Cesium borosilicate compound, nonlinear optical crystal of cesium borosilicate, and preparation method therefor and use thereof

Abstract

The present invention relates to a cesium borosilicate compound, a nonlinear optical crystal of cesium borosilicate, and a preparation method therefor and a use thereof. The cesium borosilicate compound has a chemical formula of Cs.sub.2B.sub.4SiO.sub.9 and a molecular weight of 481.15, and is prepared using a solid phase method. The nonlinear optical crystal of the cesium borosilicate compound has a chemical formula of Cs.sub.2B.sub.4SiO.sub.9 and a molecular weight of 481.15, does not have a center of symmetry, belongs to the tetragonal system with space group I4 and unit-cell parameters a=6.731(3) , c=9.871(9) and V=447.2(5) .sup.3, and has a wide transmittance range. The shortest ultraviolet cutoff edge is smaller than 190 nm, the frequency doubling effect of the crystal is 4.6 KDP, and the crystal is grown by a high-temperature solution spontaneous crystallization method and a flux method. The crystal has advantages of high growth rate, being transparent and inclusion free, low cost having a wide transmittance range, high hardness, good mechanical property, being crack resistant and not prone to deliquescence, being easy to process and store, and the like. The crystal is widely applied to manufacturing of nonlinear optical devices such as frequency doubling generators, frequency up-converters, frequency down-converters or optical parametric oscillators.

Claims

1. A cesium borosilicate compound, wherein the compound has a chemical formula of Cs.sub.2B.sub.4SiO.sub.9 with a molecular weight of 481.15.

2. A method for preparing the cesium borosilicate compound according to claim 1, wherein the method is conducted according to the following steps of: a. a Cs-containing compound, a B-containing compound and a Si-containing compound are mixed uniformly at a molar ratio of Cs:B:Si=2:4:1, grinded, loaded into a 100 mm100 mm open type corundum crucible and then compressed tightly; the corundum crucible is placed into a muffle furnace, which is heated slowly to a temperature of 550 C., held at this temperature for 24 hours and then cooled down to room temperature; the mixture is taken out, grinded once again and then put back to the muffle furnace, which is heated to 650 C., held at this temperature for 24 hours and then cooled down to room temperature; the mixture is taken out, grinded for the third time and then put back to the muffle furnace, which is further heated to 700-900 C. and held at this temperature for 3-96 hours; the mixture is taken out and grinded to obtain the single-phase polycrystalline powder of a Cs.sub.2B.sub.4SiO.sub.9 compound; b. the obtained single-phase polycrystalline powder of the Cs.sub.2B.sub.4SiO.sub.9 compound is mixed with a fluxing agent at a molar ratio of 1:0.5-10 and then loaded into a 80 mm80 mm open type platinum crucible; the platinum crucible is heated to a temperature ranging from 630 C. to 900 C. and held at this temperature range for 5-80 hours to obtain a mixed melting liquid; the temperature is then decreased to 610-835 C. and further decreased to room temperature at a temperature-decreasing rate of 1-10 C./h, allowing for spontaneous crystallization to obtain a Cs.sub.2B.sub.4SiO.sub.9 seed crystal; c. crystals are grown in the mixed melting liquid: the obtained Cs.sub.2B.sub.4SiO.sub.9 seed crystal is attached onto a seed crystal rod for forming the seed crystal from the top of a crystal growing furnace; the seed crystal is preheated on the surface of the mixed melting liquid for 10 minutes, and then immersed underneath the liquid surface so that the seed crystal is remelted in the mixed melting liquid; the temperature is kept for 30 minutes, and decreased rapidly to a temperature ranging from 610 C. to 745 C.; d. the temperature is further decreased at a rate of 2 C./day and the seed crystal rod is rotated at a rotation rate of 10 rpm; after the crystal stops growing, the crystal is drawn out of the liquid surface and cooled down to room temperature at a rate of 5-50 C./h to obtain the cesium borosilicate compound, the cesium borosilicate compound being a colorless and transparent large-size nonlinear optical crystal of Cs.sub.2B.sub.4SiO.sub.9; said fluxing agent is Cs.sub.2CO.sub.3, a Cs.sub.2CO.sub.3H.sub.3BO.sub.3 system, a PbOH.sub.3BO.sub.3 system, or a Cs.sub.2CO.sub.3PbO system.

3. The method according to claim 2, wherein said Cs-containing compound is Cs.sub.2CO.sub.3, CsNO.sub.3, Cs.sub.2O, CsOH, CsHCO.sub.3 or Cs.sub.2C.sub.2O.sub.4; said Si-containing compound is SiO.sub.2; said B-containing compound is H.sub.3BO.sub.3 or B.sub.2O.sub.3.

4. The method according to claim 2, wherein the molar ratio of Cs.sub.2CO.sub.3 to H.sub.3BO.sub.3 is 1-5:1-3 in said Cs.sub.2CO.sub.3-H.sub.3BO.sub.3 system; the molar ratio of PbO to H.sub.3BO.sub.3 is 1-5:1-3 in said PbO-H.sub.3BO.sub.3 system; and the molar ratio of Cs.sub.2CO.sub.3 to PbO is 1-5:0.2-3 in said Cs.sub.2CO.sub.3PbO system.

5. A method for preparing the cesium borosilicate compound according to claim 1, wherein the method is conducted according to the following steps of: a. a Cs-containing compound, a B-containing compound and a Si-containing compound are mixed uniformly at a molar ratio of Cs:B:Si=2:4:1, loaded into a 80 mm80 mm open type platinum crucible; the platinum crucible is heated to a temperature ranging from 630 C. to 900 C. and held at this temperature range for 5-80 hours to obtain a mixed melting liquid; the temperature is then decreased to 610-835 C. and further decreased to room temperature at a temperature-decreasing rate of 1-10 C./h, allowing for spontaneous crystallization to obtain a Cs.sub.2B.sub.4SiO.sub.9 seed crystal; b. crystals are grown in the mixed melting liquid: the obtained Cs.sub.2B.sub.4SiO.sub.9 seed crystal is attached onto a seed crystal rod for forming the seed crystal from the top of a crystal growing furnace; the seed crystal is preheated on the surface of the mixed melting liquid for 10 minutes, and then immersed underneath the liquid surface so that the seed crystal is remelted in the mixed melting liquid; the temperature is kept for 30 minutes, and decreased rapidly to a temperature ranging from 610 C. to 745 C.; c. the temperature is further decreased at a rate of 2 C./day and the seed crystal rod is rotated at a rotation rate of 10 rpm; after the crystal stops growing, the crystal is drawn out of the liquid surface and cooled down to room temperature at a rate of 5-50 C./h to obtain the cesium borosilicate compound, the cesium borosilicate compound being a colorless and transparent large-size nonlinear optical crystal of Cs.sub.2B.sub.4SiO.sub.9; said fluxing agent is Cs.sub.2CO.sub.3, a Cs.sub.2CO.sub.3-H.sub.3BO.sub.3 system, a PbO-H.sub.3BO.sub.3 system, or a Cs.sub.2CO.sub.3PbO system.

6. The method according to claim 5, wherein said Cs-containing compound is Cs.sub.2CO.sub.3, CsNO.sub.3, Cs.sub.2O, CsOH, CsHCO.sub.3 or Cs.sub.2C.sub.2O.sub.4; said Si-containing compound is SiO.sub.2; said B-containing compound is H.sub.3BO.sub.3 or B.sub.2O.sub.3.

7. The method according to claim 5, wherein the molar ratio of Cs.sub.2CO.sub.3 to H.sub.3BO.sub.3 is 1-5:1-3 in said Cs.sub.2CO.sub.3-H.sub.3BO.sub.3 system; the molar ratio of PbO to H.sub.3BO.sub.3 is 1-5:1-3 in said PbO-H.sub.3BO.sub.3 system; and the molar ratio of Cs.sub.2CO.sub.3 to PbO is 1-5:0.2-3 in said Cs.sub.2CO.sub.3PbO system.

8. A cesium borosilicate nonlinear optical crystal, wherein the crystal has a chemical formula of Cs.sub.2B.sub.4SiO.sub.9 with a molecular weight of 481.15; has no symmetric center; belongs to an tetragonal system; has a space group of 14 with unit cell parameters of a=6.731(3) , c=9.871(9) , V=447.2(5) .sup.3; has a wide transmittance range with a shortest UV cut-off edge lower than 190 nm; has a powder frequency-doubling effect of 4.6 KDP.

9. A method for preparing the cesium borosilicate nonlinear optical crystal according to claim 8, wherein the method is conducted according to the following steps of: a. a Cs-containing compound, a B-containing compound and a Si-containing compound are mixed uniformly at a molar ratio of Cs:B:Si=2:4:1, grinded, loaded into a 100 mm100 mm open type corundum crucible and then compressed tightly; the corundum crucible is placed into a muffle furnace, which is heated slowly to a temperature of 550 C., held at this temperature for 24 hours and then cooled down to room temperature; the mixture is taken out, grinded once again and then put back to the muffle furnace, which is heated to 650 C., held at this temperature for 24 hours and then cooled down to room temperature; the mixture is taken out, grinded for the third time and then put back to the muffle furnace, which is further heated to 700-900 C. and held at this temperature for 3-96 hours; the mixture is taken out and grinded to obtain the single-phase polycrystalline powder of a Cs.sub.2B.sub.4SiO.sub.9 compound; b. the obtained single-phase polycrystalline powder of the Cs.sub.2B.sub.4SiO.sub.9 compound is mixed with a fluxing agent at a molar ratio of 1:0.5-10 and then loaded into a 80 mm80 mm open type platinum crucible; the platinum crucible is heated to a temperature ranging from 630 C. to 900 C. and held at this temperature range for 5-80 hours to obtain a mixed melting liquid; the temperature is then decreased to 610-835 C. and further decreased to room temperature at a temperature-decreasing rate of 1-10 C./h, allowing for spontaneous crystallization to obtain a Cs.sub.2B.sub.4SiO.sub.9 seed crystal; c. crystals are grown in the mixed melting liquid: the obtained Cs.sub.2B.sub.4SiO.sub.9 seed crystal is attached onto a seed crystal rod for forming the seed crystal from the top of a crystal growing furnace; the seed crystal is preheated on the surface of the mixed melting liquid for 10 minutes, and then immersed underneath the liquid surface so that the seed crystal is remelted in the mixed melting liquid; the temperature is kept for 30 minutes, and decreased rapidly to a temperature ranging from 610 C. to 745 C.; d. the temperature is further decreased at a rate of 2 C./day and the seed crystal rod is rotated at a rotation rate of 10 rpm; after the crystal stops growing, the crystal is drawn out of the liquid surface and cooled down to room temperature at a rate of 5-50 C./h to obtain the cesium borosilicate nonlinear optical crystal, the cesium borosilicate nonlinear optical crystal being a colorless and transparent large-size nonlinear optical crystal of Cs.sub.2B.sub.4SiO.sub.9; said fluxing agent is Cs.sub.2CO.sub.3, a Cs.sub.2CO.sub.3H.sub.3BO.sub.3 system, a PbOH.sub.3BO.sub.3 system, or a Cs.sub.2CO.sub.3PbO system.

10. The method according to claim 9, wherein said Cs-containing compound is Cs.sub.2CO.sub.3, CsNO.sub.3, Cs.sub.2O, CsOH, CsHCO.sub.3 or Cs.sub.2C.sub.2O.sub.4; said Si-containing compound is SiO.sub.2; said B-containing compound is H.sub.3BO.sub.3 or B.sub.2O.sub.3.

11. The method according to claim 9, wherein the molar ratio of Cs.sub.2CO.sub.3 to H.sub.3BO.sub.3 is 1-5:1-3 in said Cs.sub.2CO.sub.3H.sub.3BO.sub.3 system; the molar ratio of PbO to H.sub.3BO.sub.3 is 1-5:1-3 in said PbOH.sub.3BO.sub.3 system; and the molar ratio of Cs.sub.2CO.sub.3 to PbO is 1-5:0.2-3 in said Cs.sub.2CO.sub.3PbO system.

12. A method for preparing the cesium borosilicate nonlinear optical crystal according to claim 8, wherein the method is conducted according to the following steps of: a. a Cs-containing compound, a B-containing compound and a Si-containing compound are mixed uniformly at a molar ratio of Cs:B:Si=2:4:1, loaded into a 80 mm80 mm open type platinum crucible; the platinum crucible is heated to a temperature ranging from 630 C. to 900 C. and held at this temperature range for 5-80 hours to obtain a mixed melting liquid; the temperature is then decreased to 610-835 C. and further decreased to room temperature at a temperature-decreasing rate of 1-10 C./h, allowing for spontaneous crystallization to obtain a Cs.sub.2B.sub.4SiO.sub.9 seed crystal; b. crystals are grown in the mixed melting liquid: the obtained Cs.sub.2B.sub.4SiO.sub.9 seed crystal is attached onto a seed crystal rod for forming the seed crystal from the top of a crystal growing furnace; the seed crystal is preheated on the surface of the mixed melting liquid for 10 minutes, and then immersed underneath the liquid surface so that the seed crystal is remelted in the mixed melting liquid; the temperature is kept for 30 minutes, and decreased rapidly to a temperature ranging from 610 C. to 745 C.; c. the temperature is further decreased at a rate of 2 C./day and the seed crystal rod is rotated at a rotation rate of 10 rpm; after the crystal stops growing, the crystal is drawn out of the liquid surface and cooled down to room temperature at a rate of 5-50 C./h to obtain the cesium borosilicate nonlinear optical crystal, the cesium borosilicate nonlinear optical crystal being a colorless and transparent large-size nonlinear optical crystal of Cs.sub.2B.sub.4SiO.sub.9; said fluxing agent is Cs.sub.2CO.sub.3, a Cs.sub.2CO.sub.3-H.sub.3BO.sub.3 system, a PbO-H.sub.3BO.sub.3 system, or a Cs.sub.2CO.sub.3PbO system.

13. The method according to claim 12, wherein said Cs-containing compound is Cs.sub.2CO.sub.3, CsNO.sub.3, Cs.sub.2O, CsOH, CsHCO.sub.3 or Cs.sub.2C.sub.2O.sub.4; said Si-containing compound is SiO.sub.2; said B-containing compound is H.sub.3BO.sub.3 or B.sub.2O.sub.3.

14. The method according to claim 12, wherein the molar ratio of Cs.sub.2CO.sub.3 to H.sub.3BO.sub.3 is 1-5:1-3 in said Cs.sub.2CO.sub.3-H.sub.3BO.sub.3 system; the molar ratio of PbO to H.sub.3BO.sub.3 is 1-5:1-3 in said PbO-H.sub.3BO.sub.3 system; and the molar ratio of Cs.sub.2CO.sub.3 to PbO is 1-5:0.2-3 in said Cs.sub.2CO.sub.3PbO system.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a powder XRD pattern of the Cs.sub.2B.sub.4SiO.sub.9 compound of the present invention.

(2) FIG. 2 is a working principle diagram of a nonlinear optical device made from the Cs.sub.2B.sub.4SiO.sub.9 crystal of the present invention, wherein 1 is a laser generator, 2 is incident beam, 3 is a Cs.sub.2B.sub.4SiO.sub.9 crystal, 4 is output beam and 5 is a filter.

PREFERRED EMBODIMENTS OF THE INVENTION

Example 1

(3) A Cs.sub.2B.sub.4SiO.sub.9 compound was synthesized by using the solid-phase method according to the following reaction equation:
Cs.sub.2CO.sub.3+SiO.sub.2+4H.sub.3BO.sub.3.fwdarw.Cs.sub.2B.sub.4SiO.sub.9+CO.sub.26H.sub.2O

(4) Cs.sub.2CO.sub.3, SiO.sub.2 and H.sub.3BO.sub.3 were weighed at a molar ratio of 1:1:4 and put into a mortar, mixed uniformly and grinded carefully, loaded into a 100 mm100 mm open type corundum crucible and then compressed tightly; the corundum crucible was placed into a muffle furnace, which was heated slowly to temperature of 550 C., held at this temperature for 24 hours and then cooled down to room temperature; the mixture was taken out winded once again and then put back to the muffle furnace, which was heated to a temperature of 650 C., held at this temperature for 24 hours, and then cooled to room temperature; the mixture was taken out, grinded for the third time and then put back to the muffle furnace, which was further heated to 780 C. and held at this temperature for 48 hours; the mixture was taken out and winded to obtain the single-phase polycrystalline powder of a Cs.sub.2B.sub.4SiO.sub.9 compound; the powder XRD pattern assay showed that the powder XRD pattern of the Cs.sub.2B.sub.4SiO.sub.9 powder (FIG. 1) is consistent with the theoretical XRD pattern of the single crystal structure, which verifies the synthesis of single-phase polycrystalline powder of the Cs.sub.2B.sub.4SiO.sub.9 compound;

(5) The obtained single-phase polycrystalline powder of Cs.sub.2B.sub.4SiO.sub.9 and a fluxing agent Cs.sub.2CO.sub.3 were mixed at a molar ratio of Cs.sub.2B.sub.4SiO.sub.9:Cs.sub.2CO.sub.3=1:0:5 and then loaded into a 80 mm80 mm open type platinum crucible; the platinum crucible was heated to a temperature of 900 C. and held at this temperature for 15 hours to obtain a mixed melting liquid, the temperature was then decreased to 835 C. and further decreased to room temperature slowly at a rate of 1 C./h, allowing for spontaneous crystallization to obtain a Cs.sub.2B.sub.4SiO.sub.9 seed crystal;

(6) The crystal was grown in the melting liquid of the compound: the obtained Cs.sub.2B.sub.4SiO.sub.9 seed crystal was attached onto a seed crystal rod for forming the seed crystal from the top of a crystal growing furnace; the seed crystal was preheated on the surface of the mixed melting liquid for 10 minutes, and then immersed underneath the liquid surface so that the seed crystal was remelted in the mixed melting liquid; the temperature was kept for 30 minutes, and then decreased rapidly to a temperature of 730 C.

(7) The temperature was further decreased at a rate of 2 C./day and the seed crystal rod was rotated at a rotation rate of 10 rpm; after the crystal stopped growing, the crystal was drawn out of the liquid surface and cooled to room temperature at a rate of 10 C./h to obtain a colorless and transparent Cs.sub.2B.sub.4SiO.sub.9 crystal.

Example 2

(8) A Cs.sub.2B.sub.4SiO.sub.9 compound was synthesized according to the following reaction equation:
2CsNO.sub.3+SiO.sub.2+4H.sub.3BO.sub.3.fwdarw.Cs.sub.2B.sub.4SiO.sub.9+NO.sub.2+NO+6H.sub.2O+O.sub.2

(9) The starting materials CsNO.sub.3, SiO.sub.2 and H.sub.3BO.sub.3 were weighed directly at a molar ratio of 2:1:4, the weighed starting materials and a fluxing agent Cs.sub.2CO.sub.3 were mixed at a molar ratio of 1:5, and then loaded into a 80 mm80 mm open type platinum crucible, the platinum crucible was heated to a temperature of 700 C. and held at this temperature for 60 hours to obtain a mixed melting liquid; the temperature was then decreased to 615 C. and further decreased to room temperature slowly at a rate of 1.5 C./h, allowing for spontaneous crystallization to obtain a Cs.sub.2B.sub.4SiO.sub.9 seed crystal;

(10) The obtained Cs.sub.2B.sub.4SiO.sub.9 seed crystal was attached onto a seed crystal rod for forming the seed crystal from the top of a crystal growing furnace, the seed crystal was preheated on the surface of the mixed melting liquid for 10 minutes, and then immersed underneath the liquid surface so that the seed crystal was remelted in the mixed melting liquid; the temperature was kept for 30 minutes, and then decreased rapidly to a temperature of 710 C.;

(11) The temperature was further decreased slowly at a rate of 1 C./day, after the crystal grown up to a desired size, the crystal was drawn out of the liquid surface and cooled to room temperature at a rate of 20 C./h; the crystal was then removed from the furnace and thus a colorless and transparent Cs.sub.2B.sub.4SiO.sub.9 crystal was obtained.

Example 3

(12) A Cs.sub.2B.sub.4SiO.sub.9 compound was synthesized according to the following reaction equation:
Cs.sub.2O+SiO.sub.2+4H.sub.3BO.sub.3.fwdarw.Cs.sub.2B.sub.4SiO.sub.9+6H.sub.2O

(13) Cs.sub.2O, SiO.sub.2 and H.sub.3BO.sub.3 were put into a mortar at a molar ratio of 1:1:4, mixed uniformly, grinded carefully, loaded into a 100 mm100 mm open type corundum crucible and then compressed tightly; the corundum crucible was placed into a muffle furnace, which was heated slowly to a temperature of 550 C., held at this temperature for 24 hours and then cooled down to room temperature; the mixture was taken out, grinded once again and then put back to the muffle furnace, which was heated to a temperature of 650 C., held at this temperature for 24 hours, and then cooled to room temperature; the mixture was taken out, grinded for the third time and then put back to the muffle furnace, which was further heated to 800 C. and held at this temperature for 48 hours, the mixture was taken out and grinded to obtain the single-phase polycrystalline powder of a Cs.sub.2B.sub.4SiO.sub.9 compound;

(14) The obtained Cs.sub.2B.sub.4SiO.sub.9 compound and a fluxing agent Cs.sub.2CO.sub.3PhO (in which the molar ratio of Cs.sub.2CO.sub.3 to PhO was 1:1) were mixed at a molar ratio 1:5 and then loaded into a 80 min80 mm open type platinum crucible; the platinum crucible was heated to a temperature of 820 C. and held at this temperature for 80 hours to obtain a mixed melting liquid, the temperature was then decreased to 710 C. and further decreased to room temperature slowly at a rate of 2.5 C./h, allowing for spontaneous crystallization to obtain a Cs.sub.2B.sub.4SiO.sub.9 seed crystal;

(15) The obtained Cs.sub.2B.sub.4SiO.sub.9 seed crystal was attached onto a seed crystal rod for forming the seed crystal from the top of a crystal growing furnace; the seed crystal was preheated on the surface of the mixed melting liquid for 10 minutes, and then partly immersed underneath the liquid surface so that the seed crystal was remelted in the mixed melting liquid; the temperature was kept for 20 minutes, and then decreased rapidly to a temperature of 700 C.;

(16) The temperature was further decreased slowly at a rate of 2 C./day; after the crystal grown up to a desired size, the crystal was drawn out of the liquid surface and cooled to room temperature at a rate of 30 C./h; the crystal was then removed from the furnace and thus a colorless and transparent Cs.sub.2B.sub.4SiO.sub.9 crystal was obtained.

Example 4

(17) A Cs.sub.2B.sub.4SiO.sub.9 compound was synthesized according to the following reaction equation:
2CsOH+SiO.sub.2+4H.sub.3BO.sub.3.fwdarw.Cs.sub.2B.sub.4SiO.sub.9+7H.sub.2O

(18) CsOH, SiO.sub.2 and H.sub.3BO.sub.3 were weighed directly at a molar ratio of 2:1:4 to obtain a mixture. The mixture and a fluxing agent Cs.sub.2CO.sub.3H.sub.3BO.sub.3 (in which the molar ratio of Cs.sub.2CO.sub.3 to H.sub.3BO.sub.3 was 1:1) were mixed at a molar ratio of 1:3, and then loaded into a 80 mm80 mm open type platinum crucible; the platinum crucible was heated to a temperature of 765 C. and held at this temperature for 10 hours to obtain a mixed melting liquid; the temperature was then decreased to 715 C. and further decreased to room temperature slowly at a rate of 2.5 C./h, allowing for spontaneous crystallization to obtain a Cs.sub.2B.sub.4SiO.sub.9 seed crystal;

(19) The obtained Cs.sub.2B.sub.4SiO.sub.9 seed crystal was attached onto a seed crystal rod for forming the seed crystal from the top of a crystal growing furnace; the seed crystal was preheated on the surface of the mixed melting liquid for 5 minutes, and then immersed underneath the liquid surface so that the seed crystal was remelted in the mixed melting liquid; the temperature was kept for 5 minutes, and then decreased rapidly to a temperature of 700 C.;

(20) The temperature was further decreased slowly at a rate of 2 C./day; after the crystal grown up to a desired size, it was drawn out of the liquid surface and cooled to room temperature at a rate of 40 C./h; the crystal was then removed from the furnace and thus a colorless and transparent Cs.sub.2B.sub.4SiO.sub.9 crystal was obtained.

Example 5

(21) A Cs.sub.2B.sub.4SiO.sub.9 compound was synthesized according to the following reaction equation:
2CsHCO.sub.3+SiO.sub.2+4H.sub.3BO.sub.3.fwdarw.Cs.sub.2B.sub.4SiO.sub.9+2CO.sub.2+7H.sub.2O

(22) CsHCO.sub.3, SiO.sub.2 and H.sub.3BO.sub.3 were weighed directly at a molar ratio of 2:1:4 to obtain a mixture. The mixture and a fluxing agent H.sub.3BO.sub.3PbO (in which the molar ratio of H.sub.3BO.sub.3 to PbO was 3:1) were mixed at a molar ratio of 1:5, and then loaded into a 80 mm80 mm open type platinum crucible; the platinum crucible was heated to a temperature of 680 C. and held at this temperature for 60 hours to obtain a mixed melting liquid; the temperature was then decreased to 620 C. and further decreased down to room temperature slowly at a rate of 3.5 C./h, allowing for spontaneous crystallization to obtain a Cs.sub.2B.sub.4SiO.sub.9 seed crystal;

(23) The obtained Cs.sub.2B.sub.4SiO.sub.9 seed crystal was attached onto a seed crystal rod for forming the seed crystal from the top of a crystal growing furnace; the seed crystal was preheated on the surface of the mixed melting liquid for 15 minutes, and then immersed underneath the liquid surface so that the seed crystal was remelted in the mixed melting liquid; the temperature was kept for 30 minutes, and then decreased rapidly to a temperature of 615 C.;

(24) The temperature was further decreased slowly at a rate of 3 C./day; after the crystal grown up to a desired size, it was drawn out of the liquid surface and cooled to room temperature at a rate of 7 C./h; the crystal was then removed from the furnace and thus a colorless and transparent Cs.sub.2B.sub.4SiO.sub.9 crystal was obtained.

Example 6

(25) A Cs.sub.2B.sub.4SiO.sub.9 compound was synthesized according to the following reaction equation:
Cs.sub.2CO.sub.3+SiO.sub.2+2B.sub.2O.sub.3.fwdarw.Cs.sub.2B.sub.4SiO.sub.9+CO.sub.2

(26) Cs.sub.2CO.sub.3, SiO.sub.2 and B.sub.2O.sub.3 were weighed directly at a molar ratio of 1:1:2 to obtain a mixture. The mixture and a fluxing agent H.sub.3BO.sub.3PbO (in which the molar ratio of H.sub.3BO.sub.3 to PbO was 3:1) were mixed at a molar ratio of 1:5, and then loaded into a 80 mm80 mm open type platinum crucible; the platinum crucible was heated to a temperature of 650 C. and held at this temperature for 80 hours to obtain a mixed melting liquid; the temperature was then decreased to 615 C. and further decreased down to room temperature slowly at a rate of 5 C./h, allowing for spontaneous crystallization to obtain a Cs.sub.2B.sub.4SiO.sub.9 seed crystal;

(27) The obtained Cs.sub.2B.sub.4SiO.sub.9 seed crystal was attached onto a seed crystal rod for forming the seed crystal from the top of a crystal growing furnace; the seed crystal was preheated on the surface of the mixed melting liquid for 20 minutes, and then immersed underneath the liquid surface so that the seed crystal was remelted in the mixed melting liquid; the temperature was kept for 5 minutes, and then decreased rapidly to a temperature of 610 C.

(28) The temperature was further decreased slowly at a rate of 3 C./day; after the crystal grown up to a desired size, it was drawn out of the liquid surface and cooled to room temperature at a rate of 15 C./h; the crystal was then removed from the furnace and thus a colorless and transparent Cs.sub.2B.sub.4SiO.sub.9 crystal was obtained.

Example 7

(29) A Cs.sub.2B.sub.4SiO.sub.9 compound was synthesized according to the following reaction equation:
2CsNO.sub.3+SiO.sub.2+2B.sub.2O.sub.3.fwdarw.Cs.sub.2B.sub.4SiO.sub.9+NO.sub.2+NO+O.sub.2

(30) CsNO.sub.3, SiO.sub.2 and B.sub.2O.sub.3 were weighed directly at a molar ratio of 2:1:2 to obtain a mixture. The mixture and a fluxing agent Cs.sub.2CO.sub.3PbO (in which the molar ratio of Cs.sub.2CO.sub.3 to PbO was 5:3) were mixed at a molar ratio of 1:2, and then loaded into a 80 mm80 mm open type platinum crucible; the platinum crucible was heated to a temperature of 660 C. and held at this temperature for 80 hours to obtain a mixed melting liquid; the temperature was then decreased to 610 C. and further decreased down to room temperature slowly at a rate of 10 C./h, allowing for spontaneous crystallization to obtain a Cs.sub.2B.sub.4SiO.sub.9 seed crystal;

(31) The obtained seed crystal was attached onto a seed crystal rod for forming the seed crystal from the top of a crystal growing furnace; the seed crystal was preheated on the surface of the mixed melting liquid for 25 minutes, and then partly immersed underneath the liquid surface so that the seed crystal was remelted in the mixed melting liquid; the temperature was kept for 25 minutes, and then decreased rapidly to a temperature of 600 C.;

(32) The temperature was further decreased slowly at a rate of 5 C./day; after the crystal grown up to a desired size, it was drawn out of the liquid surface and cooled to room temperature at a rate of 35 C./h; the crystal was then removed from the furnace and thus a colorless and transparent Cs.sub.2B.sub.4SiO.sub.9 crystal was obtained.

Example 8

(33) A Cs.sub.2B.sub.4SiO.sub.9 compound was synthesized according to the following reaction equation:
Cs.sub.2O+SiO.sub.2+2B.sub.2O.sub.3.fwdarw.Cs.sub.2B.sub.4SiO.sub.9

(34) Cs.sub.2O, SiO.sub.2 and B.sub.2O.sub.3 were put into a mortar at a molar ratio of 1:1:2, mixed uniformly, grinded carefully, loaded into a 100 mm100 mm open type corundum crucible and then compressed tightly; the corundum crucible was placed into a muffle furnace, which was heated slowly to a temperature of 550 C., held at this temperature for 24 hours and then cooled down to room temperature; the mixture was taken out, grinded once again and then put back to the muffle furnace, which was heated to a temperature of 650 C., held at this temperature for 24 hours, and then cooled to room temperature; the mixture was taken out, grinded for the third time and then put back to the muffle furnace, which was further heated to 860 C. and held at this temperature for 48 hours; the mixture was taken out and grinded to obtain the single-phase polycrystalline powder of a Cs.sub.2B.sub.4SiO.sub.9 compound;

(35) The synthesized Cs.sub.2B.sub.4SiO.sub.9 compound and a fluxing agent Cs.sub.2CO.sub.3H.sub.3BO.sub.3 (in which the molar ratio of Cs.sub.2CO.sub.3 to H.sub.3BO.sub.3 was 2:2) were mixed at a molar ratio 1:4 and then loaded into a 80 mm80 mm open type platinum crucible; the platinum crucible was heated to a temperature of 770 C. and held at this temperature for 70 hours to obtain a mixed melting liquid, the temperature was then decreased to 725 C. and further decreased to room temperature slowly at a rate of 4 C./h, allowing for spontaneous crystallization to obtain a Cs.sub.2B.sub.4SiO.sub.9 seed crystal;

(36) The obtained Cs.sub.2B.sub.4SiO.sub.9 seed crystal was attached onto a seed crystal rod for forming the seed crystal from the top of a crystal growing furnace; the seed crystal was preheated on the surface of the mixed melting liquid for 8 minutes, and then immersed underneath the liquid surface so that the seed crystal was remelted in the mixed melting liquid; the temperature was kept for 8 minutes, and then decreased rapidly to a temperature of 720 C.;

(37) The temperature was further decreased slowly at a rate of 0.8 C./day; after the crystal grown up to a desired size, the crystal was drawn out of the liquid surface and cooled to room temperature at a rate of 5 C./h; the crystal was then removed from the furnace and thus a colorless and transparent Cs.sub.2B.sub.4SiO.sub.9 crystal was obtained.

Example 9

(38) A Cs.sub.2B.sub.4SiO.sub.9 compound was synthesized according to the following reaction equation:
2CsOH+SiO.sub.2+2B.sub.2O.sub.3.fwdarw.Cs.sub.2B.sub.4SiO.sub.9+H.sub.2O

(39) CsOH, SiO.sub.2 and B.sub.2O.sub.3 were put into a mortar at a molar ratio of 2:1:2, mixed uniformly, grinded carefully, and then loaded into a 100 mm100 mm open type corundum crucible; the corundum crucible was placed into a muffle furnace, which was heated slowly to a temperature of 550 C., held at this temperature for 24 hours and then cooled down to room temperature; the mixture was taken out, grinded once again and then put back to the muffle furnace, which was heated to a temperature of 650 C., held at this temperature for 24 hours, and then cooled to room temperature, the mixture was taken out, grinded for the third time and then put back to the muffle furnace, which was further heated to 900 C. and held at this temperature for 3 hours; the mixture was taken out and grinded to obtain the single-phase polycrystalline powder of a Cs.sub.2B.sub.4SiO.sub.9 compound;

(40) The synthesized Cs.sub.2B.sub.4SiO.sub.9 compound and a fluxing agent H.sub.3BO.sub.3PhO (in which the molar ratio of H.sub.3BO.sub.3 to PhO was 2:1) were mixed at a molar ratio 1:4 and then loaded into a 80 mm80 mm open type platinum crucible; the platinum crucible was heated to a temperature of 630 C. and held at this temperature for 45 hours to obtain a mixed melting liquid; the temperature was then decreased to 620 C. and further decreased to room temperature slowly at a rate of 6.5 C./h, allowing for spontaneous crystallization to obtain a Cs.sub.2B.sub.4SiO.sub.9 seed crystal;

(41) The obtained Cs.sub.2B.sub.4SiO.sub.9 seed crystal was attached onto a seed crystal rod for forming the seed crystal from the top of a crystal growing furnace; the seed crystal was preheated on the surface of the mixed melting liquid for 15 minutes, and then immersed underneath the liquid surface so that the seed crystal was remelted in the mixed melting liquid; the temperature was kept for 15 minutes, and then decreased rapidly to a temperature of 615 C.;

(42) The temperature was further decreased slowly at a rate of 2 C./day; after the crystal grown up to a desired size, the crystal was drawn out of the liquid surface and cooled to room temperature at a rate of 50 C./h; the crystal was then removed from the furnace and thus a colorless and transparent Cs.sub.2B.sub.4SiO.sub.9 crystal was obtained.

Example 10

(43) A Cs.sub.2B.sub.4SiO.sub.9 compound was synthesized according to the following reaction equation:
2CsHCO.sub.3+SiO.sub.2+2B.sub.2O.sub.3.fwdarw.Cs.sub.2B.sub.4SiO.sub.9+2CO.sub.2

(44) CsHCO.sub.3, SiO.sub.2 and B.sub.2O.sub.3 were put into a mortar at a molar ratio of 2:1:2, mixed uniformly, grinded carefully, and then loaded into a 100 mm100 mm open type corundum crucible; the corundum crucible was placed into a muffle furnace, which was heated slowly to a temperature of 550 C., held at this temperature for 24 hours and then cooled down to room temperature; the mixture was taken out, grinded once again and then put back to the muffle furnace, which was heated to a temperature of 650 C., held at this temperature for 24 hours, and then cooled to room temperature; the mixture was taken out, grinded for the third time and then put back to the muffle furnace, which was further heated to 700 C. and held at this temperature for 96 hours; the mixture was taken out and grinded to obtain the single-phase polycrystalline powder of a Cs.sub.2B.sub.4SiO.sub.9 compound;

(45) The synthesized Cs.sub.2B.sub.4SiO.sub.9 compound and a fluxing agent Cs.sub.2CO.sub.3PhO (in which the molar ratio of Cs.sub.2CO.sub.3 to PhO was 2:1) were mixed at a molar ratio 3:2 and then loaded into a 80 mm80 mm open type platinum crucible, the platinum crucible was heated to a temperature of 900 C. and held at this temperature for 5 hours to obtain a mixed melting liquid, the temperature was then decreased to 750 C. and further decreased to room temperature slowly at a rate of 4.0 C./h, allowing for spontaneous crystallization to obtain a Cs.sub.2B.sub.4SiO.sub.9 seed crystal;

(46) The obtained Cs.sub.2B.sub.4SiO.sub.9 seed crystal was attached onto a seed crystal rod for forming the seed crystal from the top of a crystal growing furnace, the seed crystal was preheated on the surface of the mixed melting liquid for 20 minutes, and then immersed underneath the liquid surface so that the seed crystal was remelted in the mixed melting liquid; the temperature was kept for 25 minutes, and then decreased rapidly to a temperature of 745 C.;

(47) The temperature was further decreased slowly at a rate of 3 C./day; after the crystal grown up to a desired size, the crystal was drawn out of the liquid surface and cooled to room temperature at a rate of 45 C./h; the crystal was then removed from the furnace and thus a colorless and transparent Cs.sub.2B.sub.4SiO.sub.9 crystal was obtained.

Example 11

(48) A Cs.sub.2B.sub.4SiO.sub.9 compound was synthesized according to the following reaction equation:
Cs.sub.2C.sub.2O.sub.4+SiO.sub.2+2B.sub.2O.sub.3.fwdarw.Cs.sub.2B.sub.4SiO.sub.9+CO.sub.2+CO

(49) Cs.sub.2C.sub.2O.sub.4, SiO.sub.2 and B.sub.2O.sub.3 were put into a mortar at a molar ratio of 1:1:2, mixed uniformly, grinded carefully, and then loaded into a 100 mm100 mm open type corundum crucible; the corundum crucible was placed into a muffle furnace, which was heated slowly to a temperature of 550 C., held at this temperature for 24 hours and then cooled down to room temperature; the mixture was taken out, grinded once again and then put back to the muffle furnace, which was heated to a temperature of 650 C., held at this temperature for 24 hours, and then cooled to room temperature; the mixture was taken out, grinded for the third time and then put back to the muffle furnace, which was further heated to 810 C. and held at this temperature for 36 hours; the mixture was taken out and grinded to obtain the single-phase polycrystalline powder of a Cs.sub.2B.sub.4SiO.sub.9 compound;

(50) The synthesized Cs.sub.2B.sub.4SiO.sub.9 compound and a fluxing agent Cs.sub.2CO.sub.3 were mixed at a molar ratio 1:3 and then loaded into a 80 mm80 mm open type platinum crucible, the platinum crucible was heated to a temperature of 800 C. and held at this temperature for 50 hours to obtain a mixed melting liquid; the temperature was then decreased to 720 C. and further decreased to room temperature slowly at a rate of 4 C./h, allowing for spontaneous crystallization to obtain a Cs.sub.2B.sub.4SiO.sub.9 seed crystal;

(51) The obtained Cs.sub.2B.sub.4SiO.sub.9 seed crystal was attached onto a seed crystal rod for forming the seed crystal from the top of a crystal growing furnace; the seed crystal was preheated on the surface of the mixed melting liquid for 20 minutes, and then immersed underneath the liquid surface so that the seed crystal was remelted in the mixed melting liquid; the temperature was kept for 25 minutes, and then decreased rapidly to a temperature of 715 C.;

(52) The temperature was further decreased slowly at a rate of 2 C./day, after the crystal grown up to a desired size, the crystal was drawn out of the liquid surface and cooled to room temperature at a rate of 25 C./h; the crystal was then removed from the furnace and thus a colorless and transparent Cs.sub.2B.sub.4SiO.sub.9 crystal was obtained.

Example 12

(53) The Cs.sub.2B.sub.4SiO.sub.9 crystal obtained in any one of Examples 1-11 was processed in a phase-matching orientation into a frequency doubling device with a size of 5 mm5 mm6 mm, and disposed at the position of 3 as shown in FIG. 2. At room temperature, a Q-switched Nd:YAG laser generator was used as a light source and the incident light had a wavelength of 1064 nm. The infrared light beam 2 with a wavelength of 1064 nm emitted by the Q-switched Nd:YAG laser generator 1 shot into the Cs.sub.2B.sub.4SiO.sub.9 single crystal 3 to generate a green frequency doubling light with a wavelength of 532 nm which has an output intensity 5 times as stronger as that of KDP under the equivalent conditions. The output beam 4 comprising the infrared light with a wavelength of 1064 nm and the green light with a wavelength of 532 nm was filtered by a filter 5 to obtain a green laser with a wavelength of 532 nm.