JP2013079342A - Plate-like fluorescent substance having high luminous efficiency and coactivated with terbium or neodymium and cerium, and method for producing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fluorescent substance having higher luminous efficiency than that of a conventional one, in a fluorescent substance retaining a crystal state of a plate form, which is suitable as a material for a printing ink or a coating material used in security technique, and gives fluorescent characteristics by having zeolite as a matrix and retaining ions of a rare earth metal; and to provide a method for producing the same.SOLUTION: Zeolite Linde Q is added to Tbor Ndand ion exchanged with Ce. By firing, the fluorescent substance is obtained in which the structure of zeolite is lost but the crystal state of a plate form is maintained. A coactivated substance which has been ion-exchanged with Tband Ceemits green fluorescent light by excitation with ultraviolet ray, and the coactivated substance which has been ion-exchanged with Ndand Ceemits the fluorescent light in an infrared region by excitation with ultraviolet ray. The fluorescent substance of 10-20% is added to a printing ink or a coating material used in security technique to give a sufficient emission intensity.

Description

The present invention relates to a plate-like phosphor with high luminous efficiency co-activated with terbium or neodymium and cerium. The phosphor of the present invention emits green visible light or infrared light that can be detected only by an infrared scope when irradiated with ultraviolet light. This phosphor has a plate-like form, and when blended with an appropriate vehicle, it has excellent coatability and concealment. Therefore, the phosphor used in anti-counterfeit printing inks used for printing securities and product labels Suitable as a pigment. The present invention also relates to a method for producing the plate-like phosphor using a zeolite having a plate-like form as a mother crystal.

In security technology, forgery prevention technology such as securities and product labels, so-called “security technology”, printing using ink containing phosphor pigments, and security paper with phosphor incorporated into the paper itself that emits light. It is being used. As the phosphor used for this purpose, an ultraviolet-excited visible light-emitting phosphor or an ultraviolet-excited infrared-emitting phosphor is suitable. Since the phosphor used in the security technique is printed on a sheet-like body such as paper, it is required that the coating property and the concealing property are high, and it is desirable to be a plate-like particle. However, the solid phase reaction method and the flux method, which have been known as methods for producing this type of phosphor, cannot control the particle shape of the product phosphor, and provide a suitable plate-like phosphor. I can't.

An overview of phosphor manufacturing techniques known so far includes a method for manufacturing a borate-based plate-like phosphor by a flux method (Patent Document 1). Is difficult to control. The use of zeolite as a raw material for phosphors is often performed. One means is to uniformly disperse a phosphor made of a metal oxide-rare earth metal in the pores of zeolite (Patent Document 2). This technique does not impart fluorescent properties to the zeolite itself, nor does it provide a plate-like phosphor. In addition, there is a ceramic fine particle dispersed as a phosphor in an amorphous matrix of silica and alumina derived from zeolite (Patent Document 3). This is not a phosphor having a zeolite structure, but a plate. It also does not provide a phosphor. There is also a technique (Patent Document 4) for producing a phosphor from zeolite proposed by one of the joint applicants of the present application, but it is not related to a plate-like phosphor.

In order to obtain a plate-like phosphor, a zeolite having a plate-like crystal self-shape may be used as a mother crystal, and many techniques based on this idea have been proposed. However, since water contained in the zeolite hinders excitation, the countermeasure is to make the zeolite structure amorphous by heating, to convert it to other aluminosilicate structure compounds, or to convert rare earth metals to organic ligands. Need to be complexed with.

The applicants, together with other co-applicants, selected Linde Q-type zeolite as the zeolite having a plate-like crystal self-form, exchanged the K ⁺ ions with rare earth metal divalent or trivalent ions, and then calcined. The manufacturing technology of the fluorescent substance which consists of doing was disclosed (patent document 5). Luminescence varies depending on the type of rare earth metal. When excited by ultraviolet light, europium (Eu) is used in red, terbium (Tb) is used in green, and thulium (Tm) is used. Develops blue. However, in any case, the light emission intensity is insufficient for use in printing ink for security technology.

Further, the applicants and other joint applicants have selected neodymium (Nd) as the rare earth metal ion to be combined with Linde Q-type zeolite, and have developed a phosphor that emits fluorescence in the infrared region by ultraviolet excitation (Patent Document 6). . Subsequently, the applicants also found that a phosphor obtained by combining cerium (Ce) with Linde Q-type zeolite emits blue fluorescence, which was also disclosed (Patent Document 7). In this case, in order to prevent oxidation of cerium (III), a non-oxidizing atmosphere is required for firing.

On the other hand, it has been attempted before the invention of the above-described phosphor to perform so-called “co-activation” by using cerium and terbium together as the emission center of the phosphor. First, a phosphor phosphor (Patent Document 8) and a lanthanum magnesium aluminate phosphor (Patent Document 9) that are colored green for a lamp have been disclosed. It is not a technology that can be controlled. Proposal of a silicate phosphor that produces green color and a light emitting device using the same (Patent Document 10) and a disclosure of a borate phosphor and a white LED (Patent Document 11) using the borate phosphor continued, These techniques also cannot control the form and particle size of the phosphor. Subsequently, a cerium-terbium co-activated phosphor having a nitride-based average particle diameter of 2 μm or more and 20 μm or less was developed (Patent Document 12), but it does not reach the form control. .

Regarding neodymium-cerium co-activated phosphors, a glass material with infrared emission characteristics has been developed (Non-Patent Document 1), and it has been reported that the emission intensity is five times that of glass activated by neodymium alone. It was done.
JP 2002-309245 A JP2003-246981 JP-A-2005-314573 JP2005-048107 JP2008-069290 JP2011-001409A Japanese Patent Application No. 2010-055172 JP-A-5-171143 JP-A-6-240252 JP 2002-105449 A JP 2006-299207 A JP2008-069198 Optics and Lasers in Engineering 35 (2001) 11-17

As described above, a number of plate-like phosphors are known in which a zeolite having a plate-like crystal self-form is used as a mother crystal and the rare earth metal ions that are the emission centers are uniformly held in the pores by ion exchange. However, the emission intensity has not yet reached the level required to exhibit sufficient emission intensity on the printed surface, which is required for printing ink pigments used in security technology. On the other hand, it is also known that the luminous intensity of the phosphor can be increased by co-activation, but the specific technology does not give a plate-like phosphor, and the form can be controlled. not.

Under such circumstances, the object of the present invention is a plate-like phosphor, which is sufficient to be used as a pigment for printing ink for security technology, and exhibits a higher emission intensity than conventional products, It is in providing the manufacturing method. Since this phosphor is used in printing inks and paints, it must satisfy the condition of being hydrophobic so that it is well dispersed in the vehicle and solvent.

The phosphor of the present invention that achieves the above object, that is, the first of the phosphors having a plate-like shape and improved emission intensity is obtained by converting a zeolite having a plate-like crystal form into terbium ions and cerium ions. This is a phosphor that emits green fluorescence when excited by ultraviolet rays, by calcination of the ion exchanger obtained by ion exchange in step 1 and maintaining the plate-like crystal form while losing the zeolite structure.

The second phosphor of the present invention is obtained by calcining an ion exchanger obtained by ion exchange of zeolite having a plate-like crystal form with neodymium ions and cerium ions, and the zeolite structure is lost, but the plate-like crystals The phosphor is a phosphor that emits infrared fluorescence when excited by ultraviolet light.

In the method for producing the phosphor of the present invention, when producing the first one, the zeolite is immersed in a mixed aqueous solution of a soluble salt of terbium and a soluble salt of cerium, and K ⁺ in the zeolite at a temperature of 100 ° C. or lower. Alternatively, ion exchange between Na ⁺ and Tb ³⁺ and Ce ³⁺ is performed so that Tb ions and Ce ions are present in the zeolite at an exchange rate of at least 20%, respectively, and then in a non-oxidizing atmosphere, 850 By calcination at a temperature of at least 0 ° C, preferably at least 900 ° C, the zeolite structure is lost, but the plate-like crystal form is maintained.

In the case of producing the second one, in the above method, a neodymium soluble salt is used instead of the terbium soluble salt, the zeolite is immersed in a mixed aqueous solution of this and a cerium soluble salt, and the temperature is 100 ° C. or lower. After ion exchange between K ⁺ or Na ⁺ and Nd ³⁺ and Ce ³⁺ in the zeolite with Nd ions and Ce ions present in the zeolite at an exchange rate of at least 20%, respectively, non-oxidizing In this manufacturing method, by firing at a temperature of 850 ° C. or higher, preferably 900 ° C. or higher, the zeolite structure is lost but the plate-like crystal form is maintained.

In the phosphor of the present invention, in both the first and second phosphors, the fluorescence emission intensity caused by the presence of terbium ions or neodymium ions is increased 5 to 10 times by co-activation using cerium ions. The emission intensity required for the phosphor used as a material for printing inks and paints used in security technology can be fully satisfied.

Since the crystal structure of the zeolite used as the mother crystal has been lost due to calcination, there is no concern that the light emission intensity will be reduced by condensing during use, while maintaining the original plate-like crystal itself. Therefore, it is excellent in coating properties and hiding properties, and is suitable as a pigment for printing inks and paints.

The zeolite used in the present invention is preferably Linde Q zeolite. Other plate-like zeolites include clinoptilolite, but Linde Q zeolite has the hexagonal plate-like crystal shape and is the most promising raw material in terms of large ion exchange capacity. Whichever is used, the zeolite preferably has a diameter of 0.5 to 10 μm, a thickness of 10 to 200 nm, and an aspect ratio of 5 or more.

In order to ion-exchange potassium ions and sodium ions pre-existing in the zeolite with trivalent terbium ions or neodymium ions serving as emission centers and trivalent cerium (III) ions serving as co-active ions, terbium or Zeolite is dispersed in a mixed aqueous solution of a soluble salt such as neodymium nitrate or chloride and a soluble salt such as cerium (III) nitrate or chloride, and ion exchanged at a temperature of 100 ° C. or lower.

Needless to say, the degree of ion exchange is preferably as high as possible because the luminous efficiency increases accordingly, but it tends to saturate at a high exchange rate. Easily achieve a total amount of 80% or more by using a mixed aqueous solution with a high concentration of rare earth metal ions to be exchanged or by drying the ion-exchanged one and then dipping it again in the mixed aqueous solution. it can. However, in the region exceeding 90%, it becomes increasingly difficult to increase the exchange rate, and 95% would be the limit in practical use.

In ion exchange, it is important to appropriately select a balance between terbium ions or neodymium ions and trivalent cerium (III) ions. In the phosphor of the present invention, although it is called co-activation, it is understood that terbium or neodymium is responsible for the actual light emission, and cerium's main mission is to transmit ultraviolet light energy to them. On the other hand, for example, in the case of terbium-cerium co-activation, there is a phenomenon in which the emission of blue light caused by cerium ions themselves increases as the exchange amount of cerium increases, so to speak, the light emission power is dispersed. If the outline of a preferable exchange amount is shown, in the case of terbium-cerium coactivation, it is 10-80% of terbium + 5-50% of cerium, and also in the case of neodymium-cerium coactivation, similarly, neodymium 10-80% + It is 5 to 50% of cerium.

The ion-exchanged zeolite is washed with water, dried at a temperature of 100 ° C. or lower, and then calcined. Calcination is somewhat different depending on the type of zeolite, but in the case of typical Linde Q-type zeolite, a temperature of 850 ° C. or higher, preferably 900 ° C. or higher is required. When firing, it is necessary to completely destroy the crystal structure of the zeolite, and if left, even if no clear condensate phenomenon occurs, it has been experienced that the amount of luminescence decreases when excitation by ultraviolet rays continues. It is. However, if the temperature exceeds 1000 ° C., sintering of the zeolite crystals begins and the advantage of having a plate-like crystal self-form is lost, so an excessively high temperature must be avoided. As described above, the firing atmosphere must be non-oxidizing in order to avoid oxidation of cerium ions (III). A reducing atmosphere using a 5% hydrogen-helium mixed gas or an inert atmosphere using nitrogen gas is employed. The firing time is suitably from 30 minutes to 2 hours.

In the following examples, sample characterization and performance tests were performed as follows.
[Measurement of ion exchange rate]
An ion exchange sample (described below) is decomposed with an acid, and Tb, Nd, Ce, and K are quantified by an inductively coupled plasma emission spectrometer (“ICPS-8000” manufactured by Shimadzu Corporation) to obtain an ion exchange rate.
[Identification of crystalline phases of ion exchange and heated samples]
Using powder X-ray diffraction (XRD) (Mac Science MXP3A, Rigaku Denki RINT-2550H).
[Observation of crystal morphology]
Observed with a scanning electron microscope (SEM) (JEOL JSM-6510LA).
[Fluorescence properties]
Measure the fluorescence spectrum of the calcined sample with a spectrofluorometer (Hitachi F-2500, JOBINYVON SPEX Fluorolog-3).

Terbium-cerium co-activated Linde Q zeolite (Part 1)
Particle size of about 1 [mu] m, a thickness of about 100nm of the hexagonal K type Linde Q zeolite having a plate-like crystal form _{(K 2 O · Al 2 O} 3 · 2SiO 2 · xH 2 O hereinafter abbreviated as "Linde Q") synthesis did. To 60 mL of an aqueous solution of terbium chloride (0.1 mol / L) and 60 mL of a mixed aqueous solution of terbium chloride (0.125 mol / L) and cerium nitrate (0.125 mol / L), 8 g of this Linde Q zeolite was added. Ion exchange was performed at 90 ° C. for 24 hours. Solid-liquid separation was performed with a membrane filter, washed with distilled water, and sufficiently dried at 50 ° C. to obtain the following two types of ion exchange samples.

Their ion exchange rates were measured and the following values were obtained.
(Ion exchange sample) (Tb exchange rate) (Ce exchange rate)
Tb exchange Linde Q: 45.5% −
Tb-Ce co-activated Linde Q: 45.5% 37.1%

These ion exchange samples were placed in a platinum crucible and calcined at 900 ° C. for 1 hour in a reducing atmosphere. When the crystal structure of the obtained calcined sample was examined by X-ray diffraction, the structure of Linde Q zeolite was decomposed and became amorphous. An X-ray diffraction chart is shown in FIG.

When the fluorescence characteristics of the two kinds of fired samples were examined, green fluorescence having an emission peak near 544 nm was detected when excited by ultraviolet light having a wavelength of 370 nm. The fluorescence spectrum is shown in FIG. As shown in FIG. 2, the peak intensity of the sample subjected to Tb—Ce coactivation was about 6 times that of the Tb exchanged Linde Q that was not performed.

Terbium-cerium co-activated Linde Q zeolite (Part 2)
Manufactured Tb-Ce co-activated Linde Q zeolite with various ion exchange rates in order to see the effect of cerium ion exchange rate on luminescence properties and the effect of balance between terbium ion exchange rate and cerium ion exchange rate did. In the same manner as in Example 1, Linde Q zeolite having a hexagonal plate-like crystal form with a particle size of about 1 μm and a thickness of about 100 nm was prepared, and 12 g of each was mixed with terbium chloride (0.1 mol / L) and cerium nitrate ( (0, 0.01, 0.025, 0.05, 0.075, 0.1, or 0.125 mol / L) was added to 90 mL of each of the seven mixed aqueous solutions, and ion exchange was performed at 90 ° C. for 24 hours. . In the same manner as in Example 1, the following seven kinds of ions having various Tb exchange rates and Ce exchange rates were obtained by solid-liquid separation with a membrane filter, washing with distilled water, and sufficiently drying at 50 ° C. An exchange sample was obtained.

Their ion exchange rates were measured and the following values were obtained.
(Ion exchange sample) (Tb exchange rate) (Ce exchange rate)
Tb exchange Linde Q: 43.8% −
Tb-Ce co-activated Linde Q1: 43.4% 4.3%
2: 41.6% 10.1%
3: 41.1% 19.2%
4: 39.2% 26.4%
5: 38.5% 33.4%
6: 36.0% 38.2%

The above seven types of ion exchange samples were placed in a platinum crucible and fired at 900 ° C. for 1 hour in a reducing atmosphere in the same manner as in Example 1. An X-ray diffraction chart of the fired sample is shown in FIG. Also in this case, it was confirmed that the structure of Linde Q zeolite was decomposed and became amorphous. On the other hand, as a result of observing the calcined sample with a scanning electron microscope, it was found that the original hexagonal plate shape was maintained despite the decomposition of the zeolite structure. FIG. 4 shows electron micrographs of Tb-exchanged Linde Q, Tb—Ce co-activated Linde Q4, and the fired samples of the same.

The fluorescence characteristics of the fired sample are as shown in the spectrum of FIG. 5, and green light emission having a light emission peak in the vicinity of 544 nm was observed by ultraviolet excitation with a wavelength of 310 nm.

Neodymium-cerium co-activated Linde Q zeolite As in Example 1, Linde Q zeolite having a hexagonal plate-like crystal form with a particle size of about 1 μm and a thickness of about 100 nm was prepared. To each 60 mL of six mixed aqueous solutions of neodymium chloride (0.1 mol / L) and cerium nitrate (0, 0.01, 0.025, 0.05, 0.075 or 0.1 mol / L), 8 g of Linde Q zeolite was added and ion exchange was performed at 90 ° C. for 24 hours. In the same manner as in Examples 1 and 2, the following 6 types of ions having various Nd exchange rates and Ce exchange rates were obtained by solid-liquid separation with a membrane filter, washing with distilled water, and thoroughly drying at 50 ° C. An exchange sample was obtained.

Their ion exchange rates were measured and the following values were obtained.
(Ion exchange sample) (Nd exchange rate) (Ce exchange rate)
Nd exchange Linde Q: 42.9% −
Nd-Ce co-activated Linde Q1: 45.0% 4.4%
2: 45.3% 11.6%
3: 40.2% 20.8%
4: 37.0% 28.8%
5: 34.9% 36.5%

These six types of ion exchange samples were placed in a platinum crucible and fired at 900 ° C. for 1 hour in a reducing atmosphere in the same manner as in Examples 1 and 2. An X-ray diffraction chart of the fired sample is shown in FIG. Also in this case, it was confirmed that the structure of Linde Q zeolite was decomposed and became amorphous. On the other hand, as a result of observing the calcined sample with a scanning electron microscope, it was found that the original hexagonal plate shape was maintained despite the decomposition of the zeolite structure. FIG. 7 shows electron micrographs of Nd-Ce co-activated Linde Q5 and Nd-exchange Linde Q.

The fluorescence characteristics of the fired sample are as shown in the spectrum of FIG. 8, and when excited with ultraviolet light having a wavelength of 354 nm, infrared emission having an emission peak near 1063 nm was observed. According to FIG. 8, cerium co-activation is performed, and the higher the cerium ion exchange rate, that is, the higher the cerium ion content, the lower the neodymium exchange rate, but the lower the emission intensity. I understand that it is expensive.

In Example 1 of this invention, the X-ray-diffraction chart of the baked sample obtained by baking the ion exchange sample which ion-exchanged Linde Q zeolite with terbium or with terbium and cerium. FIG. 1 is a fluorescence spectrum of a fired sample whose X-ray diffraction chart is shown in FIG. In Example 2 of this invention, the X-ray-diffraction chart of the baking sample obtained by baking the ion exchange sample which ion-exchanged Linde Q zeolite with terbium or with terbium and various amounts of cerium. 3 is a scanning electron micrograph of three types of fired samples in Example 2. FIG. FIG. 3 is a fluorescence spectrum of a fired sample whose X-ray diffraction chart is shown in FIG. In Example 3 of this invention, the X-ray-diffraction chart of the baking sample obtained by baking the ion exchange sample which ion-exchanged Linde Q zeolite with neodymium or with neodymium and various amounts of cerium. 2 is a scanning electron micrograph of two types of fired samples in Example 3. FIG. FIG. 6 is a fluorescence spectrum of a fired sample whose X-ray diffraction chart is shown in FIG.

Claims (7)

An ion exchanger obtained by ion-exchanging zeolite having a plate-like crystal form with terbium and cerium ions is calcined, and the zeolite structure is lost, but the plate-like crystal form is maintained. A phosphor that emits light. As the zeolite, a “Linde Q” type zeolite having a composition of K ₂ O.Al ₂ O ₃ .2SiO ₂ .xH ₂ O and a hexagonal plate-like crystal form is used, and the exchange rate of terbium ions is at least 20%. The phosphor of claim 1, wherein the exchange rate of cerium ions is at least 10%. A method for producing the phosphor according to claim 1 or 2, wherein the zeolite is immersed in a mixed aqueous solution of a soluble salt of terbium and a soluble salt of cerium, and K ⁺ or Na ⁺ in the zeolite at a temperature of 100 ° C or lower. After ion exchange between Tb ³⁺ and Ce ³⁺ and calcining in a non-oxidizing atmosphere at a temperature of 850 ° C. or higher, the zeolite structure is lost but the plate-like crystal form is maintained. The manufacturing method which consists of this. An ion exchanger obtained by ion-exchanging zeolite having a plate-like crystal form with neodymium ions and cerium ions is calcined, and the zeolite structure is lost, but the plate-like crystal form is maintained. A phosphor that emits light. As the zeolite, “linde Q” type zeolite having a composition of K ₂ O.Al ₂ O ₃ .2SiO ₂ .xH ₂ O and having a hexagonal plate-like crystal form is used, and the exchange rate of neodymium ions is at least 20%. The phosphor of claim 4 wherein the exchange rate of cerium ions is at least 10%. A method for producing the phosphor according to claim 4 or 5, wherein the zeolite is immersed in a mixed aqueous solution of a soluble salt of neodymium and a soluble salt of cerium, and K ⁺ or Na ⁺ in the zeolite at a temperature of 100 ° C or lower. After performing ion exchange between Nd ³⁺ and Ce ³⁺ and calcining in a non-oxidizing atmosphere at a temperature of 850 ° C. or higher, the zeolite structure is lost but the plate-like crystal form is maintained. The manufacturing method which consists of this. A printing ink or paint for use in security technology, comprising the phosphor according to claim 1 or 4.

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