JPH08217598A - Production of single crystal of vanadate of rare earth element - Google Patents

Abstract

PURPOSE: To prevent a deviation of a compsn. and to obtain a single crystal having satisfactory quality. CONSTITUTION: High purity powder of R2 O3 (R is a rare earth element) is mixed with high purity powder of V2 O5 in a molar ratio of 1:(1.1-1.3) and the resultant mixture is fired to form high purity single-crystalline powder of RVO4 by a solid phase reaction. Unnecessary matter is then dissolved and removed by acid or alkali washing, the resultant single-crystalline powder is melted and the objective single crystal having a large diameter is grown. When a single crystal of RVO4 contg. R' (R' is other rare earth element) as an active element is produced, R'VO4 is added and growth is carried out.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a rare earth vanadate single crystal, and more particularly to a method for producing a rare earth vanadate single crystal used as an optical crystal for a solid-state laser or the like.

[0002]

2. Description of the Related Art Rare earth vanadate (RVO ₄ , R: rare earth element) single crystal such as yttrium vanadate (YVO ₄ ) single crystal is useful as a crystal for an optical device such as a polarizer or a solid-state laser. The single crystal was formed by the following growing method.

[0003] As the rare earth oxide R ₂ O ₃ as a raw material of vanadium pentoxide V ₂ O _5, such as Y ₂ O _3, 1 of these powders are crystalline composition: weighed and mixed so that a molar ratio After firing to obtain a crystallized powder, the powder is melt-filled into an iridium crucible, and R is formed by a high-frequency induction heating CZ method (Czochralski method: pulling growth method) or the like.
A VO ₄ single crystal is obtained.

A solid-state laser crystal (R ′: RVO ₄ ) in which a rare earth vanadate (RVO ₄ ) such as YVO _{4 is used} as a base crystal and another rare earth element (R ′) such as neodymium (Nd) is added as an activator. ) Is a rare earth oxide R ₂ O
₃ and R ′ ₂ O ₃ and vanadium pentoxide V ₂ O ₅ were used as raw materials, and these oxide powders were weighed and mixed according to the crystal composition and baked to obtain a crystallized powder, which was then melt-filled into an iridium crucible. However, it was manufactured by means such as the high frequency induction heating CZ method.

[0005]

In the conventional rare earth vanadate crystal growth, during the filling of the crucible with the raw material and during the crystal growth, particularly at the initial stage of the growth, the raw material melt is decomposed, and part of the raw material components, specifically, Is because vanadium oxide VO _x scatters,
The composition of the entire raw material was shifted, which was a cause of failing to obtain high quality crystals. Further, the high melting point substance generated as a result of the decomposition floats on the surface of the melt and adheres to the seed crystal, or interferes with normal crystal growth due to the vicinity of the growing solid-liquid interface,
This is taken into the crystal and has been a cause of impairing the crystal quality and optical characteristics.

In a laser crystal, Nd which is an active substance is used.
And other elements must be added. If the amount is small, good quality crystals can be obtained without much problem.
When adding more than atomic percent, usually
The active elements are not uniformly distributed in the crystal, which causes problems such as deposition as inclusions and local mechanical strain, resulting in impaired optical properties and crystal cracking. Had occurred.

The present invention has been made in view of such a situation, and firstly, its object is to suppress the decomposition of the raw material in the process from the melting of the raw material to the end of the growth as much as possible to prevent foreign matter and the like. Secondly, the present invention provides a method for growing a single crystal capable of uniformly growing an active element in a base material at a high concentration and uniformly. That is.

[0008]

In order to achieve the above object, according to the present invention, (1) a rare earth oxide (R ₂ O ₃ ,
R: a rare earth element) and vanadium pentoxide (V ₂ O ₅ ), each of high-purity powders are weighed and mixed so that the molar ratio of V ₂ O ₅ is more than 1: 1 and mixed. 2) Firing and high purity rare earth vanadite (RVO) by solid phase reaction
₄ ) Process of forming single crystal powder, (3) Process of washing with acid or alkali to dissolve and remove unnecessary substances, (4)
A method for producing a rare earth vanadate single crystal, comprising: melting the obtained rare earth vanadate single crystal powder to grow a large-diameter single crystal.

Further, according to the present invention, in order to obtain a rare earth vanadate (R ': RVO ₄ ) single crystal containing another rare earth element (R') as an active element, the above-mentioned (4)
In the process of other rare earth vanadate (R'VO
₄ ) A method for producing a rare-earth vanadate single crystal, in which crystal growth is performed by adding ₄ ).

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention has been made based on the results of a detailed examination of which process and at what time the raw material decomposition takes place from the filling of the raw material to the end of the growth in the growth of the rare earth vanadate single crystal. . According to the experimental results,
In the conventional method, the decomposition rate of the raw material up to the melting and filling operation of the raw material into the crucible and the seeding (seed) operation is the highest, and the decomposition during growing is not simply proportional to the time, but the decomposition rate is gradually increased from the initial stage of growing. Was found to decrease. From this result, it is expected that a good quality single crystal can be obtained if decomposition and scattering can be prevented in the initial operation.

[0011] Therefore, the inventors further studied the reason why the decomposition / scattering becomes dominant in the early stage of the growth. as a result,
In the conventional method, the starting material for crystal growth obtained by mixing and firing oxides is insufficient in single crystallization, and each oxide is contained as it is, and further contains a large amount of non-single-crystallized RVO _4. Therefore, it became clear that decomposition is likely to occur. Even if RVO ₄ is the same, if the material is not crystallized, it easily decomposes by melting. Furthermore, in the conventional example, a plurality of materials having different melting points are mixed, so that decomposition is easily promoted, and an oxide having a high melting point is liable to hinder growth or to be easily incorporated into the crystal as a foreign substance.

The inventor of the present invention considers that the raw material is likely to be overheated in the initial stage, and considers that it is desirable that the state of the raw material is not easily decomposed. Good results have been obtained with rare earth vanadate crystallized powders. In this case, the composition is simply RVO
If it is ₄ , it is not good and it needs to be crystalline. Crystals are in a state of being difficult to decompose due to their physical and chemical bonding forces. Experiments have shown that these materials are not easily decomposed during or after melting. In the present invention, a method is adopted in which such high-quality crystal powder is prepared by a solid-phase reaction, and impurities and unreacted substances that contribute to promotion of decomposition are washed away with a chemical. This makes it possible to use a high-purity rare earth vanadate crystal as a growth starting material.

The reason why the addition of the active element becomes more difficult as the concentration of the active element becomes higher, is basically due to the size of the rare earth ion R in the host crystal and the size of the other rare earth ion R ′ added by substituting the position. This is due to the difference in size. That is, the larger the difference, the more easily the crystal quality is hindered.
_When Nd is added to ₄ , it belongs to a difficult class. In such a case, it is necessary to select an additive that is easily soluble in the base crystal raw material melt.As a result of conducting a crystal growth experiment using various rare earth compounds, the best quality results were obtained when rare earth vanadite was used as an additive. was gotten. This is R'VO _X
It is considered that when added to the base material RVO ₄ in the form of (1), the solubility of the additive in the base material is improved, and uniformization in the crystal can be achieved.

[0014]

EXAMPLES Next, examples of the present invention which can obtain good results will be described. [First Embodiment] V ₂ O ₅ powder 47 having a purity of 99.99%
3 g and 452 g of Y ₂ O ₃ powder having a purity of 99.999% were weighed and mixed with a V-type mixer at 50 revolutions per minute for 5 hours.
This was transferred to a rotary kiln and 10 revolutions per minute
The mixture was fired in air at 00 ° C. for 30 hours, the power was cut off, and the mixture was naturally cooled to room temperature. This was washed in 2000 ml of 0.5 N nitric acid HNO ₃ to dissolve unnecessary substances, and then washed with water. The powder was filtered and dried with warm air to obtain a crystal growth raw material. FIG. 1 is an X-ray diffraction pattern of this powder. This pattern shows that the obtained powder has good crystallinity and is a single YVO ₄ substance.

Using this powder as a raw material, a single crystal of YVO ₄ was grown using a high frequency induction heating type oxide single crystal pulling apparatus. Crucible 50mm in diameter, 50mm in depth
The growth rate was 1 mm / h, the growth atmosphere was nitrogen containing 0.1% oxygen, and the seed crystal orientation was the c-axis. The grown crystal is about 15 mm in diameter and 35 mm in length, often seen in conventional crystals, cracks, twins, inclusions,
Etc. were not seen at all. Further, although the conventional crystal was colored brown, it was found that this crystal was pale yellow and improved optically.

[Second Embodiment] A case of a fixed laser YVO ₄ crystal doped with Nd will be described. NdVO ₄ powder having a molar concentration of 3.5% was added to the YVO ₄ powder for crystal growth obtained in the first example, and the mixture was mixed with a V-type mixer. The raising conditions are
Except that the growth rate was 0.8 mm / h, it was the same as that of the first example. The obtained crystal has a diameter of about 12 m.
m, the length was 30 mm, and the Nd concentration in the upper part of the crystal was 2.0 atomic%.

In the conventional method, that is, in the crystal using Nd ₂ O ₃ as an additive, most of the crystals were found to have cracks and inclusions in the case of Nd ₂ atomic%. , Such defects are not observed, and good crystallographic properties comparable to the case of Nd of 1 atomic% or less by the conventional method,
A single crystal having optical properties was obtained.

[Third Embodiment] As in the case of the second embodiment, the case of a solid-state laser crystal doped with Er will be described. Y for growing a crystal obtained by the first embodiment
ErVO ₄ powder having a molar concentration of 15.5% was added to the VO ₄ powder, mixed with a V-type mixer, and then used as a raw material for crystal growth. The growth conditions were the same as in the first embodiment. The obtained crystal has a diameter of about 17 mm and a length of 35 m.
m, the Nd concentration at the top of the crystal was 15.0 atomic%.

In the conventional method, that is, in the case of a crystal in which Er ₂ O ₃ is used as an additive, in the case of 15 atomic% of Nd, the presence of fine inclusions serving as a light scatterer was found in almost all crystals. No such defects were found in the crystals according to the invention.

[Modifications of Embodiments] The preferred embodiments have been described above, but the present invention is not limited to these embodiments, and various modifications can be made within the scope of the claims. is there. For example, in the embodiment, as an example of the rare earth Banadeito host crystal, a YVO _4, showed NdVO ₄ and ErVO ₄ Examples of active elements additives, instead of them, and other rare earth Banadeito host crystal,
Different rare earth activator additives may be used. In the embodiment, the single crystal growth by the CZ method has been described.
The same effect can be obtained by adopting another growing method such as the Z method (floating zone melting growing method) or the Brijman method. In addition, the removal of unnecessary substances after obtaining the crystallized powder may be performed using an acid other than nitric acid or an alkali. Further, the treatment can be performed using an acid and an alkali.

[0021]

As described above, according to the present invention, method for growing a rare earth Banadeito single crystal according to the present invention, the solid phase reaction with R ₂ O ₃ and V ₂ O ₅ in a state of V ₂ O ₅ over a high purity The rare earth vanadate single crystal powder is obtained, and the rare earth vanadate single crystal is produced using this as a starting material.
Scattering of vanadium oxide, which is likely to occur at the beginning of the preparation of the melt, can be suppressed, and a composition deviation of the raw material can be prevented. Impurities are not generated by scattering, and since the starting material does not contain impurities and rare earth oxides, these are not mixed in the melt and taken into the grown single crystal. Therefore, according to the present invention,
The crystallinity of the grown single crystal is remarkably improved, and rare-earth vanadate crystals with few macroscopic defects such as cracks and twins, which are observed in crystals by conventional methods, and with less coloring can be formed. Furthermore, according to the active element addition method according to the present invention, the solubility of the active element material in the base material melt is improved,
It becomes possible to uniformly add an active element into the crystal to a higher concentration than before, thereby making it possible to produce a high-performance solid-state laser device.

[Brief description of drawings]

FIG. 1 is a view showing a powder X-ray diffraction pattern of a yttrium vanadate single crystal formed in an example of the present invention.

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Claims (5)

[Claims] (1) A high-purity powder of a rare earth oxide (R ₂ O ₃ , R: rare earth element) and vanadium pentoxide (V ₂ O ₅ ) are mixed with each other in a molar ratio of V ₂ higher than 1: 1. a process in which O ₅ is mixed were weighed so that the excess (2) firing to the steps of forming a high purity rare earth Banadeito (RVO ₄₎ single-crystal powder by solid-phase reaction, (3) an acid or A process of dissolving and removing unnecessary substances by washing with an alkali; and (4) melting the obtained rare earth vanadate single crystal powder,
Growing a large diameter single crystal. A method for producing a rare earth vanadate single crystal, comprising: 2. The method according to claim 1, wherein R ₂ O ₃
1 and the V ₂ O _5, in a molar ratio: 1.1 to claim 1 a method of producing a rare-earth Banadeito single crystal, wherein the mixing in a ratio of 1.3. 3. In order to obtain a rare earth vanadate (R ′: RVO ₄ ) single crystal containing another rare earth element (R ′) as an active element, vanadate of another rare earth element (R ′: RVO ₄ ) is obtained in the step (4). 2. The method for producing a rare earth vanadate single crystal according to claim 1, wherein R′VO ₄ ) is added to grow the crystal. 4. The method according to claim 1, wherein the rare earth element (R) is yttrium (Y).
The method for producing a rare earth vanadate single crystal according to claim 1, 2 or 3. 5. The method for producing a rare earth vanadate single crystal according to claim 3, wherein the other rare earth element (R ′) is neodymium (Nd) or erbium (Er).