A method of spark plasma sintering to produce a low-hydroxyl neodymium-doped fluorophosphate glass

Abstract

This invention belongs to the field of optical glass technology and discloses a method for preparing low-hydroxyl NdFeB-doped fluorinated phosphate glass by discharge plasma sintering. Using Sr(PO3)2, Ba(PO3)2, MgF2, AlF3, NdF3, or NdI3 as raw materials, a batch is prepared by mixing in a specific ratio. The batch is then sintered by discharge plasma and cooled to obtain NdFeB-doped fluorinated phosphate glass. The sintering pressure is 250-300 kg, the sintering temperature is 1000-1200℃, and the holding time is 15-40 min. This invention successfully prepares NdFeB-doped fluorinated phosphate glass using discharge plasma sintering technology. Compared with the high-temperature melting method with the same formula, the melting temperature of this invention is reduced by 200℃, and the hydroxyl absorption coefficient is reduced from 4.77 cm⁻¹. ‑1 It dropped to 0.075cm ‑1 The lifetime increased from 339.1 μs to 388.4 μs, providing a new approach for preparing high-efficiency luminescent fluorine-phosphorus optical glass with low hydroxyl absorption coefficient.

Description

Technical Field

[0001] This invention belongs to the field of optical glass technology, and specifically relates to a method for preparing low-hydroxyl neodymium fluoride phosphate glass by discharge plasma sintering. Background Technology

[0002] Fluorophosphate glass (FP glass) is a combination of phosphate and fluoride glass components, thus combining the advantages of both to some extent. For example, it has a wide range of adjustable glass composition, resulting in a range of tunable optical properties. At the same time, FP glass features low nonlinear refractive index, high rare-earth doping solubility, and a wide transmittance range, making it a highly promising optical glass material.

[0003] Neodymium-doped FP glass, as a typical laser glass, has received widespread attention in research and application. Currently, the main method for preparing NdFeB FP glass is the traditional high-temperature melting method. However, this method has significant limitations in preparing rare-earth-doped fluorine-phosphorus glasses. Firstly, the melting temperature is high, leading to severe fluoride volatilization at high temperatures. Secondly, this method is carried out in an open system, inevitably involving contact with oxygen and water in the air. High temperatures easily cause oxidation or decomposition of components. Furthermore, phosphates have strong hydrophilicity, resulting in a significantly higher OH- content in phosphate glasses compared to other glass systems. This severely degrades the physical properties of rare-earth-doped phosphate laser glasses used in optical fibers and affects the long-term stability of the laser. In addition, laser power and efficiency decrease due to absorption losses caused by OH-, and may even prevent laser output. The OH- content in the glass directly affects the gain performance of rare-earth-doped phosphate optical fibers. Achieving low hydroxyl content in fluorine-phosphorus glasses prepared using this method requires strict and complex dehydration procedures. Currently, the main methods for dehydration of glass are as follows: (1) During the glass melting process, dry high-purity oxygen is introduced into the high-temperature glass melt to remove some moisture and reduce the OH- content in the glass. (2) Dehydration by reaction atmosphere method, that is, while using dry gas to bubble, an active gas or liquid containing chlorine (Cl2, CCl4, POCl3 or SOCl2) or other dehydrating agent is introduced, and the dehydrating agent reacts with water at high temperature to achieve the dehydration effect. The dry gas can be O2, Ar or N2, etc. (3) Melting in vacuum or dry atmosphere, the glass raw materials are weighed, mixed and melted in a dry atmosphere or vacuum environment, the main purpose of which is to reduce the introduction of OH- during the glass preparation process. (4) Using halides to replace some or all of the oxides in the designed glass composition, the dehydration effect is achieved by the reaction of OH- and F or Cl- in the glass melt at high temperature. Among the methods mentioned above, melting in a vacuum or dry atmosphere places stringent requirements on experimental equipment and the environment. The introduction of halides into phosphate glass systems alters the designed glass composition, thus affecting the glass's physical properties and the luminescence properties of the doped ions. Therefore, oxygen bubbling and reactive atmosphere methods are more commonly used, but special attention must be paid to experimental safety during operation. First, the introduction of dry gas at high temperatures carries a high risk, requiring constant supervision throughout the melting process. Second, chlorine-containing reactive gases or liquids used as dehydrating agents are toxic, especially when introduced into the high-temperature glass melt, generating large amounts of toxic gases through volatilization; experimental and monitoring personnel must strictly adhere to protective measures. Therefore, exploring a simple and safe method to prepare NdFeB-doped fluorine-phosphorus glass with low hydroxyl content and high luminescence efficiency is of great significance.

[0004] Spark plasma sintering (SPS) is a rapid, low-temperature, energy-saving, and environmentally friendly material preparation and processing technology. This technology involves directly introducing a pulsed current between pressurized powder particles, using plasma generated by a spark discharge for heating, and utilizing thermal and field effects to achieve short-time sintering at low temperatures. Currently, SPS sintering of optical functional glasses mainly focuses on quartz or silicate systems. For example, in 2013, Professor Jiang Wan and Professor Wang Lianjun's team used SPS technology to prepare Er... 3+ / Yb 3+ Co-doped quartz glass was studied, and its upconversion spectral properties were investigated. It is well known that quartz or silicate glasses exhibit excellent glass-forming properties and are relatively easy to glassen in SPS (Spectrophotometry), where the cooling rate is slower than that of high-temperature melting. However, using phosphates and fluorides as raw materials for SPS sintering often results in devitrification and crystallization due to the slow cooling rate, making glass formation difficult. Currently, there are few reports on the preparation of fluorophosphate optical functional glasses using SPS and the significant reduction in the hydroxyl absorption coefficient to further enhance rare-earth ion luminescence. Summary of the Invention

[0005] In order to overcome the shortcomings and deficiencies of the prior art, the primary objective of this invention is to provide a method for preparing low-hydroxyl neodymium fluoride phosphate glass by discharge plasma sintering.

[0006] Another object of the present invention is to provide a low-hydroxyl neodymium fluoride phosphate glass.

[0007] Another object of the present invention is to provide the application of the above-mentioned low-hydroxyl neodymium fluoride phosphate glass.

[0008] The objective of this invention is achieved through the following technical solution:

[0009] A method for preparing neodymium-doped fluorophosphate glass by discharge plasma sintering includes the following steps: using Sr(PO3)2, Ba(PO3)2, MgF2, AlF3, NdF3 or NdI3 as raw materials, mixing them in a certain proportion to obtain a batch, and then sintering and cooling the batch to obtain neodymium-doped fluorophosphate glass.

[0010] Preferably, the method includes the following steps:

[0011] (1) Using Sr(PO3)2, Ba(PO3)2, MgF2, AlF3, NdF3 or NdI3 as raw materials, mix and grind them in proportion to obtain a compound material;

[0012] (2) The batch material is filled into the mold and placed in the discharge plasma furnace for sintering and cooling in the furnace to prepare neodymium-doped fluorine phosphate glass.

[0013] Preferably, the sintering pressure is 250-300 kg and the sintering vacuum degree is 5 × 10⁻⁶.-3 ~1×10 -2 Pa, sintering temperature is 1000-1200℃, holding time is 15-40min.

[0014] Preferably, the raw material composition is as follows:

[0015]

[0016] The sum of the above molar percentages is 100%, and NdF3 or NdI3 is added externally at a weight ratio of 1 to 2.5 wt%.

[0017] Preferably, the raw material composition is as follows:

[0018]

[0019]

[0020] The sum of the above components in molar percentage is 100%, with NdF3 or NdI3 added at a weight ratio of 1 wt%.

[0021] Preferably, the mold is a graphite mold.

[0022] A neodymium-doped fluorinated phosphate glass is prepared by the above method.

[0023] Preferably, the absorption coefficient of the neodymium-doped fluorinated phosphate glass hydroxyl group is 0.02-0.2 cm⁻¹. -1 .

[0024] The above-mentioned application of neodymium-doped fluorine phosphate glass in laser glass optical fibers.

[0025] The above-mentioned applications of neodymium-doped fluorine phosphate glass in fiber lasers.

[0026] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0027] (1) The present invention uses spark plasma (SPS) sintering to prepare FP glass. This preparation method has a lower melting temperature than the high temperature melting method. Under the same formula, the melting temperature of the high temperature melting method is reduced by 200°C. It is simple and easy to implement and avoids complicated dehydration operations.

[0028] (2) Compared with FP glass prepared by the traditional high-temperature melting method, the hydroxyl absorption coefficient of NdFeB-doped FP glass prepared by SPS is significantly reduced, from 4.77 cm⁻¹. -1 It dropped to 0.075cm -1 The concentration of hydroxyl ions increased from 5.85 × 10⁻⁶. 19 ions / cm 3 Reduced to 0.09×10 19 ions / cm3 This value is very low and is difficult to achieve in phosphate glass systems using a combination of high-temperature melting and dehydration.

[0029] (3) Under 808nm laser diode pumping, stronger fluorescence intensity and fluorescence lifetime were obtained than the high temperature melting method, with the lifetime increasing from 339.1μs in the high temperature melting method to 388.4μs.

[0030] (4) The elastic modulus and hardness of the neodymium-doped FP glass prepared by SPS were improved. The hardness increased from 4628.4 MPa to 7130.6 MPa, and the Young's modulus increased from 50.5 GPa to 76.6 GPa, providing a new idea for preparing high-efficiency luminescent fluorine-phosphorus optical glass with low hydroxyl absorption coefficient. Attached Figure Description

[0031] Figure 1 The emission spectra are those of the FP glass in Examples 1-2 of this invention.

[0032] Figure 2 The Fourier transform infrared transmission spectra of the FP glass in Examples 1-2 of this invention are shown.

[0033] Figure 3 The lifetime decay curves of the FP glass in Examples 1-2 of this invention are shown, with excitation wavelength λ. ex The wavelength is 808nm, and the monitoring wavelength is λ. em It is 902nm.

[0034] Figure 4 The hardness and Young's modulus of the FP glass in Examples 1-2 of this invention are shown. Detailed Implementation

[0035] The present invention will be further described in detail below with reference to specific embodiments, but the implementation of the present invention is not limited thereto. For process parameters not specifically noted, conventional techniques can be referred to.

[0036] Discharge plasma sintering: purchased from Nanjing Boyuntong Instrument Technology Co., Ltd., model: SPS 5T 30MIN.

[0037] The glass composition of specific embodiments of the present invention is shown in Table 1. All raw materials are high-purity raw materials (>99.99%), wherein NdF3 or NdI3 is introduced into the glass composition by external doping.

[0038] Table 1

[0039]

[0040] Example 1

[0041] The preparation steps of the fluorine-phosphorus laser glass in this embodiment are as follows:

[0042] (1) Weigh 10g of raw materials according to the composition and proportion in Table 1, including Sr(PO3)2, Ba(PO3)2, MgF2, AlF3, and weigh 0.1g of NdF3;

[0043] (2) The raw materials obtained in step (1) are mixed and ground in an agate mortar to form a compound;

[0044] (3) Transfer the uniformly ground batch material from step (2) into a corundum crucible, place it in a high-temperature furnace and heat it to 1300℃. After melting for 30 minutes, a glass melt without bubbles or stones, transparent and uniform is obtained.

[0045] (4) The clarified and homogenized molten glass is poured onto a stainless steel plate to form a transparent glass block;

[0046] (5) The formed transparent glass was transferred to a muffle furnace and annealed at 550°C for 4 hours to remove the internal stress of the glass. Then, it was cooled to room temperature with the furnace at a cooling rate of 15°C / hour to obtain the fluorophosphorus glass prepared by the high temperature melting method, which was used as a control group.

[0047] Example 2

[0048] The preparation steps of the fluorine-phosphorus laser glass in this embodiment are as follows:

[0049] (1) Weigh 10g of raw materials according to their composition and proportions, including Sr(PO3)2, Ba(PO3)2, MgF2, and AlF3, and weigh 0.1g of NdF3;

[0050] (2) The raw materials obtained in step (1) are mixed and ground in an agate mortar to form a compound;

[0051] (3) The batching powder obtained in step (2) is filled into a graphite mold, and a discharge plasma sintering process is adopted, with a pressure of 250-300 kg and a vacuum degree ≤8×10⁻⁶. -3 The temperature was initially increased at Pa, and the sintering vacuum degree was 5 × 10⁻⁶. -3 ~1×10 -2 Pa, controlling the sintering temperature at 1100℃, maintaining the heat for 30 minutes during discharge plasma sintering, and then cooling with the furnace, finally obtaining NdFeB-doped FP glass with good transparency.

[0052] The emission spectrum, Fourier transform infrared transmission spectrum, lifetime decay curve, hardness, and Young's modulus of the obtained neodymium-doped fluorine phosphate laser glass were measured. Figure 1 The spectrum shown indicates that the glass prepared by SPS exhibits significantly enhanced luminescence at higher temperatures. This is due to the presence of OH groups in the glass. -The specific content of the radical cannot be directly measured. It can usually be obtained by converting the infrared spectral transmittance to obtain the hydroxyl absorption coefficient, as shown in Formula I. Figure 2 The hydroxyl absorption coefficient α was calculated from the infrared transmission spectrum. OH - The results showed that using SPS to prepare FP glass can significantly reduce the hydroxyl absorption coefficient of the glass, from 4.77 cm⁻¹ in the high-temperature melting method. -1 It dropped to 0.075cm -1 The corresponding hydroxyl ion concentration N was further calculated. OH - As shown in Formula II, from the high-temperature melting method, 5.85 × 10 19 ions / cm 3 Reduced to 0.09×10 19 ions / cm 3 . Figure 3 This indicates that Nd 3+ The lifetime has also been improved compared to the high-temperature melting method, increasing from 339.1 μs to 388.4 μs. Furthermore, such as... Figure 4 As shown, the FP glass prepared by SPS exhibits enhanced hardness and elastic modulus, with the hardness increasing from 4628.38 MPa to 7130.6 MPa and the Young's modulus increasing from 50.5 GPa to 76.6 GPa. This method achieves the preparation of FP glass with low hydroxyl content, high luminescence intensity, and enhanced mechanical properties.

[0053]

[0054] In formula I, α OH - The hydroxyl absorption coefficient of the sample (cm) -1 T0 and T are the infrared spectral transmittance (%) of the glass matrix at 2600 nm and 3000 nm, respectively.

[0055]

[0056] In Equation II, N OH - Where NA is the concentration of hydroxyl ions, and NA is Avogadro's constant (6.02 × 10⁻⁶). 23 ions / mol), where ε is the molar absorptivity of OH- in glass, typically taken as 49.1 × 10⁻⁶. 3 cm 2 / mol.

[0057] Because FP glass is composed of phosphates and fluorides, the high volatility and strong corrosiveness of fluorides pose a significant challenge to its manufacturing process. Therefore, the relative content of fluorine is a crucial parameter for FP glass. Traditional high-temperature melting methods, conducted in an open system, result in substantial volatilization of fluorides, especially in low-fluorine formulations. This leads to significant discrepancies between the nominal and actual glass composition, causing problems such as phase separation and crystallization, and discrepancies between the glass structure and expected properties. SPS sintering, on the other hand, provides a vacuum environment, significantly reducing contact with water vapor during melting and lowering the hydroxyl absorption coefficient, while also effectively minimizing fluorine volatilization. Furthermore, the unique sintering mechanism of SPS, with its lower melting temperature compared to high-temperature melting methods, further reduces fluorine volatilization to some extent.

[0058] Table 2 compares the fluorine content in the EDS test results of FP glass in Examples 1-2 of this invention. The fluorine content in FP glass prepared by SPS is higher than that prepared by high temperature melting method, which reduces the volatilization of fluorides during the melting process of fluorine-phosphorus glass.

[0059] Table 2

[0060]

[0061] Example 3

[0062] According to the composition and proportions in Table 1, the raw materials were accurately weighed and prepared using the same method as in Example 1. Glass was prepared by high-temperature melting and used as a control group for Example 4.

[0063] Example 4

[0064] The raw materials were accurately weighed according to the composition and proportions in Table 1, and glass was prepared using SPS as the experimental group for Example 3. Unlike Example 2, the phosphorus component in Example 3 was introduced as Ba(PO3)2 instead of Sr(PO3)2, and the proportion of fluorine components (MgF2, AlF3) was increased. Generally, for FP glass in this system, an increase in fluorine content reduces the glass-forming ability. However, despite increasing the proportion of fluorides compared to Example 2, glass was still obtained by SPS sintering. This method is still applicable to preparing FP glass with higher fluoride content in this system.

[0065] Example 5

[0066] According to the composition and proportions in Table 1, the raw materials were accurately weighed, and the glass was prepared using the same high-temperature melting method as in Example 1, serving as the control group for Example 6.

[0067] Example 6

[0068] The raw materials were accurately weighed according to the composition and proportions in Table 1, and glass was prepared using SPS as the experimental group for Example 5. Unlike Example 4, Example 6 increased the NdF3 doping concentration; this method is still applicable to FP glasses with higher rare-earth doping concentrations.

[0069] Example 7

[0070] According to the composition and proportions in Table 1, the raw materials were accurately weighed, and glass was prepared using SPS as the experimental group of Example 8.

[0071] Example 8

[0072] According to the composition and proportions in Table 1, the raw materials were accurately weighed, and glass was prepared using SPS, serving as the experimental group for Example 7. Unlike Example 6, Example 8 changed the ratio of Ba(PO3)2 to Sr(PO3)2 in the phosphorus component, i.e., increased the proportion of Sr(PO3)2, and also changed the rare earth ion Nd... 3+ The method still applies if the coordinating ion during doping is changed from NdF3 to NdI3, thus altering the coordinating ion of the rare earth ions.

[0073] Comparative Example 1

[0074] The high-temperature melting method, namely, the dehydration operation in Example 1 was carried out in a reaction atmosphere method using oxygen bubbling and CCl4 as a dehydrating agent in molten glass at high temperature. The hydroxyl absorption coefficient calculated by Fourier transform infrared transmission spectroscopy was still 3.67 cm⁻¹. -1 .

[0075] Comparative Example 2

[0076] In high-phosphorus (P / F molar ratio of 7.2) formulations, for the 72Sr(PO3)2-18Ba(PO3)2-5MgF2-5AlF3 (1wt% NdF3) formulation, glass can be formed using a high-temperature melting method, but glass cannot be formed using SPS.

[0077] Comparative Example 3

[0078] In a high-fluorine formulation (P / F molar ratio of 0.67), glass can be formed using a high-temperature melting method for 32Sr(PO3)2-8Ba(PO3)2-60MgF2 (1wt% NdF3), but it cannot be formed using SPS.

[0079] Comparative Example 4

[0080] Unlike Example 2, the sintering temperature was 900°C, and the holding time and pressure remained unchanged. After SPS melting, a transparent glass was not obtained, but a white heterogeneous block was obtained after the batch material was partially melted at high temperature.

[0081] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A method for preparing neodymium-doped fluorophosphate glass by discharge plasma sintering, characterized in that, The process includes the following steps: using Sr(PO3)2, Ba(PO3)2, MgF2, AlF3, NdF3 or NdI3 as raw materials, mixing them in a certain proportion to obtain a batch, and then preparing neodymium-doped fluorinated phosphate glass by discharge plasma sintering and cooling. The raw materials are composed of: Sr(PO3)2: 0~56 mol % Ba(PO3)2: 14~72 mol %, MgF2: 5~20 mol% AlF3: 5~10 mol % The sum of the above components in molar percentage is 100%, and NdF3 or NdI3 is added externally at a weight ratio of 1~2.5wt%.

2. The method for preparing neodymium-doped fluorophosphate glass by discharge plasma sintering according to claim 1, characterized in that, Includes the following steps: (1) Using Sr(PO3)2, Ba(PO3)2, MgF2, AlF3, NdF3 or NdI3 as raw materials, mix and grind them in proportion to obtain a compound material; (2) The batch material is filled into the mold and placed in the discharge plasma furnace for sintering and cooling in the furnace to prepare neodymium-doped fluorine phosphate glass.

3. The method for preparing neodymium-doped fluorophosphate glass by discharge plasma sintering according to claim 2, characterized in that, The sintering pressure is 250-300 kg, and the sintering vacuum degree is 5×10⁻⁶. -3 ~1×10 -2 Pa, sintering temperature is 1000-1200℃, holding time is 15-40 min.

4. The method for preparing neodymium-doped fluorophosphate glass by discharge plasma sintering according to claim 1, characterized in that, The raw materials are composed of: Sr(PO3)2: 18~56 mol %, Ba(PO3)2: 14~72 mol %, MgF2: 5 ~ 20 mol % AlF3: 5 ~ 10 mol % The sum of the above molar percentages is 100%, and NdF3 or NdI3 is added externally at a weight ratio of 1 wt%.

5. The method for preparing neodymium-doped fluorophosphate glass by discharge plasma sintering according to claim 2, characterized in that, The mold is a graphite mold.

6. A neodymium-doped fluorinated phosphate glass, characterized in that, It is prepared by the method described in any one of claims 1 to 5.

7. The neodymium-doped fluoride phosphate glass according to claim 6, characterized in that, The neodymium-doped fluoride phosphate glass hydroxyl absorption coefficient is 0.02-0.2 cm⁻¹. -1 .

8. The application of the neodymium-doped fluorine phosphate glass according to claim 6 or 7 in laser glass optical fibers.

9. The application of the neodymium-doped fluorine phosphate glass according to claim 6 or 7 in fiber lasers.

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