The preparation method of stoichiometric ratio double-tungstate crystal
Technical field
The present invention relates to double-tungstate crystal.Be particularly related to a kind of preparation stoichiometric ratio double-tungstate crystal, chemical general formula can be expressed as A (Re
xMe
1-x) (WO
4)
2, (wherein A represents alkali metal: K, Na; Re represents doped with rare-earth elements: Nd, Yb, Ho, Pr, Eu, Er; Me represents Y, Bi, Gd, La, Dy, elements such as Lu; 0≤x≤0.2) method is specifically related at rich alkali metal vapour (A=Na
+, K
+) in the atmosphere by the gas phase transmission with alkalimetal ion (A=Na
+, K
+) diffuse to non-metering than in the double-tungstate crystal to obtain the double-tungstate crystal of stoichiometric ratio.This serial crystal is with a wide range of applications in Solid State Laser field, scintillation crystal field and Raman shifting device.
Background technology
Double-tungstate crystal has A (Re
xMe
1-x) (WO
4)
2Chemical general formula, wherein A represents alkali metal: K, Na etc.; Re represents doped with rare-earth elements: Nd, Yb, Ho, Pr, Eu, Er etc.; Me represents Y, Bi, Gd, La, Dy, elements such as Lu; 0≤x≤0.2.They have two kinds of spacer structure: C
2/cAnd I
41/a, for example, β-KGd (WO commonly used
4)
2Crystal belongs to oblique system C
2/c, behind the rare earth ions such as this crystal doping Nd, Yb, be a kind of good laser crystal material with the big excitation-emission of low threshold value cross section; NaBi (WO commonly used
4)
2Belong to tetragonal system I in crystal
41/a, this crystal also is good laser host material, it has advantages such as the big emission of the wide absorption of low threshold value equally, in addition, pure NaBi (WO
4)
2Crystal still is a kind of good Cherenkov radiation detection scintillation crystal.In addition, double-tungstate crystal also has bigger third-order non-linear effect χ
3, the some of them host crystal also has higher gain Raman shifting Laser emission, thus double-tungstate crystal in the Solid State Laser field, Raman shifting Laser emission and flash detection field be with a wide range of applications.(referring to; Journal of Crystal Growth, 1999 the 206th phase 60-64 pages or leaves; Referring to: Journal of Physics and Chemistry of Solids, 2002 the 63rd phase 95-105 pages or leaves).
Belong to monoclinic K (Re in the double-tungstate crystal
xMe
1-x) (WO
4)
2Crystal (Re=Nd, Yb, Ho, Pr, Eu, Er etc., Me=Y, Bi, Gd, La, Dy, Lu, 0≤x≤0.2) is generally non-congruent melting compound, and (fusing assistant is K to adopt the flux method growth usually
2O and WO
3); And belong to the Na (Re of tetragonal system in the double-tungstate crystal
xMe
1-x) (WO
4)
2Crystal (Re=Nd, Yb, Ho, Pr, Eu, Er etc., Me=Y, Bi, Gd, La, Dy, Lu, 0≤x≤0.2) is generally congruent melting compound, adopts usually and grows from the melt of stoichiometric ratio, generally adopts crystal pulling method or falling crucible method to grow.(referring to: Journal of CrystalGrowth in 2002, the 240th volume (3-4 phase), 495-462 page or leaf; Referring to: calendar year 2001, Optical Materials, the 16th volume 43-46 page or leaf).
Owing to contain basic metal in the double-tungstate crystal: as Na, K etc. because alkaline carbonate has lower fusing point, are generally less than 900 ℃ of (for example, NaCO
3Fusing point is 850 ℃), in the process of growing crystal, often be easy to volatilization and cause serious scarce alkali metal in the double-tungstate crystal, thereby in double-tungstate crystal, formed the point defect of a large amount of non-stoichiometrics.
Formerly the double-tungstate crystal of technology growth has following significant disadvantages: (1) is because the low saturated vapo(u)r of alkaline carbonate fusing point forces down easy volatilization, easy nonstoichiometry ratio in crystal growing process, cause the skew of fusing point to bring difficulty to crystal growth on the one hand, Sheng Chang double-tungstate crystal is the non-stoichiometric crystal on the other hand; (2) have more point defect in the double-tungstate crystal of non-stoichiometric, be called as the trap center of photon-electron etc., cause the reduction of laser or scintillation photons quantum yield, this will limit the application of crystal in fields such as laser and flash detections greatly.
Summary of the invention
The technical problem to be solved in the present invention is to overcome the deficiency that prior art can not obtain the stoichiometric ratio double-tungstate crystal, and a kind of method for preparing the double-tungstate crystal of homogeneous and controllable stoichiometric ratio is provided.
Technical solution of the present invention is to make full use of Na
2CO
3, K
2CO
3Feature etc. the volatile diffusion of low melting point, adopt vapor transport equilibration (Vapor Transport Equilibration, be called for short VTE) technology, in the atmosphere of high temperature, rich alkali metal vapour, by regulating parameters such as mixing component proportioning, temperature and time, the control alkalimetal ion spreads in the non-stoichiometric double-tungstate crystal, treats to prepare after the diffusive equilibrium double-tungstate crystal of stoichiometric ratio, to satisfy the needs in fields such as laser and flash detection.
Stoichiometric ratio double-tungstate crystal A (Re of the present invention
xMe
1-x) (WO
4)
2The preparation method, its concrete processing step is as follows:
<1〉in platinum crucible, is placed with the A (Re of band pore
xMe
1-x) (WO
4)
2Polycrystal piece and corresponding alkali metal carbonate A
2CO
3(A represents alkali metal, Na and K) mixture block;
<2〉the double-tungstate wafer with non-stoichiometric places or is suspended from the platinum wire, adds to be coated with A (Re
xMe
1-x) (WO
4)
2Polycrystal piece and corresponding alkali metal carbonate A
2CO
3It is airtight that the mixture block of (A represents alkali metal, Na and K) and the crucible cover of thermopair, crucible top add the platinum lid, places resistance furnace;
<3〉about this resistance furnace heat temperature raising to 600~800 ℃, constant temperature 20~100 hours, basic metal A (Na
+Perhaps K
+) ion diffusion is to the double-tungstate A (Re of non-metering ratio
xMe
1-x) (WO
4)
2In the wafer, the rate of temperature fall with 40-60 ℃/h is cooled to the A (Re that room temperature can obtain stoichiometric ratio then
xMe
1-x) (WO
4)
2Double-tungstate crystal.
Above-mentioned processing step<1〉described in A (Re
xMe
1-x) (WO
4)
2And A
2CO
3The scope of choosing of the weight ratio of mixture block is [A (Re
xMe
1-x) (WO
4)
2]/[A
2CO
3]=(10~98): (90~2).Double-tungstate A (Re wherein
xMe
1-x) (WO
4)
2A represents alkali metal in the polycrystal piece: K, Na; Re represents doped with rare-earth elements: Nd, Yb, Ho, Pr, Eu, elements such as Er; Me represents Y, Bi, Gd, La, Dy, elements such as Lu; 0≤x≤0.2.
Above-mentioned processing step<2〉described in the non-stoichiometric double-tungstate crystal can pass through the A (Re of growth such as crystal pulling method, falling crucible method or flux method
xMe
1-x) (WO
4)
2Crystal, (wherein A represents alkali metal: K, Na; Re represents doped with rare-earth elements: Nd, Yb, Ho, Pr, Eu, Er; Me represents Y, Bi, Gd, La, Dy, elements such as Lu; 0≤x≤0.2).
Above-mentioned processing step<2〉described in resistance furnace also available silicon kryptol stone, Si-Mo rod stove or other stove by Electric heating replace.
Above-mentioned processing step<3〉described in constant temperature time look size, thermostat temperature and the double-tungstate polycrystal of double-tungstate wafer and the ratio of alkaline carbonate mixture block changes in above-mentioned constant temperature time scope.Generally speaking, wafer big more (thickness is thick, area is big), thermostat temperature are low more, and then constant temperature time is longer.
The present invention prepares the stoichiometric ratio double-tungstate crystal and compares than double-tungstate crystal with formerly technology growth is non-metering, its advantage is: made full use of the volatile characteristics of alkali-metal low melting point, by gas phase transmission diffusion alkalimetal ion is diffused in the double-tungstate crystal of non-metering ratio, thereby obtained the double-tungstate crystal of stoichiometric ratio, significantly reduced the non-stoichiometric point defect that exists in the crystal, can satisfy the needs of double-tungstate crystal in luminous fields such as laser, flickers.
Description of drawings
Fig. 1 is a vapor transport equilibration experimental installation synoptic diagram.
Embodiment
Used vapor transport equilibration (VTE) technology of the present invention prepares the experimental installation synoptic diagram of stoichiometric ratio double-tungstate crystal and sees Fig. 1, in the platinum crucible 1, be placed with the double-tungstate polycrystal and the alkaline carbonate mixture block 3 of certain proportioning of band pore 2, material piece 3 tops are platinum wires 4, use crystal pulling method, the double-tungstate wafer 5 of the non-metering ratio of descent method or flux method growth places on the platinum wire 4, material piece 3 tops have platinum sheet 6 and double-tungstate polycrystal and alkaline carbonate mixed powder 7 to cover, thermopair 8 inserts in the powders 7, and crucible 1 top adds platinum and covers 9 airtight.
Adopt the VTE technology how to prepare the concrete process flow steps of the double-tungstate crystal of stoichiometric ratio below in conjunction with the specific embodiment explanation.
Embodiment 1: the doping 20%Nd ionic NaBi (WO of preparation stoichiometric ratio
4)
2Crystal
Step of preparation process is as follows:
<1〉in platinum crucible 1, is placed with 20% adulterated NaBi (WO of band pore 2
4)
2And Na
2CO
3Mixture block 3 is chosen [NaNd
0.2Bi
0.8(WO
4)
2]/[Na
2CO
3]=98: 2 weight ratio;
<2〉with 20% adulterated Nd of the non-metering ratio of crystal pulling method or descent method for growing: NaBi (WO
4)
2Crystal places or is suspended from the platinum wire, adds to be coated with NaBi (WO
4)
2And Na
2CO
3The crucible cover of mixed powder 7 and thermopair 8, crucible top add platinum and cover 9 airtightly, place resistance furnace;
<3〉about heat temperature raising to 800 ℃, constant temperature 100 hours, the Na ion diffusion is to NaBi (WO
4)
2In the crystal, reduce to room temperature with the cooling rate of 40 ℃/h then, obtain the NaBi (WO that mixes Nd of stoichiometric ratio at last
4)
2Crystal.
Embodiment 2: the pure NaBi (WO of preparation stoichiometric ratio
4)
2Crystal
The processing step of preparation is as follows:
<1〉in platinum crucible 1, is placed with the NaBi (WO of band pore 2
4)
2And Na
2CO
3Mixture block 3 is chosen [NaBi (WO
4)
2]/[Na
2CO
3]=50: 50 weight ratio;
<2〉with the NaBi (WO of the non-metering ratio of crystal pulling method or descent method for growing
4)
2Crystal places or is suspended from the platinum wire, adds to be coated with NaBi (WO
4)
2And Na
2CO
3The crucible cover of mixed powder 7 and thermopair 8, crucible top add platinum and cover 9 airtightly, place resistance furnace;
<3〉about heat temperature raising to 700 ℃, constant temperature 40 hours, the Na ion diffusion is to NaBi (WO
4)
2In the crystal, reduce to room temperature with the cooling rate of 50 ℃/h then, obtain stoichiometric ratio NaBi (WO at last
4)
2Crystal.
Embodiment 3: the KGd (WO of the doping 5%Yb of preparation stoichiometric ratio
4)
2Crystal
The processing step of preparation is as follows:
<1〉in platinum crucible 1, is placed with the KGd (WO that mixes 15%Yb of band pore 2
4)
2And K
2CO
3Mixture block 3 is chosen [KYb
0.05Gd
0.95(WO
4)
2]/[K
2CO
3]=80: 20 weight ratio;
<2〉KGd (WO of the 5%Yb of the non-metering ratio that flux method is grown
4)
2Crystal places or is suspended from the platinum wire, adds to be coated with KYb
0.05Gd
0.95(WO
4)
2And K
2CO
3The crucible cover of mixed powder 7 and thermopair 8, crucible top add platinum and cover 9 airtightly, place resistance furnace;
<3〉about heat temperature raising to 650 ℃, constant temperature 60 hours, the K ion diffusion is to the adulterated KGd (WO of 5%Yb
4)
2In the crystal, reduce to room temperature with the cooling rate of 60 ℃/h then, obtain the adulterated KGd (WO of stoichiometric ratio 5%Yb at last
4)
2Crystal.
Embodiment 4: the KGd (WO of the doping 2%Er of preparation stoichiometric ratio
4)
2Crystal
The processing step of preparation is as follows:
<1〉in platinum crucible 1, is placed with the KGd (WO that mixes 2%Er of band pore 2
4)
2And K
2CO
3Mixture block 3 is chosen [Ker
0.02Gd
0.98(WO
4)
2]/[K
2CO
3]=10: 90 weight ratio;
<2〉KGd (WO of the 2%Er of the non-metering ratio that flux method is grown
4)
2Crystal places or is suspended from the platinum wire, adds to be coated with Ker
0.02Gd
0.98(WO
4)
2And K
2CO
3The crucible cover of mixed powder 7 and thermopair 8, crucible top add platinum and cover 9 airtightly, place resistance furnace;
<3〉about heat temperature raising to 750 ℃, constant temperature 50 hours, the K ion diffusion is to the adulterated KGd (WO of 2%Er
4)
2In the crystal,, obtain the adulterated KGd (WO of stoichiometric ratio 2%Er at last then with the near room temperature of the cooling rate of 50 ℃/h
4)
2Crystal.