JP2796632B2 - Transparent polycrystalline yttrium aluminum garnet and method for producing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a transparent polycrystalline yttrium aluminum garnet (composition Y ₃ Al ₅ O ₁₂ in simple terms, sometimes simply referred to as YAG hereinafter) and the like. A manufacturing method. The yttrium aluminum garnet in the present invention is used for an optical material for oscillation or light emission such as a laser or a scintillator.

[Prior Art] Yttrium aluminum garnet is well known as an optical material for oscillation and light emission. For example, YA in which yttrium of yttrium aluminum garnet is replaced with Nd
The G laser is one of the typical high-power lasers. A single crystal is mainly used for yttrium aluminum garnet as an optical material. The single crystal can be grown by, for example, the Czochralski method (hereinafter simply referred to as CZ method) in which the single crystal is pulled from the molten YAG using an iridium crucible, or the floating zone method in which a sintered rod of YAG is melted into a single crystal by band melting ( Hereinafter, simply referred to as FZ method) or a flux method using a flux is known. However CZ
The iridium crucible by the method is expensive, and contamination by iridium from the crucible becomes a problem. In the FZ method, the diameter of a single crystal is limited, and a large single crystal cannot be obtained. Further, in the flux method, contamination by the flux occurs.

Note that substitution of single crystal YAG, particularly substitution of Y element, is well known. For example, Sekida and Kimura replaced the Y element with 1 atm% Nd
Report on the optical activity of YAG (Journal of Applied Physics 54: 3415-3421, 198
3 years).

Here, other related prior art is shown. We have found that Y
It has been proposed that YAG be obtained by precipitating ions and Al ions using urea (Japanese Patent Application No. 62-248,957). Furthermore, the present inventors have proposed that sulfate ions be present in the mother liquor during precipitation with urea to improve the properties of the precipitation (Japanese Patent Application No. Sho 63).
-242,890).

[Problems of the Invention] An object of the present invention is to provide a transparent polycrystalline YAG having optical properties substantially equal to those of a single crystal YAG, and a method for producing the same.

[Constitution of the Invention] The invention according to claim 1 is to replace the Y element of YAG with at least one member of the group consisting of a lanthanide element having an atomic number of 58 to 71 and a Cr element of 0.1 to 5 at. It was added SiO ₂ of 100~2500wtppm a ratio, in the transparent polycrystalline yttrium aluminum garnet. The addition amount of SiO ₂ is shown based on the weight ratio to the YAG amount before addition of SiO ₂ .

 The invention according to claims 2 and 3 is a manufacturing method thereof.

The invention of claim 2 provides an acidic aqueous solution containing yttrium ions, aluminum ions, and ions of at least one member of the group consisting of lanthanide elements and atomic Cr elements having atomic numbers of 58 to 71 in an amount of 0.8 to 1 mol of yttrium aluminum garnet. Neutralized with urea in the presence of sulfate ions at a ratio of ~ 10 mol to form a granular precipitate, and the formed precipitate was calcined and then subjected to oxygen-free conditions.
Sintered at 1650 ~ 1900 ℃, 0.1 ~ 5 atomic% of Y element of YAG
A lanthanide element having an atomic number of 58 to 71 and a YAG substituted with at least one member of the group consisting of a Cr element, and at a stage before sintering of the YAG, a weight ratio to the YAG of 100 to 250.
A method for producing a transparent polycrystalline yttrium aluminum garnet, comprising a step of adding 0 wtppm of SiO ₂ . SiO ₂
The addition form is optional, and the addition time is, for example, the time of formation of a precipitate, the precipitation after formation, or the YAG after calcination.

The invention according to claim 3 is characterized in that the substitution element is Ce, Pr, Nd, Sm,
At least one member of the group consisting of Eu, Tb, Dy, Ho, Er, Tm, Yb, and Cr, the sintering atmosphere being vacuum, and the substitution ratio being limited to 0.1 to 3 atomic%. Features.

In this specification, the term “transparent” means that the light absorption coefficient α is 4 cm ⁻¹ or less when the light is subjected to Lambert-Barre attenuation according to Exp (−α · t) in YAG. . Here, t is the thickness of the medium, and the extinction coefficient is measured at a wavelength where there is no inherent absorption by the substitute ions. When the extinction coefficient α exceeds 5 cm ⁻¹ , it becomes opaque to the naked eye, and under the conditions of the present invention, a transparent YAG sintered body can be obtained.

The YAG of the present invention is a conventional single crystal YAG in that it is polycrystalline.
Is different from In the present invention, in order to bring out the optical activity of YAG, the Y element of YAG is substituted with 0.1 to 5 atomic%, more preferably 0.1 to 3 atomic%. A substituted ion (hereinafter simply referred to as R
Lanthanide elements with atomic numbers 58-71)
Cr element is used. It is considered that the substituted R ion occupies the position of the Y ion in the crystal, but the details are unknown. The R element is more preferably Ce, Pr, Nd, Sm, Eu, Tb,
Dy, Ho, Er, Tm, Yb or Cr element. Of course, these elements need not be used alone but may be added in combination.

Explaining the degree of substitution, it is necessary to substitute at least 0.1 atomic% or more in order to obtain a sufficient luminous intensity, and to maintain the emission lifetime, the amount of substitution is 5 atomic% or less, more preferably 3 atomic% or less. It is necessary to:

Next, the addition of SiO ₂ is necessary to obtain dense YAG, to remove the irregular distribution of crystal grain size in YAG after sintering, and to eliminate light scattering accompanying the irregular distribution of crystal grain size. It is. Si
With respect to the amount of O ₂ is YAG, (against YAG excluding the SiO ₂ minutes), limited to 100～2500Wtppm, be less than this,
Also, if it is more than this, opaque YAG polycrystal cannot be obtained.

The method for producing the transparent polycrystalline YAG of the present invention will be described. YAG
Requires the precipitation of urea to raise the pH in the presence of sulfate ions. The amount of sulfate ion is 0.8 to 10 moles per mole of YAG, more preferably 1.2 to 10 moles.
Limited to 8 moles. When neither urea nor sulfate ion is used,
When precipitated (eg, with ammonia only), the precipitate is jelly-like and cannot be filtered. When urea alone is used, the precipitate is gel-like, contains a large amount of impurities such as ammonium chloride, and secondary particles are growing.

On the other hand, when precipitation is performed with urea in the presence of sulfate ions, a granular precipitate is obtained, which facilitates filtration and has a low impurity content. Furthermore, in this precipitation, secondary particle growth is small, and it is easy to obtain a dense sintered body. If the amount of sulfate ions is more than 10 moles per 1 mole of YAG, the sinterability decreases.

R ions used for YAG substitution are present in the solution at the time of precipitation, and are mixed into the precipitate by coprecipitation.

The precipitate is molded after calcination and sintered. Before sintering, 100 to 2500 wtppm of SiO ₂ is added to YAG. The addition of SiO ₂ can be performed, for example, during precipitation of YAG or after drying YA
G or YAG after calcination and before sintering. The form of addition of SiO ₂ is optional.

Sintering is carried out under oxygen-free conditions, such as in hydrogen or Ar, N ₂
Medium or in a vacuum. In sintering in oxygen or air, the crystal grain size distribution of YAG is irregular, light scattering occurs at crystal grain boundaries and the like, and the sintered body becomes opaque. The sintering temperature is 16
The temperature is limited to 50 to 1900 ° C, below which a dense sintered body cannot be obtained, and above this temperature, melting and evaporation of YAG occur during sintering.

[Examples] Example 1 In order to obtain Nd-substituted YAG, 30 (1-x) milliliters of yttrium chloride, 50 milliliters of aluminum chloride, and 30 x milliliters of neodymium chloride were prepared from aqueous solutions each having a concentration of 1 mol / liter. 30 ml of ammonium sulfate was mixed. Water was added thereto to make the total volume 1 liter, and 3 mgr of colloidal silica was further added. The form of ions such as yttrium, aluminum, and neodymium is arbitrary, and may be, for example, nitrate or acetate. To this solution was added 72 gr of urea, and after dissolution,
The reaction was carried out for minutes to obtain a coprecipitation of yttrium with aluminum, neodymium and silica.

This precipitation corresponded to 10 mmol of YAG, and the composition of YAG was changed by changing the amount of neodymium chloride. Next, the amount of urea is 2.4 equivalents, which is 10 times 0.24 equivalents of YAG. Also SiO ₂
The amount is 500 wtppm with respect to YAG.

The resulting precipitate is granular, has a low content of impurities such as ammonium chloride, and has little secondary particle growth. For this reason, it becomes easy to obtain a dense sintered body. In addition, filtration is easy due to the granular nature of the precipitate.

The solution was cooled to room temperature, and the precipitate was filtered, washed with water, dried, and calcined in air at 1000 ° C. for 3 hours. The calcination condition is preferably a temperature at which impurities can be sufficiently removed within a range that does not reduce the sinterability of YAG, for example, 500 to 1400 ° C.
Preferably it is 900-1300 degreeC. The precipitate is converted to YAG by calcination. The calcined YAG is pulverized, isostatically pressed at ² t / cm ² and shaped into a disk, and heated to 1700 ° C in vacuum.
For 3 hours. The sintering atmosphere may be oxygen-free, and is not limited to vacuum.

The spectral characteristics of this disk were evaluated. Laser transition wavelength when Nd-substituted YAG disk is excited by another high-frequency laser
FIG. 1 shows the emission lifetime at 1.064 μm. The emission lifetime in the case of 1 atomic% substitution is 220 μs, and the value in the above-mentioned document by Sekida and Kimura (1 atomic% Nd
), Approximately equal to 226 μs. Here, the light emission lifetime means a time during which the light emission intensity decreases to 1 / e of the initial intensity. Also contributes to laser oscillation with 1 atomic% Nd substitution
The line width of the emission spectra at 1.0634μm and 1.0638μm are respectively 5.02Cm ^-1 and 5.27cm ^-1. This is the value reported by Sekida et al., 4.53-4.80 cm ^-1 and 4.95-5.46 cm
It is about the same as ^-1 . Therefore, the Nd-substituted YAG in the present invention is
It has almost the same spectroscopic properties as a single crystal of the same composition, and no deterioration in spectroscopic properties due to being a polycrystal can be found.

Further, the laser oscillation induced transition cross section is calculated to be 4.9 × 10 ^-19 cm ² based on the method reported in the same report. This is the CZ method or FZ in the report and the reports cited there.
Literature value of single crystal Nd-substituted YAG by the method, 2.7 × 10 ⁻¹⁹ cm ² to 8.
^{Equivalent to} 8 × 10 ^-19 cm ² . The laser oscillation induced transition cross-sectional area is a constant indicating the relationship between the input energy and the output energy to the laser, and the higher the value, the higher the efficiency of the laser.

Returning to FIG. 1, the Nd substitution amount will be examined. In order to maintain the inversion distribution state of electrons necessary for laser oscillation, the emission lifetime at 1.064 μm is preferably set to about 100 μs or more. In order to satisfy this condition, the Nd content needs to be 5 atomic% or less, more preferably 3 atomic% or less. On the other hand, sufficient laser emission intensity is required to cause laser oscillation. The emission intensity increases in proportion to the amount of substitution ions, and the increase in intensity slows down from about 0.5 atomic%,
It is not proportional to the replacement amount. In the case of the Nd-substituted YAG laser, substitution of 0.1 atomic% or more was necessary to obtain the emission intensity required for laser oscillation. The effect of the substitution amount was the same for the other substitution elements other than Nd. For example, in the case of Pr or Ho, substitution of 0.1 atomic% or more was required to obtain sufficient luminescence intensity, and substitution of 5 atomic% or less was required to obtain sufficient luminescence lifetime.

Example 2 Table 1 shows the color of the YAG composition, the main emission peak wavelength, and the emission life of the substituted ions other than Nd with the substitution amount of 1 atomic% as an example. The production method of transparent polycrystalline YAG is as follows.
It is the same as Example 1 except that the ion of each substituent is used instead of neodymium ion. The colors in the table are the color tone at 1 atomic% substitution, and the color tone varies depending on the substitution amount.

So far, we have mainly described applications to lasers,
An application to a scintillator will be described. Polycrystalline compositions for scintillators have been studied for Pr-substituted Gd ₂ O ₂ S and the like. In the case of Pr-substituted Gd ₂ O ₂ S, the transmittance in the literature is 60% at a thickness of 1 mm, which translates into an extinction coefficient of 5.1 cm ⁻¹ . On the other hand, in the sample of 1 atomic% Pr substitution in Table 1, the transmittance at a thickness of 1 mm is 82%, and the extinction coefficient is 2 cm ^-1 . That is, the scintillator material in the embodiment is transparent, and the scintillator efficiency is high.

Example 3 In the above description, discussion was made on the assumption that transparent polycrystalline YAG was obtained. The conditions for obtaining a transparent polycrystalline YAG are shown below. In this case, the influence of substitution ions such as Nd is as follows.
This is the same as in the case of the first and second embodiments, and the addition of the substitute ion may be performed in exactly the same manner as in the first and second embodiments.

Urea is used for neutralization in order to moderate the precipitation reaction and to facilitate the control of the reaction. If ammonia is used as the neutralizing agent instead of urea, the control of the reaction is difficult and generally results in a jelly-like unfilterable precipitate. Although the amount of urea is not particularly limited, it is preferable to add at least twice the acid equivalent in the aqueous solution, more preferably at least 5 times, in order to enable quantitative precipitation. Next, since an excessive amount of urea is decomposed in the course of the reaction and vaporized as CO ₂ and NH ₃ , the upper limit of the amount of urea is not particularly limited, and may be, for example, 20 equivalents or less. The precipitation reaction with urea is preferably performed at 70 ° C. to the boiling point. This is because the decomposition of urea is slow at 70 ° C. or lower, and the reaction time is too long. And preferably, 80-100
Perform the neutralization reaction at ℃.

Next, the effect of the sulfate ion is to obtain a precipitate in which the growth of secondary particles is small. In a precipitate where the growth of secondary particles is small,
There is little contamination of the precipitate with impurities and it is easy to obtain a dense sintered body. Further, the precipitates using sulfate ions are generally granular, and the treatment such as filtration of the precipitates is easy. Table 2
The results when the sulfate ion content in Example 1 was changed are shown below. In addition, this result shows that the calcination condition is 1300 ° C for 1 hour in oxygen,
The sintering conditions were at 1600 ° C. for 30 hours in oxygen.
For simplicity, plain YAG was used, and SiO ₂ , Nd, etc. were not added. The particle size in the table represents the secondary particle size after calcination. The density indicates a relative density with respect to the theoretical density. By using 1 to 10 mol of sulfate ions per 1 mol of YAG, a dense sintered body can be obtained.

Next, Table 3 shows the sintering atmosphere and the effect of SiO ₂ . In this experiment, Nd-free YAG was used, and the calcination condition was 100
The sintering conditions were set at 1700 ° C. for 3 hours in each atmosphere at 0 ° C. for 3 hours.

[Effects of the Invention] According to the present invention, a polycrystalline transparent YAG optical material having optical performance comparable to that of a single crystal can be obtained.

In addition, since the production method of the present invention uses precipitation from an aqueous solution, there is an advantage that contamination by impurities is small, a YAG sintered body of any shape can be obtained at low cost, which is rich in mass productivity.

[Brief description of the drawings]

FIG. 1 is a characteristic diagram showing the influence of the Nd substitution amount on the light emission lifetime in the example.

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Akio Watanabe 3-106-105 Takezono, Tsukuba City, Ibaraki Prefecture (72) Inventor Masami Sekida 1-406-402 Azuma, Tsukuba City, Ibaraki Prefecture (72) Inventor Toshihiro Kuroki Kagawa Prefecture 3500-3 Takuma, Takuma-cho, Mitoyo-gun (72) Takayuki Yanagiya Inventor 610-5 Takuma, Takuma-cho, Mitoyo-gun, Kagawa (58) Field surveyed (Int. Cl. ⁶ , DB name) C04B 35/42-35/50

Claims (3)

(57) [Claims] 1. The method according to claim 1, wherein the Y element of yttrium aluminum garnet (composition formula Y ₃ Al ₅ O ₁₂ ) is 0.1 to 5 atomic% atomic number 58.
A transparent polycrystalline yttrium aluminum garnet, which is substituted with at least one member of the group consisting of lanthanide elements and Cr elements of up to 71, and to which 100 to 2500 wtppm of SiO ₂ is added in a weight ratio to yttrium aluminum garnet. 2. An acidic aqueous solution containing yttrium ions, aluminum ions and ions of at least one member of the group consisting of a lanthanide element and an Cr element having an atomic number of 58 to 71 is added to 0.1 mol / mol of yttrium aluminum garnet.
Neutralize with urea in the presence of sulfate ions at a ratio of 8 to 10 moles to form a granular precipitate, mold the formed precipitate after calcination, and at the stage before sintering, the yttrium aluminum garnet A step of adding 100 to 2500 wtppm of SiO ₂ by weight ratio, and the above-mentioned molded body is subjected to oxygen-free conditions of 1650 to 19
By sintering at 00 ° C., yttrium aluminum garnet is replaced by yttrium aluminum garnet in which the Y element of yttrium aluminum garnet is replaced with at least one member of the group consisting of a lanthanide element having an atomic number of 58 to 71 and a Cr element of 0.1 to 5 atomic%. Of producing a transparent polycrystalline yttrium aluminum garnet. 3. The method according to claim 2, wherein the substitution element is Ce, Pr, Nd, Sm, Eu, Tb, D
y, Ho, Er, Tm, Yb, and at least one member of the group consisting of Cr, and the substitution ratio of the Y element is 0.1 to 3 atomic%.
The method for producing a transparent polycrystalline yttrium aluminum garnet according to claim 2, wherein the firing atmosphere is in a vacuum.