CN102560647A - Bridgman-stockbarge method for preparing cerium-doped lanthanum bromide scintillating crystal - Google Patents
Bridgman-stockbarge method for preparing cerium-doped lanthanum bromide scintillating crystal Download PDFInfo
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Abstract
The present invention relates to a bridgman-stockbarge method for preparing a cerium-doped lanthanum bromide scintillating crystal. According to the present invention, the modified bridgman-stockbarge method is adopted to prepare the scintillating crystal Cex:La(1-x)Br3; with the modified bridgman-stockbarge method, during the raw material melting stage, the upper temperature zone is divided into an upper temperature zone a and an upper temperature zone b through independent three temperature zone control, wherein the temperature of the upper temperature zone is higher than the melting point of the crystal, and the temperature of the upper temperature zone b is slightly higher than the temperature of the upper temperature zone a; during the spontaneous crystal nucleation stage, the embedded transparent quartz optical fiber is adopted to introduce helium neon laser, and the light loss change of the laser is observed to determine whether the single crystal of the spontaneously-nucleated seed crystal is formed after screening; after the crystal grows, the annealing treatment is performed for a long time under the reduction hydrogen atmosphere, the crystal thermal stress is eliminated, and the useless Ce<4+> in the crystal is subjected to valence variation to obtain the Ce<3+>.
Description
Technical field
The present invention relates to the synthetic and crystal growth technique field of crystalline raw material, the improvement falling crucible method of cerium lanthanum bromide scintillation crystal is mixed in particularly a kind of preparation.
Background technology
Scintillation crystal can be made detector, in high energy physics, nuclear physics, image nuclear medicine diagnostic (XCT, PET), geological prospecting, astronomical Space Physics and safe inspection field, great application prospect is arranged.Along with the develop rapidly of nuclear science technology and other correlation technique, its Application Areas is constantly being widened.The different application field has also proposed more higher requirements to inorganic scintillator.Scintillation crystals such as traditional NaI (Tl), BGO can't satisfy the particular requirement of new Application Areas.
People are exploring the novel good scintillation crystal that is applicable to the different application field.These novel scintillation crystals maybe be on over-all properties and production cost, and are bigger with traditional scintillation crystal gaps such as existing sophisticated NaI (Ti), BGO.But people hope that they can have special performance and purposes in some aspects, satisfy the particular requirement in different application field.To these new crystalline basic demands be exactly: physical and chemical performance is stable, high-density, fast decay of luminescence, high-luminous-efficiency, high irradiation hardness and low cost.Except that should having the good characteristics of luminescence and stability, also need certain size and optical homogeneity as outstanding scintillation crystal.At present the development trend of scintillation crystal is to be the center around performances such as high output, fast-response, high-density, carries out the exploratory development of novel scintillation crystal.
The allowed transition of Ce3+ ion 5d → 4f energy level can produce the fast decay fluorescence of tens nanoseconds.Realizing scintillation properties through mixing the Ce ion, is novel scintillation crystal exploratory development focus.People obtain many novel scintillation crystals, such as Ce:LSO, Ce:LuAP, Ce:GSO, Ce:YSO, Ce:YAP through in crystal substrates such as silicate, aluminate, phosphoric acid salt, mixing the Ce ion at present.They have high light output, characteristics such as fast decay, and as the flash detection material, to improving time, the spatial resolution of detector, miniaturized and multifunction are significant.Obtained very big success although mix at present the research of Ce high temperature scintillation crystal, also there are many problems in they, cost an arm and a leg etc. such as self-absorption phenomenon, fusing point height, difficult growth, high pure raw material, have restricted their application greatly.
Mix cerium lanthanum bromide crystal (LaBr3:Ce) after coming to light in 1999, because its excellent scintillation properties has started the upsurge of research research.Mix the output of cerium lanthanum bromide light and can reach 78000Ph/MeV; Reach 30ns its fall time soon, its density is 5.1g/cm3, and the receptivity of energetic ray obviously is better than the NaI:Tl crystal; And the risk of its environmental pollution is far smaller than NaI:Tl; Therefore the LaBr3:Ce crystal has become high, the fast flicker crystalline representative that decays of light output at present, and this crystal is expected to replace the NaI:Tl crystal comprehensively, thereby is used widely in fields such as Medical Instruments, safety inspection and oil well detections.But the LaBr3:Ce crystal growth is difficult, and component seriously volatilizees, and is very easy to and oxygen, water reaction; And crystal is very easy to cracking.Therefore LaBr3:Ce crystalline productive rate is very low, and the large-size crystals growth is difficulty particularly, and price is also extremely expensive.
All be to adopt the improvement falling crucible method to mix the growth of cerium lanthanum bromide crystalline at present both at home and abroad.The improvement falling crucible method, the Bridgman-Stockbarger method that is otherwise known as is a kind of method of growing crystal from melt.; Its ultimate principle is that raw material is packed in the crucible of specified shape, is placed into heat fused in the decline stove, slowly descends through crucible then; Through the big zone of thermograde, crystallization begins from the crucible bottom, upwards passes gradually; Carry out the method for crystal growth, be referred to as to improve falling crucible method or gradient oven process.
Summary of the invention
The objective of the invention is to overcome the shortcoming of prior art, provide a kind of improvement falling crucible method of improvement to prepare not have cracking and mix cerium lanthanum bromide scintillation crystal, this method can overcome the crystalline cracking effectively, guarantees the crystalline monocrystallineization.
The present invention realizes through following technique means:
One. three-temperature-zone is independently controlled.
Conventional descent method for growing furnace structure is as shown in Figure 1, is to adopt the design of upper heat and lower cold two warm areas, and last warm area is the high-temperature zone, and temperature surpasses the crystalline fusing point, mainly is to guarantee melting raw materials.Following warm area is a cold zone, and temperature is more lower slightly than crystalline fusing point, and distribution gradient, mainly is the progressively crystallisation by cooling that guarantees raw material.The thermograde of last warm area is very little, and the upper end temperature is higher relatively.In the raw material material, the temperature of upper end raw material can't form convection current than the height of hypomere in the silica tube, makes that raw material is difficult to mix like this, and changes the bubble that forms in the material process and can't eliminate.
What present method adopted is that three-temperature-zone control is as shown in Figure 2, warm area be will go up and a warm area and last b warm area will be divided into, and upper cold and lower heat, temperature is higher than crystalline fusing point, and the temperature in b district is a little more than a district.Silica tube is in last warm area like this, because upper cold and lower heat, the melt in the silica tube just can be realized convection current, not only can mixing raw material, and can easily bubble be discharged melt.
The 2nd, the monitoring of crystallization selection process.
Conventional reactors is airtight growth, and whole crystal growing process can't be observed.Growing a heat crystal need experience material (taking 2d), crystal sporadic nucleation with eliminate screening (taking 3d), isodiametric growth of crystal (taking 20d), crystal cooling (taking 5d) four-stage; Need about 30 day time altogether; And wherein crystal sporadic nucleation is the stage of most critical with eliminating screening; If there is not fine completion monocrystalline process, the crystal that late growing stage goes out can burst and can't use because of polycrystalline.And crystal sporadic nucleation and superseded screening have a process that produces at random, if this process is not monitored, the yield rate of crystal growth can be very low.
What present method adopted is to determine whether to realize the monocrystalline screening through the monitoring optical loss; Promptly in the nucleation site of silica tube; Adopt 2 relative vitreous silica optical fiber of oxyhydrogen flame welding, import He-Ne Lasers, through the optical loss changing conditions of observation laser; The seed crystal of confirming sporadic nucleation through screening after monocrystallineization whether, the concrete structure synoptic diagram is as shown in Figure 3.Changing the material stage, because raw material is that He-Ne light can pass through relative vitreous silica optical fiber uniformly, optical loss is less; When crystal sporadic nucleation with eliminate screening not exclusively, in the time of on-monocrystalline, because polycrystalline, cause He-Ne light to be reflected and reflect, He-Ne light is through relative vitreous silica optical fiber, optical loss is just very big.Complete when crystal sporadic nucleation with superseded screening, in the time of monocrystalline,, cause He-Ne light through crystal and relative vitreous silica optical fiber because crystal is an one, optical loss is just smaller.In crystal growing process, if find that sporadic nucleation is incomplete with superseded screening, then can shake high silica tube again, the polycrystalline crystal of fusing sporadic nucleation, sporadic nucleation and superseded screening again is until the monocrystalline completion.Owing to only need again experienceization material (taking 2d), crystal sporadic nucleation and eliminate screening (taking 3d) process; And avoided isodiametric growth of crystal (taking 20d), crystal cooling (taking 5d) process; Under the situation that guarantees the crystal high yield, need not spend the too many extra time.
The 3rd, the crystalline aftertreatment:
Ordinary method is that crystal growth finishes and just cuts and polish, and prepares device then.But because the crystal internal stress is bigger, crystal is easy of crack in process of growth.In addition, also have partial C e4+ compound in the crystal, it not only can not send fluorescence under radiation exposure, also can absorb the fluorescence that Ce3+ sends, and causes the crystalline luminous efficiency low.
What present method adopted is later stage atmosphere annealed method, and promptly after crystal growth, long term annealing under the reduction nitrogen atmosphere is eliminated the crystal thermal stresses and the useless Ce4+ in the crystal appraised at the current rate and is Ce3+.
Description of drawings
Fig. 1 be conventional descent method for growing furnace structure synoptic diagram wherein 11 for last warm area, 12 are warm area down
Fig. 2 21 be last a warm area wherein for three-temperature-zone control descent method for growing furnace structure synoptic diagram, and 22 be last b warm area, and 23 is time warm area
Fig. 3 wherein 31 is vitreous silica optical fiber for the structural representation that determines whether to realize the monocrystalline screening through the monitoring optical loss
Fig. 4 fills for the silica tube raw material and the tube sealing synoptic diagram 41 is a raw material wherein, and 42 is the tube sealing material
Embodiment
Embodiment 1: the tube sealing of raw material; Mix that cerium lanthanum bromide scintillation crystal raw material has city pin or the anhydrous lanthanum bromide of synthetic, comprise cerium bromide mix voluntarily.The chemical constitution of mixing the cerium lanthanum bromide is Cex:La (1-x) Br3, and wherein x is the mol ratio of Ce displacement La, and scope is 0.0001＜x＜0.1.Suppose that it is 0.5% lanthanum bromide crystal raw material that synthetic 100g mixes cerium concentration, choose x=0.005, be Ce0.005: La0.995Br3; According to 0.005: 0.995 mol ratio, in glove box, in the nitrogen atmosphere of the exhausted water of anoxybiotic; Take by weighing CeBr3 raw material 0.189 gram respectively, LaBr3 raw material 37.793 grams mix in the agate alms bowl; Packing into then is used for the special silica tube of crystal growth, blocks the quartzy mouth of pipe with quartz wedge then, seals the mouth of pipe with epoxy resin then; Take out glove box, utilize the hydrogen flame that the mouth of pipe fusing of silica tube is sealed.
Crystal growth: home-made descent method crystal growing furnace, the Si-Mo rod well heater, two warm area step-by-step design, double platinum rhodium (Pt/Rh30-Pt/Rh10) thermopair, Britain Continental Europe 818 type thermoswitchs, temperature-controlled precision reach ± and 0.1 ℃.
The technical parameter of table 1 crystal growth
The cleaning burner hearth is fixed on the decline stove with quartz crucible and rotates on the decline bar, and quartz crucible is dropped to specific position; The head of silica tube is positioned at warm area; The a district of going up warm area then is warmed up to 800 ℃, and the b district is warmed up to 830 ℃, and following warm area is warmed up to 750 ℃; Constant temperature 2d lets the raw material fusing fully then.
Quartz crucible is dropped to the crucible head be positioned at the warm area interface position of warm area warm area extremely down; Adopt the fall off rate of 0.5mm/d then, the district drops to warm area with the seed crystal nucleation, lets its sporadic nucleation, polycrystalline screen; Optical loss changing conditions through observation laser; The seed crystal of confirming sporadic nucleation through screening after monocrystallineization whether, if the monocrystalline completion then continues the decline silica tube and accomplishes isodiametric growth and temperature-fall period; If monocrystallineization is incomplete, then can shake high silica tube again, the polycrystalline crystal of fusing sporadic nucleation, sporadic nucleation and superseded screening again is until the monocrystalline completion.
Adopt the fall off rate of 1.0～2.5mm/d, carry out the crystalline isodiametric growth.
Warm area under quartz crucible all gets into, crystal growth finishes, and stops to descend.Adopt 5～15K/h (high-temperature zone,＞6000c), (cold zone ,≤6000C) speed is carried out the reactors cooling to 15～50K/h, until dropping to room temperature.Take out quartz crucible then.
Crystal aftertreatment: silica tube is put into glove box; In the nitrogen atmosphere of the exhausted water of anoxybiotic, crystal is taken out, put into the quartzy annealing pipe of heavy caliber of band sealed interface; Take out quartzy annealing pipe and put into lehre; Lehre is warmed up to specified temp, under logical reduction nitrogen atmosphere, carries out long term annealing then, eliminate the crystal thermal stresses and the useless Ce4+ in the crystal appraised at the current rate and be Ce3+.
The technical parameter of table 2 crystal annealing
Claims (6)
1. one kind prepares the falling crucible method of mixing cerium lanthanum bromide scintillation crystal, it is characterized in that: adopt a kind of falling crucible method of improvement to prepare not have cracking and mix cerium lanthanum bromide scintillation crystal.
2. falling crucible method as claimed in claim 1 is characterized in that: the chemical constitution of said scintillation crystal is Ce
x: La
(1-x)Br
3, wherein x is the mol ratio of Ce displacement La, scope is 0.0001＜x＜0.1.
3. falling crucible method as claimed in claim 1; It is characterized in that: the falling crucible method of said improvement was independently controlled through three-temperature-zone in the raw material fusion stage; To go up warm area and be divided into a warm area and last b warm area, last warm area temperature is higher than crystalline fusing point, and the temperature of last b warm area is a little more than last a warm area.
4. falling crucible method as claimed in claim 1 is characterized in that: in the crystal sporadic nucleation stage, utilize preembedded vitreous silica optical fiber, import He-Ne Lasers.
5. falling crucible method as claimed in claim 1 is characterized in that: through the optical loss changing conditions of observation He-Ne Lasers, the seed crystal of confirming sporadic nucleation is through monocrystallineization whether after screening.
6. falling crucible method as claimed in claim 1 is characterized in that: anneal under the nitrogen atmosphere in reduction after the crystal growth, eliminate the crystal thermal stresses and with the useless Ce in the crystal
4+Appraise at the current rate and be Ce
3+
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Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN107268068A (en) * | 2017-06-09 | 2017-10-20 | 厦门中烁光电科技有限公司 | The method that lanthanum bromide crystal is prepared using totally enclosed type crucible |
| WO2021083316A1 (en) * | 2019-11-01 | 2021-05-06 | 有研稀土新材料股份有限公司 | Rare earth halide scintillating material |
Citations (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN202465955U (en) * | 2012-02-07 | 2012-10-03 | 中国科学院福建物质结构研究所 | Bridgman-Stockbarger growth equipment for preparing cerium-doped lanthanum bromide scintillation crystals |
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- 2012-02-08 CN CN2012100276760A patent/CN102560647A/en active Pending
Patent Citations (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN202465955U (en) * | 2012-02-07 | 2012-10-03 | 中国科学院福建物质结构研究所 | Bridgman-Stockbarger growth equipment for preparing cerium-doped lanthanum bromide scintillation crystals |
Non-Patent Citations (1)
| Title |
|---|
| HONGSHENG SHI等: "The LaBr3:Ce Crystal Growth by Self-Seeding Bridgman Technique and Its Scintillation Properties", 《CRYSTAL GROWTH & DESIGN》 * |
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN107268068A (en) * | 2017-06-09 | 2017-10-20 | 厦门中烁光电科技有限公司 | The method that lanthanum bromide crystal is prepared using totally enclosed type crucible |
| CN107268068B (en) * | 2017-06-09 | 2018-07-06 | 厦门中烁光电科技有限公司 | The method that lanthanum bromide crystal is prepared using totally enclosed type crucible |
| WO2021083316A1 (en) * | 2019-11-01 | 2021-05-06 | 有研稀土新材料股份有限公司 | Rare earth halide scintillating material |
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Inventor after: Wu Shaofan Inventor after: Hong Maochun Inventor after: Ye Ning Inventor after: Su Weiping Inventor after: Zheng Fakun Inventor before: Wu Shaofan Inventor before: Ye Ning Inventor before: Su Weiping |
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Free format text: CORRECT: INVENTOR; FROM: WU SHAOFAN YE NING SU WEIPING TO: WU SHAOFAN HONG MAOCHUN YE NING SU WEIPING ZHENG FAKUN |
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Application publication date: 20120711 |