A divalent ion regulated neodymium ion doped alkaline earth fluoride laser crystal, its preparation method and application

Abstract

This invention relates to a divalent ion-controlled neodymium ion-doped alkaline earth fluoride laser crystal, its preparation method, and its applications. The chemical formula of the laser crystal is xNd,yMe:MF2; where x ranges from 0.001 to 0.3, y ranges from 0.01 to 0.1, M is Ca or Ba, and Me is any one of Ba, Ca, or Mg, different from M. Compared with existing technologies, this invention uses divalent alkaline earth ions of the same valence state, which can break the Nd... 3+ -Nd 3+ While achieving clustering, it can also ensure that the thermal conductivity does not drop significantly. This can solve the key problems of concentration quenching caused by the clustering effect and the significant drop in thermal conductivity caused by the modulation of heterovalent ion doping in neodymium ion-doped alkaline earth fluoride laser crystals. It can accelerate the application of new alkaline earth fluorides in high repetition rate, high energy, and high-energy laser devices.

Description

Technical Field

[0001] This invention relates to the field of laser materials technology, and in particular to an alkaline earth fluoride laser crystal with divalent ion-controlled neodymium ion doping, its preparation method, and its application. Background Technology

[0002] All-solid-state high-power ultrafast lasers have significant application needs in advanced manufacturing, radar communications, high-energy physics, and cutting-edge scientific fields. Currently, rare-earth ion luminescence is mainly concentrated in Nd... 3+ Pr 3+ Dy 3+ 、Tb 3+ 、Sm 3+ Ho 3+ and Er 3+ Among the many luminescent ions, Nd... 3+ It is currently the most widely used and mature near-infrared laser ion in the 1μm range. Alkaline earth fluorides such as CaF2 and BaF2 are ideal Nd: fluorides due to their extremely wide transmission range, low phonon energy, long fluorescence lifetime, and good mechanical properties, as well as their ease of large-size crystal growth. 3+ Ion-doped laser matrix materials. Represented by CaF₂ and BaF₂, these alkaline earth fluoride crystals have melting points of 1418 °C and 1368 °C, respectively, and belong to the cubic fluorite-type structure with space group Fm-3m. The divalent alkaline earth metal cations in the matrix interact with the surrounding eight F₂ atoms. - The ions form an eight-coordinate cubic structure. This crystal not only exhibits an extremely weak lattice field and extremely low phonon energy, but also the pure alkaline earth fluoride crystal itself has extremely high thermal conductivity. For example, the room temperature thermal conductivity of pure CaF2 is close to 10 W / m·K, which is very suitable for meeting the thermal management requirements in high-power lasers.

[0003] However, when trivalent rare earth ions Nd 3+ When doped into a divalent alkaline earth fluoride matrix, a charge imbalance inevitably arises (Su, L., & Xu, J. (2006). Calcium Fluoride Crystal Materials and Their Applications. Science Press). In this case, interstitial fluoride ions are introduced into the lattice to compensate for the charge imbalance. - and Nd 3+ The electrostatic attraction between them leads to Nd 3+ Nd+ readily aggregates within the matrix lattice, forming complex aggregates and exhibiting a clustering effect. Even at extremely low doping concentrations below 1 at.%, Nd+... 3+ Clusters will also form in large quantities. On the one hand, this clustering effect will cause adjacent Nd... 3+The close proximity of ions induces strong cross-relaxation, leading to severe concentration quenching and a significant decrease in luminescence efficiency. Furthermore, large clusters within the crystal form strong defect scattering centers, severely increasing lattice phonon scattering and causing adverse reactions in Nd-doped ions. 3+ The thermal conductivity of the crystal decreased significantly. This indicates that the clustering effect is the fatal bottleneck restricting the realization of high-power, ultrafast laser output from neodymium-doped alkaline earth fluoride crystals.

[0004] Therefore, it is necessary to find an effective method that can break Nd 3+ Clustering effects can be achieved in crystals that maintain a stable or non-significant thermal conductivity, allowing for effective control of spectral and thermomechanical properties. This holds promise for further breakthroughs in Nd-doped crystals. 3+ Applications of crystals in high-repetition-rate, high-energy high-energy laser devices. Summary of the Invention

[0005] The purpose of this invention is to overcome the defects of the prior art by providing a divalent ion-controlled neodymium ion-doped alkaline earth fluoride laser crystal, its preparation method, and its application.

[0006] The objective of this invention can be achieved through the following technical solutions: The first aspect of the present invention provides a divalent ion-controlled neodymium ion-doped alkaline earth fluoride laser crystal, wherein the chemical formula of the laser crystal is xNd,yMe:MF2; Where x ranges from 0.001 to 0.3 and y ranges from 0.01 to 0.1. Where M is Ca or Ba, and Me is any one of Ba, Ca, or Mg that is different from M.

[0007] Furthermore, the chemical formula of the laser crystal is xNd,yMe:MF2; wherein x ranges from 0.01 to 0.1 and y ranges from 0.01 to 0.1.

[0008] Furthermore, the chemical formula of the laser crystal is any one of 0.5%Nd,2%Ca:BaF2, 0.5%Nd,5%Ca:BaF2, and 0.5%Nd,8%Ca:BaF2, preferably 0.5%Nd,5%Ca:BaF2.

[0009] A second aspect of this invention provides a method for preparing a neodymium-doped alkaline earth fluoride laser crystal controlled by divalent ions, the method comprising the following steps: S1: Weigh NdF3, CaF2, MgF2 and BaF2 raw materials according to the stoichiometric ratio, mix them evenly and then put them into a crucible; S2: Place the crucible in a vacuum atmosphere, heat up to melt the material and remove impurities, and then cool down to grow the crystal. S3: After growth is complete, the temperature is lowered to room temperature to obtain the alkaline earth fluoride laser crystal.

[0010] Furthermore, in step S1, the purity of the NdF3, CaF2, MgF2 and BaF2 single crystal particles or powders is 5N.

[0011] Furthermore, in step S1, PbF2 is added to the raw materials as an oxygen scavenger, and the amount of PbF2 added is 0.5~2% of the total mass of the raw materials, preferably 1%.

[0012] Furthermore, in step S2, the entire cooling growth process of the crystal is carried out in an atmosphere below 8 Pa.

[0013] Furthermore, in step S2, the heating rate is 200-300 ℃ / h, the temperature is raised to 1300-1500℃, and the holding time is 8-12h.

[0014] Furthermore, in step S2, the cooling rate of the cooling growth is 1-2 ℃ / h.

[0015] Furthermore, in step S2, the cooling range for the cooling growth is 130-170 ℃.

[0016] Furthermore, in step S3, the cooling rate to room temperature is 30-50 °C / h.

[0017] The third aspect of this invention provides an application of divalent ion-controlled neodymium ion-doped alkaline earth fluoride laser crystals in the field of high repetition rate, high energy, and high-energy lasers, such as near-infrared all-solid-state high-power femtosecond ultrafast lasers.

[0018] Compared with the prior art, the present invention has the following technical advantages: (1) The matrix CaF2 or BaF2 crystals selected in this invention belong to the cubic crystal system. Besides having an extremely wide light transmission range and low phonon energy, which effectively reduces the probability of non-radiative transitions, a series of xNd,yMe:MF2 alkaline earth fluoride laser crystals were successfully obtained by using isovalent alkaline earth metal ions (Me) for substitution and regulation. With the incorporation of non-luminescent isovalent regulating ions, the Nd transition probability can be effectively broken. 3+ -Nd 3+ Clusters between them reduce the adjacent Nd 3+ Interionic cross-relaxation and concentration quenching; reducing the amount of extra interstitial F within the lattice. - The large-size defect scattering centers caused by clusters prevent a significant decrease in thermal conductivity or maintain a "constant" thermal conductivity. Simultaneously, the diverse local lattice environments and disorder of Nd... 3+The emission energy level undergoes Stark splitting and non-uniform broadening, achieving fluorescence spectrum overlap and broadening, thus solving the problem of existing Nd-doped Nd... 3+ The key scientific challenge of alkaline earth fluorides readily forming clusters, leading to severe concentration quenching and a significant decrease in thermal conductivity, can be addressed by combining near-infrared femtosecond laser technology with effective thermal management. Further breakthroughs in Nd-doped fluorides are expected. 3+ Applications of crystals in high-repetition-rate, high-energy high-energy laser devices.

[0019] (2) The xNd,yMe:MF2 alkaline earth fluoride laser crystal prepared by this invention can achieve stronger emission gain, smaller thermal conductivity reduction or maintain "constant" thermal conductivity than conventional Nd:BaF2 or Nd:CaF2 crystals, and a wider fluorescence emission band in the near-infrared (around 1 μm), which is expected to further accelerate the Nd doping process. 3+ Applications of crystals in high-repetition-rate, high-energy high-energy laser devices and the realization of higher power, higher energy all-solid-state femtosecond laser output.

[0020] (3) The crystal material of the present invention can solve the thermal distortion barrier of neodymium-doped alkaline earth fluoride crystals under high power pumping, and can accelerate the research and development and commercial application of near-infrared all-solid-state high-power femtosecond ultrafast lasers. It can be widely used in major demand fields such as fusion energy, advanced high-end manufacturing, space radar communication, high-energy physics and biomedicine. Attached Figure Description

[0021] Figure 1 The images show the room-temperature fluorescence spectra of the laser crystals prepared in Examples 2-4 under 808 nm light excitation.

[0022] Figure 2 The fluorescence lifetime spectra of the laser crystals prepared in Examples 1-4 are shown at the emission peak at 1064 nm under 808 nm light excitation.

[0023] Figure 3 The graph shows a comparison of the thermal conductivity of the laser crystals prepared in Example 5 and Comparative Example 1 at varying temperatures from room temperature to 300 °C. Detailed Implementation

[0024] 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.

[0025] Each of the above embodiments can be implemented individually, or in any combination of two or more. The following detailed description of specific examples will further illustrate these embodiments.

[0026] Unless otherwise specified, the reagents, methods, instruments, and equipment used in this invention are conventional in the art. Unless otherwise specified, the reagents and materials used in the following examples are all commercially available.

[0027] The purpose of this invention is to overcome the problems of neodymium-doped alkaline earth fluoride crystals easily forming clusters, causing concentration quenching and a decrease in thermal conductivity. By introducing a divalent alkaline earth ion with the same valence but different radius as a control ion, neodymium ion clusters are successfully broken, thereby reducing the decrease in crystal thermal conductivity or achieving constant thermal conductivity. This invention also provides a laser crystal and its growth method, which accelerates the research and application of high-power, near-infrared all-solid-state ultrafast lasers.

[0028] Specifically, this invention provides a divalent ion-controlled neodymium ion-doped alkaline earth fluoride laser crystal with "constant" thermal conductivity. The chemical formula of the laser crystal is xNd,yMe:MF2, where x ranges from 0.001 to 0.3, y ranges from 0.01 to 0.1, M is Ca or Ba, and Me is Ba, Ca, or Mg that is different from M (i.e., forming a radius mismatch with the same valence substitution).

[0029] CaF2 and BaF2 crystals belong to the cubic fluorite crystal system, exhibiting an extremely wide transmission range and low phonon energy. When trivalent Nd... 3+ When Nd+ ions are incorporated into a divalent alkaline earth fluoride MF2 (M=Ba or Ca) matrix, interstitial fluoride ions are introduced into the lattice to maintain charge balance due to valence mismatch. 3+ With gap F - There is a strong electrostatic attraction between opposite valences among ions, Nd 3+ It readily combines with F in the matrix. - They combine and further aggregate to form complex Nd 3+ Clusters. Nd 3+ Large-size clustering effects will, on the one hand, make Nd 3+ Insufficient interionic spacing leads to strong cross-relaxation and concentration quenching. Furthermore, clusters form large defect scattering centers within the lattice, severely increasing phonon scattering and causing a significant decrease in lattice thermal conductivity, making it unsuitable for high-power laser operation. The introduction of isovalent ions does not require additional charge compensation and, as non-luminescent ions, can also break the Nd... 3+ -Nd 3+ The clustering effect between them enables its efficient luminescence.

[0030] When the clusters are broken up, it can effectively suppress Nd 3+ The concentration quenching effect of ions can significantly improve fluorescence lifetime, reduce large-size lattice defects, and significantly reduce phonon scattering in the lattice, thereby reducing the decrease in crystal thermal conductivity or maintaining constant thermal conductivity. Furthermore, the introduction of isovalent ions with different radii makes Nd...3+ The presence of a diverse local crystal field with minute differences leads to a non-uniform broadening of the Stark level, resulting in Nd... 3+ The emission spectrum is significantly broadened, which is beneficial for the generation of femtosecond-level ultrafast pulsed lasers.

[0031] The fluoride laser crystal of the present invention is grown using the temperature gradient method (or crucible descent method), which mainly includes the following steps: (1) Using single crystal particles or powders of NdF3, CaF2 and BaF3 with a purity of 5N as raw materials, calculate the required mass of each raw material according to the stoichiometric ratio and weigh them accurately.

[0032] (2) Grind the weighed raw material powder thoroughly to make it evenly mixed, then put it into a graphite crucible and cover it with a lid. Grinding is carried out in an agate mortar for 40-60 minutes; put the ground raw material into a graphite crucible and cover it with a crucible lid to prevent the large amount of volatilization of the raw material and the entry of an oxygen environment.

[0033] (3) Place the graphite crucible filled with material in a hot field and evacuate it to a vacuum level below 8 Pa. Raise the temperature to ensure complete material melting and impurity removal, then slowly cool it down to grow the crystal. After growth, cool it down to room temperature and then remove the crystal. The evacuation is performed by coarse evacuation using a mechanical pump and fine evacuation using a molecular pump. The entire crystal growth process is carried out under high vacuum.

[0034] The heating rate to ensure complete material processing and impurity removal is 200-300 ℃ / h, and the temperature is raised to 1400 ℃, with a holding time of 8-10 h.

[0035] The slow cooling program involves gradually decreasing the temperature at a rate of 1.5 °C / h, with a cooling gradient of 150 °C. This process is primarily aimed at improving crystal quality.

[0036] After the slow cooling growth is completed, the temperature is rapidly reduced to room temperature at a rate of 30-50 °C / h. This process is mainly to release the thermal stress inside the crystal.

[0037] The alkaline earth fluoride laser crystal developed in this invention is expected to further accelerate Nd-doped lasers. 3+ Applications of crystals in high-repetition-rate, high-energy high-energy laser devices and the realization of higher power, higher energy all-solid-state femtosecond laser output.

[0038] Example 1: In this embodiment, a temperature gradient method is used to grow 0.5%Nd,2%Ba:CaF2 crystals. The specific method is as follows: 150 g of raw material was placed in a graphite crucible, then the crucible was covered, and the furnace was evacuated to below 8 Pa. The temperature was then increased to ~1400 °C at a rate of 200 °C / h and held at this temperature for 10 hours until the raw material was completely melted and impurities were thoroughly removed. The temperature was then slowly decreased at a rate of 1.5 °C / h over a 150 °C range. After the slow cooling growth was complete, the temperature was rapidly reduced to room temperature at a rate of 30 °C / h. The entire growth process was carried out under high vacuum. The crystal was then removed, yielding a 0.5%Nd,2%Ba:CaF2 crystal with good optical quality.

[0039] Example 2: In this embodiment, a 0.5% Nd, 2% Ca:BaF2 crystal is grown using a temperature gradient method. The specific method is as follows: 0.5%Nd,2%Ca:BaF2 crystals were grown using a temperature gradient method. 150 g of the raw material was placed in a graphite crucible, which was then covered and the furnace was evacuated to below 8 Pa. The temperature was then increased to ~1400 °C at a rate of 200 °C / h and held at this temperature for 10 hours until the raw material was completely melted and impurities were thoroughly removed. The temperature was then slowly decreased at a rate of 1.5 °C / h over a 150 °C range. After the slow cooling growth was complete, the temperature was rapidly reduced to room temperature at a rate of 30 °C / h. The entire growth process was carried out under high vacuum. The crystal was then removed, yielding 0.5%Nd,2%Ca:BaF2 crystals with good optical quality.

[0040] Example 3: In this embodiment, a temperature gradient method is used to grow 0.5%Nd,5%Ca:BaF2 crystals. The specific method is as follows: 150 g of raw material was placed in a graphite crucible, then the crucible was covered, and the furnace was evacuated to below 8 Pa. The temperature was then increased to ~1400℃ at a rate of 200℃ / h and held at this temperature for 10 hours until the raw material was completely melted and impurities were thoroughly removed. The temperature was then slowly decreased at a rate of 1.5℃ / h over a period of 150℃. After the slow cooling growth was complete, the temperature was rapidly reduced to room temperature at a rate of 30℃ / h. The entire growth process was carried out under high vacuum. The crystal was then removed, yielding a 0.5%Nd,5%Ca:BaF2 crystal with good optical quality.

[0041] Example 4: In this embodiment, a 0.5% Nd, 8% Ca: BaF2 crystal is grown using a temperature gradient method. The specific method is as follows: 150 g of raw material was placed in a graphite crucible, then the crucible was covered, and the furnace was evacuated to below 8 Pa. The temperature was then increased to ~1400 °C at a rate of 200 °C / h and held at this temperature for 10 hours until the raw material was completely melted and impurities were thoroughly removed. The temperature was then slowly decreased at a rate of 1.5 °C / h over a period of 150 °C. After the slow cooling growth was completed, the temperature was rapidly reduced to room temperature at a rate of 30 °C / h. The entire growth process was carried out under high vacuum. The crystal was then removed, yielding a 0.5%Nd,8%Ca:BaF2 crystal with good optical quality.

[0042] Example 5: In this embodiment, a temperature gradient method is used to grow 0.5%Nd,2%Mg:CaF2 crystals. The specific method is as follows: 0.5%Nd,2%Mg:CaF2 crystals were grown using a temperature gradient method. 150 g of the raw material was placed in a graphite crucible, which was then covered and the furnace was evacuated to below 8 Pa. The temperature was then increased to ~1400℃ at a rate of 200 ℃ / h and held at this temperature for 10 hours until the raw material was completely melted and impurities were thoroughly removed. The temperature was then slowly decreased at a rate of 1.5 ℃ / h over a 150 ℃ interval. After the slow cooling growth was complete, the temperature was rapidly reduced to room temperature at a rate of 30 ℃ / h. The entire growth process was carried out under high vacuum. The crystals were then removed, yielding 0.5%Nd,2%Mg:CaF2 crystals with good optical quality.

[0043] Comparative Example 1: This comparative example uses a temperature gradient method to grow 0.5% Nd, 3% Gd:CaF2 crystals. The difference from Example 5 is that in this comparative example, trivalent Gd ions replace divalent Mg ions.

[0044] Based on the successful preparation of the laser crystals in the above embodiments and comparative examples, the present invention further tested the fluorescence performance of the laser crystals.

[0045] Figure 1 The images show the room-temperature fluorescence spectra of the laser crystals prepared in Examples 2-4 under 808 nm light excitation. Figure 2 The fluorescence lifetime spectra of the laser crystals prepared in Examples 1-4 under 808 nm light excitation are shown, corresponding to the emission peak at 1064 nm. Fluorescence spectroscopy tests reveal that, compared to undoped 0.5% Nd:CaF2 or 0.5% Nd:BaF2, the emission intensity of the laser crystals doped with divalent ions in Examples 1-4 is increased, with the 0.5% Nd, 5% Ca:BaF2 crystal prepared in Example 3 exhibiting the highest emission intensity. The fluorescence lifetime is also improved compared to single-doped crystals. This indicates that the present invention, through the incorporation of non-luminescent isovalent ions, can effectively break the Nd... 3+ -Nd 3+Clusters between them reduce the adjacent Nd 3+ Cross-relaxation and concentration quenching between ions.

[0046] Figure 3 The thermal conductivity of the laser crystal prepared in Example 5 varies at different temperatures. The variable-temperature thermal conductivity test shows that, compared to 0.5% Nd:CaF2 without divalent ions, the thermal conductivity of the laser crystal prepared in Example 5, doped with divalent Mg, is significantly higher. 2+ The thermal conductivity of the laser crystal decreased slightly, but the rate of decrease decreased with increasing temperature. Compared to the 0.5% Nd, 3% Gd:CaF2 doped with trivalent ions in Comparative Example 1, the thermal conductivity was significantly improved. This indicates that the doping of divalent ions in this invention can break the Nd... 3 + -Nd 3+ While achieving clustering, it also ensures that the thermal conductivity does not decrease significantly.

[0047] In summary, this invention uses divalent alkaline earth ions of the same valence as substitutes, which can break the Nd... 3+ -Nd 3+ While achieving clustering, it can also ensure that the thermal conductivity does not drop significantly. This can solve the key scientific problems of concentration quenching caused by the clustering effect and the significant drop in thermal conductivity caused by the regulation of heterovalent ion doping in neodymium ion-doped alkaline earth fluoride laser crystals. It can accelerate the application of new "constant" thermal conductivity alkaline earth fluorides in high repetition rate, high energy, and high-energy laser devices.

[0048] 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 divalent ion-controlled neodymium ion-doped alkaline earth fluoride laser crystal, characterized in that, The chemical formula of the laser crystal is xNd,yMe:MF2; Where x ranges from 0.001 to 0.3 and y ranges from 0.01 to 0.

1. Where M is Ca or Ba, and Me is any one of Ba, Ca, or Mg that is different from M.

2. The alkaline earth fluoride laser crystal with divalent ion-controlled neodymium ion doping according to claim 1, characterized in that, The chemical formula of the laser crystal is xNd,yMe:MF2; Where x ranges from 0.01 to 0.1, and y ranges from 0.01 to 0.

1.

3. The alkaline earth fluoride laser crystal with divalent ion-controlled neodymium ion doping according to claim 1, characterized in that, The chemical formula of the laser crystal is any one of 0.5%Nd,2%Ba:CaF2, 0.5%Nd,2%Ca:BaF2, 0.5%Nd,5%Ca:BaF2, 0.5%Nd,8%Ca:BaF2, or 0.5%Nd,2%Mg:CaF2.

4. A method for preparing a divalent ion-controlled neodymium ion-doped alkaline earth fluoride laser crystal according to any one of claims 1-3, characterized in that, The preparation method includes the following steps: S1: Weigh NdF3, CaF2, MgF2 and BaF2 raw materials according to the stoichiometric ratio, mix them evenly and then put them into a crucible; S2: Place the crucible in a vacuum atmosphere, heat up to melt the material and remove impurities, and then cool down to grow the crystal. S3: After growth is complete, the temperature is lowered to room temperature to obtain the alkaline earth fluoride laser crystal.

5. The method for preparing a divalent ion-controlled neodymium ion-doped alkaline earth fluoride laser crystal according to claim 4, characterized in that, In step S1, PbF2 is added to the raw material as an oxygen scavenger, and the amount of PbF2 added is 0.5~2% of the total mass of the raw material.

6. The method for preparing a divalent ion-controlled neodymium ion-doped alkaline earth fluoride laser crystal according to claim 4, characterized in that, In step S2, the entire cooling growth process of the crystal is carried out in an atmosphere below 8 Pa.

7. The method for preparing a divalent ion-controlled neodymium ion-doped alkaline earth fluoride laser crystal according to claim 4, characterized in that, In step S2, the heating rate is 200-300 ℃ / h, the temperature is raised to 1300-1500℃, and the holding time is 8-12h.

8. The method for preparing a divalent ion-controlled neodymium ion-doped alkaline earth fluoride laser crystal according to claim 4, characterized in that, In step S2, the cooling rate of the cooling growth is 1-2 ℃ / h; The cooling range for the cooling growth is 130-170 ℃.

9. The method for preparing a divalent ion-controlled neodymium ion-doped alkaline earth fluoride laser crystal according to claim 4, characterized in that, In step S3, the cooling rate to room temperature is 30-50 °C / h.

10. The application of a divalent ion-controlled neodymium ion-doped alkaline earth fluoride laser crystal as described in any one of claims 1-3 in the field of high repetition rate, high energy, and high-energy lasers.

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