JP5127778B2 - Fluoride crystals, vacuum ultraviolet light emitting devices, and vacuum ultraviolet light emitting scintillators - Google Patents

Description

  The present invention relates to a novel fluoride crystal. The fluoride crystals are used in photolithography, semiconductor and liquid crystal substrate cleaning, sterilization, next-generation large-capacity optical discs, vacuum ultraviolet light emitting devices used in medicine (ophthalmic treatment, DNA cutting), etc., and PET cancer diagnosis and X-ray CT. Can be publicly used as a vacuum ultraviolet light emission scintillator for radiation detectors.

  The ultraviolet light emitting material is used as an ultraviolet light emitting element. In particular, high-intensity ultraviolet light-emitting elements are materials that support advanced technologies in the semiconductor field, information field, medical field, and the like. In recent years, they have been shortened to meet many demands such as an increase in recording density on recording media. Development of an ultraviolet light emitting element that emits light at a wavelength is in progress. As the ultraviolet light-emitting element that emits light at a short wavelength, a light-emitting element having an emission wavelength of about 360 nm made of a material such as GaN is commercially available.

  Although a vacuum ultraviolet light emitting material having a shorter wavelength of 200 nm or less can be suitably used for photolithography, semiconductor or liquid crystal substrate cleaning, sterilization, etc. as a vacuum ultraviolet light emitting element, development is desired. It is not easy to obtain a vacuum ultraviolet light emitting element, and only a few examples are known at present.

  Those that emit light when irradiated with radiation can also be used as scintillators.

  A radiation detector used for cancer diagnosis by PET or X-ray CT is composed of a material called a scintillator that emits light when irradiated with a weak light detector such as a photomultiplier tube or a semiconductor light receiving element. .

  Although the mainstream is the use of photomultiplier tubes and Si light receiving elements for weak light detectors, vacuum ultraviolet light receiving elements using diamond or AlGaN as the light receiving surface have been developed in recent years. Compared with a conventional Si semiconductor light receiving element, it is insensitive to visible light having a lower energy than vacuum ultraviolet light, so that low background noise can be realized and it is a promising light receiving element to be incorporated in a radiation detector. Therefore, development of a new vacuum ultraviolet light emission scintillator suitable for these light receiving elements is demanded.

  Conventionally, since a visible light receiving element has been used, scintillator crystals that emit visible light have been mainly developed, and a vacuum ultraviolet light emitting scintillator has not been sufficiently studied.

  As an example, there is a lanthanum fluoride crystal to which Nd is added (see Non-Patent Document 1), but it is 175 nm shorter than LYSO or LSO (Ce-added Lu-based oxide having an emission wavelength of about 400 nm) that has already been put to practical use. Although wavelength emission is realized, La (Z = 57) whose atomic number is lower than Lu (atomic number Z = 71) is mainly contained as a base material. The atomic number of La is relatively high among all the elements, and the gamma ray stopping power of the lanthanum fluoride crystal added with Nd has good characteristics, but is not sufficient as compared with LYSO and LSO.

  A factor that makes it difficult to develop a vacuum ultraviolet light emitting material is that vacuum ultraviolet rays are absorbed by many substances, so that substances that do not cause self-absorption are limited.

  Furthermore, the emission characteristics in the vacuum ultraviolet region are easily affected by impurities in the material, and even a material having an emission energy level in the vacuum ultraviolet region has a long wavelength based on a lower energy level. In many cases, the desired vacuum ultraviolet light emission cannot be obtained due to reasons such as light emission being dominant or loss due to non-radiative transition being significant.

  Therefore, it is extremely difficult to predict the emission characteristics in the vacuum ultraviolet region in advance, and this is a big barrier in the development of vacuum ultraviolet light emitting materials.

P. SHOTAUS et al. , “DETECTION OF LaF3: Nd3 + SCINTILLATION LIGHT IN A PHOTOSENSITIVE MULTIWIRE CHAMBER” Nuclear Instruments and Methods in Physics16, 1987.

  The present invention provides a fluoride crystal that emits light with high brightness in the vacuum ultraviolet region. Also, a new vacuum ultraviolet light-emitting device comprising the fluoride crystal, which can be suitably used for photolithography, semiconductor and liquid crystal substrate cleaning, sterilization, next-generation large-capacity optical disk, medical treatment (ophthalmic treatment, DNA cutting), and the like, An object of the present invention is to provide a vacuum ultraviolet light emission scintillator for a radiation detector that can be used for cancer diagnosis by PET and X-ray CT.

As a result of searching for materials that emit light in the vacuum ultraviolet region and conducting various studies, the present inventors obtained high-intensity vacuum ultraviolet light emission by exciting crystals made of a mixed phase of K ₃ LuF ₆ and KF with radiation. As a result, the present invention has been completed.

That is, the present invention is a fluoride crystal composed of a mixed phase of K ₃ LuF ₆ and KF, and a vacuum ultraviolet light emitting device and a vacuum ultraviolet light emitting scintillator using the fluoride crystal.

  According to the fluoride crystal of the present invention, high-luminance light emission in the vacuum ultraviolet region can be obtained by radiation irradiation. The vacuum ultraviolet light emitting element made of the fluoride can be suitably used for photolithography, semiconductor and liquid crystal substrate cleaning, sterilization, next-generation large-capacity optical disk, medical treatment (ophthalmic treatment, DNA cutting), and the like. Further, it can be suitably used as a vacuum ultraviolet light emission scintillator for a weak light detector for vacuum ultraviolet light such as a diamond light receiving element or an AlGaN light receiving element.

This figure is a schematic view of an apparatus for producing a crystal by the micro pull-down method. This figure is a powder X-ray diffraction pattern of a fluoride crystal composed of a mixed phase of K ₃ LuF ₆ and KF of the present invention. This figure is a schematic diagram of an X-ray excitation emission spectrum measuring apparatus. This figure is an X-ray excitation emission spectrum of a fluoride crystal composed of a mixed phase of K ₃ LuF ₆ and KF of the present invention.

Hereinafter, a fluoride crystal composed of a mixed phase of K ₃ LuF ₆ and KF of the present invention will be described. In the present invention, vacuum ultraviolet light emission means light emission having a wavelength of 200 nm or less.

The fluoride crystal comprising a mixed phase of K ₃ LuF ₆ and KF of the present invention is generally represented by potassium fluoride lutesium represented by the chemical formula K ₃ LuF ₆ (hereinafter referred to as K ₃ LuF ₆ ) and the chemical formula KF. It consists of crystals of mixed phase of potassium fluoride (hereinafter referred to as KF).

The fluoride crystal of a mixed phase of _K 3 LuF ₆ and KF of the present _invention, K 3 LuF phases ₆ and KF are both present, crystals of _K 3 LuF ₆ the presence of KF by powder X-ray diffraction method can be confirmed It is. However, it is not the case that the crystals are separately prepared and then mixed, but rather than the case where the single crystal K ₃ LuF ₆ is prepared at the raw material stage, KF is excessively mixed and melted and crystallized. Preferably there is.

In general light-emitting materials, when an impurity is added to an extent that can be confirmed by powder X-ray diffraction, the light emission intensity often decreases, but the fluoride crystal of the present invention has an exceptionally low light emission intensity. Absent. Although the principle is not clear, it is conceivable that KF is effectively dispersed at the grain boundaries to enhance the crystallinity. _Moreover, the abundance ratio of KF for K 3 LuF ₆ is not particularly limited, both KF and _K 3 LuF ₆ may if confirmed by powder X-ray diffraction method.

Method for producing a K ₃ LuF ₆ and mixed phase consisting of a fluoride crystal of KF is not particularly limited, may be prepared by conventional melt growth method represented by a Czochralski method or a micro pulling-down method.

  The micro pulling-down method is a method for producing a crystal by drawing a raw material melt from a hole provided in the bottom of the crucible 5 using an apparatus as shown in FIG.

Hereinafter, a general method for producing a fluoride crystal composed of a mixed phase of K ₃ LuF ₆ and KF by the micro pull-down method will be described.

  First, a predetermined amount of raw material is filled into a crucible 5 having a hole at the bottom. Although the shape of the hole provided in the crucible bottom is not particularly limited, it is preferably a cylindrical shape having a diameter of 0.5 to 4 mm and a length of 0 to 2 mm.

In the present invention, the raw material is not particularly limited, but it is preferable to use a mixed raw material in which KF and LuF ₃ having a purity of 99.99% or more are mixed. By using such a mixed raw material, the purity of the crystal composed of the mixed phase of K ₃ LuF ₆ and KF can be increased, and characteristics such as luminance of light emission are improved. The mixed raw material may be used after being sintered or melted and solidified after mixing.

The molar ratio of KF to LuF ₃ in the mixed raw material is usually 4.0 to 6.0. This is because the volatility of KF is higher than that of LuF ₃ . Since the easiness of volatilization of KF varies depending on manufacturing conditions such as the growth atmosphere and temperature, it is difficult to generalize the KF mixing ratio at the time of raw material charging, and it is desirable to determine by preliminary experiments.

Next, the crucible 5 filled with the raw materials, the after heater 1, the heater 2, the heat insulating material 3, and the stage 4 are set as shown in FIG. After evacuating the inside of the chamber 6 to 1.0 × 10 ⁻³ Pa or less using a vacuum evacuation apparatus, an inert gas such as high-purity argon is introduced into the chamber 6 to perform gas replacement. The pressure in the chamber after gas replacement is not particularly limited, but atmospheric pressure is common.

  By the gas replacement operation, moisture attached to the raw material or the chamber can be removed, and deterioration of crystals derived from the moisture can be prevented. In order to avoid the influence of moisture that cannot be removed by the gas replacement operation, it is preferable to use a solid scavenger such as zinc fluoride or a gas scavenger such as tetrafluoromethane. When using a solid scavenger, a method of mixing in the raw material in advance is preferable, and when using a gas scavenger, a method of mixing with the above inert gas and introducing it into the chamber is preferable.

  After performing the gas replacement operation, the raw material is heated and melted by the high-frequency coil 7, and the melted raw material melt is drawn out from the hole at the bottom of the crucible to start crystal growth.

  Here, the metal wire is provided at the tip of the pull-down rod, the metal wire is inserted into the crucible through the hole at the bottom of the crucible, the raw material melt is attached to the metal wire, and then the raw material melt is pulled down together with the metal wire. This makes it possible to grow crystals.

  That is, while adjusting the output of the high frequency and gradually raising the temperature of the raw material, the metal wire is inserted into the hole at the bottom of the crucible and pulled out. This operation is repeated until the raw material melt is drawn together with the metal wire, and crystal growth is started. The material of the metal wire can be used without limitation as long as it is a material that does not substantially react with the raw material melt, but a material excellent in corrosion resistance at high temperatures such as a W-Re alloy is preferable.

After pulling out the raw material melt with the metal wire, the crystal can be obtained by continuously pulling it down at a constant pulling rate.
The pulling speed is not particularly limited, but is preferably in the range of 0.5 to 10 mm / hr.

In the production of a fluoride crystal comprising a mixed phase of K ₃ LuF ₆ and KF of the present invention, an annealing operation may be performed after the production for the purpose of removing crystal defects caused by thermal strain.

The obtained fluoride crystal composed of a mixed phase of K ₃ LuF ₆ and KF has good processability and can be easily processed into a desired shape and used. In processing, a known cutting machine such as a blade saw or wire saw, a grinding machine, or a polishing machine can be used without any limitation.

A fluoride crystal composed of a mixed phase of K ₃ LuF ₆ and KF can be processed into a desired shape to obtain the vacuum ultraviolet light emitting device and the vacuum ultraviolet light emitting scintillator of the present invention. The vacuum ultraviolet light emitting device of the present invention can be made into a vacuum ultraviolet light generator by combining with a radiation source as an excitation source. Such a vacuum ultraviolet light generator is suitably used in fields such as photolithography, sterilization, next-generation large-capacity optical disks, and medicine (ophthalmic treatment, DNA cutting). In addition, the vacuum ultraviolet light emission scintillator of the present invention can be suitably used as a radiation detector with low background noise in combination with a weak light detector for vacuum ultraviolet light such as a diamond light receiving element or an AlGaN light receiving element.

  Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited to these examples.

Example 1
Fluoride crystals made of a mixed phase of K ₃ LuF ₆ and KF were produced using the crystal production apparatus shown in FIG. As a raw material, KF and LuF ₃ having a purity of 99.99% were used. The after-heater 1, the heater 2, the heat insulating material 3, the stage 4, and the crucible 5 are made of high-purity carbon, and the shape of the hole provided at the bottom of the crucible is 2 mm in diameter and 0.5 mm in length. did.

First, 0.546 g and 0.454 g of KF and LuF ₃ were weighed, mixed well, and then charged in the crucible 5.

The crucible 5 filled with the raw material was set on the upper part of the after heater 1, and the heater 2 and the heat insulating material 3 were sequentially set around the crucible. Next, the inside of the chamber 6 is evacuated to 1.0 × 10 ⁻⁴ Pa using an evacuation apparatus including an oil rotary pump and an oil diffusion pump, and then an argon-tetrafluoromethane mixed gas is introduced into the chamber 6. Then, gas replacement was performed.

  After the gas replacement, the pressure in the chamber 6 was changed to atmospheric pressure, and then the raw material was heated to about 400 ° C. with the high-frequency coil 7. Then, while adjusting the high frequency output and gradually raising the temperature of the raw material melt, the W-Re wire provided at the tip of the pull-down rod 8 was inserted into the hole and pulled down repeatedly. The liquid could be drawn out from the hole.

  The high frequency output was fixed so that the temperature at this time was maintained, the raw material melt was lowered, and crystallization was started. The crystal was continuously pulled down at a speed of 6 mm / hr for 12 hours to finally obtain a crystal having a diameter of 2 mm and a length of about 70 mm.

  The obtained single crystal was cut into a length of about 10 mm with a wire saw, the side surface was ground and processed into a shape having a length of 10 mm, a width of about 2 mm, and a thickness of 1 mm, and then a length of 10 mm and a width of about 2 mm. Both surfaces were mirror-polished to prepare a sample for measuring light emission characteristics.

From the results of the analysis by the X-ray diffraction method, it was confirmed that the crystal of Example 1 was a crystal from which a powder X-ray diffraction pattern of a mixed phase of K ₃ LuF ₆ and KF shown in FIG. 2 was obtained.

  The vacuum ultraviolet light emission characteristics by X-ray excitation of the obtained single crystal of Example 1 were measured as follows using the measuring apparatus shown in FIG. The measurement was performed at room temperature.

  The sample 9 of the present invention was set at a predetermined position in the measuring apparatus, and the entire interior of the apparatus was replaced with nitrogen gas. The sample 9 is irradiated with X-rays from the X-ray generator 10 (X-ray generator for RIGAKU SA-HFM3), which is an excitation source, at an output of 60 kV and 35 mA, and emission from the sample 9 is emitted into the emission spectrometer 11 (spectrometer instrument). Manufactured by KV201 type extreme ultraviolet spectrometer). The wavelength of the spectrum by the emission spectrometer 11 was swept in the range of 120 to 250 nm, and the emission intensity at each emission wavelength was recorded by the photomultiplier tube 12. The obtained emission spectrum is shown in FIG.

Reference example 1
In addition, as Reference Example 1, a K ₃ LuF ₆ single-phase crystal was prepared in the same manner as in Example 1 except that 0.453 g and 0.547 g of KF and LuF ₃ were weighed, respectively, and a vacuum by X-ray excitation was used. Ultraviolet emission characteristics were measured. The obtained emission spectrum is shown in FIG.

Comparative Example 1
As Comparative Example 1, a KF single-phase crystal was prepared in the same manner as in Example 1 except that 1.000 g of KF was weighed, and vacuum ultraviolet emission characteristics by X-ray excitation were measured. The obtained emission spectrum is shown in FIG.

From the emission spectrum shown in FIG. 4, a fluoride crystal composed of a mixed phase of K ₃ LuF ₆ and KF has a K ₃ LuF ₆ single-phase crystal (Reference Example 1) and a KF single-phase crystal (at a wavelength of 200 nm or less). In addition to showing an emission spectrum different from that of Comparative Example 1), the emission intensity was higher than these, and it was confirmed that the device emits light with sufficient luminance and operates as a vacuum ultraviolet light emitting device. It was also confirmed to operate as a scintillator because it emits vacuum ultraviolet light when excited by radiation. Thereby, it turned out that this invention can be utilized suitably as a vacuum ultraviolet light emitting element and a vacuum ultraviolet light emission scintillator.

DESCRIPTION OF SYMBOLS 1 After heater 2 Heater 3 Heat insulation material 4 Stage 5 Crucible 6 Chamber 7 High frequency coil 8 Pulling rod 9 Sample 10 X-ray generator 11 Emission spectrometer 12 Photomultiplier tube

Claims (3)

A fluoride crystal composed of a mixed phase of KF and K ₃ LuF ₆ . A vacuum ultraviolet light emitting device comprising the fluoride crystal according to claim 1. A vacuum ultraviolet light emitting scintillator comprising the fluoride crystal according to claim 1.

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