JPH05330913A - Polycrystalline transparent y2o3 ceramics for laser - Google Patents

Abstract

PURPOSE:To avoid structural defects of a single crystal or those of a produced material and provide a technique unapplicable to the single crystal by including ThO2, HfO2, ZrO2, Li2O, LiF, BeO or Al2O3 and a lanthanoid and specifying the average particle diameter and porosity. CONSTITUTION:The objective polycrystalline transparent Y2O3, ceramics for laser comprise one or more of ThO2, HfO2, ZrO2, Li2O, LiF, BeO and Al2O3 and one or more lanthanoid elements and have an average particle diameter within the range of 5-3000mum and <=1% porosity. When the density of the sintered compact is <99.0% (>=1% porosity) that of the theoretical one, the light transmittance is extremely lowered. The relative density of the sintered compact is obtained by comparing densities of both a single crystal and a polycrystal of the same composition measured according to the method of the Japan Society for the Promotion of Science or X-ray method. As other methods, the relative density is obtained by measuring pores present in the interior of the sintered compact from the surface with a microscope, a scanning electron microscope (SEM), etc.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polycrystalline transparent Y ₂ O ₃ ceramics for laser which is preferably used as a laser oscillator.

[0002]

2. Description of the Related Art Solid-state lasers represented by YAG (yttria aluminum garnet) have about 9% of the market.
It is an important material that accounts for 5%. The fields of application of this laser are various applications such as microfabrication of semiconductors, cutting and heat treatment of steel materials and ceramics, medical laser scalpels, etc. In recent years, wavelength-converted green and blue lasers using SHG (second harmonic) elements have been applied. It is also used for writing operation of magneto-optical recording material.

By the way, YAG is manufactured by the Czochralski method by adding Nd and other light emitting elements as elements involved in light emission, but all of them are single crystals.

When a single crystal YAG is manufactured by such a method, a growth temperature of about 2000 ° C. is required, and the growth rate is extremely slow at 0.2 to 0.3 mm / hr. From this, it takes about one month to produce one single crystal,
Moreover, it is difficult for the manufactured single crystal YAG to have uniform light emitting elements. Particularly, in the case of growing a single crystal only when the Nd element is added, it is not only difficult to uniformly disperse the light emitting element in the host material, but also its concentration is limited to about 1 atom%. From this fact, even single crystal YAG
Even if manufactured, only a small part can be used as a laser material. In addition, the single crystal growth technique requires an extremely expensive iridium crucible, so the single crystal YAG produced
In addition to being expensive, the current situation is that they are not fully satisfactory in terms of productivity.

On the other hand, Y ₂ O _{3 has been} used as a noticeable laser single crystal other than a single crystal having a garnet structure such as YAG.
However, since this crystal has an extremely high melting point of 2400 ° C., it must rely on the Bernoulli method, which is unsuitable as a technique for growing a single crystal for a laser. For this reason, not only a practical high-quality single crystal cannot be produced, but also the size thereof is limited (because of the phase transition, the diameter is at most about 1 cm). Therefore, the crystal having the garnet structure described above is commonly used. Has been done.

[0006]

The problem to be solved by the present invention is to apply polycrystalline Y ₂ O ₃ ceramics having excellent transparency to this field, rather than the conventional single crystal for solid-state laser represented by YAG. In this way, it is possible to avoid the structural defects of the single crystal and the defects of the manufactured material itself, and at the same time provide a technology that is impossible for the single crystal.

[0007]

The present invention provides ThO ₂ , H
fO ₂ , ZrO ₂ , Li ₂ O, LiF, BeO and Al
_The above problems were solved by containing one or more of ₂ O ₃ and one or more of a lanthanide element, and setting the average particle diameter of the sintered body in the range of 5 to 3000 μm and the porosity to be 1% or less.

This sintered body is a solid phase method, that is, Y ₂ O ₃
It is also possible to obtain it by using a raw material obtained by an alkoxide method, a coprecipitation method, a uniform precipitation method, etc., in addition to the method of mixing each of these and other oxide components.

For example, in the case of the solid phase method, Y ₂ O ₃ powder having a particle size of 1 μm or less and a purity of 99.9% by weight or more is added to a sintering aid (Th).
O ₂ , HfO ₂ , ZrO ₂ , Li ₂ O, LiF, Be
O, Al ₂ O ₃ ) and oxides of lanthanide elements (La ₂ O ₃ , CeO ₂ , Pr) of 1 μm or less.
₆ O ₁₁ , Nd ₂ O ₃ , Pm ₂ O ₃ , Sm ₂ O ₃ , Eu ₂
O ₃ , Gd ₂ O ₃ , Tb ₂ O ₃ , Dy ₂ O ₃ , Ho ₂ O
₃ , Er ₂ O ₃ , Tm ₂ O ₃ , Yb ₂ O ₃ , Lu
₂ O ₃ ) is added in an appropriate amount. As a method of adding the light emitting element, an appropriate means may be taken depending on the concentration. For example, when a small amount is added, an oxide produced by a thermal decomposition reaction such as an alkoxide method or a nitrate may be used as a chlorination source.

Using Y ₂ O ₃ as a main raw material, these oxides are weighed so as to have a desired composition, an organic solvent such as ethyl alcohol is added and mixed in a pot mill. After this mixed powder is dried, it is molded by a uniaxial press or CIP (cold isostatic press) and sintered. As a sintering method, a conventional method such as vacuum sintering, atmosphere sintering (atmosphere of hydrogen or oxygen), HP (hot press) or HIP (hot isostatic press) can be used. It is preferable that the particles are uniform in composition and structure and, as a result, the sintered body has excellent transparency. 1700 to 2270 for vacuum sintering or atmosphere sintering
At HP, in the case of HP and HIP, the target sintered body can be obtained by sintering at a temperature range of 1400 to 2200 ° C for an appropriate time.

Oxide components such as LiF, ThO ₂ and HfO ₂ significantly improve the microstructure of the sintered body as long as the amount thereof is appropriate, so that the transparency of the material (transparency of the host material) is remarkably increased. It is possible to improve the laser oscillation. Li
Oxides and fluorides of ₂ O, LiF, BeO, and Al ₂ O ₃ have no electronic structure such as d and f electrons, and therefore addition of these elements has almost no effect on laser oscillation. Further, elements such as ThO ₂ , HfO ₂ and ZrO ₂ are d,
Although f-electrons are present, there is no band involved in laser emission, and therefore, there is no adverse effect due to addition. Regarding the amount of addition, based on the total amount of Y ₂ O ₃ and the lanthanide oxide, Th
O ₂ is 0.1 to 10 wt%, HfO ₂ is 0.05 to 5 wt%, ZrO ₂ is 0.01 to 4.0 wt%, Li ₂ O is 0.5 to 5 wt%, and LiF is 0 wt%. 1 to 5.0% by weight, B
eO is 0.01 to 1.0% by weight, Al ₂ O ₃ is 0.01
In the range of up to 1.0% by weight, they may be added alone or in appropriate combination. When these elements are added and sintered, they enter the Y ₂ O ₃ lattice, but all have a different charge from Y in the ionized state except Al. Since this difference in charge (valence) causes lattice defects of Y ₂ O ₃ , for example, defects of cation and anion sites, it is important to reduce the amount as much as possible when added alone. However, it is important to combine them so as to avoid these defects (for example, combining tetravalent Th and monovalent Li so that they are apparently close to trivalent). This can further reduce the generation of defective structures,
The optical properties can be further improved. Further, La and Gd in the lanthanide element do not become active elements involved in laser oscillation, but they are LiF and ThO ₂
Like the above, it can be an important element in producing a transparent sintered body.

[0012]

[Function] For use as a solid-state laser, the density of the sintered body is 99.0% or more of the theoretical density (porosity is 1% or less).
And the average particle size of the particles constituting the polycrystal is 5 to 30
It must be in the range of 00 μm. If the density of the sintered body is less than 99.0% of the theoretical density, the light transmittance will be extremely reduced. The relative density of the sintered body can be obtained by comparing the densities of a single crystal and a polycrystal having the same chemical composition measured by the Gakushin method or the X-ray method. The other method is to use a microscope or SE
It can also be obtained by analyzing the image of which the surface is observed with M or the like. When the particle size of the sintered body exceeds 3000 μm, the luminescent element cannot be uniformly solid-dissolved, or the luminescent element is segregated in the grain boundary portion, and thus it is difficult to be an optically transparent one.
If it is less than 5 μm, the transparency for practical use cannot be obtained.

Further, it is desirable that the transparency of the sintered body is as high as possible because it is closely related to the oscillation efficiency when the laser is oscillated. This value can be expressed by a light absorption coefficient that represents the absorption loss inside the base material. That is, Lambert
Beer's law, log (I _o / I) = αd [where
Α in I _o : incident light intensity, I: transmitted light intensity (intensity of light transmitted through the sample), α: light absorption coefficient, d: sample thickness
Value of 0.204 cm ^-1 or less, preferably 0.125 c
It is necessary to stop below m ^-1 . This light absorption coefficient is a light absorption loss that occurs when light passes through a sample having a certain thickness. For example, when a 10 mm-thick sample is irradiated with linear light, its internal loss must be 30% or less. This means that in samples having the same surface processing accuracy, the difference in linear transmittance between samples having a thickness of 1 mm and 11 mm is within 30%. If the absorption loss inside the base material is larger than this, the absorption loss becomes larger than the amplified amount of light, so that not only laser oscillation does not occur, but also the base material is broken in some cases. The absorption loss of the base material is determined by the slope when the transmittance is plotted against the thickness of the sample in the visible wavelength range (or the background level of the transmittance with respect to the measurement wavelength) where there is no absorption of the luminescent element. It is possible to predict that the laser oscillation efficiency will depend on the transparency of the base material, but it is more preferable to limit the loss to 20% or less (α = 0.125 cm ^-1 or less in terms of α value). It is essential. Also, regarding the absolute value of the transmittance, a sample having a thickness of 1 mm has a wavelength range of 400 to 900 nm (limited to the case where the surface roughness of the sample is 0.1 μm or less), and the transmission of a portion excluding the absorption of a luminescent element or the like is performed. It is also necessary that the rate is 75% or more.

Further, the uniformity of the light emitting element is the greatest advantage when producing a solid-state laser material from a sintered body, and is an important technique especially when a large-sized large-power laser is intended. Regarding the homogeneity, 80% or more of the particles constituting the sintered body have a concentration difference within a range of ± 15% (for example, a range containing 2 atomic% of a luminescent element is within a range of 2 ± 0.3%).
Need to be in. The concentration distribution is determined by randomly analyzing about 50 particles, at least about 20 particles of the sintered body. The concentration distribution of the luminescent element in the sintered body can be easily measured by an instrument analyzer such as EDX (energy dispersive X-ray spectrometer) or IMA (ion microanalyzer) that measures a minute region.

The laser is originally a flash lamp or LD
A (laser diode) excites a light emitting element existing inside the material and continuously amplifies the light emitting element, so that a strong laser beam can be oscillated. Here, when a material having grain boundaries such as polycrystalline ceramics is excited to cause laser oscillation, the laser light amplified inside the grains is lost at the grain boundary portion (attenuation due to different phase or crystal defect). Generally, it is considered impossible to oscillate a laser in a polycrystalline body. Moreover, even if laser oscillation occurs, the optical loss at the grain boundary should be large, and it is expected that the characteristic deterioration will be remarkable compared to the single crystal material, so it is considered that all solid-state laser materials should be single crystals. The current situation is exactly the same. Since the polycrystal does not melt, the level of crystal defects (lattice defects) inside the grain should be lower than that of the single crystal,
Since it is difficult for mass transfer to occur near perfect during the sintering process, structural or crystalline defects remain inside the particles. However, if such an inconvenience is avoided, the optical characteristics inside the grains of the polycrystalline ceramic exceed that of the single crystal, and the amplification capability of the laser becomes high. Therefore, Y _{2 having} extremely good sinterability
The use of O ₃ powder is a key technology for producing this ceramic. Further, although the optical loss at the grain boundary portion of the sintered body cannot be denied, by reducing the loss as much as possible, it can be put to practical use sufficiently.
Further, the characteristics of a laser material are not only all of this transmittance but also various factors such as the uniformity of the luminescent element, the concentration of the luminescent element in the host material, and the distortion of the material. Since it is highly possible that the crystalline body is superior to the single crystalline body, there are some that are equivalent to or superior to the single crystalline body in view of the entire characteristics. For example, regarding the strain of the material, a single crystal produced by the Bernoulli method has a value of 2 when the crystal is grown and when the grown crystal is cooled.
Due to the phase transition (cubic and hexagonal) existing near 280 ° C, a considerable residual strain and, in some cases, minute cracks can be confirmed when observed through a polarizing plate. It has excellent features such as almost no detection.

The single crystal Y ₂ O ₃ containing Nd is
The Nd concentration distribution cannot be said to be sufficiently uniform for a laser crystal, and its concentration is limited. In the case of polycrystalline Y ₂ O ₃ ceramics obtained by sintering, its Nd concentration can be arbitrarily selected, and its distribution becomes extremely uniform. From this, application to a new type solid-state laser having characteristics such as small size and high power, and application as a high-power laser can be considered by taking advantage of the large-sized laser production possible by the sintering method.

[0017]

EXAMPLES Table 1 shows oscillation characteristics of Y ₂ O ₃ ceramics as a host, to which various light emitting elements and elements such as La and Li are added, which are excited by an LD or a xenon flash lamp. ..

As an example, Y ₂ O ₃ powder having a purity of 99.9% by weight and a particle size of 0.5 μm or less, one or more kinds of LiF and ThO ₂ and a particle size of 0.5 μm or less and a purity of 99.9% by weight. 150 g of the lanthanide element oxides in Example 1 were weighed out, and each powder and ethyl alcohol 300c were placed in a pot mill.
c, and further 500 g of a plastic ball containing a steel ball core was put therein and mixed for 24 hours. 500 mmHg of mixed powder
The dried powder was lightly remixed in a mortar.

This powder was preformed into a tablet having a diameter of 50 mm and a height of 15 mm and then rubber-pressed at a pressure of 1000 kg / cm ² .

This molded product was placed in an electric furnace and heated to 100 ° C /
The temperature was raised at hr and after firing at a predetermined temperature, it was cooled at 100 ° C / hr. Diameter 6 mm, thickness 10 m from the obtained sintered body
m sample is prepared, the surface roughness of both sides is 5 nm, and the flatness is 1
Finished to / 8λ.

Table 1 shows the average grain size of the sintered body changed by changing the amount of the luminescent element added, the sintering time and the temperature thereof.

[0022]

[Table 1] Table 2 shows a comparative example, a Y ₂ O ₃ single crystal containing 1 atom% of Nd grown by Bernoulli method as a luminescent element, and a polycrystal having an average particle diameter and relative density outside the scope of claims. The oscillation characteristics of Y ₂ O ₃ are shown.

[0023]

[Table 2] From the test results of Examples 1 to 6 in Table 1, it is understood that when only Nd is added as a light emitting element, the laser output increases as the concentration increases. 1 atomic% N of Example 4
The oscillation efficiency of the d-doped polycrystalline Y ₂ O ₃ is 25.0%, the output of the single crystal Y ₂ O ₃ of the same Nd concentration shown in Comparative Example 1 is 106 mW, and the laser output is higher than that of 15.1%. You can see that it is getting higher. Although the high-concentration Nd type lasers of Examples 5 and 6 do not increase their output in proportion to the Nd concentration due to concentration quenching, they are lasers having a high output 2-3 times that of Comparative Example 1. Further, Examples 7 to 11 are Nd.
Other than that, an example in which Nd and another lanthanide element are added is shown, but it can be seen that both of them oscillate at a considerably high level. In the examples shown here, the relative densities are all within the scope of the claims. Although the influence of the particle size is shown in Examples 1 to 3, laser oscillation is strong in all cases, and of these, Example 2 having an average particle size of 220 μm has the best oscillation efficiency.

In Comparative Examples 2 and 3 shown in Table 2, the particle size of the sintered body is outside the scope of the claims, and in Comparative Example 4, the density is outside the scope of the claims, and neither laser oscillation occurs. Even if it oscillated, its efficiency dropped extremely.

[0025]

According to the present invention, it becomes possible to oscillate a laser by using a polycrystalline transparent Y ₂ O ₃ ceramics. In terms of material characteristics, it is possible to increase the concentration of the light emitting element (particularly Nd), and it is possible to increase the size of a material in which the light emitting element is uniform and the like. In addition, the YAG single crystal containing Nd is characterized by a low energy storage capability (high gain) due to the narrow fluorescence spectrum width of the laser, and the glass laser containing Nd is characterized by a low gain due to the wide spectrum width. Has become. These materials currently in practical use cannot satisfy both a high spectral peak and a high average output. The Y ₂ O ₃ ceramics of the present invention have an intermediate property between the two, and it is highly possible that new applications will start if this feature is utilized. Therefore, in addition to being suitable for use as a normal solid-state laser industrially, it is possible to downsize and increase the output of the laser. It is expected to be applied to laser processing, laser nuclear fusion, etc. by taking advantage of its large size, uniformity, and high output.

Also, in consideration of economical efficiency, an expensive single crystal growing apparatus, which is indispensable in the conventional single crystal growing technique, becomes unnecessary. In addition, in the sintering method, the temperature required for sintering the material is lower than its melting point, and the sintering time is about several hours to several tens hours, so that the amount of electric power consumed for synthesis is remarkably small. Furthermore, since a large number of sintered bodies can be produced in one sintering furnace and efficient production can be performed with the near net shape technology while maintaining a shape close to the shape of the material used, cost, mass production and economic efficiency (effective use of rare earth resources and (Electricity cost reduction) etc.

Claims (1)

[Claims] 1. ThO ₂ , HfO ₂ , ZrO ₂ , Li ₂
O / LiF, BeO, and one or more of Al ₂ O ₃ and one or more of lanthanide elements, and the average particle diameter of the sintered body is in the range of 5 to 3000 μm and the porosity is 1% or less. Crystal clear Y ₂ O ₃ ceramics.