Applications of Rare Earth Ion-Doped Fluoride Crystals

Abstract

The present invention provides applications of rare earth ion-doped alkaline earth metal fluoride crystals, including applications in solid-state lasers, laser imaging, environmental detection, satellite guidance, information storage, or underwater detection. The rare earth ion-doped alkaline earth metal fluoride comprises a matrix crystal and dysprosium ions or Dy / RE co-doped ions doped in the cation lattice of the matrix crystal, wherein the RE comprises at least one of Tm, Pr, and Sm; the matrix crystal comprises calcium strontium fluoride or barium fluoride crystals. The crystals employed in the present invention have low phonon energy and high fluorescence quantum efficiency. The introduction of calcium improves the stability of the crystals; the Dy / RE co-doping enhances energy level transfer. The crystals employed in the present invention have an absorption wavelength range of 250 to 600 nm. Upon excitation with ultraviolet or blue light, they can produce a broad emission spectrum spanning the violet to orange wavelength range, making them ideal working materials for direct pumping of semiconductor lasers.

Description

Technical Field

[0001] The present invention relates to the technical field of solid-state lasers, and in particular to the application of rare earth ion-doped fluoride crystals, in particular to the application of dysprosium-doped barium fluoride crystals, Dy / RE (RE represents rare earth ions, which can be Tm, Pr, or Sm) co-doped barium fluoride crystals, and dysprosium-doped calcium strontium fluoride crystals. Background Art

[0002] Visible light lasers mainly include: (1) dye lasers; (2) sum frequency, frequency doubling and four-wave mixing of 1μm lasers; (3) laser conversion of nonlinear optical effects such as Raman lasers. Among them, although dye lasers have the advantages of adjustable wavelength and high power, they require long-term maintenance, are expensive, and are difficult to apply in specific fields. 3+ The laser crystal can generate dual-frequency laser characteristics of 1064nm and 1319nm at the same time, and can generate yellow laser by combining laser sum-frequency technology. 3+ Crystal or Raman laser can obtain frequency-doubled visible light in the wavelength range of 1.14 to 1.17 μm. In addition, pulsed laser pumping Yb-doped 3+ Nonlinear fiber excitation cascade four-wave mixing and Raman frequency shifting can also be used to generate visible lasers. However, these visible light lasers suffer from poor overall performance, including low pumping efficiency, difficulty in preparing some crystals, poor optical quality, high maintenance costs, large size, and complex systems. Consequently, there is an urgent need to develop an all-solid-state visible light laser directly pumped by a semiconductor laser (LD).

[0003] Prior art "Ruan Fangfang, Yang Long, Hu Guang, Wang Aimei, Xue Yanyan, Yang Longliang, Wang Zexu, Wu Shaohua, Zheng Lihe. Multi-crucible temperature gradient method for the growth of Dy 3+ :LaF3 crystal and luminescence properties[J]. Journal of Luminescence, 2021, 42(02):158-164." discloses a Dy 3+ : LaF3 crystal, using near-ultraviolet or visible light excitation. However, the LaF3 phonon energy in this crystal is 350cm -1 , its phonon energy is high, resulting in low fluorescence efficiency of its crystal. Summary of the Invention

[0004] In view of this, the purpose of the present invention is to provide an application of rare earth ion-doped fluoride crystals. The rare earth ion-doped fluoride crystals used in the present invention are based on ultraviolet light or blue light excitation, and can obtain a wide emission spectrum covering the wavelength range from purple to orange-yellow, and have high fluorescence efficiency. They have good application prospects in solid-state lasers, laser imaging, environmental detection, satellite guidance, information storage or underwater detection.

[0005] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0006] The present invention provides applications of rare earth ion-doped alkaline earth metal fluoride crystals, including applications in solid-state lasers, laser imaging, environmental detection, satellite guidance, information storage, or underwater detection.

[0007] The rare earth ion-doped alkaline earth metal fluoride comprises a host crystal and dysprosium ions or Dy / RE co-doped ions doped at the cation lattice of the host crystal, wherein the RE comprises at least one of Tm, Pr and Sm;

[0008] The host crystals include calcium strontium fluoride or barium fluoride crystals.

[0009] Preferably, the rare earth ion-doped alkaline earth metal fluoride includes one or more of dysprosium-doped barium fluoride crystals, dysprosium-doped calcium strontium fluoride crystals, Dy / RE co-doped barium fluoride crystals, and Dy / RE co-doped calcium strontium fluoride crystals;

[0010] The chemical formula of the dysprosium-doped barium fluoride crystal is Dy a Ba 1-a F 2+a , where 0.0001≤a≤0.7;

[0011] The chemical formula of the Dy / RE co-doped barium fluoride crystal is Dy i RE j Ba 1-i-j F i+j+2 , where 0.005≤i≤0.5, 0.005≤j≤0.5;

[0012] The chemical formula of the dysprosium-doped calcium strontium fluoride crystal is Ca 1-x-y Sr y Dy x F 2+x , where 0.0001≤x≤0.6, 0.1≤y≤0.9;

[0013] The chemical formula of the Dy / RE co-doped calcium strontium fluoride crystal is Ca 1-p-s Sr s Dy (p-t) RE t F 2+p , where 0.05≤p≤0.5, 0.2≤s≤0.6, and 0.05≤t≤0.15.

[0014] Preferably, the Dy a Ba 1-a F 2+a The value range of a is 0.01≤a≤0.5;

[0015] The Dy i RE jBa 1-i-j F i+j+2 In , the value range of i is 0.03≤i≤0.3, and the value range of j is 0.01≤j≤0.3;

[0016] The Ca x Sr y Dy 1-x-y F 2+x In the equation, the value range of x is 0.3≤x≤0.7, and the value range of y is 0.3≤y≤0.7;

[0017] The Ca 1-p-s Sr s Dy (p-t) RE t F 2+p In the equation, the value range of p is 0.05≤p≤0.5, the value range of s is 0.2≤s≤0.6, and the value range of t is 0.05≤t≤0.15.

[0018] Preferably, the rare earth ion-doped alkaline earth metal fluoride crystal has Space group structure.

[0019] Preferably, the method for preparing the rare earth ion-doped alkaline earth metal fluoride crystals comprises the following steps:

[0020] The metal fluoride of the matrix crystal, the rare earth ion fluoride and the oxygen scavenger are mixed, and the mixing, tableting, sintering, heating, heat preservation and melting and cooling are carried out in sequence to obtain rare earth ion doped alkaline earth metal fluoride crystals;

[0021] The metal fluoride of the host crystal includes BaF2, or a mixture of CaF2 and SrF2,

[0022] The rare earth ion fluoride includes DyF3, or a mixture of DyF3 and REF3.

[0023] Preferably, the oxygen scavenger comprises at least one of lead fluoride, sodium fluoride, copper fluoride and cadmium fluoride;

[0024] The mass ratio of DyF3 to the deoxidizer is 1:10-500.

[0025] Preferably, the sintering temperature is 500-1100° C., and the sintering time is 3-48 hours.

[0026] Preferably, the heating rate of the heating is 0.5 to 200° C. / h.

[0027] Preferably, the temperature of the heat preservation melting is 1300-1700° C., and the time is 1-48 hours.

[0028] Preferably, the initial temperature of the cooling crystal growth is the temperature of the heat preservation melting, the final temperature is room temperature, and the cooling rate is 0.5-80°C / h.

[0029] The present invention provides applications of rare earth ion-doped alkaline earth metal fluoride crystals, including applications in solid-state lasers, laser imaging, environmental detection, satellite guidance, information storage, or underwater detection. The rare earth ion-doped alkaline earth metal fluoride comprises a host crystal and dysprosium ions or Dy / RE co-doped ions doped in the cation lattice of the host crystal, wherein the RE comprises at least one of Tm, Pr, and Sm. The host crystal comprises calcium strontium fluoride or barium fluoride crystals. The phonon energy of BaF2 crystals is 319 cm -1 , the phonon energy of CaSrF2 crystal is 302cm -1 , the phonon energy is lower than that of LaF3 crystal. Low phonon energy is conducive to weakening the non-radiative decay of rare earth ions from the intermediate state to the lower ground state, thereby improving the fluorescence quantum efficiency. 3+ The ionic radius is 91.2 pm, Tm 3+ The ionic radius is 99.4 pm, Eu 3+ The ionic radius is 106pm, Sm 3+ The ionic radius is 107.9 pm, Pr 3+ The ionic radius is 112 pm, Ca 2+ The ionic radius is 100 pm, Sr 2+ The ionic radius is 118 pm, Ba 2+ The ionic radius is 135pm. The present invention introduces Ca into the strontium fluoride crystal. 2+ It is beneficial to obtain more stable dysprosium-doped calcium strontium fluoride crystals; introducing Dy into barium fluoride crystals 3+ With RE 3+ Co-doping is beneficial for achieving RE 3+ The phonon energy in Dy is transferred to 3+ The cluster structure present in the rare earth ion-doped alkaline earth metal fluoride crystals, barium fluoride crystals, and calcium strontium fluoride crystals provided by the present invention is conducive to obtaining a broad emission band after co-doping with dysprosium ions and Dy / RE. This results in an absorption wavelength range of 250 to 700 nm for the dysprosium-doped barium fluoride crystals, Dy / RE co-doped barium fluoride crystals, and dysprosium-doped calcium strontium fluoride crystals. Based on ultraviolet or blue light excitation, a broad emission spectrum covering the violet to orange wavelength range can be obtained. This is an ideal working material for direct pumping of semiconductor lasers and has great application prospects in solid-state lasers, laser imaging, environmental detection, satellite guidance, information storage, underwater detection, and medical detection and treatment.

[0030] As shown in the test results of the examples, the dysprosium-doped barium fluoride crystals, Dy / RE (RE represents a rare earth ion, and can be selected from Tm, Pr, or Sm) co-doped barium fluoride crystals, and dysprosium-doped calcium strontium fluoride crystals provided by the present invention have absorption wavelengths ranging from 250 to 700 nm. The ultraviolet absorption peaks of the 5% Dy:CaF2-SrF2 crystals are primarily located at 324 nm, 348 nm, and 364 nm, enabling effective coupling with ultraviolet diode pump sources (UV-LDs). The visible light absorption peaks are located at 427 nm, 452 nm, and 474 nm, enabling effective coupling with GaN-LDs or InGaN-LDs. When pumped with a 324 nm UV-LD, two strong emission bands are obtained, covering wavelengths of 450 to 500 nm (blue) and 555 to 595 nm (green and yellow). Using a 348nm UV-LD pump, the wavelength range covers 450-525nm (blue-green) and 555-600nm (green + yellow + orange), with center wavelengths of 478nm, 493nm, and 571nm respectively. Using a pump wavelength of 364nm, two main emission bands can be obtained, with a maximum half-wave width (FWHM) of 78nm. The wavelength range covers 385-540nm (purple + blue + green) and 560-595nm (green + yellow), with the latter emission peak center wavelengths located at 410nm, 434nm, 461nm, and 493nm. Using a 452nm LD pump, the wavelength range covers 488-512nm (blue + green), 512-555nm (green), and 556-600nm (green + yellow + red). The strongest emission peak is located at 564nm (green), with a theoretical fluorescence quantum efficiency of 75%. When the emission peak is located at 497nm and 506nm, the corresponding theoretical fluorescence quantum efficiency can reach 88% and 90%, respectively. The Judd-Ofelt intensity parameters Ω2, Ω4, and Ω6 of the 5% Dy:CaF2-SrF2 crystal are 3.93×10 -21 cm 2 , 1.83×10 -20 cm 2 and 1.58×10 -20 cm 2 The substrate transmittance of 10% Dy:CaF-SrF2 crystal is greater than 94%. This shows that the dysprosium-doped calcium strontium fluoride crystal prepared by the present invention has a wide emission band, high optical transmittance and high fluorescence quantum efficiency, and is an ideal laser matrix for direct pumping of semiconductor lasers.

[0031] Furthermore, the present invention's method for preparing rare earth ion-doped alkaline earth metal fluoride crystals utilizes different ratios of raw materials in different crucibles to simultaneously produce multiple crystals with different chemical compositions in a single preparation process. This method offers the advantages of a short preparation cycle and high efficiency. High-quality, large-sized dysprosium-doped calcium strontium fluoride crystals can be produced using a multi-crucible temperature gradient method and a multi-crucible descent method. Furthermore, the preparation method provided by the present invention is simple to operate, low-cost, and suitable for industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 This is a picture of the Dy, Tm: BaF2 crystal blank prepared in Example 1.

[0033] Figure 2 This is a picture of the Dy, Pr: BaF2 crystal blank prepared in Example 2.

[0034] Figure 3 This is the absorption spectrum of the Dy, Sm: BaF2 crystal prepared in Example 3.

[0035] Figure 4 This is the absorption spectrum of the Dy, Tm: BaF2 crystal prepared in Example 1.

[0036] Figure 5 This is the absorption spectrum of the Dy, Pr: BaF2 crystal prepared in Example 2.

[0037] Figure 6 This is the absorption spectrum of the Dy, Sm: BaF2 crystal prepared in Example 3.

[0038] Figure 7 This is the absorption spectrum of the Dy:CaF2-SrF2 crystal prepared in Example 4.

[0039] Figure 8 The absorption and emission spectra of the 5% Dy:CaF2-SrF2 crystal prepared in Example 4 at an excitation wavelength of 324 nm are shown;

[0040] Figure 9 The absorption and emission spectra of the 5% Dy:CaF2-SrF2 crystal prepared in Example 4 at an excitation wavelength of 348 nm are shown;

[0041] Figure 10 The absorption and emission spectra of the 5% Dy:CaF2-SrF2 crystal prepared in Example 4 at an excitation wavelength of 364 nm are shown;

[0042] Figure 11 The absorption and emission spectra of the 5% Dy:CaF2-SrF2 crystal prepared in Example 4 at an excitation wavelength of 452 nm are shown;

[0043] Figure 12 This is the luminescence decay curve of the 5% Dy:CaF2-SrF2 crystal prepared in Example 4, which emits a wavelength of 573 nm under 348 nm excitation. DETAILED DESCRIPTION

[0044] The present invention provides applications of rare earth ion-doped alkaline earth metal fluoride crystals, including applications in solid-state lasers, laser imaging, environmental detection, satellite guidance, information storage, or underwater detection. The rare earth ion-doped alkaline earth metal fluoride comprises a host crystal and dysprosium ions or Dy / RE co-doped ions doped in the cation lattice of the host crystal, wherein the RE comprises at least one of Tm, Pr, and Sm. The host crystal comprises calcium strontium fluoride or barium fluoride crystals.

[0045] In the present invention, the rare earth ion doped alkaline earth metal fluoride preferably includes one or more of dysprosium doped barium fluoride crystals, dysprosium doped calcium strontium fluoride crystals, Dy / RE co-doped barium fluoride crystals and Dy / RE co-doped calcium strontium fluoride crystals. In the present invention, the rare earth ion doped alkaline earth metal fluoride crystals preferably have Space group structure.

[0046] In the present invention, the dysprosium-doped barium fluoride crystal comprises barium fluoride crystal and dysprosium ions doped in the cation lattice of the barium fluoride crystal; the chemical formula of the dysprosium-doped barium fluoride crystal is preferably Dy a Ba 1-a F 2+a The value range of a is preferably 0.0001≤a≤0.7, more preferably 0.01≤a≤0.5, and even more preferably 0.05≤a≤0.3. In the present invention, the diameter of the dysprosium-doped barium fluoride crystal is preferably 10 to 100 mm, more preferably 12.7 to 76.2 mm; the thickness of the dysprosium-doped calcium strontium fluoride crystal is preferably 10 to 250 mm, more preferably 25 to 100 mm.

[0047] In the present invention, the Dy / RE co-doped barium fluoride crystal comprises barium fluoride crystal and Dy / RE co-doped ions doped in the cation lattice of the barium fluoride crystal; the chemical formula of the Dy / RE co-doped barium fluoride crystal is preferably Dy i RE j Ba 1-i-j F i+j+2, wherein the value range of i is preferably 0.005≤i≤0.5, more preferably 0.03≤i≤0.3, and further preferably 0.05≤i≤0.2; the value range of j is preferably 0.005≤j≤0.5, more preferably 0.01≤j≤0.3, and further preferably 0.05≤j≤0.2. In the present invention, the diameter of the Dy / RE co-doped barium fluoride crystal is preferably 10 to 250 mm, more preferably 20 to 100 mm; the thickness of the Dy / RE co-doped barium fluoride crystal is preferably 10 to 700 mm, more preferably 25 to 250 mm.

[0048] In the present invention, the dysprosium-doped calcium strontium fluoride crystal comprises calcium strontium fluoride crystal and dysprosium ions doped in the cation lattice of the calcium strontium fluoride crystal; the chemical formula of the dysprosium-doped calcium strontium fluoride crystal is preferably Ca x Sr y Dy 1-x- y F 2+x , wherein the value range of x is preferably 0.1≤x≤0.9, more preferably 0.3≤x≤0.7, and even more preferably 0.4≤x≤0.6; the value range of y is preferably 0.1≤y≤0.9, more preferably 0.3≤y≤0.7, and even more preferably 0.4≤y≤0.6. In the present invention, the diameter of the dysprosium-doped calcium strontium fluoride crystal is preferably 10 to 100 mm, more preferably 12.7 to 76.2 mm; the thickness of the dysprosium-doped calcium strontium fluoride crystal is preferably 30 to 300 mm, more preferably 50 to 150 mm.

[0049] In the present invention, the chemical formula of the Dy / RE co-doped calcium strontium fluoride crystal is preferably Ca 1-p-s Sr s Dy (p-t) RE t F 2+p , wherein the value range of p is preferably 0.0001≤p≤0.9, more preferably 0.05≤p≤0.5, and further preferably 0.06≤p≤0.25; the value range of y is preferably 0.1≤s≤0.9, more preferably 0.2≤s≤0.6, and further preferably 0.4≤s≤0.55; the value range of t is 0.0001≤t≤0.3, more preferably 0.05≤t≤0.15, and further preferably 0.06≤t≤0.1. In the present invention, the diameter of the Dy / RE co-doped calcium strontium fluoride crystal is preferably 10 to 300 mm, more preferably 12.7 to 200 mm; the thickness of the Dy / RE co-doped calcium strontium fluoride crystal is preferably 25 to 350 mm, and more preferably 50 to 200 mm.

[0050] In the present invention, the preparation method preferably includes one or more of the temperature gradient method, crucible descent method, multi-crucible temperature gradient method and multi-crucible descent method, and more preferably the multi-crucible temperature gradient method.

[0051] In the present invention, the method for preparing rare earth ion-doped alkaline earth metal fluoride crystals preferably comprises the following steps:

[0052] The metal fluoride of the matrix crystal, the rare earth ion fluoride and the oxygen scavenger are mixed, and the mixing, tableting, sintering, heating, heat preservation and melting and cooling are carried out in sequence to obtain rare earth ion doped alkaline earth metal fluoride crystals;

[0053] The metal fluoride of the host crystal includes BaF2, or a mixture of CaF2 and SrF2,

[0054] The rare earth ion fluoride includes DyF3, or a mixture of DyF3 and REF3.

[0055] In the present invention, unless otherwise specified, all raw material components are commercially available products well known to those skilled in the art.

[0056] The present invention has no particular limitation on the ratio of the metal fluoride to the rare earth ion fluoride in the matrix crystal. Preferably, the ingredients are prepared according to the chemical formula of the rare earth ion-doped alkaline earth metal fluoride crystal.

[0057] In the present invention, when the rare earth ion-doped alkaline earth metal fluoride crystal is dysprosium-doped barium fluoride crystal, the metal fluoride and rare earth ion fluoride of the host crystal are BaF2 and DyF3, and the molar ratio of BaF2 to DyF3 is preferably (1-a):a.

[0058] In the present invention, when the rare earth ion-doped alkaline earth metal fluoride crystal is a Dy / RE co-doped barium fluoride crystal, the metal fluoride and rare earth ion fluoride of the host crystal are BaF2, DyF3 and REF3, and the molar ratio of DyF3, REF3 and BaF2 is preferably i:j:(1-ij).

[0059] In the present invention, when the rare earth ion-doped alkaline earth metal fluoride crystal is a dysprosium-doped calcium strontium fluoride crystal, the metal fluoride and rare earth ion fluoride of the host crystal are CaF2, SrF2 and DyF3, and the molar ratio of CaF2, SrF2 and DyF3 is preferably x:y:(1-xy).

[0060] In the present invention, when the rare earth ion-doped alkaline earth metal fluoride crystal is a Dy / RE co-doped calcium strontium fluoride crystal, the metal fluoride and rare earth ion fluoride of the host crystal are CaF2, SrF2, DyF3 and REF3, and the molar ratio of CaF2, SrF2, DyF3 and REF3 is preferably (1-ps):s:(pt):t.

[0061] In the present invention, the purity of the BaF2, CaF2, SrF2, TmF3, PrF3, SmF3 and DyF3 is preferably >99.995% independently, and the BaF2, CaF2, SrF2, TmF3, PrF3, SmF3 and DyF3 are preferably dry raw materials.

[0062] In the present invention, the oxygen scavenger preferably includes at least one of lead fluoride, sodium fluoride, copper fluoride, and cadmium fluoride, and more preferably includes lead fluoride, sodium fluoride, copper fluoride, or cadmium fluoride. In the present invention, the mass ratio of DyF3 to the oxygen scavenger is preferably 1:10 to 500, and more preferably 1:50 to 200.

[0063] In the present invention, the tableting pressure is preferably 20 to 1000 N, more preferably 50 to 500 N; the tableting time is preferably 1 to 60 min, more preferably 5 to 30 min; and the tableting temperature is preferably room temperature.

[0064] In the present invention, the sintering temperature is preferably 200 to 1200° C., more preferably 400 to 1000° C.; the sintering time is preferably 3 to 48 hours, more preferably 10 to 24 hours.

[0065] In the present invention, the heating rate is preferably 0.5 to 200° C. / h, more preferably 5 to 100° C. / h, and further preferably 10 to 50° C. / h. The temperature is preferably raised from room temperature.

[0066] In the present invention, the temperature of the heat preservation and melting is preferably 1300-1700°C, more preferably 1350-1650°C, and further preferably 1400-1600°C; the time of the heat preservation and melting is preferably 1-48h, more preferably 3-40h, and further preferably 5-35h.

[0067] In the present invention, the initial temperature of the cooling crystal growth is preferably the temperature of the insulation melting, the final temperature of the cooling crystal growth is preferably room temperature, and the cooling rate of the cooling crystal growth is preferably 0.5 to 80°C / h, more preferably 1 to 70°C / h, and further preferably 2 to 60°C / h.

[0068] After the cooling and crystal growth, the present invention preferably further comprises cutting, grinding, and polishing the obtained crystals in sequence. The present invention is not particularly limited to the cutting, grinding, and polishing methods, as long as rare earth ion-doped alkaline earth metal fluoride crystals of the above size are obtained.

[0069] The rare earth ion-doped alkaline earth metal fluoride crystals used in the present invention have a wide emission band, high optical transmittance and high fluorescence efficiency. They are an ideal laser matrix that can be used for direct pumping of semiconductor lasers. They have good application prospects in solid-state lasers, laser imaging, environmental detection, satellite guidance, information storage, underwater detection, ophthalmic detection and treatment, prostate hyperplasia treatment and vascular disease treatment.

[0070] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions of the present invention. Obviously, the embodiments described are only some of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0071] The purity of BaF2, CaF2, SrF2, TmF3, PrF3, SmF3 and DyF3 used in the following examples and comparative examples is >99.995% and they are dry raw materials.

[0072] Example 1

[0073] The temperature gradient method was used to prepare dysprosium-thulium co-doped barium fluoride crystals. The specific steps are as follows: BaF2, DyF3, TmF3 and deoxidizer were ground evenly, pressed into a sheet at room temperature and 300N for 60 minutes, sintered at 800℃ for 20 hours, and placed in a graphite crucible. A hole with a diameter of about 2mm was opened in the center of the graphite crucible lid. The graphite crucible with the lid was sealed and placed in the crystal growth furnace chamber, and vacuumed to 10 -4 Pa was heated to 1580°C at a heating rate of 200°C / h, melted for 8 hours, and then cooled to room temperature at a cooling rate of 50°C / h. The crystals were cut, ground and polished to obtain dysprosium-doped barium fluoride crystals; the mass ratio of DyF3 to oxygen scavenger was 1:120.

[0074] Example 2

[0075] The crucible descent method was used to prepare dysprosium-praseodymium co-doped barium fluoride crystals. The specific steps are as follows: BaF2, DyF3, PrF3 and deoxidizer were ground evenly, pressed into pellets at room temperature and 500N for 50 minutes, sintered at 900℃ for 15 hours, and placed in a graphite crucible. A hole with a diameter of about 1.5mm was opened in the center of the graphite crucible lid. The graphite crucible with the lid was sealed and placed in the crystal growth furnace chamber, and vacuumed to 10 -4Pa was heated to 1550°C at a heating rate of 180°C / h, melted for 16 hours, and then cooled to room temperature at a cooling rate of 45°C / h. Dysprosium-praseodymium-doped barium fluoride crystals were obtained by cutting, grinding, and polishing. The mass ratio of DyF3 to oxygen scavenger was 1:120.

[0076] Example 3

[0077] The temperature gradient method was used to prepare dysprosium and samarium doped barium fluoride crystals. The specific steps are as follows: BaF2, DyF3, SmF3 and deoxidizer were ground evenly, pressed into a sheet at room temperature and 600N for 30 minutes, sintered at 1000℃ for 10 hours, and placed in a graphite crucible. A hole with a diameter of about 2mm was opened in the center of the graphite crucible lid. The graphite crucible with the lid was sealed and placed in the crystal growth furnace chamber, and vacuumed to 10 -4 Pa was heated to 1500°C at a heating rate of 150°C / h, melted for 20 hours, and then cooled to room temperature at a cooling rate of 40°C / h. The crystals were cut, ground and polished to obtain dysprosium-doped barium fluoride crystals; the mass ratio of DyF3 to oxygen scavenger was 1:120.

[0078] Example 4

[0079] Dysprosium-doped calcium strontium fluoride crystals were prepared using a multi-crucible (3) temperature gradient method. The specific steps are as follows: CaF2, SrF2, DyF3 and deoxidizer were ground evenly, pressed into pellets at room temperature and 1000N for 10 minutes, sintered at 750℃ for 30 hours, and placed in a graphite crucible. A hole was opened in the center of the graphite crucible lid with a diameter of about 0.8mm. The graphite crucible with a lid was sealed and placed in a crystal growth furnace chamber, and vacuumed to 10 -4 Pa, heated to 1480°C at a rate of 165°C / h, melted for 24 hours, and then cooled to room temperature at a rate of 30°C / h. Dysprosium-doped calcium strontium fluoride crystals were obtained by cutting, grinding, and polishing. The mass ratio of DyF3 to the oxygen scavenger was 1:100.

[0080] The molar percentage of CaF2:SrF2:DyF3 in the first crucible is 0.475:0.475:0.05, and the deoxidizer is PbF2. 0.475 Sr 0.475 Dy 0.05 F 2.05 Crystal (abbreviated as 5% Dy:CaF2-SrF2), Dy 3+ The doping concentration is 5at.%, and the crystal size is Dia.20mm×68mm;

[0081] The molar percentage of CaF2:SrF2:DyF3 in the second crucible is 0.425:0.425:0.15, and the deoxidizer is CuF2, and Ca0.425 Sr 0.425 Dy 0.15 F 2.15 Crystal (abbreviated as 15% Dy:CaF2-SrF2), Dy 3+ The doping concentration is 15at.%, and the crystal size is Dia.20mm×54mm;

[0082] The molar percentage of CaF2:SrF2:DyF3 in the third crucible is 0.45:0.45:0.1, and the deoxidizer is NaF, and Ca 0.45 Sr 0.45 Dy 0.1 F 2.1 Crystal (abbreviated as 10% Dy:CaF2-SrF2), Dy 3+ The doping concentration is 10at.%, and the crystal size is Dia.20mm×65mm.

[0083] Comparative Example 1

[0084] "Ruan Fangfang, Yang Long, Hu Guang, Wang Aimei, Xue Yanyan, Yang Longliang, Wang Zexu, Wu Shaohua, Zheng Lihe. Multi-crucible temperature gradient method for the growth of Dy 3+ :LaF3 crystal and luminescence properties[J]. Journal of Luminescence, 2021, 42(02):158-164." The disclosed 2% Dy:LaF3 crystal.

[0085] The transmission spectrum was measured using infrared spectroscopy (Tensor 207, Bruker).

[0086] Under the same test conditions, the base transmittance of the 2% Dy:LaF3 crystal is 71%, and the base transmittance of the 10% Dy:CaF-SrF2 crystal prepared in Example 1 of the present invention is greater than 94%; the transmittance when the sample thickness is 10mm is greater than 87%. Theoretically, the transmittance may decrease slightly with higher doping, although the Dy content in the CaF2-SrF2 crystal is 3+ The doping concentration is higher, but the substrate shows a higher transmittance, indicating that the CaF2-SrF2 matrix has a high optical transmittance, proving that the Dy:CaF-SrF2 crystal prepared by the present invention has a higher optical transmittance and better optical quality.

[0087] Comparative Example 2

[0088] Dysprosium-doped calcium strontium fluoride crystals were prepared according to the method of Example 4. The only difference from Example 4 was that the temperature for melting was 1200° C., which did not reach the melting point of the crystal, and transparent crystals could not be successfully prepared.

[0089] Comparative Example 3

[0090] Dysprosium-doped calcium strontium fluoride crystals were prepared according to the method of Example 4, the only difference from Example 1 being that the melting temperature was 1800° C. However, this comparative example required high thermal conditions for the equipment, and the preparation cycle was increased by 48 hours compared to Example 1.

[0091] Comparative Example 4

[0092] Dysprosium-doped calcium strontium fluoride crystals were prepared according to the method of Example 4, the only difference from Example 1 being that the cooling rate was 0.2° C. / h. However, the crystal growth time of this comparative example was too long (7625 h).

[0093] Comparative Example 5

[0094] Dysprosium-doped calcium strontium fluoride crystals were prepared according to the method of Example 1, with the only difference from Example 1 being that the cooling rate was 120° C. / h. However, the cooling rate of this comparative example was too fast, resulting in cracks inside the crystals.

[0095] Comparative Example 6

[0096] CaF2 and SrF2 were replaced by LaF3, with the molar percentage of LaF3:DyF3 being 0.095:0.05.

[0097] Test Example 1

[0098] Absorption spectra of Dy:CaF2-SrF2 crystals were measured using a UV / Vis / NIR spectrophotometer (Varian Cary 5000, Palo Alto, USA) with a xenon lamp as the pump source, a resolution of 1 nm, and a measurement range of 23 to 2000 nm. Fluorescence spectra were measured using a steady-state time-resolved fluorescence spectrometer (FLS-980, Edinburgh, UK) using a xenon lamp as the pump source at center wavelengths of 324 nm, 348 nm, and 364 nm, with a spectral resolution of 0.5 nm. Red photomultiplier tubes (PMTs, 200 to 900 nm) were used as detectors. All measurements were performed at room temperature with a sample thickness of 1 mm.

[0099] (1) Absorption spectrum and Judd-Ofelt analysis

[0100] Figure 7 The absorption coefficient and corresponding energy level of 5% Dy:CaF2-SrF2 prepared in Example 4 from ultraviolet to infrared spectrum range. Figure 4 It can be seen that the central wavelengths of the three strong absorption bands are located at 324nm, 348nm and 364nm, corresponding to the ground state 6 H 15 / 2 arrive 6 P 3 / 2 + 4 M 17 / 2、 6 P 7 / 2 +4I 11 / 2 and 6 P 5 / 2 + 4 D 3 / 2 + 4 M 19 / 2 Typical absorption spectrum of the visible spectrum. The absorption bands in the visible spectrum are centered at 427nm, 452nm and 474nm, corresponding to the absorption bands from the ground state to the 6 H 15 / 2 arrive 4 G 11 / 2 、 4 I 15 / 2 、 4 F 9 / 2 Energy level transition. Dy in 5% Dy:CaF2-SrF2 prepared in Example 1 3+ The absorption cross section σ abs By σ abs =α / N formula, where α refers to the absorption coefficient and N represents Dy 3+ The lattice concentration of ions in 5% Dy:CaF2-SrF2 is 1.22×10 21 ion·cm -3 The absorption cross sections of 5% Dy:CaF2-SrF2 at 348nm and 364nm are 3.41×10 -21 cm 2 , 2.59×10 -21 cm 2 .

[0101] Table 1 Central wavelength, absorption cross section, experimental spectral line intensity and theoretical spectral line intensity, experimental electric dipole intensity and theoretical electric dipole intensity corresponding to the absorption spectrum of 5% Dy:CaF2-SrF2 crystal

[0102]

[0103] The Judd-Ofelt intensity parameters were calculated based on 22 absorption bands. The root mean square deviation (RMSΔS) between the experimental and calculated oscillator intensities was calculated to be 5.16×10 -21 cm 2 , the root mean square deviation (RMSΔf ed ) is 6.31×10 -7 cm 2 . The least squares method is used to fit S exp (J-J'), S cal (J-J'), determine the three Judd-Ofelt intensity parameters Ω2, Ω4 and Ω6, where Ω2 is 3.93×10-20 cm 2 Ω4 is 1.83×10 -20 cm 2 Ω6 is 1.58×10 -20 cm 2 The results are shown in Table 2. It shows that Dy:CaF2-SrF2 has a smaller Ω2 value and the covalency of the Dy-F bond is weaker.

[0104] Table 2 Judd-Ofelt intensity parameters and spectral quality factors (χ = Ω4 / Ω6) of 5% Dy:CaF2-SrF2 and existing Dy-doped crystals

[0105]

[0106]

[0107] Among them, [1] Y. Pan, S. Zhou, D. Li, B. Liu, Q. Song, J. Liu, P. Liu, Y. Ding, X. Wang, X. Xu, and J. Xu, "Growth and optical properties ofDy:Y3Al5O 12 crystal,” PhysicaB-CondensedMatter 530, 317-321 (2018).

[0108] [2] R.Lisiecki, G.Dominiak-Dzik, P.Solarz, W.Ryba-Romanowski, M.Berkowski, andM.Glowacki, "Optical spectra and luminescence dynamics of the Dy-dopedGd2SiO5 single crystal," Applied Physics B-Lasers and Optics 98, 337-346 (2010).

[0109] [3] J.Shi, B.Liu, Q.Wang, H.Tang, F.Wu, D.Li, H.Zhao, Z.Wang, W.Deng,

[0110] [4] W. Ryba-Romanowski, G. Dominiak-Dzik, P. Solarz, and R. Lisiecki, “Transition intensities and excited state relaxation dynamics of Dy 3+ incrystals andglasses: Acomparative study,” Optical Materials 31, 1547-1554 (2009).

[0111] [5]AAKaminskii, JBGruber, SNBagaev, K.Ueda, U.Hommerich, JTSeo, D.Temple, B.Zandi, AAKornienko, EBDunina, AAPavlyuk, RFKlevtsova, andF.A.Kuznetsov, “Optical spectroscopy and visible stimulated emission of Dy 3+ ions in monoclinic alpha-KY(WO4)2and alpha-KGd(WO4)2crystals,” Physical ReviewB65,125108(2002).

[0112] [6]X.Lu, Z.You, J.Li, Z.Zhu, G.Jia, B.Wu, and C.Tu, “The optical properties of Dy 3+ -doped NaY(MoO4)2crystal,” Journal of Luminescence 126, 63-67 (2007).

[0113] As shown in Table 2, the spectral quality factors χ of Dy:YAG and Dy:Gd2SiO5 are 0.29 and 0.57 respectively, the spectral quality factor χ of Dy:Lu2O3 is 1.15, and the spectral quality factor χ of Dy:YAG and Dy:Gd2SiO5 is 0.29 and 0.57 respectively. 3+ :Yal(BO3)4、Dy 3+ :KGd(WO4)2、Dy 3+ :NaY(MoO4)2、Dy 3+ :YVO4 and Dy 3+The spectral quality factor χ of YVO4 ranges from 1.32 to 2.13, while the spectral quality factor χ of 5% Dy:CaF2-SrF2 is 1.16, close to that of Dy:Lu2O3 (χ = 1.15). Dy:CaF2-SrF2 has smaller Ω4 and Ω6 values, indicating greater basicity.

[0114] Table 35% Dy:CaF2-SrF2 for 4 M 17 / 2 (324nm), 6 P 7 / 2 (350nm) and 6 P 5 / 2 (364nm) Radiative transition rate A in the crystal JJ’ , branching ratio β JJ and radiation energy levels in Dy:CaF2-SrF2 crystals

[0115]

[0116] From Table 3, we can see that 5%Dy:CaF2-SrF2 crystal has 6 P 3 / 2 + 4 M 17 / 2 (324nm), 6 P 7 / 2 + 4 I 11 / 2 (348nm), 6 P 5 / 2 + 4 D 3 / 2 + 4 M 19 / 2 (364nm) and 4 I 15 / 2 (452nm) to the ground state 6 H J 、 6 F J 、 4 F 9 / 2 The radiative transition rate A JJ’ and fluorescence branching ratio β JJ The corresponding main emission peaks are located at 515nm, 570nm, and 663nm. This shows that Dy:CaF2-SrF2 crystals have rich absorption and emission bands. In particular, the 364nm excitation wavelength can be used to generate multi-band excitation radiation at 461nm, 577nm, and 663nm.

[0117] (2) Room temperature emission spectrum in the visible light band

[0118] Figure 8The absorption and emission spectra of the 5% Dy:CaF2-SrF2 crystal prepared in Example 4 at an excitation wavelength of 324 nm are shown in FIG. Figure 8 It can be seen that when 324nm UV-LD is used for pumping, the corresponding energy level is 6 P 3 / 2 + 4 M 17 / 2 Two strong emission bands were observed, with the spectral wavelength ranges of 450-500nm (blue light) and 555-595nm (green light + yellow light), and the central wavelength peaks were located at 472nm and 493nm ( 6 P 3 / 2 + 4 M 17 / 2 → 6 H 9 / 2 +6F 11 / 2 , blue light), 570nm ( 6 P3 / 2+ 4 M 17 / 2→ 6 F 7 / 2 , yellow light).

[0119] Figure 9 The absorption and emission spectra of the 5% Dy:CaF2-SrF2 crystal prepared in Example 4 at an excitation wavelength of 348 nm are shown in FIG. Figure 9 It can be seen that using 348nm UV-LD pumping corresponds to 6 P 7 / 2 + 4 I 11 / 2 Energy level transition, two strong emission bands covering 450 ~ 525nm (blue light + green light), 555 ~ 600nm (green light + yellow light + orange light), the central wavelength peak is located at 478nm and 493nm (6P 7 / 2 + 4 I 11 / 2→ 6 H 9 / 2 + 6 F11 / 2, blue light), 571nm(6P7 / 2+ 4 I 11 / 2→ 6 F 7 / 2 , yellow light). This shows that the excitation wavelengths of 324nm and 348nm can be used to obtain blue light and yellow light. Among them, the normalized yellow light intensity obtained by using the excitation wavelength of 348nm is stronger than the blue light intensity.

[0120] Figure 10 The absorption and emission spectrum characteristics of the 5% Dy:CaF2-SrF2 crystal prepared in Example 4 at an excitation wavelength of 364nm are shown in FIG. Figure 10It can be seen that the pump wavelength is 364nm, corresponding to the energy level 6 P 5 / 2 + 4 D 3 / 2 + 4 M 19 / 2 The 364nm excitation wavelength provides two main emission bands, covering wavelengths of 385-540nm (violet, blue, and green) and 560-595nm (green and yellow). The former has a full width at half maximum (FWHM) of 78nm, with peak wavelengths at 410nm, 434nm, 461nm, and 493nm. The quantum efficiency at 410nm reaches 87%. This suggests that a continuously tunable Dy:CaF2-SrF2 laser from violet to green can be achieved based on a 364nm excitation wavelength.

[0121] Figure 11 The absorption and emission spectra of the 5% Dy:CaF2-SrF2 crystal prepared in Example 4 at an excitation wavelength of 452 nm are shown in FIG. Figure 11 It can be seen that using 452nm LD pump should be at the energy level 4 I 15 / 2 The theoretical quantum efficiency of green light emission centered at 564nm (the strongest emission peak), 506nm and 497nm reaches 75%, 88% and 90% respectively. Although the absorption intensity of 452nm is weaker than that of 324nm, 348nm or 364nm, due to its high quantum efficiency, further research on green and yellow laser output based on 452nm is of great significance.

[0122] It shows that the ultraviolet absorption peaks of 5% Dy:CaF2-SrF2 crystal are mainly located at 324nm, 348nm and 364nm, which can be effectively coupled with ultraviolet diode pump source (UV-LD); the absorption peaks in the visible light band are located at 427nm, 452nm and 474nm, which can be effectively coupled with GaN-LD or InGaN-LD.

[0123] (3) Fluorescence lifetime

[0124] The fitting formula of the attenuation curve is y=y0+A1×exp(-x / t1)+A2×exp(-x / t2)+A3×exp(-x / t3).

[0125] Fluorescence lifetime calculation formula:

[0126] Among them, the values of t1, t2 and t3 are 2.716μs, 31.327μs and 136.080μs respectively;

[0127] A1, A2, and A3 are equal to 123560.34, 10084.83, and 1903.15, respectively.

[0128] Figure 12 The luminescence decay curve of the 5% Dy:CaF2-SrF2 crystal prepared in Example 1 with an emission wavelength of 573 nm under 348 nm excitation is shown in FIG. 1 . The corresponding energy transition is 6 P 7 / 2 + 4 I 11 / 2 → 6 F 7 / 2 .Depend on Figure 12 It can be seen that energy level 6 P 7 / 2 The fluorescence lifetime at 573 nm is 50.58 μs, and the radiation lifetime is τ rad The fluorescence lifetime is longer than the radiation lifetime mainly because Dy 3+ Caused by electric dipole-dipole transfer between donor and acceptor.

[0129] In summary, the dysprosium-doped barium fluoride crystals, Dy / RE (RE represents a rare earth ion; Eu, Tm, Sm, or Pr can be selected) co-doped barium fluoride crystals, and dysprosium-doped calcium strontium fluoride crystals produced by this invention represent ideal laser matrices for direct semiconductor laser pumping. Using ultraviolet diode pumping and rationally designed cavity parameters, they are expected to produce continuous-wave tunable lasers ranging from violet to blue and from green to yellow. Using blue diode pumping, they are expected to achieve high-quantum-efficiency green and yellow laser output.

[0130] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. Applications of rare earth ion-doped alkaline earth metal fluoride crystals, including applications in solid-state lasers, laser imaging, environmental detection, satellite guidance, information storage, or underwater detection; The rare earth ion-doped alkaline earth metal fluoride comprises a host crystal and Dy / RE co-doping ions doped at the cation lattice of the host crystal, wherein the RE comprises at least one of Tm, Pr and Sm; the host crystal comprises calcium strontium fluoride or barium fluoride crystal; The rare earth ion-doped alkaline earth metal fluoride includes one or more of Dy / RE co-doped barium fluoride crystals and Dy / RE co-doped calcium strontium fluoride crystals; The chemical formula of the Dy / RE co-doped barium fluoride crystal is Dy i RE j Ba 1-i-j F i+j+2 ,in, 0.03≤i≤0.3, 0.01≤j≤0.3; The chemical formula of the Dy / RE co-doped calcium strontium fluoride crystal is Ca 1-p-s Sr s Dy (p-t) RE t F 2+p , where 0.05≤p≤0.5, 0.2≤s≤0.6, and 0.05≤t≤0.

15.

2. The use according to claim 1, characterized in that The rare earth ion doped alkaline earth metal fluoride crystal has Space group structure.

3. The use according to claim 1 or 2, characterized in that The method for preparing rare earth ion-doped alkaline earth metal fluoride crystals comprises the following steps: The metal fluoride of the matrix crystal, the rare earth ion fluoride and the oxygen scavenger are mixed, and the mixing, tableting, sintering, heating, heat preservation and melting and cooling are carried out in sequence to obtain rare earth ion doped alkaline earth metal fluoride crystals; The metal fluoride of the host crystal includes BaF2, or a mixture of CaF2 and SrF2; The rare earth ion fluoride includes a mixture of DyF3 and REF3.

4. The use according to claim 3, characterized in that The oxygen scavenger comprises at least one of lead fluoride, sodium fluoride, copper fluoride and cadmium fluoride; The mass ratio of DyF3 to the deoxidizer is 1:10-500.

5. The use according to claim 3, characterized in that The sintering temperature is 500-1100° C., and the sintering time is 3-48 hours.

6. The use according to claim 3, characterized in that The heating rate of the heating is 0.5 to 200° C. / h.

7. The use according to claim 3, characterized in that The temperature of the thermal insulation melting is 1300-1700°C, and the time is 1-48 hours.

8. The use according to claim 3, characterized in that The initial temperature of the cooling crystal growth is the temperature of the heat preservation melting, the final temperature is room temperature, and the cooling rate is 0.5-80°C / h.

Images