Holmium, praseodymium and scandium doped composite calcium fluoride single crystal and preparation method and application thereof

Abstract

The invention belongs to the technical field of laser materials, and relates to a holmium, praseodymium and scandium doped composite calcium fluoride single crystal and a preparation method and application thereof, the chemical formula of the composite calcium fluoride single crystal is Ho < 0.01 > Pr < x > Scy Ca < 0.99-x-y > F < 2.01 + x + y, x is more than or equal to 0.005 and less than or equal to 0.015, and y is more than or equal to 0.005 and less than or equal to 0.05; the crystal is grown in a vacuum environment by adopting a temperature gradient method. Compared with the prior art, high-efficiency laser output can be realized in the middle infrared band of 2-3 microns, and the grown crystal has the characteristics of high thermal conductivity, high chemical stability, high transmittance, high quality and the like, and has the advantages of high gain bandwidth, high gain section, high power, high slope efficiency and the like in the middle infrared band; the method has remarkable advantages in the fields of environmental monitoring, industrial processing, national defense, safety and the like.

Description

Technical Field

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

[0002] Mid-infrared lasers are becoming one of the hot research fields in optics and laser technology due to their unique optical properties and broad application prospects. This wavelength band covers the core region of molecular characteristic absorption peaks, such as the strong absorption bands of molecules like water, ammonia, and methane. Therefore, it has significant advantages in fields such as spectral analysis, environmental monitoring, and gas sensing. Lasers in this wavelength band also play an important role in the medical field, especially in surgical cutting, tissue ablation, and non-invasive diagnosis. Due to their high absorption efficiency for water in biological tissues, they can achieve high-precision and low-damage treatment effects. 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 difficult to process. In the field of national defense and security, lasers in this wavelength band are used in technologies such as laser communication, infrared countermeasure, and target detection due to their excellent atmospheric transmission performance and low scattering characteristics. Mid-infrared lasers are also used in basic scientific research to explore the mechanism of light-matter interaction and promote the development of new materials and new technologies.

[0003] Ho3+-doped mid-infrared laser materials have unique characteristics and advantages in laser technology. Due to its rich energy level structure and effective excited state characteristics, Ho3+ ions can achieve efficient laser output in the 2 - 3μm mid-infrared wavelength band, especially with outstanding laser performance near 2.1μm. In addition, the energy level transition characteristics of Ho3+ ions also make it suitable for high-efficiency long-wavelength laser operation with low non-radiative transition losses. Compared with laser materials doped with other ions (such as Er 3 + and Tm 3 +), Ho-ion-doped materials have higher energy conversion efficiency in the mid-infrared wavelength band and stronger adaptability to pump light sources, especially showing better performance in diode-pumped systems. In addition, Ho3+-doped materials have a longer fluorescence lifetime, which helps to achieve high gain and high power output and is suitable for more complex laser cavity designs.

[0004] However, for Ho 3+ ions, the research on the ~2μm wavelength band is relatively mature. As early as 1965, Ho 3+ ions achieved laser output at this wavelength in a YAG crystal. Currently, high-power laser output with a maximum output power of 146W and a highest slope efficiency of 89.2% has also been achieved in this wavelength band. For the ~3μm wavelength band, Ho 3+There has been relatively little research on ion-doped laser gain media because Ho 3+ ions have rich energy levels, which easily lead to non-radiative transitions, excited-state absorption, and cross-relaxation. At the same time, due to the fact that the lifetime of the lower energy level of the 3μm emission of Ho 3+ ions is much longer than that of the upper energy level, resulting in the "self-termination" effect. Therefore, it is necessary to select a host material with a relatively weak crystal field strength and a relatively low phonon energy.

[0005] The prior art CN115261986A discloses a laser material, specifically a holmium and praseodymium co-doped scandium oxide mid-infrared band laser crystal and its preparation method and application. The chemical formula of the crystal is (Ho x Pr y Sc 1-x-y )2O3, where x is 0.001 - 0.05 and y is 0.0001 - 0.01; the crystal is of cubic crystal system. By co-doping holmium and praseodymium into the crystal, the population of the lower energy level 3+ I7 of the 3μm laser of Ho 5 ions is effectively reduced, and its energy level lifetime is effectively decreased. However, there is still a problem that the difference between the lower energy level lifetime and the upper energy level lifetime is relatively large, and the "self-termination" effect cannot be well suppressed, which affects its application as a mid-infrared laser crystal. At the same time, the melting point of (Ho x Pr y Sc 1-x-y )2O3 is as high as 2400°C, which poses a high challenge to crystal growth. The excessively high melting point makes it difficult to grow large-size high-quality single crystals with high throughput, which also limits the further application of the holmium and praseodymium co-doped scandium oxide crystal. Summary of the Invention

[0006] The purpose of the present invention is to provide a preparation method and application of a holmium, praseodymium, and scandium co-doped composite calcium fluoride single crystal, which is used to solve the problem of how to suppress the "self-termination" effect of mid-infrared laser materials doped with Ho3+ ions in the ~3μm band. The prepared crystal has excellent crystal quality and high-power mid-infrared laser output ability.

[0007] The purpose of the present invention can be achieved through the following technical solutions:

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

[0009] The present invention uses Ho 3+ ions as luminescent ions in the mid-infrared band and Pr3+ ions as Ho 3+ ions as the deactivating ions of 3+ ions, and Sc

[0010] ions as the structure regulating ions of the crystal structure. The prepared laser crystal can achieve efficient laser output in the mid-infrared band of 2-3 μm. The grown crystal has characteristics such as high thermal conductivity, high chemical stability, high transmittance, and high quality. At the same time, it has advantages such as high gain bandwidth, high gain cross-section, high power, and high slope efficiency in the mid-infrared band, and has significant advantages in the fields of environmental monitoring, industrial processing, national defense, and security.

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

[0012] In some specific embodiments, the temperature gradient method is specifically the porous graphite crucible temperature gradient method, including 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 accurately weigh it, and then weigh and add PbF2 powder;

[0014] (2) After weighing the above raw materials, grind and mix them evenly, then load them into a porous graphite crucible and cover the crucible lid;

[0015] (3) Load the crucible into the hot field, start the vacuum pump to pump the furnace cavity to high vacuum, and maintain high vacuum throughout the crystal growth process, then start the power supply and heat up to the target temperature according to the heating program, and keep it at a constant temperature until the raw materials are fully melted and the impurity removal is completed;

[0016] (4) Start the slow cooling process for crystal growth, ensure that the crystal grows fully and the thermal stress is removed, and then perform 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 respectively adopt single crystal particles or powdered raw materials.

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

[0019] In some specific embodiments, in the mixing, PbF2 is further added, and the dosage is 0.1 - 2% of the total mass of the raw materials. The PbF2 is used as a water and oxygen remover in the raw materials.

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

[0021] In some specific embodiments, in the crucible and the crucible cover for growth, the center of the crucible cover has a vent hole with a diameter of 0.8 - 1.2 mm, which is used to remove impurities during the growth process.

[0022] In some specific embodiments, the growth of the crystal includes: heat preservation treatment at 1400 - 1500 °C, then slowly cooling to 1000 - 1100 °C, and then rapidly cooling.

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

[0024] In some specific embodiments, during the heat preservation treatment, the heat preservation time is 10 - 20 h.

[0025] In some specific embodiments, during the slow cooling, the cooling rate is 0.5 - 2 °C / h.

[0026] In some specific embodiments, during the rapid cooling, the cooling rate is 20 - 30 °C / h.

[0027] The 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 for preparing a mid - infrared band laser, which can be applied to fields such as space exploration, atmospheric exploration, pollution monitoring, and biomedicine.

[0028] Based on the Ho:CaF2 single crystal, the present invention selects Pr 3+ ions as deactivating ions to achieve rapid pumping of the population in the lower energy level, inhibit the "self - termination" effect, and achieve population inversion; at the same time, Sc 3+ ions are doped to regulate the local coordination structure of Ho 3+ ions to form a weak field, which is more conducive to obtaining high - efficiency 3 - μm band laser output. Finally, a composite calcium fluoride single crystal with better crystal quality and higher - power mid - infrared laser output ability is prepared.

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

[0030] The present invention provides a composite calcium fluoride single crystal doped with holmium, praseodymium and scandium, which has low matrix phonon energy, high thermal conductivity and high output power. It has the advantages of high chemical stability, high transmittance (reaching more than 90% in the visible to mid-infrared band), low phonon energy, low melting point (1400 - 1500 °C), high thermal conductivity, etc. It can achieve efficient mid-infrared band laser output, and at the same time has a high gain bandwidth (>100 nm), high gain cross-section (~3 μm band, 10 -20 cm 2 magnitude), high power (>10 W) and high slope efficiency (theoretical efficiency >80%) in the mid-infrared band, and is more suitable for applications in laser medicine, environmental monitoring, industrial processing, national defense and security and other fields as an optical parametric oscillation (OPO) pump source to achieve the output of mid-infrared lasers in the range of 3 - 15 μm;

[0031] A holmium, praseodymium and scandium doped composite calcium fluoride infrared band laser crystal (Ho 0.01 Pr x Sc y Ca 0.99-x-y F 2.01+x+y ) provided by the present invention, under the excitation of 640 nm light, the energy level lifetime of the lower energy level 5 I7 of the ~3 μm band is 2.38 - 2.50 ms, 5 the energy level lifetime of the upper energy level I6 is 3.24 - 3.56 ms. Comparing with the 5 I7 and 5 I6 energy level lifetime relationship (17.59 ms and 3.7 ms) of Ho:CaF crystal, the gap between the lower energy level lifetime and the upper energy level lifetime is significantly shortened, and the lower energy level lifetime is lower than the upper energy level lifetime, realizing population inversion, avoiding the "self-termination" caused by 5 the energy level lifetime of the upper energy level I6 being much lower than 5 the energy level lifetime of the lower energy level I7, making it possible to achieve efficient laser output in the ~3 μm band. It can be known that Pr ions and Sc ions are successfully co-doped into the crystal, playing the role of deactivating ions and effectively suppressing the "self-termination" effect.

[0032] The present invention grows a holmium, praseodymium and scandium doped composite calcium fluoride single crystal by the temperature gradient method based on a porous graphite crucible, and the growth is carried out in a high vacuum atmosphere. Compared with existing technologies such as the guided mode method, the Czochralski method and the micro-pulling method, it has the advantages of easy growth, low preparation difficulty and can prepare various large-size single crystals with high throughput. Description of the Drawings

[0033] Figure 1 For the Ho 0.01 Pr 0.001 Sc 0.02 Ca 0.969F 2.031 X-ray diffraction pattern of;

[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 to 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 Under the excitation of 640nm red light, 5 I7→ 5 Fluorescence spectrum corresponding to the I8 energy level transition;

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

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

[0039] Figure 7 Ho prepared in Example 1 0.01 Pr 0.001 Sc 0.02 Ca 0.969 F 2.031 Under the excitation of 640nm red light,5 Energy level lifetime decay curve of I6 energy level. Detailed implementation mode

[0040] The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments. This embodiment is implemented on the premise of the technical solution of the present invention, and the detailed implementation mode and specific operation process are given, but the protection scope of the present invention is not limited to the following embodiments.

[0041] The following are more detailed implementation cases, 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 material reagents or treatment techniques are all conventional commercially available products or conventional treatment techniques in the art.

[0043] Example 1:

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

[0045] 1. Accurately weigh 141.656 g of CaF2, 4.155 g of HoF3, 0.371 g of PrF3 and 3.818 g of ScF3 according to the corresponding stoichiometric ratio of the chemical formula Ho 0.01 Pr 0.001 Sc 0.02 Ca 0.969 F 2.031 and weigh 1.5 g of PbF2 as a water and oxygen remover. All the raw materials used are polycrystalline raw materials with a purity of 99.99% and the weighing error does not exceed 0.001 g;

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

[0047] 3. Install the graphite crucible into the hot field, first use a mechanical pump to pump the air pressure in the furnace cavity to a low vacuum of 10 Pa, and then start the molecular pump to pump the furnace cavity to a high vacuum of 1.0×10 -4 Pa, start the power supply and heat up to 1450 °C at a rate of 450 °C / h and keep it at a constant temperature for 12 h;

[0048] 4. Start the slow cooling process for crystal growth at a rate of 1.5 °C / h, start the fast cooling process at a rate of 30 °C / h after the temperature drops to 1050 °C, and take out the crystal after cooling to room temperature.

[0049] Comparative Example 1:

[0050] A method for growing Ho 0.01 Ca 0.99 F 2.01 is different from Example 1 only in that:

[0051] 1. Weigh CaF2 and HoF3 accurately according to the stoichiometric ratio corresponding to the chemical formula Ho 0.01 Ca 0.99 F 2.01 ; the rest is the same as in Example 1.

[0052] Comparative Example 2:

[0053] A method for growing Ho

[0054] is different from Example 1 only in that: 0.01 Pr 0.001 Ca 0.989 F 2.011 1. Weigh CaF2, HoF3, and PrF3 accurately according to the stoichiometric ratio corresponding to the chemical formula Ho

[0055] ; the rest is the same as in Example 1. 0.01 Pr 0.001 Ca 0.989 F 2.011 Comparative Example 3:

[0056] A method for growing Ho

[0057] is different from Example 1 only in that:

[0058] 1. Weigh CaF2, HoF3, and ScF3 accurately according to the stoichiometric ratio corresponding to the chemical formula Ho 0.01 Sc 0.02 Ca 0.97 F 2.03 ; the rest is the same as in Example 1.

[0059] 1. Weigh CaF2, HoF3, and ScF3 accurately according to the stoichiometric ratio corresponding to the chemical formula Ho 0.01 Sc 0.02 Ca 0.97 F 2.03 ; the rest is the same as in Example 1.

[0060] Comparative Example 4:

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

[0062] like Figure 2 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 peak, the crystal maintains a transmittance of more than 90% in the visible to mid-infrared bands, proving that the crystal is of high quality.

[0063] like Figure 3 Shown is Ho 0.01 Pr 0.001 Sc 0.02 Ca 0.969 F 2.031 The absorption coefficient spectrum of Ho 3+ The ions have characteristic absorption peaks at 1150nm and 1940nm, which correspond to commercial pump sources.

[0064] like Figure 4 and Figure 5 Shown is Ho 0.01 Pr 0.001 Sc 0.02 Ca 0.969 F 2.031 The room temperature fluorescence spectra in the ~2μm and ~3μm bands, where the equivalent emission cross section of the crystal in the ~3μm band reaches 10 -20 cm 2 The magnitude is 1.056×10 -20 cm 2 .

[0065] like Figure 6 and Figure 7 Shown is Ho 0.01 Pr 0.001 Sc 0.02 Ca 0.969 F 2.031 exist 5 I7 and 5 Energy level lifetime spectrum of I6, where the crystal is 5 The lifetime of the lower level of I7 is 2.41ms, which is similar to that of Ho 0.01 Ca 0.99 F 2.01 Compared with 17.59ms of 5 The deactivation effect of the lower energy level of I7; the crystal 5 The 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 with 3.7 ms of 5 I6 upper energy level, this crystal has a better energy storage effect, and the calculated spectral quality factor of this crystal in the ~3 μm band is 3.611×10 -20 cm 2 ·ms, which is much higher than 2.41×10 0.01 Pr 0.001 Ca 0.989 F 2.011 cm -20 ·ms of 2 Combined with the shorter 5 I7 lower energy level lifetime and larger spectral quality factor, this proves that the crystal can achieve more efficient laser output in the ~3 μm band.

[0066] Example 2:

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

[0068] Accurately weigh polycrystalline raw materials with a total weight of 150 g according to the stoichiometric ratio corresponding to the chemical formula Ho 0.01 Pr 0.001 Sc 0.03 Ca 0.968 F 2.032 , and use 1% of the total weight of PbF2 as the water and oxygen remover. The rest is the same as in Example 1.

[0069] After cutting and polishing, a crystal with good optical quality is obtained. The optical transmittance is more than 90%. Its emission cross-section in the ~3 μm band reaches 10 -20 cm 2 order of magnitude, which is 1.072×10 -20 cm 2 . The 5 I6 upper energy level lifetime of the sample is 3.31 ms, and the calculated spectral quality factor is 3.548×10 -20 cm 2 ·ms, which has a relatively high improvement compared with 2.41×10 0.01 Pr 0.001 Ca 0.989 F 2.011 cm -20 ·ms of 2 . At the same time, its 5 I7 lower energy level lifetime is 2.50 ms. The large spectral quality factor and short lower energy level lifetime are very beneficial to the laser output in the ~3 μm band.

[0070] Example 3:

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

[0072] Weigh precisely a total of 150 g of polycrystalline raw materials according to the stoichiometric ratio corresponding to the chemical formula Ho 0.01 Pr 0.001 Sc 0.05 Ca 0.966 F 2.034 and use PbF2 with a total weight of 1% as a water and oxygen remover. The rest is the same as in Example 1.

[0073] After cutting and polishing, a crystal with good optical quality is obtained. The optical transmittance is above 90%. Its emission cross-section in the ~3μm band reaches 10 -20 cm 2 order of magnitude, which is 1.058×10 -20 cm 2 . For the sample, 5 the upper level lifetime of I6 is 3.56 ms, and the calculated spectral quality factor is 3.766×10 -20 cm 2 ·ms, showing a relatively high improvement compared with 2.41×10 0.01 Pr 0.001 Ca 0.989 F 2.011 of -20 cm 2 ·ms. At the same time, its 5 lower level lifetime of I7 is 2.38 ms. The large spectral quality factor and short lower level lifetime are very conducive to laser output in the ~3μm band.

[0074] The above description of the embodiments is for those of ordinary skill in the art to understand and use the invention. It is obvious that those skilled in the art can easily make various modifications to these embodiments and apply the general principles described herein to other embodiments without creative work. Therefore, the present invention is not limited to the above embodiments, and the improvements and modifications made by those skilled in the art without departing from the scope of the present invention should be within the protection scope of the present invention.

Claims

1. A composite calcium fluoride single crystal doped with holmium, praseodymium and scandium, characterized in that: 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 , where 0.005≤x≤0.015, 0.005≤y≤0.

05.

2. The holmium-praseodymium-scandium doped composite calcium fluoride single crystal according to claim 1, characterized in that: The composite calcium fluoride single crystal belongs to the cubic system, and the unit cell parameters are 3. A method for preparing a composite calcium fluoride single crystal doped with holmium, praseodymium and scandium as claimed in claim 1 or 2, characterized in that: include: HoF3, PrF3, ScF3 and CaF2 are mixed as raw materials and crystals are grown in a vacuum environment using a temperature gradient method.

4. The method for preparing the holmium-praseodymium-scandium doped composite calcium fluoride single crystal according to claim 3, characterized in that: During the mixing, PbF2 is also added in an amount of 0.1-2% of the total mass of the raw materials.

5. The method for preparing the holmium-praseodymium-scandium doped composite calcium fluoride single crystal according to claim 3, characterized in that: The crystal growing process comprises: heat preservation treatment at 1400-1500° C., slowly cooling down to 1000-1100° C., and then rapidly cooling down.

6. The method for preparing the holmium-praseodymium-scandium doped composite calcium fluoride single crystal according to claim 5, characterized in that: Before the heat preservation treatment, the heating rate is 400-500°C / h.

7. The method for preparing the holmium-praseodymium-scandium doped composite calcium fluoride single crystal according to claim 5, characterized in that: In the heat preservation treatment, the heat preservation time is 10-20 hours.

8. The method for preparing the holmium-praseodymium-scandium doped composite calcium fluoride single crystal according to claim 5, characterized in that: In the slow cooling, the cooling rate is 0.5-2°C / h.

9. The method for preparing the holmium-praseodymium-scandium doped composite calcium fluoride single crystal according to claim 5, characterized in that: In the rapid cooling, the cooling rate is 20-30°C / h.

10. An application of the holmium-praseodymium-scandium doped composite calcium fluoride single crystal as claimed in claim 1 or 2, characterized in that: The composite calcium fluoride single crystal is used for preparing a mid-infrared band laser.

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