RU2668247C1 - Method for producing crystals of solid solutions of halogenides of silver and thallia (i) - Google Patents

Abstract

FIELD: manufacturing technology.SUBSTANCE: invention relates to the production of crystals based on solid solutions of silver bromide (AgBr) and monovalent thallium iodide (TlI). Crystals are transparent from the visible to the far infrared (IR) region of the spectrum (0.5–67.0 mcm), are plastic, do not have the cleavage effect, therefore, the optical products (lenses, windows, films) are made out of them using the hot pressing method and the microstructured light guides for medium IR (2.0–25.0 mcm) are obtained using the method of extrusion. Such optical products and infrared light guides are necessary for creating fiber lasers and amplifiers, optical fiber systems for IR spectroscopy, including those in conditions of high radiation background, low-temperature IR pyrometry, for the transmission of IR radiation CO (5.3–6.2 mcm) and CO-lasers (9.2–11.4 mcm). Method involves the synthesis of solid solutions using the aqueous method, their melting and subsequent crystal growth in a growth furnace according to the Bridgman method, while in the upper zone of the growth furnace the temperature of 450–470 °C is set, in the lower zone 250–260 °C, and the crystal growth is carried out at an axial temperature gradient in the crystallization zone of 50–60 °C/cm between the upper and lower zones and at the growth rate of 0.2–0.4 mm/h. Crystals of solid solutions contain silver bromide and monovalent thallium iodide with the following ratio of ingredients, WT%: silver bromide 1.0–20.0; monovalent thallium iodide 99.0–80.0. Obtained crystals of the AgBr-TlI system, containing from 1.0 up to 20.0 WT% AgBr in TlI, have the following advantages: expanded range of crystal transparency to the far IR spectral region, that is, the spectral transmission is from 0.5 up to 67.0 mcm; the crystals are resistant to prolonged UV radiation (more than 10 hours); the crystals are resistant to radiation gamma irradiation with the dose of up to 1,000 kGy or more.EFFECT: creation of fiber lasers and amplifiers, fiber optic systems for IR spectroscopy is provided.1 cl, 2 dwg, 3 ex

Description

The proposed method relates to the field of obtaining crystals of solid solutions of silver halides and monovalent thallium, specifically to a method for producing crystals based on solid solutions of silver bromide (AgBr) and monovalent thallium iodide (TlI). The crystals are transparent (spectral transmission) from the visible to far infrared (IR) spectral regions (0.5-67.0 μm), plastic, do not have a cleavage effect, therefore optical products (lenses, windows, films) are made from them by hot pressing , and receive by extrusion microstructured optical fibers for the mid-IR range (2.0-25.0 μm). Such optical products and IR fibers are necessary for creating fiber lasers and amplifiers, fiber-optic systems for IR spectroscopy, including under conditions of increased radiation background, low-temperature IR pyrometry, and for transmitting IR radiation of CO (5.3-6.2 μm) and CO ₂ lasers (9.2-11.4 microns).

A known method of producing crystals with defects based on solid solutions of metal halides [Zhukova L.V., Zhukov V.V., Pilyugin V.P. RF patent №2287620. Claim 05/13/2005. Publ. 11/20/2006. Bull. No. 32]. Silver or thallium is used as the metal, and chlorine, bromine or iodine are used as the halogen. A multicomponent mixture for growing crystals from a melt is obtained in the form of single-phase solid solutions from aqueous solutions of 5-6 M hydrochloric acid using certain modes. For this purpose, TlCl, TlBr, TlI, AgCl, AgBr, AgI are taken in amounts corresponding to their content in solid solutions AgCl _x Br _1-x , AgCl _x Br _y I _1-xy , KRS-5, KRS-6. The transparency range of crystals is from 0.35 to 40.0 μm, their mechanical strength is increased, radiation and radiation resistance are increased compared with crystals of individual metal halides.

But the authors do not give specific values about radiation, radiation and mechanical strength, which is necessary for practical application. In addition, crystals are opaque in the far infrared spectrum, i.e. from 50 microns onwards.

It is known to grow by the Bridgman method solid solutions based on oxide, semiconductor and other materials. At the same time, crystal growth modes are developed specifically for each chemical composition of crystals and in accordance with their melting diagrams. The melting temperatures are taken into account on which the crystal growth regimes depend - the axial temperature gradient in the crystallization zone and the growth rate, which in turn is determined by the growth of the furnace [Non-stoichiometric phases based on cadmium and zinc tellurides E.N. Mozhevitin. Abstract of the candidate dissertation. Moscow, 2013.S. 12; "Crystal growth processes" A.A. Mayer. Moscow, 1999. S. 85-86].

Also known from literature is the state diagram of the AgBr-TlI system, in which the region of existence of substitutional solid solutions on the left side of the diagram is established [1. “Synthesis of new nanostructured crystals of AgBr-TlI, AgCl _x Br _1-x , including doped TlI” A.S. Korsakov, L.V. Zhukova, E.V. Zharikov, D.S. Vrublevsky, BC Korsakov. Non-ferrous metals. 2010, No. 1, S. 69-72; 2. “Thermodynamic study of crystals of the AgBr-TlI system and the preparation of infrared optical fibers of a nanocrystalline structure based on them” A.S. Korsakov, L.V. Zhukova, E.A. Korsakova, V.V. Zhukov, BC Korsakov. Non-ferrous metals. 2013, No. 4, S. 62-76]. However, at present, the melting diagram of the AgBr - TlI system has been additionally investigated and the region of existence of homogeneous solid solutions in the right part of the diagram from 1 to 33 mol% (20 wt.%) AgBr in TlI (Fig. 1), where α is solid solution of TlI in AgBr (rhombic modification; β - solid solution of TlI in AgBr (cubic modification); γ - solid solution of AgBr in γTlI (cubic modification); δ - solid solution of AgBr in δTlI (rhombic modification); λ - inclusion of the adjacent phase; X1 and X2 are chemical compounds; L is the liquid phase.

For infrared technology and fiber optics, crystals with a wider spectral range of transparency in the infrared region, increased photo and radiation resistance, and also an increased refractive index are needed. These properties are achieved with a high TlI content in AgBr, which corresponds to the right side of the AgBr - TlI system diagram.

The closest technical solution ["Crystals for IR fiber optics. "Physicochemical principles of obtaining crystals of solid solutions of silver and waist (I) halides for IR fiber optics." A. Korsakov, L. Zhukova. LAP LAMBERT Academic Publishing GmbH & Co. KG, 2011, c. 83-109], adopted as a prototype of the method for producing crystals of solid solutions of the AgBr-TlI system, includes the synthesis of solid solutions by the hydrochemical method called by the authors (TZKS) thermozone crystallization synthesis ["Method for producing highly pure substances". Zhukova L.V., Zhukov V.V., Kitaev G.A. RF patent No. 2160795. Claim 07/06/1999. Publ. 12/20/2000. Bull. No. 33], the melting of the obtained high-purity salts of solid solutions containing AgBr and TlI in the following ratio of ingredients, in wt.%:

silver bromide 88.0-99.5; monovalent thallium iodide 12.0-0.5

and subsequent crystal growth by the Bridgman method in a growth furnace at a temperature of the upper zone (BW) from 380 to 440 ° C, the lower zone (BW) from 280 to 300 ° C, while the axial temperature gradient in the crystallization zone between BH and NC is set within from 20 to 40 ° C / cm. The crystal growth rate is from 0.6 to 6.0 mm / h. But the modes of the method, namely crystal growth for the left side of the composition diagram from 0 to 12 wt.% TlI in AgBr, are not applicable to crystals corresponding to the compositions for the right side of the diagram (from 1 to 20 wt.% AgBr in TlI), where the region of existence of substitutional solid solutions with a high TlI content in the solid solution of the AgBr-TlI system is found (Fig. 1). In addition, the crystals for the left side of the diagram are not transparent in the far infrared range of the spectrum, i.e. from 50.0 μm and further, which follows from the transmission spectra of crystals of solid solutions (Fig. 2) of the composition, wt.%: 1) AgBr - 1.0, TlI - 99.0; 2) AgBr - 10.0, TlI - 90.0; 3) AgBr - 20.0, TlI - 80.0; 4) AgBr - 88.0, TlI - 12.0. The crystals have a maximum refractive index of 2.240, which is not enough to create microstructured optical fibers with an increased mode field diameter, up to 100-160 microns, to transmit high-power CO ₂ laser radiation (λ = 10.6 microns). It should also be noted that crystals and infrared optical fibers based on them are unstable to long-term ultraviolet radiation and especially to radiation gamma radiation with a dose of up to 1000 kilograms (kGy), which is required for practical use.

There is a problem of obtaining crystals based on solid solutions of silver halides and monovalent thallium, transparent from visible to far infrared, having a high refractive index, resistant to gamma radiation and long-term ultraviolet (UV) radiation.

The solution to the problem is achieved in that in the method for producing crystals of solid solutions of silver and thallium halides (I), including the synthesis of solid solutions by the hydrochemical method, their melting and subsequent crystal growth in a growth furnace according to the Bridgman method, characterized in that it is previously in the upper zone of the growth furnace set the temperature to 450-470 ° C, in the lower zone 250-260 ° C, and the crystals are grown at an axial temperature gradient in the crystallization zone of 50-60 ° C / cm between the upper and lower zones and the speed of that 0.2-0.4 mm / hr, the crystals of solid solutions contain silver bromide and iodide monovalent thallium in the following ratio of ingredients, wt.%:

silver bromide 1.0-20.0; monovalent thallium iodide 99.0-80.0.

The essence of the invention lies in the fact that, guided by the melting diagram of the AgBr-TlI system (Fig. 1), the chemical compositions of the crystals are determined for the right side of the diagram, where the region of existence of substitutional solid solutions stable at 25 ° C is determined from 1.0 to 20 wt.% AgBr in TlI. Then, hydrochemical synthesis (TZKS) of solid solutions is carried out in the form of dispersed salts, salts are loaded into ampoules, ampoules are placed in a growth furnace that implements the Bridgman method. The temperature in the upper zone (OZ) is set from 450 to 470 ° C, and in the lower zone (NC) from 250 to 260 ° C, depending on the composition of the solid solutions. The salts are melted and the ampoule is transferred from the OT to the NS at a rate of 0.2-0.4 mm / h (crystal growth rate) with an axial temperature gradient of 50-60 ° C / cm in the crystallization zone.

The existing problem is solved due to the fact that crystals of solid solutions containing from 1.0 to 20.0 wt.% AgBr in TlI and the modes of their preparation were developed. The crystals are resistant to long-term (more than 10 hours) UV irradiation (λ = 290-360 nm), radiation-resistant to gamma radiation (at a dose of more than 1000 kGy), have a high refractive index (n = 2.35-2.53 at λ = 10.6 μm), which is necessary to create various photonic-crystal structures of crystal-based optical fibers, have an expanded range of spectral transmission in the far infrared region to 67 μm. It should be noted that, due to their plasticity and lack of cleavage effect, these crystals are used to fabricate optical products (windows, prisms, lenses, films) by hot pressing and by extrusion of infrared optical fibers with an extended transmission range from 2 to 25 μm.

Example 1

The hydrochemical method performs the synthesis of single-phase solid solutions in the form of dispersed high-purity salts of the composition wt.%:

silver bromide 1.0; monovalent thallium iodide 99.0.

The salts are dried, loaded into ampoules made of Pyrex glass and placed in a growth furnace that implements the Bridgman method. Melting of salts is carried out at a temperature of the upper zone (OZ) of the furnace 470 ° C, the lower zone (NC) of the furnace 250 ° C. The ampoules with the melt are transferred in the furnace from the high-temperature region (OW) to the low-temperature region (NC) at a rate of 0.2 mm / h (crystal growth rate) and crystals are grown at a temperature axial gradient of 60 ° C / cm in the crystallization zone.

By hot pressing, an optical plate with a diameter of 10 mm, 1 mm thick, and a refractive index of 2.53 at a radiation wavelength of a CO ₂ laser (10.6 μm) is made from a part of the crystal. Spectral transmittance is from 0.56 to 67.0 μm. With ultraviolet (UV) irradiation of the plate for 10 hours or more in the wavelength range of 290-360 nm with a radiation power of 2 W, the spectral transmission does not change (Fig. 2). With gamma irradiation of a plate with a dose of up to 1000 ± 150 kGy, the spectral transmission does not change.

Example 2

Hydrochemical method get high-purity salts of the composition, wt.%:

silver bromide 10.0; monovalent thallium iodide 90.0.

Then, a crystal is grown, as in Example 1, at a temperature of ВЗ 460 ° С, НЗ 255 ° С, axial temperature gradient of 55 ° С per cm in the crystallization zone and a growth rate of 0.3 mm / h. Plates are made, a refractive index of 2.43 is measured at a wavelength of 10.6 μm, and spectral transmittance is determined, which is between 0.55 and 65.0 μm. When the UV plate is irradiated for more than 9 hours and with gamma irradiation with a dose of 950 ± 135 kGy, the spectral transmission does not change (Fig. 2).

Example 3

The experiments are carried out analogously to example 1 and grow crystals containing in wt.%:

silver bromide 20.0; monovalent thallium iodide 80.0

at a temperature of ВЗ 450 ° С, НЗ 250 ° С, axial temperature gradient of 50 ° С per cm in the crystallization zone and a growth rate of 0.4 mm / h. An optical plate is made with a refractive index of 2.35 at a radiation wavelength of a CO ₂ laser, which is irradiated with UV for more than 8 hours, and gamma radiation of more than 800 ± 120 kGy, while the spectral transmission does not change. The spectral transmission range of the plate without absorption windows is from 0.50 to 60.0 μm (Fig. 2).

Crystals of solid solutions do not grow due to polymorphic transformations when the content of silver bromide in the monovalent thallium iodide (for the right side of the system) is less than 1 wt.% Or more than 20 wt.%.

Technical result

The crystals of the AgBr-TlI system for the right side of the diagram, where stable solid solutions exist, contain from 1.0 to 20.0 wt.% AgBr in TlI, compared with crystals in the prototype composition from 0.5 to 12.0 wt.% TlI in AgBr and have the following advantages:

1. The range of transparency of crystals is expanded to the far infrared region of the spectrum, i.e. spectral transmittance is from 0.5 to 67.0 μm, in the prototype from 0.4 to 40.0 μm (Fig. 2).

2. The crystals are resistant to prolonged UV radiation (more than 10 hours).

3. The crystals are resistant to radiation gamma radiation with a dose of up to 1000 kGy or more (examples 1-3).

Claims (3)

A method of producing crystals of solid solutions of silver and thallium (I) halides, including the synthesis of solid solutions by the hydrochemical method, their melting and subsequent crystal growth in a growth furnace according to the Bridgman method, characterized in that the temperature of 450-470 ° C is first set in the upper zone of the growth furnace , in the lower zone - 250-260 ° C, and the crystal growth is carried out at an axial temperature gradient in the crystallization zone of 50-60 ° C / cm between the upper and lower zones and the growth rate of 0.2-0.4 mm / h, while solid crystals solutions contain silver bromide and monovalent thallium iodide in the following ratio of ingredients, wt.%: silver bromide 1.0-20.0; monovalent thallium iodide 99.0-80.0.

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