JP5317952B2 - 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 suitably used as a vacuum ultraviolet light emission scintillator for radiation detectors used in the above.

  High-intensity ultraviolet light-emitting devices are materials that support advanced technologies in the semiconductor field, information field, medical field, etc. In recent years, in order to respond to many demands such as an increase in recording density on recording media, a shorter wavelength is required. Development of ultraviolet light-emitting elements that emit light at room temperature is underway. As an ultraviolet light emitting element that emits light at a short wavelength, an LED having an emission wavelength of about 360 nm using an ultraviolet light emitting 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 light emission characteristics in the vacuum ultraviolet region in advance, and this is a big barrier in the development of vacuum ultraviolet light emitting elements.

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

  An object of the present invention is to provide 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 scintillator for a radiation detector used for cancer diagnosis by PET or 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 replaced part of K in K ₃ LuF ₆ with Na, and determined the total number of atoms of K and Na and the number of atoms of Lu. It has been found that a high-luminance light is emitted at a wavelength in the vacuum ultraviolet region by exciting a fluoride crystal produced with a composition having a different ratio with radiation. Further, K ₃ LuF ₆ has deliquescence, but it has been found that the deliquescence can be reduced by replacing part of K with Na, and the present invention has been completed.

That is, the present invention has the formula _{K 3-X Na X Lu Y} F 3 + 3Y ( wherein, 0.7 <X <1.3,0.85 <Y < 1.1), characterized by being represented by And a vacuum ultraviolet light emitting element and a vacuum ultraviolet light emitting scintillator characterized by comprising the fluoride crystal.

(Wherein, 0.7 <X <1.3,0.85 <Y < 1.1) Formula _{K 3-X Na X Lu Y} F 3 + 3Y of the present invention according to a fluoride represented by crystalline High-luminance light emission in the vacuum ultraviolet region can be obtained by irradiation with radiation. The vacuum ultraviolet light emitting element made of the crystal can be suitably used for photolithography, semiconductor or 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 scintillator for a weak light detector for vacuum ultraviolet, such as a diamond light receiving element or an AlGaN light receiving element.

  In addition, the fluoride crystal of the present invention has low deliquescence and can be handled in the atmosphere. Therefore, there is an advantage that it can be produced and processed without being in a specially humidity-controlled drying facility.

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 Examples 1 to 5 and Comparative Examples 1 and 2. This figure is a powder X-ray diffraction pattern of Examples 1 and 6 to 8 and Comparative Examples 3 and 4. This figure is a schematic diagram of an X-ray excitation emission spectrum measuring apparatus. This figure is the X-ray excitation emission spectrum of Examples 1 and 9. This figure is the X-ray excitation emission spectrum of Examples 2-8.

Hereinafter, (wherein, 0.7 <X <1.3,0.85 <Y < a is 1.1) Formula _{K 3-X Na X Lu Y} F 3 + 3Y of the present invention for fluoride crystal represented by explain. In the present invention, vacuum ultraviolet light emission means light emission having a wavelength of 200 nm or less.

The fluoride crystal of the present invention has a composition in which part of K in K ₃ LuF ₆ is replaced with Na and the ratio of the total number of atoms of K and Na to the number of atoms of Lu is changed. X represents the ratio of Na to the total number of atoms of K and Na, and Y represents the ratio of the number of atoms of Lu to the total number of atoms of K and Na.

A crystal represented by the chemical formula in which X or Y is outside the specified range (for example, K _1.5 Na _1.5 LuF ₆ , K ₂ NaLu _0.5 F _4.5, etc.) is usually obtained. I can't.

  When a powder X-ray diffraction pattern similar to that of the crystal of the present invention can be confirmed in a crystal grown by weighing the raw material powder in such a ratio of the number of atoms, X and Y are within the specified range. A crystal of the present invention represented by a chemical formula is formed, and crystals having a crystal structure different from that of the present invention are mixed as a different phase. For example, when the raw material powder is weighed with X = 1.3 as a target, a crystal having the same crystal structure as that of the crystal of the present invention and a heterogeneous phase are obtained, and a crystal with X = 1.3 cannot be obtained.

  Furthermore, when X is 0.7 or less or Y is 0.85 or less, excessive KF may be included as a heterogeneous phase. In general, KF is known to have strong deliquescence, and deliquescence occurs in a mixture containing KF as a heterogeneous phase.

(Wherein, 0.7 <X <1.3,0.85 <Y < a is 1.1) Formula _{K 3-X Na X Lu Y} F 3 + 3Y of the present invention represented fluoride crystal by the chemical formula It has a crystal structure similar to the fluoride crystal represented by K ₂ NaYF ₆ .

  The fluoride crystal of the present invention has a trace amount (5% or less) of metal ions (Li, Rb, Cs, Sc, Y, La, Ce) as long as a crystal phase different from the crystal structure is not generated as an impurity. , Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Yb, etc.) may be contained in the crystal structure.

  The crystal of the present invention may be in any state of single crystal, polycrystal, or crystal powder, and can emit vacuum ultraviolet light in any state. Therefore, even a solid sample having a large size can be easily taken out without attenuating light emission from the inside, and therefore, it is suitable for any use of a vacuum ultraviolet light emitting device and a vacuum ultraviolet light emitting scintillator.

  Although the production method is not particularly limited, it can be produced by a general melt growth method represented by the Czochralski method or the micro pull-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 the fluoride crystal of the present invention 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, NaF, and LuF ₃ powders each having a purity of 99.99% or more are mixed. By using such a mixed raw material, the purity of the crystal can be increased, and characteristics such as emission intensity are improved. The mixed raw material may be used after being sintered or melted and solidified after mixing.

The mixing ratio of the raw material powders in the mixed raw material is expressed by the chemical formula K _3-X Na _X Lu _Y F _{3 + 3Y} (where 0.7 <X <1.3, 0.85 <Y <1 .1) can be used as it is. However, depending on the crystal growth conditions (for example, when the temperature is significantly higher than the melting point), there may be a difference in the volatilization amount during the growth of each raw material powder. In that case, it is necessary to weigh more easily the volatilized powder than the composition ratio defined by the chemical formula.

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 if it is too fast, the crystallinity tends to be poor, and if it is too slow, the crystallinity is improved, but the time required for crystal growth becomes enormous. / Hr is preferable.

  In the production of the fluoride crystal of the present invention, an annealing operation may be performed after the production of the crystal for the purpose of removing crystal defects caused by thermal strain.

  The obtained crystal has good workability and can be easily processed into a desired shape. 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. Further, since the crystal of the present invention has low deliquescence, it can be processed without being in a specially humidity-controlled drying facility.

  The crystal of the present invention has good vacuum ultraviolet emission characteristics, and can be excited to emit light by radiation such as X-rays, gamma rays, and beta rays.

  The fluoride crystal of the present invention can be processed into a desired shape to obtain the vacuum ultraviolet light emitting device and vacuum ultraviolet light emitting scintillator of the present invention.

  The vacuum ultraviolet light emitting device comprising the fluoride crystal 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). The 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 rays 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.

Examples 1 to 9, Comparative Examples 1 to 4, Reference Example 1
(Production of fluoride crystals)
Crystals of Examples 1 to 9, Comparative Examples 1 to 4, and Reference Example 1 were manufactured using the crystal manufacturing apparatus shown in FIG. Hereinafter, although the produced method is explained in full detail about Example 1, as shown in Table 1 also about Examples 2-9, Comparative Examples 1-4, and Reference Example 1, except that the measured value of each raw material differs. The same method was used.

As raw materials, KF, NaF, 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, each raw material was weighed as shown in Table 1, 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 a 90% argon-tetrafluoromethane 10% mixed gas is added to the chamber. The gas was replaced by introducing the gas into 6.

  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, but no leaching of the raw material melt from the bottom of the crucible 5 was observed. 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, and finally a crystal having a diameter of 2 mm and a length of about 70 mm was obtained.

  The crystals of Examples 1 to 9 and Reference Example 1 were colorless and transparent, but Comparative Examples 1 to 4 gave white turbid crystals.

（結晶相の同定）
実施例１〜８、比較例１〜４で得られたフッ化物結晶の結晶相の同定を下記の方法で行った。

(Identification of crystal phase)
The crystal phases of the fluoride crystals obtained in Examples 1 to 8 and Comparative Examples 1 to 4 were identified by the following method.

Part of the obtained crystal was pulverized into powder, and powder X-ray diffraction measurement was performed. As a measuring device, D8 DISCOVER manufactured by Bruker AXS was used. The diffraction pattern by the powder X-ray diffraction method is shown in FIGS. From the result of analyzing the diffraction pattern obtained by the powder X-ray diffraction method, it was found that the crystals of Examples 1 to 8 were crystals having a powder X-ray diffraction pattern similar to K ₂ NaYF ₆ .

  2 and 3, X is 0.7 or less, X is 1.3 or more, Y is 0.85 or less, or Y is 1.1 or more. It was not obtained in the phase, a heterogeneous phase was confirmed, and a fluoride crystal having the target composition was not obtained.

  Moreover, the diffraction peak of the fluoride crystal of the present invention obtained in a single phase showed a peak shift corresponding to the composition. In general, when a site of a small element is replaced with an element having a large ionic radius, the lattice constant increases and the diffraction peak shifts to a lower angle side. Conversely, when a site of a large element is replaced with an element having a small ionic radius, the lattice constant is decreased, and the diffraction peak is shifted to the high angle side. When the constituent elements are arranged in descending order of ion radius, K> Na> Lu.

  As shown in FIG. 2, when K is increased with respect to Na, the diffraction peak tends to shift to the lower angle side, so the lattice constant is large, and K is Na having a small ionic radius and the same valence. Probably replacing the site.

  From FIG. 3, it can be considered that when Lu is increased with respect to the total number of atoms of K and Na, the diffraction peak tends to shift to the high angle side, so that the lattice constant is reduced. Lu is presumed to be substituted for K or Na sites having a large ionic radius, but since the valence is different, it is not certain how it exists in the crystal.

  From these facts, when single-phase crystals with different compositions are obtained, it is considered that a similar structure in which some elements are substituted is generated.

(Evaluation of luminous characteristics)
The obtained crystals of Examples 1 to 9 were cut into a length of about 10 mm with a wire saw, the side surfaces were 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. Both surfaces of a surface with a width of about 2 mm were mirror-polished to prepare a sample for measuring the light emission characteristics.

  The vacuum ultraviolet emission characteristics by X-ray excitation at room temperature of the processed crystal were measured as follows using the measuring apparatus shown in FIG.

  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 100 to 280 nm, and the emission intensity at each emission wavelength was recorded by the photomultiplier tube 12.

  The line excitation emission spectra are shown in FIGS. From FIG.5 and FIG.6, light emission was confirmed in the wavelength of about 140-200 nm wavelength in the vacuum ultraviolet region with all the crystals of Examples 1-9. From this, it was confirmed that the crystal of the present invention emits light with sufficient intensity at a wavelength of 200 nm or less and operates as a vacuum ultraviolet light emitting device.

Among Examples 1 to 9, the highest emission intensity was obtained in Example 9 of FIG. Although the present invention has a similar structure to K ₂ NaYF ₆ , it is not necessarily limited to a composition represented by the chemical formula of K ₂ NaLuF ₆ (X = 1, Y = 1) in order to obtain high-intensity vacuum ultraviolet light emission. It is not necessary, and it can be seen that high emission intensity can be obtained even in a crystal having a high K ratio (low values of X and Y) as in Example 9.

  It was also confirmed to operate as a scintillator because it emits vacuum ultraviolet light when excited by radiation.

(Evaluation of deliquescence)
The deliquescence properties of K ₃ LuF ₆ crystals (Reference Example 1) before the replacement of a part of K with Na in order to obtain the fluoride crystals of the present invention were compared with the crystals of Examples 1-9.

  Since deliquescence is a phenomenon in which solids take in moisture from the atmosphere to form an aqueous solution, the crystals of Examples 1 to 9 and Reference Example 1 (solids ground and polished to 1 × 2 × 10 mm) are about 25 ° C. in humidity. In the atmosphere of about 70%, it was left at the same place for about 1 hour at the same time for comparison. In Examples 1 to 9, no change was observed, whereas in Reference Example 1, adhesion of moisture was confirmed on the crystal surface.

  Next, in order to investigate the influence of moisture on the crystals more clearly, two bottles containing about 100 ml of pure water were prepared, and the crystals of Example 1 and the crystals of Reference Example 1 were put into each bottle.

  Here, when the bottle was well shaken and stirred, the crystal of Example 1 did not change, whereas the crystal of Reference Example 1 partially dissolved and its shape collapsed, and when stirred for a sufficient time, it shattered. It was. This shows that the fluoride crystal of the present invention is less affected by moisture than the crystal of Reference Example 1.

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)

Chemical (wherein, 0.7 <X <1.3,0.85 <Y < 1.1) Formula _{K 3-X Na X Lu Y} F 3 + 3Y fluoride crystal characterized by being represented by. 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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