RU2777297C1 - Optical alkali-aluminum-borate glass ceramics with chromium ions - Google Patents

Abstract

FIELD: optical technology.

SUBSTANCE: invention relates to optical materials science and can be used in the creation of solid-state lasers, including fiber lasers, and luminescent optical materials. The claimed optical alkali-aluminum-borate glass ceramics refers to a potassium-lithium-aluminum-borate system with trivalent chromium ions and has the following composition, mol. %: Li₂O 0-25; Al₂O₃ 5-35; K₂O 0-20; B₂O₃ 30-90; Sb₂O₃ 0-6; Cr₂O₃ 0.005-0.4; NH₄F 0-5; NH₄F⋅HF 0-5.5; NH₄H₂PO₄ 0-10.

EFFECT: increase in the quantum yield and lifetime of the luminescence of the material, as well as an increase in transparency in the visible region of the spectrum of optical alkali-aluminum-borate glass ceramics with chromium ions.

1 cl, 1 ex, 6 dwg

Description

The invention relates to optical materials science and can be used to create solid-state lasers, including fiber lasers, and luminescent optical materials.

One of the most common and powerful pulsed lasers is known - a laser based on a synthetic ruby single crystal (Al ₂ O ₃ :Cr ³⁺ ). A ruby crystal in such a laser is an active element, the generating centers of which are Cr ³⁺ ions (Handbook of lasers / edited by A.M. Prokhorov. In 2 volumes. T.I. - M .: Sov. radio, 1978 . - 504 p.). The disadvantages of this optical material are the high cost and high requirements for the purity of the starting reagents, high temperatures of crystal synthesis - more than 2000 degrees, the laborious and lengthy process of growing crystals, as well as the complexity of their further processing due to high hardness. Laser elements based on a single crystal (rods, plates) are made only by grinding and polishing. The drawing of laser fibers, as well as the use of pressing and milling technologies for single crystals, is not possible due to the violation of the crystal stoichiometry when using such technologies.

Known optical glass ceramics with chromium ions of the SiO ₂ - Al ₂ O ₃ -MgO-K ₂ O system containing forsterite nanocrystals with Cr ³⁺ and Cr ⁴⁺ ions (M. Yu. Sharonov, AB Bykov, S. Owen, V. Petricevic , and R.R. Alfano, Spectroscopic study of transparent forsterite nanocrystalline glass-ceramics doped with chromium, J. Opt. Soc. Am. B, V. 21, No. 11 (2004), P. 2046-2052. The disadvantage of this material is the high synthesis temperature (1600°C) and high glass transition temperature (750-900°C), at which the formation and growth of the crystalline phase occurs. This complicates the production of glass ceramics and increases its cost. Another disadvantage is that some of the chromium ions are in the tetravalent state, which reduces the luminescence intensity in the visible region of the spectrum. The disadvantage is a narrower range of transparency of the material in the visible region of the spectrum due to the fact that the edge of the fundamental absorption band of glass ceramics lies in the spectral range of 500-600 nm.

Known optical nanoglass ceramics with chromium ions, selected as a prototype (patent RU No. 2658109, IPC G02B 1/02, priority date 04/07/2017, publication date 06/19/2018). This optical nanoglass-ceramic with chromium ions belongs to the lithium-potassium-aluminum-borate system with trivalent chromium ions and has the following composition (mol.%): Li ₂ O 0-15.0; Al ₂ O ₃ 20.0-30.0; K ₂ O 10.0-20.0; B ₂ O ₃ 40.0-60.0; Sb ₂ O ₃ 0-6.0; Cr ₂ O ₃ 0.05-0.2. The disadvantages of this optical material are its low level of transparency in the visible range of the spectrum, a small quantum yield, and short luminescence lifetimes.

The problem of increasing the quantum yield and lifetime of the luminescence of the material, as well as increasing the transparency in the visible region of the spectrum of optical alkali-aluminum-borate glass-ceramics with chromium ions is being solved.

The essence of the proposed technical solution lies in the fact that the optical alkali-aluminum-borate glass ceramics refers to the potassium-lithium-aluminum-borate system with trivalent chromium ions and has the following composition (mol.%): Li ₂ O 0-25; Al ₂ O ₃ 5-35; K ₂ O 0-20; B ₂ O ₃ 30-90; Sb ₂ O ₃ 0-6; Cr ₂ O ₃ 0.005-0.4; NH ₄ F 0-5; NH ₄ F⋅HF 0-5.5; _{NH4H2PO4 0-10 .}

Our experiments have shown that in optical alkali-aluminum-borate glass ceramics of the K ₂ O-Li ₂ O-Al ₂ O ₃ -B ₂ O ₃ system, chromium ions are in the trivalent state and are part of LiAl ₇ B ₄ O ₁₇ :Cr nanocrystals ³⁺ . This optical alkali-aluminum-borate glass-ceramic is synthesized at a temperature of 1300-1400°C, and the formation and growth of LiAl ₇ B ₄ O ₁₇ :Cr ³⁺ nanocrystals occurs in the process of two-stage heat treatment: primary, at a temperature of 400-450°C for 1-10 hours and secondary, at a temperature of 580-700°C for 10-600 minutes.

The advantages of the proposed optical alkali-aluminum-borate glass ceramics are high quantum yield and luminescence lifetime in comparison with the prototype. The advantage is also a higher level of transparency in the visible region of the spectrum in comparison with the prototype.

The set of features set forth in the formula characterizes optical alkali-aluminum-borate glass ceramics with chromium ions of the K ₂ O-Li ₂ O-Al ₂ O ₃ -B ₂ O ₃ system.

The invention is illustrated by the following figures, where:

fig. one shown photograph of optical alkali-aluminum-borate glass,

fig. 2 shows photographs of optical alkali-aluminum-borate glass containing Cr ₂ O ₃ before heat treatments (a), after primary and secondary heat treatment (b), as well as a single crystal of synthetic ruby (c),

fig. Figure 3 shows a photograph of the luminescence of optical alkali-aluminum-borate glass containing Cr ₂ O ₃ before heat treatments (a) and optical alkali-aluminum-borate glass-ceramics with chromium ions after primary and secondary heat treatment (b), as well as a photograph of the luminescence of a single crystal of synthetic ruby (c). Luminescence excitation wavelength 365 nm,

fig. 4 shows the spectra of the absorption coefficient of the prototype (a) and optical alkali-aluminum-borate glass ceramics with chromium ions after two-stage heat treatment (b),

fig. Figure 5 shows the luminescence spectra of the prototype (a) and optical alkali-aluminum-borate glass ceramics with chromium ions after two-stage heat treatment (b), as well as the luminescence spectrum of a synthetic ruby single crystal (c). Luminescence excitation wavelength 532 nm,

fig. Figure 6 shows the luminescence decay curves at a wavelength of 700 nm of the prototype (a) and optical alkali-aluminum-borate glass ceramics with chromium ions after two-stage heat treatment (b), as well as the luminescence decay curve of a synthetic ruby single crystal at a wavelength of 694 nm (c). The luminescence excitation wavelength is 532 nm.

The essence of the invention is revealed by an example, which should not be considered by the expert as limiting the claims of the invention.

Information confirming the possibility of carrying out the invention.

Example 1

To implement the invention, optical alkali-aluminum-borate glass-ceramic with chromium ions is synthesized, based on glass of the potassium-lithium-aluminum-borate system, of the following composition (mol.%): Li ₂ O 17.5; Al ₂ O ₃ 25; K ₂ O 7.5; _{B2O3 50} ; Sb ₂ O ₃ 1; Cr ₂ O ₃ 0.1.

For the synthesis of the original glass, reagents of the class ChDA, ChDA, chemical purity and high purity are used. To create reducing conditions during synthesis, NH ₄ F⋅HF with a concentration of 3.3 mol. %. The melting of the mixture is carried out at a temperature of 1300-1400°C in an air atmosphere, with stirring the melt with a platinum-rhodium stirrer. Synthesis is carried out in corundum crucibles. When carrying out the synthesis, Gero laboratory high-temperature furnaces with casting in metal molds and quartz or corundum crucibles are used. After synthesis, the glass is annealed in a muffle furnace from 400°C to room temperature.

A photograph of the synthesized optical alkali-aluminum-borate glass is shown in Fig. 1. Immediately after synthesis, alkali-aluminum-borate glass is optically transparent and has a rich green color. For the formation of LiAl nanocrystals in glass₇B_fourO₁₇:Cr³⁺carry out primary and secondary heat treatments. Heat treatment temperatures are determined using differential scanning calorimetry of the synthesized optical alkali-aluminum-borate glass. To find the optimal heat treatment parameters, the glass transition temperature and crystallization peak temperature of some compositions are determined using a Netzsch STA 449F1 Jupiter differential scanning calorimeter with an accuracy of ±10°C. Powdered glass weighing 20–50 mg is placed in a platinum crucible and scanned in the temperature range of 30–700°C at a rate of 10°C/min. The mode of primary heat treatment, corresponding to the glass transition region of the synthesized optical alkali-aluminum-borate glass, consists of heating the sample to 400-450°C and holding it for 1-10 hours at a given temperature. The secondary heat treatment mode, corresponding to the crystallization region of the synthesized optical alkali-aluminum-borate glass, consists of heating the previously heat-treated sample to 580-700°C and holding it at a given temperature for 10-600 minutes. The duration of heat treatment was determined experimentally. Primary and secondary heat treatment is carried out in program-controlled Nabertherm muffle furnaces at temperatures above the glass transition temperature of the compositions. In FIG. 2 shows photographs of optical alkali-aluminum-borate glass with Cr content₂O₃ before heat treatment (a), after primary and secondary heat treatment (b), as well as a single crystal of synthetic ruby (c). From FIG. 2 shows that after two-stage heat treatment in optical alkali-aluminum-borate glass with Cr content₂O₃ LiAl nanocrystals are formed₇B_fourO₁₇:Cr³⁺, optical alkali-aluminum-borate glass becomes optical alkali-aluminum-borate glass-ceramic and acquires a red color characteristic of Cr ions³⁺ in a crystalline matrix. In FIG. 3 shows: luminescence photograph of optical alkali-aluminum-borate glass with Cr content₂O₃ before heat treatments (a) and optical alkali-aluminum-borate glass ceramics with chromium ions after primary and secondary heat treatment (b), as well as a photograph of the luminescence of a synthetic ruby single crystal (c). The luminescence excitation wavelength is 365 nm. From FIG. It can be seen from Fig. 3 that the optical alkali-aluminum-borate glass-ceramic with chromium ions after two-stage heat treatment demonstrates a fairly intense luminescence, similar to the luminescence of a single crystal of synthetic ruby, when irradiated with ultraviolet radiation, while optical alkali-aluminum-borate glass with a Cr content₂O₃ before heat treatments does not luminesce. In FIG. four shown: spectra of the absorption coefficient of the prototype (a) and optical alkali-aluminum-borate glass ceramics with chromium ions after two-stage heat treatment (b).Registration of the absorption spectra of the original and heat-treated samples is carried out at room temperature using a two-beam spectrophotometer Lambda 650 (Perkin Elmer) in the wavelength range of 300-800 nm with a step of 1 nm. From FIG. 4 is seen that in the absorption coefficient spectrum of optical alkali-aluminum-borate glass ceramics with chromium ions there are two absorption bands characteristic of Cr ions³⁺ in a crystalline environment. Spectral measurements have shown that the edge of the fundamental absorption band of the synthesized alkali-aluminum-borate glass-ceramic lies in the spectral range of 250–380 nm. It can be seen that the absorption level of the prototype is one and a half times greater than that of optical alkali-aluminum-borate glass-ceramics after two-stage processing. In FIG. Figure 5 shows: luminescence spectra of the prototype (a) and optical alkali-aluminum-borate glass ceramics with chromium ions after two-stage heat treatment (b), as well as the luminescence spectrum of a synthetic ruby single crystal (c). The luminescence excitation wavelength is 532 nm. Luminescence spectra were recorded on an LS 55 luminescent spectrofluorimeter (Perkin Elmer). From FIG. Figure 5 shows that the luminescence spectra of optical alkali-aluminum-borate glass ceramics with chromium ions (a, b) are located in the same spectral region as the luminescence spectrum of a single crystal of synthetic ruby, which indicates the crystalline environment of Cr ions³⁺. The luminescence intensity is normalized to the value of the quantum yield: for a single crystal of synthetic ruby, the quantum yield is 90%, for optical alkali-aluminum-borate glass ceramics with chromium ions after two-stage heat treatment, the quantum yield is 50%, and for the prototype - 40%. It can be seen that the luminescence intensity and quantum yield of optical alkali-aluminum-borate glass ceramics with chromium ions after two-stage heat treatment is higher than that of the prototype. In FIG. Figure 6 shows: luminescence decay curves at a wavelength of 700 nm of the prototype (a) and optical alkali-aluminum-borate glass ceramics with chromium ions after two-stage heat treatment (b), as well as the luminescence decay curve of a synthetic ruby single crystal at a wavelength of 694 nm (c) . The luminescence excitation wavelength is 532 nm. Decay curves were recorded using a SpectraPro 300i monochromator (Princeton Instruments), a silicon-based visible light detector, and an Infiniium 4-Channel Oscilloscope oscilloscope (Agilent). Based on these decay curves, it can be calculated that the luminescence lifetime of a single crystal of synthetic ruby is about 3.3 ms, the luminescence lifetime of optical alkali-aluminum-borate glass-ceramics with chromium ions after two-stage heat treatment is 7.5 ms, and for the prototype - 5 .3 ms.

Thus, the formation of nanocrystals with chromium ions in glass is carried out in two stages, compared with the prototype. This increases the quantum yield and lifetime of the luminescence of glass ceramics with chromium ions, and also increases the level of transparency of the synthesized alkali-aluminum-borate glass ceramics in the visible region of the spectrum in comparison with the prototype.

Claims (2)

Optical alkali-aluminum-borate glass ceramics with chromium ions, characterized in that it additionally contains NH ₄ F 0-5 mol.%, NH ₄ F⋅HF 0-5.5 mol.%, NH ₄ H ₂ PO ₄ 0-10 mol.% at the following ratio of components, mol.%: _Li2O 0-25 _{Al2O3 _} 5-35 _K2O 0-20 _{B2O3 _} 30-90 _{Sb2O3 _} 0-6 _{Cr2O3 _} 0.005-0.4

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