Li4Sr(BO3)2 compound, Li4Sr(BO3)2 nonlinear optical crystal, preparation method and use thereof

Abstract

The present invention relates to the field of nonlinear optical crystal materials and provided herein a Li.sub.4Sr(BO.sub.3).sub.2 compound, a Li.sub.4Sr(BO.sub.3).sub.2 nonlinear optical crystal as well as preparation method and use thereof. The Li.sub.4Sr(BO.sub.3).sub.2 nonlinear optical crystal has a second harmonic conversion efficiency at 1064 nm of about two times that of a KH.sub.2PO.sub.4 (KDP) crystal, and an UV absorption cut-off edge less than 190 nm. Furthermore, the crystal did not disintegrate. By flux method with Li.sub.2O, Li.sub.2OB.sub.2O and Li.sub.2OB.sub.2O.sub.3LiF used as flux agent, large-size and transparent Li.sub.4Sr(BO.sub.3).sub.2 nonlinear optical crystal can grow. The Li.sub.4Sr(BO.sub.3).sub.2 crystal had stable physicochemical properties, moderate hardness, and was easy to cut, processing, preserve and use. Therefore it can be used for preparing nonlinear optical devices and thus for developing nonlinear optical applications in the ultraviolet and deep-ultraviolet band.

Claims

1. A compound having a chemical formula of Li.sub.4Sr(BO.sub.3).sub.2.

2. A nonlinear optical crystal of a Li.sub.4Sr(BO.sub.3).sub.2 compound according to claim 1, wherein the crystal does not contain symmetric center and belongs to monoclinic space group C.sub.c with lattice parameters of a=9.117(5) , b=5.239(2) , c=11.762(6) , =105.22(1), V=542.08 (127) .sup.3, and Z=4.

3. A preparation method of a Li.sub.4Sr(BO.sub.3).sub.2 nonlinear optical crystal according to claim 2, wherein the growth of the Li.sub.4Sr(BO.sub.3).sub.2 nonlinear optical crystal is carried out by flux method, and the flux agent is chosen from Li.sub.2O, Li.sub.2OB.sub.2O.sub.3, or Li.sub.2OB.sub.2O.sub.3LiF.

4. The preparation method according to claim 3, comprising: mixing Li.sub.2O, SrO and B.sub.2O.sub.3 at a molar ratio of 4-8:1:1-3 (equivalent to a molar ratio of Li.sub.4Sr(BO.sub.3).sub.2:Li.sub.2O:B.sub.2O.sub.3=1:2-6:0-2), or Li.sub.2O, SrO, B.sub.2O.sub.3 and LiF at a molar ratio of 4-8:1:1-3:1-3 (equivalent to a molar ratio, Li.sub.4Sr(BO.sub.3).sub.2:Li.sub.2O:B.sub.2O.sub.3:LiF=1:2-6:0-2:1-3), grounding and melting the mixture to form a melt, and growing a crystal on the surface of or inside the melt.

5. The preparation method according to claim 3, wherein the flux agent is Li.sub.2O or Li.sub.2OB.sub.2O.sub.3, comprising: mixing Li.sub.2O, SrO, and B.sub.2O.sub.3 at a molar ratio of 4-8:1:1-3 (equivalent to a molar ratio of Li.sub.4Sr(BO.sub.3).sub.2:Li.sub.2O:B.sub.2O.sub.3=1:2-6:0-2), grounding and melting the mixture to form a melt, and growing a crystal on the surface of or inside the melt.

6. The preparation method according to claim 3, wherein the flux agent is a flux agent system of Li.sub.2OB.sub.2O.sub.3LiF, comprising: mixing Li.sub.2O, SrO, B.sub.2O.sub.3 and LiF at a molar ratio of 4-8:1:1-3:1-3 (equivalent to a molar ratio of Li.sub.4Sr(BO.sub.3).sub.2:Li.sub.2O:B.sub.2O.sub.3=1:2-6:0-2:1-3), homogeneously grounding and melting the mixture, and growing a crystal on the surface of or inside the melt.

7. The preparation method according to claim 3, further comprising annealing the crystal to room temperature at a rate of no more than 100 C./h.

8. The preparation method according to claim 1, wherein said Li.sub.2O is a hydroxide, an oxide, a carbonate, a nitrate, or an oxalate of lithium, said SrO is a hydroxide oxide, a carbonate, a nitrate, or an oxalate of strontium, and said B.sub.2O.sub.3 is boric acid or boron oxide.

9. A nonlinear optical device comprising a Li.sub.4Sr(BO.sub.3).sub.2 nonlinear optical crystal according to claim 2.

10. The preparation method according to claim 4, wherein the crystal grows at a cooling rate of 0.1 C.-5 C./day, a rotational speed of 0-50 rpm, and under unidirectional or bidirectional rotations.

11. The preparation method according to claim 4, wherein, when the crystal is grown to a predetermined size, lifting the crystal from the melt, cooling the crystal to room temperature at a rate of no more than 100 C./h to obtain the Li.sub.4Sr(BO.sub.3).sub.2 nonlinear optical crystal.

12. The preparation method according to claim 4, wherein the molar ratio of Li.sub.2O:SrO:B.sub.2O.sub.3 is 4-7:1:1-2.

13. The preparation method according to claim 4, wherein the molar ratio of Li.sub.2O:SrO:B.sub.2O.sub.3:LiF is 4-6:1:1-2:1-2.

14. The preparation method according to claim 5, wherein the molar ratio of Li.sub.2O:SrO:B.sub.2O.sub.3 is 4-7:1:1-2.

15. The preparation method according to claim 6, wherein the molar ratio of Li.sub.2O:SrO:B.sub.2O.sub.3:LiF is 4-6:1:1-2:1-2.

16. The preparation method according to claim 11, wherein the cooling rate is no more than 50 C./h.

Description

BRIEF DESCRIPTION OF DRAWING

(1) FIG. 1 is a diagram of the working principle of a typical nonlinear optical device made from the Li.sub.4Sr(BO.sub.3).sub.2 crystal.

(2) FIG. 2 shows the X-ray diffraction pattern of Li.sub.4Sr(BO.sub.3).sub.2 polycrystal powders according to the invention and the simulated X-ray diffraction pattern based on the crystal structure of the Li.sub.4Sr(BO.sub.3).sub.2 crystal.

(3) FIG. 3 is a diagram of the crystal structure of the Li.sub.4Sr(BO.sub.3).sub.2 according to the invention, wherein 1 is a laser device, 2 is an incident laser beam, 3 is a Li.sub.4Sr(BO.sub.3).sub.2 crystal subjected to crystal post-treatment and optical processing, 4 is the generated laser beam, and 5 is a optical filter.

(4) The nonlinear optical device made from the Li.sub.4Sr(BO.sub.3).sub.2 crystal according to the present invention will be illustrated in detail with reference to FIG. 1 hereinafter. The light beam 2 emitted from the laser device 1 irradiated into the Li.sub.4Sr(BO.sub.3).sub.2 crystal 3. The generated light beam 4 passed through the optical filter 5 to obtain a desired laser beam. The nonlinear optical laser device can be a harmonic generator, an up/down frequency converter or an optical parametric oscillator, etc.

EMBODIMENTS

(5) The present invention will be further illustrated with reference to the examples and drawings hereinbelow. A person skilled in the art should know that the following examples do not constitute a limitation of the protection scope of the present invention. Any improvement and modification made based on the present invention should be construed as being within the protection scope of the present invention.

Example 1

(6) A Li.sub.4Sr(BO.sub.3).sub.2 crystal was grown in a flux agent system of Li.sub.2OB.sub.2O.sub.3 by flux method.

(7) Li.sub.2CO.sub.3, 49.2 g (0.333 mol) SrCO.sub.3 and 61.8 g (1.000 mol) H.sub.3BO.sub.3 (wherein 1.500 mol Li.sub.2CO.sub.3 and 0.333 mol H.sub.3BO.sub.3 served as the flux agent) were weighed, mixed and homogeneously ground, and then batch fed into a 60 mm60 mm open crucible. The obtained mixture was melted in a muffle furnace at 750 C. Subsequently, it was heated rapidly to 750 C. in a vertical crystal growth furnace, hold at this temperature for 24 hours, and then cooled to 550 C. at a rate of 20 C./day to precipitate Li.sub.4Sr(BO.sub.3).sub.2 crystals on the surface of the melt. Finally they were cooled to room temperature at a rate of 50 C./day. Transparent Li.sub.4Sr(BO.sub.3).sub.2 crystals were selected and subjected to powder X-ray diffraction analysis. The X-ray pattern was consistent with the simulated pattern based on the analysis result of single crystal X-ray diffraction, as shown in FIG. 2. Therefore, the obtained crystal was the Li.sub.4Sr(BO.sub.3).sub.2 crystal.

(8) The part of relatively good quality was cut to give a seed crystal. The raw material was heated to melt again, and then cooled down rapidly to 10 C. above the saturation temperature. A seed crystal rod fitted with the seed crystal was slowly inserted into the melt in the crucible, and the rotation unit at the top of the seed crystal rod was started with a rotation speed of 25 rpm. The temperature was hold for half an hour, cooled down rapidly to the saturation temperature, and then cooled at a rate of 0.5 C./day. After the crystal is grown to a desired size, the seed crystal rod was lifted so that the crystal was separated from the surface of the liquid. The crystal remained in the furnace to be annealed so that it was cooled to room temperature at a rate of 30 C./h. A centimeter-grade Li.sub.4Sr(BO.sub.3).sub.2 crystal was thus obtained.

Example 2

(9) A Li.sub.4Sr(BO.sub.3).sub.2 crystal was grown in a flux agent system of Li.sub.2OB.sub.2O.sub.3LiF by flux method.

(10) 135.5 g (1.833 mol) Li.sub.2CO.sub.3, 49.2 g (0.333 mol) SrCO.sub.3, 61.8 g H.sub.3BO.sub.3 (1.000 mol) and 8.6 g (0.333 mol) LiF (wherein 1.167 mol Li.sub.2CO.sub.3, 0.333 mol H.sub.3BO.sub.3 and 0.333 mol LiF served as the flux agent) were weighed, mixed and homogeneously ground, and then batch fed into a 60 mm60 mm open crucible. The obtained mixture was melted in a muffle furnace at 750 C. Subsequently, it was heated rapidly to 750 C. in a vertical crystal growth furnace, hold at this temperature for 24 hours, and then cooled down rapidly to 10 C. above the saturation temperature. A seed crystal rod fitted with the seed crystal was slowly inserted into the melt in the crucible, and the rotation unit at the top of the seed crystal rod was started with a rotation speed of 35 rpm. The temperature was hold for half an hour, cooled down rapidly to the saturation temperature, and then cooled at a rate of 0.8 C./day. After the crystal is grown to a desired size, the seed crystal rod was lifted so that the crystal was separated from the surface of the liquid. The crystal was still remained in the furnace to be annealed so that it was cooled to room temperature at a rate of 25 C./h. A centimeter-grade Li.sub.4Sr(BO.sub.3).sub.2 crystal was thus obtained.

Example 3

(11) A Li.sub.4Sr(BO.sub.3).sub.2 crystal was grown using Li.sub.2O as a flux agent by flux method.

(12) 123.2 g (1.667 mol) Li.sub.2CO.sub.3, 49.2 g (0.333 mol) SrCO.sub.3 and 41.2 g (0.667 mol) H.sub.3BO.sub.3 (wherein 1.000 mol Li.sub.2CO.sub.3 served as the flux agent) were weighed, mixed and homogeneously ground, and then batch fed into a 60 mm60 mm open crucible. The obtained mixture was melted in a muffle furnace at 750 C. Subsequently, it was heated rapidly to 750 C. in a vertical crystal growth furnace, hold at this temperature for 24 hours, and then cooled down rapidly to 10 C. above the saturation temperature. A seed crystal rod fitted with the seed crystal was slowly inserted into the melt in the crucible, and the rotation unit at the top of the seed crystal rod was started with a rotation speed of 40 rpm. The temperature was hold for half an hour, rapidly cooled down to the saturation temperature, and then cooled at a rate of 0.5 C./day. After the crystal is grown to a desired size, the seed crystal rod was lifted so that the crystal was separated from the surface of the liquid. The crystal was still remained in the furnace to be annealed so that it was cooled to room temperature at a rate of 35 C./h. A centimeter-grade Li.sub.4Sr(BO.sub.3).sub.2 crystal was thus obtained.

Example 4

(13) A Li.sub.4Sr(BO.sub.3).sub.2 crystal was grown in a flux agent system of Li.sub.2OB.sub.2O.sub.3 by flux method.

(14) 129.3 g (1.75 mol) Li.sub.2CO.sub.3, 36.9 g (0.25 mol) SrCO.sub.3 and 34.8 g (0.50 mol) B.sub.2O.sub.3 (wherein 1.83 mol Li.sub.2CO.sub.3, 0.25 mol B.sub.2O.sub.3 served as the flux agent) were weighed, mixed and homogeneously ground, and then batch fed into a 60 mm60 mm open crucible. The obtained mixture was melted in a muffle furnace at 750 C. Subsequently, it was heated rapidly to 750 C. in a vertical crystal growth furnace, hold at this temperature for 24 hours, and then cooled down rapidly to 10 C. above the saturation temperature. A seed crystal rod fitted with the seed crystal was slowly inserted into the melt in the crucible, and the rotation unit at the top of the seed crystal rod was started with a rotation speed of 30 rpm. The temperature was hold for half an hour, rapidly cooled down to the saturation temperature, and then cooled at a rate of 0.8 C./day. After the crystal is grown to a desired size, the seed crystal rod was lifted so that the crystal was separated from the surface of the liquid. The crystal was still remained in the furnace to be annealed so that it was cooled to room temperature at a rate of 30 C./h. A centimeter-grade Li.sub.4Sr(BO.sub.3).sub.2 crystal was thus obtained.

Example 5

(15) A Li.sub.4Sr(BO.sub.3).sub.2 crystal was grown using Li.sub.2O as a flux agent by flux method.

(16) 147.8 g (2.00 mol) Li.sub.2CO.sub.3, 51.8 g (0.5 mol) SrO and 61.8 g (1.00 mol) H.sub.3BO.sub.3 (wherein 1.00 mol Li.sub.2CO.sub.3 served as the flux agent) were weighed, mixed and homogeneously ground, and then batch fed into a 60 mm60 mm open crucible. The obtained mixture was melted in a muffle furnace at 750 C. Subsequently, it was heated rapidly to 750 C. in a vertical crystal growth furnace, hold at this temperature for 24 hours, and then cooled down rapidly to 10 C. above the saturation temperature. A seed crystal rod fitted with the seed crystal was slowly inserted into the melt in the crucible, and the rotation unit at the top of the seed crystal rod was started with a rotation speed of 30 rpm. The temperature was hold for half an hour, rapidly cooled down to the saturation temperature, and then cooled at a rate of 0.5 C./day. After the crystal is grown to a desired size, the seed crystal rod was lifted so that the crystal was separated from the surface of the liquid. The crystal was still remained in the furnace to be annealed so that it was cooled to room temperature at a rate of 30 C./h. A Li.sub.4Sr(BO.sub.3).sub.2 crystal was thus obtained.

Example 6

(17) A Li.sub.4Sr(BO.sub.3).sub.2 crystal was grown in a flux agent system of Li.sub.2OB.sub.2O.sub.3LiF by flux method.

(18) 140.1 g (1.375 mol) Li.sub.2C.sub.2O.sub.4, 36.9 g (0.250 mol) SrCO.sub.3, 46.4 g (0.750 mol) H.sub.3BO.sub.3 and 13.0 g (0.500 mol) LiF (wherein 0.875 mol Li.sub.2CO.sub.3, 0.250 mol H.sub.3BO.sub.3 and 0.500 mol LiF served as the flux agent) were weighed, mixed and homogeneously ground, and then batch fed into a 60 mm60 mm open crucible. The obtained mixture was melted in a muffle furnace at 750 C. Subsequently, it was heated rapidly to 750 C. in a vertical crystal growth furnace, hold at this temperature for 24 hours, and then cooled down rapidly to 10 C. above the saturation temperature. A seed crystal rod fitted with the seed crystal was slowly inserted into the melt in the crucible, and the rotation unit at the top of the seed crystal rod was started with a rotation speed of 20 rpm. The temperature was hold for half an hour, rapidly cooled down to the saturation temperature, and then cooled at a rate of 0.5 C./day. After the crystal is grown to a desired size, the seed crystal rod was lifted so that the crystal was separated from the surface of the liquid. The crystal was still remained in the furnace to be annealed so that it was cooled to room temperature at a rate of 20 C./h. A Li.sub.4Sr(BO.sub.3).sub.2 crystal was thus obtained.

(19) By using any of the three above-mentioned flux agents, the centimeter-grade Li.sub.4Sr(BO.sub.3).sub.2 nonlinear optical crystal can be obtained. Furthermore, by using large size crucible and prolonging the growth period, a Li.sub.4Sr(BO.sub.3).sub.2 nonlinear optical crystal with corresponding relative large size could be obtained.

(20) According to the single-crystal X-ray diffraction analysis, the Li.sub.4Sr(BO.sub.3).sub.2 crystals prepared in the above Example 1-6 did not contain symmetric center and belong to monoclinic space group C.sub.c with lattice parameters of =9.117(5) , b=5.239(2) , c=11.762(6) , =105.22(1), V=542.08 (127) .sup.3 and Z=4. FIG. 3 shows the schematic crystal structure of the Li.sub.4Sr(BO.sub.3).sub.2 crystal.

Example 7

(21) The Li.sub.4Sr(BO.sub.3).sub.2 nonlinear optical crystal obtained in Example 1 was subjected to a transmittance spectra test. The crystal had an UV absorption cut-off edge less than 190 nm and was transmissive within the wavelength range of 190-2500 nm. The crystal was not easy to crack but was easy to cut, polishing processing, preserve and was not easy to disintegrate. The Li.sub.4Sr(BO.sub.3).sub.2 nonlinear optical crystal obtained in Example 1 was placed in the equipment at the position 3 as shown in FIG. 1. At room temperature, when the Q-switched Nd:YAG laser was adopted as the fundamental frequency light source and a near-infrared light with a wavelength of 1064 nm was used as the incident light, the output light was a 532 nm green laser, with a laser intensity of about equivalent to two times that of KDP (KH.sub.2PO.sub.4). Moreover, the Li.sub.4Sr(BO.sub.3).sub.2 nonlinear optical crystal obtained in Example 2 was placed in the equipment at the position 3 as shown in FIG. 1. At room temperature, when a green laser with a wavelength of 532 nm was adopted as the fundamental frequency light source and a 532 nm green laser was used as the incident light, the output light was a 266 nm green laser, with a laser intensity of about equivalent to of that of BBO.