2 1,200 Example 20 0.1 0.2 7 2 1,200 Example 21 0.1 0.2 10 2 1,200 Example 22 0.1 0.2 13 2 1,200 Example 23 0.1 0.2 15 2 1,200 Example 24 0.1 0.2 20 2 1,200 Example 25 0.1 0.2 13 0 1,200 Example 26 0.1 0.2 13 0.5 1,200 Example 27 0.1 0.2 13 One 1,200 Example 28 0.1 0.2 13 3 1,200 Example 29 0.1 0.2 13 4 1,200 Comparative Example 1 0 0.2 13 0 1,300 Comparative Example 2 0 0.2 13 0 1,200 Comparative Example 3 0 0.2 13 0 1,100 Comparative Example 4 0 0.2 13 0 1,000 Comparative Example 5 0 0.2 13 0 900

<Experimental example>

Experimental Example 1: ZrO ₂ Luminescence characteristics according to post-heat treatment temperature of UC phosphor particles

The light emission characteristics of the upconverted phosphor particles according to Comparative Examples 1 to 5 were analyzed as follows. After filling an appropriate amount of sample in a round holder with a diameter of 2 cm (with a transparent quartz window), a 980 nm infrared light source (Optoenergy, 600 mA) was irradiated toward the quartz window. At this time, the PL spectrum emitted from the sample was measured using a spectrophotometer (PerkinElmer LAMBDA 550). In addition, the crystal structure of the prepared phosphor powder was measured using an X-ray diffraction analyzer (Rigaku, MiniFlex600).

The measurement results are shown in FIG. 6 .

Referring to FIG. 6A , the highest luminance at a wavelength of about 550 nm is exhibited at a post-heat treatment temperature of 900° C. to 1,300° C., and as the temperature increases, the luminance gradually increases, showing the highest luminance at 1,100° C., and 1,200° C. and at 1,300°C, it can be seen that the emission luminance is almost 0.

Referring to FIG. 6B , it can be seen that the XRD pattern of the phosphor particles is the same as that of monoclinic ZrO 2 at 1,200° C. or higher.

_{Accordingly, it can be seen that the upconversion phosphor particles having ZrO 2} as a matrix not containing cerium lose their upconversion luminescence properties because the crystal structure changes from a tetragonal system to a monoclinic system at a high temperature.

Experimental Example 2: ZrO according to rare earth metal addition ₂ Comparison of luminescence properties of UC phosphor particles

The PL spectrum and XRD pattern of the upconversion phosphor particles according to Examples 6 to 11 and Comparative Example were measured in the same manner as in Experimental Example 1, and the results are shown in FIG. 7 , and the PL spectrum of Example 1 and Comparative Example 1 is shown in FIG. 8 . In addition, a graph showing the emission intensity at the maximum emission peak of Example 1 and Comparative Example 1 according to the post-heat treatment temperature is shown in FIG. 10 .

Checking the PL spectrum on the left of FIG. 7, it can be seen that when the content of cerium is 0, there is no upconversion fluorescence property at all. Referring to the figure on the right, when y=0, it has a monoclinic crystal structure, and cerium has a It can be seen that when y is not 0, it has a tetragonal crystal structure.

Referring to FIG. 8 , it can be seen that the upconverted phosphor particles of Example 1 in which y=0.1 and Comparative Example 1 in which y=0 have significantly different emission luminance at the maximum emission wavelength. Referring to FIG. 10 , it can be seen that the luminescence brightness of the upconversion phosphor particles of Comparative Example 1 decreases to almost 0 when the post-heat treatment temperature exceeds 1,100° C., but the phosphor particles of Example 1 emit light even when the temperature exceeds 1,100° C. It can be seen that the luminance increases.

Therefore, at a high temperature exceeding 1,100°C, the crystal structure of the matrix to which cerium is not added does not cause upconversion emission, whereas when cerium is added, the tetragonal crystal structure is maintained even at 1,200°C to improve the upconversion emission performance. was found to keep. In addition, it was found that the higher y, that is, the higher the cerium content, the better the light emission luminance.

Experimental Example 3: (Zr, Ce)O ₂ Luminescence characteristics according to post-heat treatment temperature of UC phosphor particles

For the upconversion phosphor particles according to Examples 1 to 5, PL spectra and XRD patterns were measured in the same manner as in Experimental Example 1, and are shown in the left and right drawings of FIG. 9, respectively.

Referring to the PL spectrum of FIG. 9 , it can be seen that the luminance of the UC phosphor particles to which cerium is added increases even when the post-heat treatment temperature rises. In addition, referring to the XRD pattern on the right side of FIG. 9 , it can be confirmed that the tetragonal crystal structure is maintained even at a post-heat treatment temperature exceeding 1,100°C.

Experimental Example 4: ZrO according to the content of the active agent / sub-active agent ₂ Luminescence Characteristics of UC Phosphor Particles

PL spectra of the upconverted phosphor particles of Examples 12 to 24 were measured in the same manner as in Experimental Example 1, and are shown in FIGS. 11 and 12 . Specifically, the PL spectra of Examples 12 to 16 are shown in FIG. 12 , and the PL spectra of Examples 17 to 24 are shown in FIG. 11 .

Referring to FIG. 12 , it can be seen that the maximum emission luminance is obtained when the ^{Ho 3+ concentration is 0.2 mol%, and when the concentration of Ho 3+ exceeds 0.4 mol%, the emission luminance drops sharply.}

In addition, referring to FIG. 11 , it can be seen that the maximum emission luminance is obtained when the ^{Yb 3+ concentration is 13 mol%, and when the Yb 3+} concentration is less than 5 mol% or exceeds 15 mol%, the emission luminance drops sharply. .

Experimental Example 5: ZrO according to the addition of flux ₂ Luminescence Characteristics of UC Phosphor Particles

For the upconversion phosphor particles of Examples 1 and 25 to 29, PL spectra and XRD patterns were measured in the same manner as in Experimental Example 1, and are shown in FIG. 13 .

Referring to FIG. 13 , it was found that the light emission luminance at the maximum emission wavelength was the highest when the flux was added in 2 wt%, and when it was less than 1 wt% or more than 4 wt%, the emission luminance was significantly reduced. could check

Claims (16)

(1) an activator precursor comprising at least one metal selected from holmium (Ho), thulium (Tm) and erbium (Er); a co-activator precursor comprising a ytterbium (Yb) metal; and zirconium (Zr) as a first metal and lanthanum (La), cerium (Cerium, Ce), gadolinium (Gd), yttrium (Y) and lutetium (Lutetium, Lu) as the second metal ) preparing an up-conversion (UC) phosphor composition comprising a host precursor including at least one selected from among rare earth metals;
(2) forming droplets by spraying the UC phosphor composition; and
(3) pyrolyzing and drying the droplets to form a precursor powder; UC phosphor particle manufacturing method comprising a. According to claim 1,
UC phosphor particle manufacturing method, characterized in that the mole fraction of the first metal is greater than the mole fraction of the second metal. According to claim 1,
After step (3) above
(4) post-heating the precursor powder at a temperature of 700° C. to 1,300° C.; UC phosphor particle manufacturing method further comprising a. According to claim 1,
In the step (1), the method for producing UC phosphor particles, characterized in that the second metal is added so as to be included in a molar fraction of 5 mol% to 20 mol%. According to claim 1,
The method for producing UC phosphor particles, characterized in that the activator and the deactivator are included in the UC phosphor composition in mole fractions of 0.1 mol% to 0.5 mol% and 1 mol% to 20 mol%, respectively. According to claim 1,
The thermal decomposition in step (3) is a UC phosphor particle manufacturing method, characterized in that it is carried out at a temperature in the range of 700 ℃ to 1,100 ℃. According to claim 1,
The first metal is a UC phosphor particle manufacturing method, characterized in that it is included in the form of a nitrate (nitrate) or sulfate (sulfate) of zirconium. According to claim 1,
UC phosphor particle production method, characterized in that the upconversion phosphor particle composition is prepared by further adding a flux to the active solution in step (1). 9. The method of claim 8,
The flux is at least one selected _{from Li 2} CO ₃ , LiCl, LiNO ₃ , Na ₂ CO ₃ , NaHCO _{3 and KCl.} 9. The method of claim 8,
Method for producing UC phosphor particles, characterized in that the flux is added to the UC phosphor particle composition in an amount of 0.5 wt% to 5 wt% in step (1). a mother precursor including zirconium as a first metal and at least one rare earth metal selected from lanthanum, cerium, gadolinium, yttrium, and lutetium as a second metal;
an active agent comprising at least one metal selected from holmium, thulium and erbium; and
UC phosphor composition comprising; a deactivator comprising a ytterbium metal. 12. The method of claim 11,
The second metal is UC phosphor composition, characterized in that it is included in a molar fraction of 5 mol% to 20 mol%. It is prepared by spray pyrolysis of the phosphor composition according to claim 11,
UC phosphor particles comprising a compound represented by the following formula (1):
[Formula 1]
(Zr _1-xyz A _x Yb _y M _z )O ₂
In Formula 1, A is an activator containing at least one metal selected from holmium, thulium and erbium, M is a second metal containing at least one rare earth metal selected from lanthanum, cerium, gadolinium, yttrium and lutetium, and 0.06≤ x+y+z≤0.45. 14. The method of claim 13,
Formula 1 is a UC phosphor particle, characterized in that it satisfies at least one of the following conditions 1) to 3):
1) 0.001≤x≤0.005
2) 0.01≤y≤0.2
3) 0.05≤z≤0.2. 14. The method of claim 13,
UC phosphor particles, characterized in that the crystal structure of the matrix is tetragonal at a temperature of 900°C to 1,300°C. A secure luminescent ink comprising the UC phosphor particles according to claim 13 .

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