Method for growing carbon-magnesium co-doped sapphire crystal by vertical gradient condensation method

Abstract

The invention provides a method for growing a carbon-magnesium co-doped sapphire crystal by using a vertical gradient condensation method, alpha-Al2O3, graphite and magnesium oxide or aluminum-magnesium spinel are used as raw materials, large-size (phi 50mm) alpha-Al2O3: C, Mg crystals are grown by using the vertical gradient condensation method, compared with alpha-Al2O3: C, Mg crystals prepared by using the prior art, the method has the advantages that the growth process can be simplified, the production cost is reduced, and the production efficiency is improved. The crystal growth efficiency is improved. Experimental results show that the large-size alpha-Al2O3: C, Mg crystal grown by the method has good performance, and can be used for manufacturing high-sensitivity fluorescent nuclear track detectors and thermoluminescence detectors.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of ionizing radiation detection materials, and particularly relates to a method for growing carbon-magnesium co-doped sapphire crystal (α-Al2O3:C,Mg) by vertical gradient freeze method. BACKGROUND

[0002] In 2003, M.S. Akselrod et al. first reported α-Al2O3:C,Mg crystal (Akselrod, M.S. et al. Fluorescent Aluminum Oxide Crystals for Volumetric Optical Data Storage and Imaging Applications. Journal of Fluorescence 13, 503-511 (2003)), which was initially used for optical information storage and imaging, and later used as a fluorescent nuclear track detector, having important advantages in neutron dose monitoring, radon daughter measurement, etc., and has been successfully used for mixed neutron gamma radiation field dose monitoring. As an ionizing radiation detection material, charged particles deposit energy in the α-Al2O3:C,Mg crystal to generate electrons, and the electrons are captured by the color centers to form radiation-induced color centers Color centers are converted into radiation-induced color centers after capturing free electrons 620 nm light excitation After the transition from the ground state to the excited state, the 750 nm fluorescence (lifetime 75±5 ns) is emitted by the back relaxation, which can be used for proton, alpha particle and heavy charged particle fluence measurement. The α-Al2O3:C,Mg crystal has many advantages for manufacturing fluorescent nuclear track detectors, such as wider sensitive range for heavy ion energy transfer line density, unlimited readout and reuse; no need for special packaging due to insensitivity to visible light and high temperature stability up to 600℃; and the ability to distinguish between thermal neutrons, slow neutrons and fast neutrons (G.J. Sykora et al. Performance of fluorescence nuclear track detectors in mono-energetic and broad spectrum neutron fields, Radiation Measurements, Volume 44, Issues 9-10, 2009, Pages 988-991). In addition, the α-Al2O3:C,Mg crystal can also be used to manufacture thermoluminescence and optically stimulated luminescence detectors (M.G. Rodriguez et al. Thermoluminescence, optically stimulated luminescence and radioluminescence properties of Al2O3:C,Mg, Radiation Measurements, Volume 46, Issue 12, 2011, Pages 1469-1473).

[0003] The principle of crystal growth by vertical gradient condensation method is to heat the crystal growth raw materials configured according to the designed ratio to above the melting point, melt to obtain a superheated uniform melt, and cool the melt from bottom to top in a one-dimensional temperature gradient to realize directional growth of the crystal. During the crystal growth process, the crucible and the furnace of the VGF method are static, the heater power is controlled to change the temperature field in the furnace, the relative melt movement in the temperature gradient zone is realized, the directional cooling of the melt is realized by sequential cooling, and directional crystallization is realized. The main difference between the vertical gradient condensation method and the pulling method is that the VGF method crystal, melt and crucible remain static, there is no mechanical transmission device, the influence of mechanical transmission error and mechanical vibration on the melt and crystallization interface can be eliminated, the generation of crystal dislocation density is reduced, and the atmosphere control and crystal growth under high pressure conditions are more easily realized.

[0004] At present, the growth of the alpha-Al2O3:C,Mg crystal is mainly monopolized by the American Landauer Company, which adopts the Czochralski method to grow the alpha-Al2O3:C,Mg crystal. In the crystal growth process of the method, the crystal or the crucible or both are rotated, defects are easily generated on the crystallization surface, the process is relatively complex, and it is difficult to ensure the uniform distribution of carbon and magnesium in the sapphire crystal, that is, it is difficult to obtain the alpha-Al2O3:C,Mg crystal with consistent quality. SUMMARY

[0005] (One) technical problems to be solved

[0006] The application provides a method for growing a carbon-magnesium co-doped sapphire crystal by a vertical gradient condensation method, so as to solve the technical problem of how to grow a larger size alpha-Al2O3:C,Mg crystal.

[0007] (Two) technical solutions

[0008] In order to solve the above technical problems, the application provides a method for growing a carbon-magnesium co-doped sapphire crystal by a vertical gradient condensation method, which comprises the following steps:

[0009] S1. Mixing alpha-Al2O3 and a dopant and pressing into a block;

[0010] S2. Putting a sapphire seed crystal in a seed crystal groove of a crucible, putting the block pressed in the step S1 into the crucible, and covering the crucible cover;

[0011] S3. Putting the crucible into a vertical gradient condensation furnace to grow an alpha-Al2O3:C,Mg crystal.

[0012] Further, in the step S1, the dopant comprises two types of first dopant and second dopant.

[0013] Further, in the step S1, the first dopant is high-purity graphite; and the second dopant is one or both of magnesium oxide and aluminum-magnesium spinel.

[0014] Further, in the step S1, the first dopant is 100-10000 ppm of high-purity graphite; and the second dopant is 100-1000 ppm of one or both of magnesium oxide and aluminum-magnesium spinel.

[0015] Further, in the step S3, the crucible is put into the vertical gradient condensation furnace, vacuumized to 10 -2 Pa or less, continuously heated to 2060℃, kept at a constant temperature for 1-2 h, then reduced to room temperature at a rate of 2-5℃ / h, and the alpha-Al2O3:C,Mg crystal is taken out.

[0016] In addition, the application also provides a carbon-magnesium co-doped sapphire crystal, which is prepared by the above method.

[0017] Furthermore, this invention also proposes an application of the above-mentioned carbon-magnesium co-doped sapphire crystal, using the carbon-magnesium co-doped sapphire crystal in a thermoluminescent detector or a fluorescent nuclear track detector.

[0018] (III) Beneficial Effects

[0019] This invention proposes a method for growing carbon-magnesium co-doped sapphire crystals using a vertical gradient condensation method. Using α-Al₂O₃, graphite, and magnesium oxide or aluminum-magnesium spinel as raw materials, large-size (Φ50mm) α-Al₂O₃:C,Mg crystals are grown using this method. Compared with α-Al₂O₃:C,Mg crystals prepared using existing techniques, this invention simplifies the growth process and improves crystal growth efficiency. Experimental results show that the large-size α-Al₂O₃:C,Mg crystals grown by this invention exhibit excellent performance and can be used to fabricate high-sensitivity fluorescent nuclear track detectors and thermoluminescent detectors. Attached Figure Description

[0020] Figure 1 This is a cross-sectional view of the internal structure of the vertical gradient condenser furnace used in this invention;

[0021] Wherein: 1-Upper heating screen, 2-Crucible, 3-Seed crystal tank, 4-Lower heating screen, 5-High temperature hot field, 6-Graphite heater, 7-Graphite electrode, 8-Copper electrode;

[0022] Figure 2 The absorption spectrum of the α-Al₂O₃:C,Mg crystals grown in this invention is shown.

[0023] In the figure: the horizontal axis represents wavelength in nm; the vertical axis represents absorption coefficient in cm. -1 ;

[0024] Figure 3 α-Al₂O₃:C,Mg crystals were subjected to... 90 Sr / 90 Thermoluminescence curve after irradiation with a Y source for 100 mSv;

[0025] In the figure: the horizontal axis represents temperature, in °C; the vertical axis represents thermoluminescence intensity, in 10⁻⁶. 5 cps;

[0026] Figure 4 The thermoluminescent dose response of α-Al₂O₃:C,Mg crystals;

[0027] In the figure: the horizontal axis represents the dose, in μSv; the vertical axis represents the thermoluminescence intensity, in arbitrary units (au). Detailed Implementation

[0028] To make the objectives, contents, and advantages of the present invention clearer, the specific embodiments of the present invention will be described in further detail below with reference to the accompanying drawings and examples.

[0029] Figure 1 This is a cross-sectional view of the internal structure of the vertical gradient condensing furnace used in this invention. The furnace employs graphite heaters for heating and includes a graphite heater 6 and a graphite electrode 7. A crucible 2 is positioned at the center of a high-temperature thermal zone 5, surrounded by the graphite heaters 6. An upper heat shield 1 is positioned above the crucible 2, and the graphite electrode 7 is positioned below it. A lower heat shield 4 is positioned below the graphite electrode 7, and the graphite electrode 7 is connected to a copper electrode 8. A vacuum system and a circulating water system are attached to the furnace chamber.

[0030] Example 1

[0031] α-Al₂O₃:C,Mg crystals with 5000 ppm carbon and 500 ppm magnesium were grown using the vertical gradient condensation method.

[0032] Weigh out 500g of α-Al₂O₃:C, 2.5g of high-purity graphite (5N), and 0.25g of high-purity magnesium oxide (4N), respectively, and mix them in a mixer for 24 hours. Then, use a cold isostatic press to cold-press them into blocks at 100MPa for later use. Place a sapphire seed crystal in the seed crystal slot at the tail end of a Φ50×100mm crucible 2, place the pressed blocks into crucible 2, and cover the crucible with the lid. During crystal growth, the radial temperature inside the furnace must be kept axially symmetrical. Adjust crucible 2, graphite heater 6, and high-temperature hot zone 5 to make their centers coincide, install heat shield 1, and seal the furnace to complete the loading. Turn on the mechanical pump and diffusion pump in sequence, and evacuate to 9×10⁻⁶. -3 Pa, heat to 2060℃, hold at that temperature for 1.5h, then cool to room temperature at a rate of 3℃ / h, open the furnace, and remove the crystal.

[0033] Upon inspection, the α-Al₂O₃:C,Mg crystals grown in this embodiment were found to be intact, without cracks or bubbles. A 6×4×1 mm single crystal wafer was cut along the axial direction within the crystal, and its absorption spectrum and thermoluminescence curve were tested. Figure 2 This is the absorption spectrum of the α-Al₂O₃:C,Mg crystals grown in this embodiment. Obvious F and F₂ can be observed in the figure. + and Lust. Figure 3 The α-Al₂O₃:C,Mg crystals grown in this embodiment were subjected to... 90 Sr / 90 Thermoluminescence curves of α-Al₂O₃:C,Mg crystals grown by this method after irradiation with a Y source for 100 mSv at a heating rate of 5 °C / s are shown in the figure. The figure reveals three thermoluminescence peaks, with the thermoluminescence intensity reaching a maximum of 3.6 × 10⁻⁶ at 192 °C. 5 cps. Figure 4The thermoluminescence dose response curve of the α-Al2O3:C,Mg crystal is linear with the irradiation dose in the range of 1×10 -6 μSv~10Sv.

[0034] In summary, the α-Al2O3:C,Mg crystal grown by the vertical gradient freeze method has the same performance as the α-Al2O3:C,Mg crystal reported by M.S.Akselrod et al., but the growth process is relatively simple.

[0035] Example 2

[0036] The α-Al2O3:C,Mg crystal with 2000 ppm of carbon doping and 500 ppm of magnesium doping is grown by the vertical gradient freeze method

[0037] Except that the added graphite is 2000 ppm, the crystal is grown by reducing the temperature to room temperature at a rate of 2 ℃ / h, and the magnesium doping amount and the growth steps are the same as in Example 1. The α-Al2O3:C,Mg crystal grown in this example is complete, without cracks and bubbles, and the crystal F, F + and The F intensity and the thermoluminescence intensity are relatively reduced, but the 192 ℃ thermoluminescence peak and the color center position do not change.

[0038] Example 3

[0039] The α-Al2O3:C,Mg crystal with 5000 ppm of carbon doping and 100 ppm of magnesium doping is grown by the vertical gradient freeze method

[0040] Except that the added magnesium oxide is 100 ppm, the magnesium doping amount and the growth steps are the same as in Example 1. The α-Al2O3:C,Mg crystal grown in this example is complete, without cracks and bubbles, and the crystal F, F + and The F intensity and the thermoluminescence intensity are relatively reduced, but the 192 ℃ thermoluminescence peak and the color center position do not change.

[0041] The above only describes the preferred embodiments of the present application, and it should be noted that those skilled in the art can make several improvements and modifications without departing from the technical principles of the present application, and these improvements and modifications should also be considered as the protection scope of the present application.

Claims

1. A method for growing carbon-magnesium co-doped sapphire crystals using a vertical gradient condensation method, characterized in that, The method includes the following steps: S1. Mix α-Al2O3 with dopant and press it into a block; S2. Place the sapphire seed crystal in the seed crystal slot of the crucible, put the block material pressed in step S1 into the crucible, and cover the crucible with the lid. S3. Place the crucible in a vertical gradient condensation furnace to grow α-Al2O3:C,Mg crystals.

2. The method for growing carbon-magnesium co-doped sapphire crystals using the vertical gradient condensation method as described in claim 1, characterized in that, In step S1, the dopant includes two types: first dopant and second dopant.

3. The method for growing carbon-magnesium co-doped sapphire crystals using the vertical gradient condensation method as described in claim 2, characterized in that... In step S1, the first dopant is high-purity graphite; the second dopant is one or both of magnesium oxide and aluminum-magnesium spinel.

4. The method for growing carbon-magnesium co-doped sapphire crystals using the vertical gradient condensation method as described in claim 3, characterized in that, In step S1, the first dopant is high-purity graphite of 100 to 10,000 ppm; the second dopant is one or both of magnesium oxide or aluminum-magnesium spinel of 100 to 1,000 ppm.

5. The method for growing carbon-magnesium co-doped sapphire crystals using the vertical gradient condensation method as described in claim 1, characterized in that, In step S3, the crucible is placed in a vertical gradient condensation furnace and evacuated to 10°C. -2 Below Pa, the temperature is continuously increased to 2060℃ and held for 1-2 hours. Then, it is cooled to room temperature at a rate of 2-5℃ / h, and the α-Al2O3:C,Mg crystals are removed.

6. A carbon-magnesium co-doped sapphire crystal, characterized in that, The carbon-magnesium co-doped sapphire crystal was prepared by the method described in any one of claims 1 to 5.

7. The application of the carbon-magnesium co-doped sapphire crystal as described in claim 6, characterized in that, The carbon-magnesium co-doped sapphire crystal is used in thermoluminescent detectors or fluorescent nuclear track detectors.

Images