CN1355333A - Method for growing titanium gem crystal - Google Patents

Abstract

A process for growing titanium gem crystal features that it is growing in nitrogen-helium mixed gas, and it is annealed in high-temp. hydrogen and then in lower-temp. air for improving the optical quality and quality factor of titanium gem.

Description

The growth method of titanium gem crystal

The present invention relates to field of crystal growth, more particularly, relate to the growth and the heat treating method of titanium-doped sapphire (hereinafter to be referred as the titanium jewel) laser crystals.

Titanium jewel (molecular formula Ti ³⁺: Al ₂O ₃, english abbreviation Ti: Sapphire) be a kind of widely used tunable laser crystal, its matrix is sapphire (Sapphire), and active ions are titanium ion (Ti ^{+ 3}).During this crystal growth, have two more special problems to need conscientiously to solve: 1, because Ti ^{+ 3}Its metathetical of ratio of ionic radii Al ^{+ 3}Ion very large many (big about 26%) is so Ti ^{+ 3}Ion is at Al ₂O ₃Segregation coefficient in the melt very little (about 0.1) easily produces scattering particles shape defectives such as bubble, Bao Guoti in the process of growth; 2, titanium ion can Ti ^{+ 2}, Ti ^{+ 3}, and Ti ^{+ 4}Three kinds of valence state forms exist, and wherein have only Ti ^{+ 3}Be only real effectively active ions.

People have proposed several method, in the production of titanium jewel, take into account the valence state of titanium ion in crystalline optical quality and the crystal.As patent EP0241614 (1987), its technology point is, in common crystal growth atmosphere (as nitrogen), add a small amount of reducing gas (as hydrogen or carbon monoxide), with reductibility of regulating growth atmosphere or the valence state (being trivalent) that oxygen partial pressure is controlled titanium ion, also improve titanium jewel optical quality simultaneously.

But subsequently, the contriver of patent EP024614 finds, the effect of controlling titanium ion valence state or raising titanium jewel quality factor in this way is very limited, the quality factor FOM that can reach mostly is 60-80, higher as not to be a lot of than the titanium jewel that under inert growth atmosphere condition, grows out, far do not reach the requirement (more than 150) of actual use.Therefore propose patent US4836453 (1989) again, thought the titanium jewel that adopts this method to grow out, still the same with the titanium jewel that under inert growth atmosphere condition, grows out, could use after must in stronger reducing atmosphere, annealing.But its effect of improving the crystal optics quality is tangible.

In fact, under the temperature of titanium jewel growth, alumina melt is to be in a kind of oxidation-reduction equilibrium state, as what in patent US4836453, point out, " wherein exist active oxygen or contain the material of active oxygen ", can produce more immediate influence to the state of oxidation of titanium, the valence state of titanium can not be controlled by the oxygen partial pressure of growth atmosphere simply.

In patent JP5-186297 (1993), then be in helium-atmosphere, to add a spot of reducing gas (as hydrogen or carbon monoxide) also to have reached similar effect.But what point out a bit is, above-mentioned two patents at crystalline size obvious difference is arranged, what EP0241614 discussed is large size titanium jewel, 4000 grams that feed intake, crystal Ф 1.5 " * 3 " (Ф 38 * 76mm); And JP5-186297 has only discussed small size titanium jewel, and feeding intake, (crystal is about about Ф 20 * 40mm for Ф 47 * 48.5mm) estimations, about 200-240 gram, because thermal stresses increases and obviously strengthens along with crystalline size the crystalline influence by the crucible volume.So the growth technique condition of the two also is not quite similar.The growth conditions that is applicable to small-crystalline differs and is applicable to the growth of macrocrystal surely.

In addition, because hydrogen and carbon monoxide explosive and carbon monoxide are toxic, these reducing gas use under titanium jewel growth temperature (more than 2050 ℃) and environment (high-temperature fusant) and exist potential safety hazard.

As for the existing method that adopts annealing to improve titanium precious stone laser efficient, as U.S. Pat 4836453 (1989), its technology point is, in the inert atmosphere that contains (20-100) % (volume) hydrogen, crystal remained on 1750-2000 ℃ the temperature enough long-time, so that the titanium ion in the crystal is converted into trivalent state as much as possible, thus the quality factor of raising titanium jewel.But the annealing in this strongly reducing atmosphere when making the titanic ionic valence condition be converted into three valence states, also can produce oxygen room or divalence titanium ion in crystal.The former reduces the residual Infrared Absorption of titanium jewel, and the latter produces new infrared absorption, is difficult to the two and takes into account.

The purpose of this patent is to propose a kind of growing method on the one hand, does not use explosive or virose hydrogen or CO (carbon monoxide converter) gas, and employing nitrogen helium gas mixture atmosphere, do not need the specific installation input,, still can improve the optical quality of titanium jewel with simple and easy to do, low-cost technology; Simultaneously, adopt the two-step annealing method, improve the annealing effect of titanium jewel.Thereby reach the final purpose of the lasing efficiency that improves Ti doped saphire.

The present invention adopts nitrogen helium gas mixture atmosphere growth titanium gem crystal, and adopts the two-step annealing method, is that the inventor creates, and does not have any prior art to mention this method so far.

The main points of the inventive method are, in the titanium gem crystal growth furnace, adopt the mixed atmosphere of inert gas nitrogen helium, and (nitrogen is 5.81 * 10 because the thermal conductivity of nitrogen and helium differs greatly ^-5Cal/sec.cm. ℃, helium then is 34.31 * 10 ^-5Cal/sec.cm. ℃), so nitrogen helium gas mixture atmosphere can be by regulating blending ratio, adjust the thermal conductivity of furnace atmosphere easily, thereby adjust the thermograde in zone, crystal growth forward position flexibly, remain the inert state of furnace atmosphere simultaneously, the titanium gem stick that grows out like this has optical quality preferably.The inventive method can be used for any growing method, preferred crystal pulling method.Another main points of the inventive method are; for the oxide crystal as the titanium jewel; under strongly reducing atmosphere, can cause the appearance in oxygen room usually near the high temperature annealing of fusing point; the present invention adopts uniquely subsequently at a lower temperature and anneals in the air; can eliminate the oxygen room of growing nonparasitically upon another plant, improve the crystalline quality.

In embodiments of the invention, the titanium jewel contains the titanium of 0.10-0.15% (at.), is high-purity Al ₂O ₃And high-purity Ti ₂O ₃Mixture melt in the iridium pot, grow out, add the thermal recovery induction heating.Raw material fusing and crystal growth are carried out under nitrogen helium gas mixture atmosphere, and melt temperature is controlled at about 2050 ℃ and kept 2-3 hour, uses corundum seed crystal pulling growth titanium jewel crystal bar then.Experiment shows when with purity nitrogen atmosphere, in the titanium jewel of growth a large amount of micro-bubbles are arranged.Adopt nitrogen helium gas mixture atmosphere by the present invention, and helium accounts for cumulative volume and reach 30% when above, microbubble mainly focuses on the core area of crystal central authorities.Reach 40% when above when helium accounts for cumulative volume, microbubble further significantly reduces, and microbubble has become a desultory line.Reach 50% when above when helium accounts for cumulative volume, microbubble disappears substantially.Further increase the helium ratio and surpass at 80% o'clock to helium, find since near the melt liquid level thermograde excessive, the crystals stress of growth is very big, the titanium jewel that takes out in the stove is at room temperature placed and cracking phenomena can be occurred in several days.Therefore, we are eliminating microbubble and are reducing need make between the crystal internal stress selection of compromise.So the proportioning of preferred nitrogen helium gas mixture atmosphere is the 50-80% that helium accounts for cumulative volume, further preferred 70-80%.

The crystal color that grows out like this is pink band violet tint, and tangible infrared remaining absorption band is arranged near the 800nm in absorption spectrum.After annealing in the strongly reducing atmosphere under the high temperature of prior art in 1850-2000 ℃ of scope, crystal color becomes dense pink, and violet tint disappears substantially.But the absorption band of 750-850nm can not be eliminated fully.Our experiment shows, if with further in air 1000-1350 ℃ of titanium gem crystal, preferred 1100-1300 ℃ inferior high temperature is annealed down, kept 24-48 hour, with 15-40 ℃/hour speed cooling, the absorption of 750-850nm is further reduced then, just can address the above problem.Thereby the laser output of titanium jewel is further enhanced.Therefore, inference thus also, issuable oxygen room or Ti during annealing in strongly reducing atmosphere ^{+ 2}, may be the another kind of factor that causes residual Infrared Absorption.

Below, will further the present invention be described, but not limit this with this with specific embodiment

Scope of invention.

Embodiment 1:

Raw material is the aluminum oxide (Al of 59 purity ₂O ₃) titanium sesquioxide (Ti of powder and 49 purity ₂O ₃) powder.Proportioning raw materials is: titanium trioxide (Ti ₂O ₃) 12 grams, aluminum oxide (Al ₂O ₃) 1200 grams.Behind the raw material uniform mixing, be pressed into bulk and place the iridium pot.Iridium pot size Ф 80 * 80mm.The iridium pot places in the laser single crystal growing furnace, is evacuated down to 5 * 10 behind the closed furnace door ^-3Pa, and under the prerequisite that keeps high vacuum, be heated to about 1/3 of crystal melting power demand, charge into then high purity nitrogen helium gas mixture body to 0.035MPa (fill the nitrogen of 59 purity earlier, fill the helium of 59 purity then, and helium in the stove is reached account for cumulative volume 50%.).Inflate the follow-up continuous raw material fusing that is warming up to, by common Czochralski grown technology seeding, shouldering, isodiametric growth and ending cooling, rotating speed 10rpm, pulling rate 0.4mm/h, grew about 25 days, and can obtain being of a size of the high-quality titanium jewel primary crystal bar of Ф (30-35) * (160-180) about mm.

Primary crystal bar is pink band violet tint, after roughing and screening, and the thermal treatment of annealing: at first at pure H ₂Annealed 48 hours for 1920 ℃ in the atmosphere, reduce to 1700 ℃ with 3-30 degree/hour speed then, reduce to room temperature with 40 ℃/hour speed again.Crystal color generation considerable change, pinkiness, the violet tint that had originally disappears greatly.From this crystal bar, choose high-quality partly, be processed into the laser bar that end face is a Brewster angle, be of a size of 6.4 * 6.4 * 16.7mm, FOM～150.With frequency multiplication YAG laser pumping, when the input laser energy was the 110mJ/ pulse, maximum laser output energy was the 36mJ/ pulse.

Then again this laser crystals is placed muffle furnace, 1100 ℃ of annealing is 36 hours in air, and reduces to room temperature with the speed that is no more than 30 ℃/hour.Again polish two logical light end faces, testing laser performance under the same conditions, maximum laser output is increased to the 45mJ/ pulse.

Embodiment 2:

The titanium gem crystal growth technique is with embodiment 1, but Ti in the melt ₂O ₃Concentration is 1.2%, and helium accounts for 70% of cumulative volume in the interior nitrogen helium gas mixture atmosphere of stove.At pure H ₂Annealing temperature in the atmosphere is 1950 ℃.From this crystal bar, choose high-quality partly, be processed into the laser bar that end face is a Brewster angle, be of a size of 8 * 9 * 24mm, FOM～180.With frequency multiplication YAG laser pumping, when the input laser energy was the 280mJ/ pulse, maximum laser output energy was the 95mJ/ pulse.

Then again this laser crystals is placed in the muffle furnace in air 1150 ℃ of annealing 24 hours, and reduces to room temperature with the speed that is no more than 20 ℃/hour.Again polish two logical light end faces, testing laser performance under the same conditions, maximum laser output is increased to the 120mJ/ pulse.

Embodiment 3:

The titanium gem crystal growth technique is with embodiment 1, but Ti in the melt ₂O ₃Concentration is 1.1%, and helium accounts for 70% of cumulative volume in the interior nitrogen helium gas mixture atmosphere of stove.At pure H ₂Annealing temperature in the atmosphere is 1950 ℃.From this primary crystal bar stock, choose high-quality partly, be processed into the titanium precious stone laser rod that the lamp pump is used, be of a size of φ 8 * 124mm, FOM～156.With the pumping of two straight tube xenon flash lamp, when intake was the 130J/ pulse, maximum laser output energy was the 1.3J/ pulse.

Then again this laser crystals is placed in the muffle furnace, in air, annealed 24 hours for 1100 ℃, and reduce to room temperature with 15 ℃/hour speed.Again polish two logical light end faces and plated film, testing laser performance under the same conditions, maximum laser output is increased to the 1.6J/ pulse.

Claims (9)

1; a kind of growth method of titanium gem crystal; proportioning mixing, extrusion forming are placed in the crucible routinely with aluminum oxide and titanium sesquioxide; in stove, grow the crystal blank under the inert atmosphere protection after the heat fused; in strongly reducing atmosphere, anneal then; it is characterized in that inert atmosphere is nitrogen helium gas mixture atmosphere in the stove.

2, the described method of claim 1 is characterized in that, the proportioning of said nitrogen helium gas mixture atmosphere is the 50-80%. that helium accounts for helium nitrogen cumulative volume.

3, the described method of claim 1 is characterized in that, the proportioning of said nitrogen helium gas mixture atmosphere is the 70-80% that helium accounts for helium nitrogen cumulative volume.

4, the described method of claim 1-3 is characterized in that, said growing method is a crystal pulling method.

5, the described method of claim 1-3 is characterized in that, said crucible is the iridium pot, adopts the induction heating method growing crystal.

6, the described method of claim 1-3 is annealed in strongly reducing atmosphere, it is characterized in that, in the strongly reducing atmosphere then anneal in air in the annealing back.

7, the described method of claim 6 is characterized in that, saidly anneals in air, is in air crystal to be heated on a certain steady temperature in the 1000-1350 ℃ of scope, keeps 24-48 hour, then with 15-40 ℃/hour speed cooling.

8, the described method of claim 7 is characterized in that, the thermostat temperature when annealing in the said air is 1100-1300 ℃.

9, the titanium gem crystal that requires one of any method to produce by aforesaid right.