A holmium-praseodymium-scandium doped composite calcium fluoride single crystal, a preparation method thereof and application thereof

Abstract

The application belongs to the technical field of laser materials, and relates to a holmium-praseodymium-scandium doped composite calcium fluoride single crystal as well as a preparation method and application thereof. 0.01 Pr x Sc y Ca 0.99‑x‑y F 2.01+x+y , wherein 0.005 <= x <= 0.015, 0.005 <= y <= 0.05; the crystal is obtained by growing the crystal in a vacuum environment through a temperature gradient method. Compared with the prior art, the application can realize high-efficiency laser output in a 2-3 mu m mid-infrared wave band, the grown crystal has the characteristics of high thermal conductivity, high chemical stability, high transmittance and high quality, and has the advantages of high gain bandwidth, high gain cross section, high power and high slope efficiency in the mid-infrared wave band, and has significant advantages in the fields of environmental monitoring, industrial processing, national defense and safety.

Description

Technical Field

[0001] This invention belongs to the field of laser materials technology, and relates to a holmium-praseodymium-scandium doped composite calcium fluoride single crystal, its preparation method and application, and particularly to a holmium-praseodymium-scandium doped composite calcium fluoride single crystal, its preparation method and its application in the preparation of mid-infrared lasers. Background Technology

[0002] Mid-infrared lasers, with their unique optical properties and broad application prospects, are becoming a hot research area in optics and laser technology. This band covers the core region of molecular characteristic absorption peaks, such as the strong absorption bands of molecules like water, ammonia, and methane, thus offering significant advantages in fields like spectral analysis, environmental monitoring, and gas sensing. Lasers in this band also play a crucial role in the medical field, particularly in surgical cutting, tissue ablation, and non-invasive diagnosis, achieving high-precision, low-damage treatment due to their high water absorption efficiency in biological tissues. In industrial processing, mid-infrared lasers can be used for precision machining and surface treatment of special materials, suitable for materials with high reflectivity or those difficult to process. In defense and security, this band of lasers, due to its superior atmospheric transmission performance and low scattering characteristics, is used in technologies such as laser communication, infrared countermeasures, and target detection. Mid-infrared lasers are also used in basic scientific research to explore the mechanisms of light-matter interaction, driving the development of new materials and technologies.

[0003] Ho3+ ion-doped mid-infrared laser materials possess unique characteristics and advantages in laser technology. With their abundant energy level structure and efficient excited-state properties, Ho3+ ions can achieve highly efficient laser output in the 2–3 μm mid-infrared band, with particularly outstanding laser performance near 2.1 μm. Furthermore, the energy level transition characteristics of Ho3+ ions make them suitable for high-efficiency long-wavelength laser operation, exhibiting low non-radiative transition losses. Compared with other ions (such as Er...), Ho3+ ions... 3 +、Tm 3 Compared to α-doped laser materials, Ho3+-doped materials exhibit higher energy conversion efficiency in the mid-infrared band and greater adaptability to pump sources, particularly demonstrating superior performance in diode-pumped systems. Furthermore, Ho3+-doped materials have a longer fluorescence lifetime, which helps achieve high gain and high power output, and is suitable for more complex laser cavity designs.

[0004] But for Ho 3+ For ions, research in the ~2μm band is relatively mature, dating back to 1965 when Ho... 3+ Ions have enabled laser output at this wavelength within the YAG crystal, and currently, high-power laser output with a maximum output power of 146W and a maximum slope efficiency of 89.2% has been achieved in this band. For the ~3μm band, Ho... 3+There is limited research on ion-doped laser gain media because Ho 3+ The ion energy levels are relatively abundant, making it easy to generate nonradiative transitions, excited-state absorption, and cross-relaxation. Simultaneously, due to Ho... 3+ The lifetime of the lower energy level of ion emission at 3 μm is much longer than that of the upper energy level, resulting in a "self-termination" effect. Therefore, it is necessary to select a matrix material with weak crystal field strength and low phonon energy.

[0005] Prior art CN115261986A discloses a laser material, specifically relating to a holmium-praseodymium co-doped scandium oxide mid-infrared laser crystal, its preparation method, and its application. The chemical formula of this crystal is (Ho... x Pr y Sc 1-x-y Holmium praseodymium (HPrO3) is used, where x is 0.001-0.05 and y is 0.0001-0.01; the crystal is cubic. By co-doping HPrO3 into the crystal, the HoO content is effectively reduced. 3+ Energy level under 3μm laser of ions 5 The reduced particle number of I7 effectively lowers its energy level lifetime. However, the significant difference between the lower and upper energy level lifetimes still exists, failing to effectively suppress the "self-termination" effect and hindering its application as a mid-infrared laser crystal. Meanwhile, (Ho...) x Pr y Sc 1-x-y The melting point of 2O3 is as high as 2400℃, which poses a great challenge to crystal growth. The excessively high melting point makes it difficult to grow large-sized, high-quality single crystals in high throughput, which also limits the further application of holmium-praseodymium co-doped scandium oxide crystals. Summary of the Invention

[0006] The purpose of this invention is to provide a method for preparing and applying a holmium-praseodymium-scandium doped composite calcium fluoride single crystal, which solves the problem of how to suppress the "self-termination" effect of Ho3+ ion-doped mid-infrared laser materials in the ~3μm band. The prepared crystal has excellent crystal quality and high-power mid-infrared laser output capability.

[0007] The objective of this invention can be achieved through the following technical solutions:

[0008] The first aspect of this invention provides a holmium-praseodymium-scandium doped composite calcium fluoride single crystal, the chemical formula of which is Ho. 0.01 Pr x Sc y Ca 0.99-x-y F 2.01+x+y , where 0.005≤x≤0.015, 0.005≤y≤0.05.

[0009] This invention uses Ho 3+ Ions, as luminescent ions in the mid-infrared band, with Pr3+ Ions as Ho 3+ Deactivation of ions, with Sc 3+ Ions serve as structure-regulating ions in crystal structures. The prepared laser crystals can achieve efficient laser output in the mid-infrared band of 2-3 μm. The grown crystals have characteristics such as high thermal conductivity, high chemical stability, high transmittance, and high quality. At the same time, they have advantages such as high gain bandwidth, high gain cross-section, high power, and high slope efficiency in the mid-infrared band, which have significant advantages in environmental monitoring, industrial processing, national defense, and security fields.

[0010] In some specific embodiments, the composite calcium fluoride single crystal belongs to the cubic crystal system with a space group of Fm-3m (225), and the corresponding cell parameters within the doping range are as follows:

[0011] A second aspect of the present invention provides a method for preparing a holmium-praseodymium-scandium doped composite calcium fluoride single crystal, comprising: mixing HoF3, PrF3, ScF3 and CaF2 as raw materials, and growing the crystal in a vacuum environment using a temperature gradient method.

[0012] In some specific embodiments, the temperature gradient method is specifically a porous graphite crucible temperature gradient method, which includes the following steps:

[0013] (1) Using HoF3, PrF3, ScF3 and CaF2, single crystal particles or powders as raw materials, according to the chemical formula Ho 0.01 Pr x Sc y Ca 0.99-x-y F 2.01+x+y Calculate the required mass of each raw material and weigh it accurately, then weigh and add PbF2 powder;

[0014] (2) After weighing the above raw materials, grind them thoroughly and mix them evenly. Then put them into a porous graphite crucible and cover the crucible with the lid.

[0015] (3) Place the crucible into the hot zone, start the vacuum pump to evacuate the furnace cavity to a high vacuum, and maintain the high vacuum throughout the crystal growth process. Then start the power supply and heat up to the target temperature according to the heating program. Maintain the temperature until the raw materials are fully melted and impurities are removed.

[0016] (4) Start the slow cooling process to grow the crystal, ensure that the crystal grows fully and eliminate thermal stress, and then carry out the fast cooling process to cool to room temperature and take out the crystal.

[0017] In some specific embodiments, the HoF3, PrF3, ScF3 and CaF2 are respectively made of single crystal particles or powdered raw materials.

[0018] In some specific embodiments, the purity of the raw material is 99.99% (4N).

[0019] In some specific embodiments, PbF2 is also added to the mixture, at a dosage of 0.1-2% of the total mass of the raw materials. The PbF2 is used as a water and oxygen removal agent in the raw materials.

[0020] In some specific implementations, the vacuum level of the vacuum environment is <3 Pa.

[0021] In some specific embodiments, the crucible and crucible lid used for growth have a vent hole with a diameter of 0.8 to 1.2 mm at the center of the crucible lid to remove impurities during the growth process.

[0022] In some specific embodiments, the crystal growth includes: holding at 1400-1500°C, then slowly cooling to 1000-1100°C, followed by rapid cooling.

[0023] In some specific implementations, the heating rate before the heat preservation treatment is 400-500℃ / h.

[0024] In some specific implementations, the heat preservation time is 10-20 hours.

[0025] In some specific implementations, the cooling rate during the slow cooling is 0.5-2℃ / h.

[0026] In some specific implementations, the rapid cooling rate is 20-30℃ / h.

[0027] A third aspect of the present invention provides an application of a holmium-praseodymium-scandium doped composite calcium fluoride single crystal, including using the composite calcium fluoride single crystal to prepare a mid-infrared laser, which can be applied to fields such as space exploration, atmospheric detection, pollution monitoring and biomedicine.

[0028] This invention selects Pr based on Ho:CaF2 single crystal. 3+ Ions, acting as deactivating ions, enable rapid pumping of the population at lower energy levels, suppressing the "self-termination" effect and achieving population inversion; simultaneously, Sc is incorporated. 3+ Ion regulation Ho 3+ The localized coordination structure of ions creates a weak field, which is more conducive to obtaining efficient 3μm band laser output. Ultimately, a composite calcium fluoride single crystal with better crystal quality and higher power mid-infrared laser output capability was fabricated.

[0029] Compared with the prior art, the present invention has the following characteristics:

[0030] This invention provides a holmium-praseodymium-scandium doped composite calcium fluoride single crystal with low matrix phonon energy, high thermal conductivity, and high output power. It possesses advantages such as high chemical stability, high transmittance (over 90% in the visible to mid-infrared band), low phonon energy, low melting point (1400–1500℃), and high thermal conductivity, enabling efficient mid-infrared laser output. Simultaneously, it exhibits a high gain bandwidth (>100nm) and a high gain cross-section (~3μm band, 10) in the mid-infrared band. -20 cm 2 With its advantages of high power (>10W) and high slope efficiency (theoretical efficiency >80%), it is more suitable for use as an optical parametric oscillator (OPO) pump source to achieve the output of mid-infrared lasers in the fields of laser medicine, environmental monitoring, industrial processing, national defense and security.

[0031] This invention provides a holmium-praseodymium-scandium doped composite calcium fluoride infrared laser crystal (Ho). 0.01 Pr x Sc y Ca 0.99-x-y F 2.01+x+y Under 640nm light excitation, the energy level in the ~3μm band 5 The energy level lifetime of the lower I7 level is 2.38–2.50 ms. 5 The energy level lifetime of the upper level in I6 is 3.24–3.56 ms, compared to that of the Ho:CaF crystal. 5 I7 and 5 The I6 level lifetime relationship (17.59 ms and 3.7 ms) shows a significant reduction in the gap between the lower and upper level lifetimes, with the lower level lifetime being shorter than the upper level lifetime. This achieves population inversion and avoids the effects of [other factors]. 5 The energy level lifetime of the upper level of I6 is much shorter than 5 The self-termination caused by the energy level lifetime of I7 makes it possible to achieve efficient laser output in the ~3μm band. It can be seen that Pr ions and Sc ions were successfully co-doped into the crystal, playing the role of deactivating ions and effectively suppressing the self-termination effect.

[0032] This invention utilizes a temperature gradient method based on porous graphite crucibles to grow holmium-praseodymium-scandium doped composite calcium fluoride single crystals. The growth is carried out in a high vacuum atmosphere. Compared with existing technologies such as the mode guiding method, Czochralski method, and micro-pull-down method, this invention has the advantages of easy growth, low preparation difficulty, and high throughput preparation of various large-size single crystals. Attached Figure Description

[0033] Figure 1 Ho prepared in Example 1 0.01 Pr 0.001 Sc 0.02 Ca 0.969F 2.031 X-ray diffraction pattern;

[0034] Figure 2 Ho prepared in Example 1 0.01 Pr 0.001 Sc 0.02 Ca 0.969 F 2.031 Transmission spectrum in the ultraviolet to mid-infrared band (200nm-3000nm);

[0035] Figure 3 Ho prepared in Example 1 0.01 Pr 0.001 Sc 0.02 Ca 0.969 F 2.031 Transmission spectrum in the visible mid-infrared band (400nm-3000nm);

[0036] Figure 4 Ho prepared in Example 1 0.01 Pr 0.001 Sc 0.02 Ca 0.969 F 2.031 Excited by 640nm red light 5 I7→ 5 Fluorescence spectrum corresponding to the I8 level transition;

[0037] Figure 5 Ho prepared in Example 1 0.01 Pr 0.001 Sc 0.02 Ca 0.969 F 2.031 Excited by 640nm red light 5 I6→ 5 Fluorescence spectrum corresponding to the I7 level transition;

[0038] Figure 6 Ho prepared in Example 1 0.01 Pr 0.001 Sc 0.02 Ca 0.969 F 2.031 Excited by 640nm red light 5 The lifetime decay curve of the I7 level;

[0039] Figure 7 Ho prepared in Example 1 0.01 Pr 0.001 Sc 0.02 Ca 0.969 F 2.031 Excited by 640nm red light5 The lifetime decay curve of the I6 level. Detailed Implementation

[0040] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. These embodiments are based on the technical solution of the present invention and provide detailed implementation methods and specific operating procedures. However, the scope of protection of the present invention is not limited to the following embodiments.

[0041] The following are more detailed implementation examples, which further illustrate the technical solution of the present invention and the technical effects that can be obtained.

[0042] In the following embodiments, unless otherwise specified, the raw materials, reagents or processing techniques are all conventional commercial products or conventional processing techniques in the art.

[0043] Example 1:

[0044] A temperature gradient method for growing Ho 0.01 Pr 0.001 Sc 0.02 Ca 0.969 F 2.031 The method includes the following steps:

[0045] 1. According to the chemical formula Ho 0.01 Pr 0.001 Sc 0.02 Ca 0.969 F 2.031 The corresponding stoichiometric ratios were precisely measured as follows: 141.656g of CaF2, 4.155g of HoF3, 0.371g of PrF3 and 3.818g of ScF3 were weighed, and 1.5g of PbF2 was weighed as a water and oxygen removal agent. All raw materials used were polycrystalline raw materials with a purity of 99.99% and the weighing error did not exceed 0.001g.

[0046] 2. Place the weighed raw materials into an agate mortar and grind and stir until the raw materials are fully mixed; transfer the well mixed raw materials into a porous graphite crucible;

[0047] 3. Place the graphite crucible into the heating zone. First, use a mechanical pump to evacuate the furnace cavity to a low vacuum of 10 Pa. Then, turn on the molecular pump to evacuate the furnace cavity to a pressure of 1.0 × 10 Pa. -4 Under high vacuum of Pa, the power supply was started to heat the temperature to 1450℃ at a rate of 450℃ / h and held at that temperature for 12h.

[0048] 4. Start the slow cooling process at a rate of 1.5℃ / h to grow crystals. After the temperature drops to 1050℃, start the fast cooling process at a rate of 30℃ / h. Remove the crystals after they have cooled to room temperature.

[0049] Comparative Example 1:

[0050] A temperature gradient method for growing Ho 0.01 Ca 0.99 F 2.01 The method differs from that in Example 1 only in that:

[0051] 1. According to the chemical formula Ho 0.01 Ca 0.99 F 2.01 Weigh out CaF2 and HoF3 precisely according to their corresponding stoichiometric ratios;

[0052] The rest is the same as in Example 1.

[0053] Comparative Example 2:

[0054] A temperature gradient method for growing Ho 0.01 Pr 0.001 Ca 0.989 F 2.011 The method differs from that in Example 1 only in that:

[0055] 1. According to the chemical formula Ho 0.01 Pr 0.001 Ca 0.989 F 2.011 Accurately weigh CaF2, HoF3, and PrF3 according to the corresponding stoichiometric ratios;

[0056] The rest is the same as in Example 1.

[0057] Comparative Example 3:

[0058] A temperature gradient method for growing Ho 0.01 Sc 0.02 Ca 0.97 F 2.03 The method differs from that in Example 1 only in that:

[0059] 1. According to the chemical formula Ho 0.01 Sc 0.02 Ca 0.97 F 2.03 Accurately weigh CaF2, HoF3, and ScF3 according to their corresponding stoichiometric ratios;

[0060] The rest is the same as in Example 1.

[0061] like Figure 1 The image shown is Ho 0.01 Pr 0.001 Sc 0.02 Ca 0.969 F 2.031 The X-ray powder diffraction pattern of the sample corresponds well with the standard diffraction pattern of CaF2, indicating that the crystal is still a single-crystal phase of CaF2. The calculated unit cell parameters of the crystal are as follows:

[0062] like Figure 2 The image shown is Ho 0.01 Pr 0.001 Sc 0.02 Ca 0.969 F 2.031 The transmittance spectrum shows that, except for Ho 3+ and Pr 3+ In addition to the characteristic absorption peaks, the crystal maintains a transmittance of over 90% in the visible and mid-infrared bands, proving that the crystal has high quality.

[0063] like Figure 3 The image shown is Ho 0.01 Pr 0.001 Sc 0.02 Ca 0.969 F 2.031 The absorption coefficient spectrum can be seen in Ho. 3+ The characteristic absorption peaks of the ions at 1150 nm and 1940 nm correspond to commercially available pump sources.

[0064] like Figure 4 and Figure 5 The image shown is Ho 0.01 Pr 0.001 Sc 0.02 Ca 0.969 F 2.031 Room temperature fluorescence spectra in the ~2μm and ~3μm wavelength ranges, with the crystal exhibiting an equivalent emission cross-section of 10-1 in the ~3μm band. -20 cm 2 The order of magnitude is 1.056 × 10⁻⁶. -20 cm 2 .

[0065] like Figure 6 and Figure 7 The image shown is Ho 0.01 Pr 0.001 Sc 0.02 Ca 0.969 F 2.031 exist 5 I7 and 5 The energy level lifetime spectrum of I6, in which the crystal is in 5 The energy level lifetime of the I7 lower level is 2.41 ms, which is similar to that of Ho. 0.01 Ca 0.99 F 2.01 Compared to 17.59ms, this crystal achieves very good performance. 5 The deactivation effect of the I7 energy level; the crystal in 5 The energy level lifetime of the upper level of I6 is 3.24 ms, which is similar to that of Ho. 0.01 Ca0.99 F 2.01 Compared to 3.7ms, this crystal... 5 The upper energy level of I6 exhibits better energy storage performance, and the spectral quality factor of this crystal in the ~3μm band is calculated to be 3.611 × 10⁻⁶. -20 cm 2 ·ms, far higher than Ho 0.01 Pr 0.001 Ca 0.989 F 2.011 2.41×10 -20 cm 2 ·ms, combined with shorter 5 The I7 energy level lifetime and larger spectral quality factor demonstrate that the crystal can achieve more efficient laser output in the ~3μm wavelength range.

[0066] Example 2:

[0067] A temperature gradient method for growing Ho 0.01 Pr 0.001 Sc 0.03 Ca 0.968 F 2.032 The method includes the following steps:

[0068] According to the chemical formula Ho 0.01 Pr 0.001 Sc 0.03 Ca 0.968 F 2.032 The corresponding stoichiometric ratio was used to accurately weigh 150g of polycrystalline raw material, with 1% PbF2 as the water and oxygen removal agent. The rest was the same as in Example 1.

[0069] After cutting and polishing, a crystal with good optical quality was obtained, with an optical transmittance of over 90% and an emission cross-section of 10 in the ~3μm wavelength band. -20 cm 2 The order of magnitude is 1.072 × 10⁻⁶. -20 cm 2 , sample 5 The lifetime of the upper level of I6 is 3.31 ms, and the calculated spectral quality factor is 3.548 × 10⁻⁶. -20 cm 2 ·ms, with Ho 0.01 Pr 0.001 Ca 0.989 F 2.011 2.41×10 -20 cm 2 It has a significant improvement over ms, and its 5 The I7 lower level lifetime is 2.50 ms. The large spectral quality factor and short lower level lifetime are very beneficial for laser output in the ~3 μm band.

[0070] Example 3:

[0071] A temperature gradient method for growing Ho 0.01 Pr 0.001 Sc 0.05 Ca 0.966 F 2.034 The method includes the following steps:

[0072] According to the chemical formula Ho 0.01 Pr 0.001 Sc 0.05 Ca 0.966 F 2.034 The corresponding stoichiometric ratio was used to accurately weigh 150g of polycrystalline raw material, with 1% PbF2 as the water and oxygen removal agent. The rest was the same as in Example 1.

[0073] After cutting and polishing, a crystal with good optical quality was obtained, with an optical transmittance of over 90% and an emission cross-section of 10 in the ~3μm wavelength band. -20 cm 2 The order of magnitude is 1.058 × 10⁻⁶. -20 cm 2 , sample 5 The lifetime of the upper level of I6 is 3.56 ms, and the calculated spectral quality factor is 3.766 × 10⁻⁶. -20 cm 2 ·ms, with Ho 0.01 Pr 0.001 Ca 0.989 F 2.011 2.41×10 -20 cm 2 It has a significant improvement over ms, and its 5 The I7 lower level lifetime is 2.38 ms. The large spectral quality factor and short lower level lifetime are very beneficial for laser output in the ~3 μm band.

[0074] The above description of the embodiments is provided to enable those skilled in the art to understand and use the invention. It will be apparent to those skilled in the art that various modifications can be made to these embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, the present invention is not limited to the above embodiments, and any improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the invention should be within the protection scope of the present invention.

Claims

1. A holmium-praseodymium-scandium doped complex calcium fluoride single crystal, characterized by, The chemical formula of the composite calcium fluoride single crystal is Ho 0.01 Pr x Sc y Ca 0.99-x-y F 2.01+x+y , wherein 0.005≤x≤0.015, 0.005≤y≤0.05; the composite calcium fluoride single crystal belongs to cubic system, and the cell parameter is a=b=c=5.4631-5.4912 Å.

2. A method of producing holmium-praseodymium-scandium doped complex calcium fluoride single crystal as claimed in claim 1, characterized by, The application relates to a composite calcium fluoride single crystal and a preparation method thereof. The crystal is grown by using a temperature gradient method in a vacuum environment, and HoF3, PrF3, ScF3 and CaF2 are used as raw materials.

3. The method of producing holmium-praseodymium-scandium doped complex calcium fluoride single crystal according to claim 2, characterized by, In the mixing process, PbF2 is added in an amount of 0.1-2% of the total mass of the raw materials.

4. The method of producing holmium-praseodymium-scandium doped complex calcium fluoride single crystal according to claim 2, characterized by, The crystal growth process comprises the following steps: heat preservation treatment at 1400-1500 DEG C, slow cooling to 1000-1100 DEG C, and then rapid cooling.

5. The method of producing holmium-praseodymium-scandium doped complex calcium fluoride single crystal according to claim 4, characterized by, Before the heat preservation treatment, the heating rate is 400-500 DEG C / h.

6. The method of producing holmium-praseodymium-scandium doped complex calcium fluoride single crystal according to claim 4, wherein In the heat preservation treatment, the heat preservation time is 10-20 h.

7. The method of producing holmium-praseodymium-scandium doped complex calcium fluoride single crystal according to claim 4, wherein In the slow cooling process, the cooling rate is 0.5-2 DEG C / h.

8. The method of producing holmium-praseodymium-scandium doped complex calcium fluoride single crystal according to claim 4, wherein In the rapid cooling process, the cooling rate is 20-30 DEG C / h.

9. Use of holmium praseodymium scandium doped complex fluorite calcium single crystals as claimed in claim 1, wherein, The composite calcium fluoride single crystal is used for preparing a middle infrared wave band laser.

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