CN114540935A - A kind of rare earth praseodymium borate crystal material and preparation method thereof - Google Patents

Abstract

The invention discloses a rare earth praseodymium borate crystal material and a preparation method thereof. The rare earth metal borate crystal material is Pr[B ₅ O ₈ (OH)]NO ₃ ·2H ₂ O crystal, which belongs to P2 ₁ / c space group. The preparation method includes the following steps: adding boric acid, praseodymium nitrate hexahydrate, alumina and deionized water into a polytetrafluoroethylene lining and mixing evenly, reacting at 260° C. and autogenous pressure for one day, and then cooling down to 240° C. to continue the reaction Day 4, the rare earth praseodymium borate Pr[B ₅ O ₈ (OH)]NO ₃ ·2H ₂ O crystal material was obtained. The compound in the present invention is synthesized by hydrothermal at medium temperature, the synthesis steps are simple, the obtained crystal quality is high, it is not deliquescent in the air, and it is insoluble in water, and the specific structure can be obtained by single crystal diffraction test, and the synthesis process consumes energy Low, the raw materials used are readily available and cheap. The obtained rare earth borate compound has the characteristic luminescence properties of Pr.

Description

A kind of rare earth praseodymium borate crystal material and preparation method thereof

technical field

The invention belongs to the technical field of crystal materials, in particular to a rare earth praseodymium borate crystal material and a preparation method thereof.

Background technique

Rare earth borates have received extensive attention and research in recent years. This binary system can combine the characteristics of rare earth and borates to obtain materials with excellent properties, which are used in multi-band photoluminescence, lasers, nonlinear optics, biosensors, and medical diagnosis, etc. In the borate structure, boron and oxygen coordinate to form two basic configurations, namely BO ₃ triangular configuration and BO ₄ tetrahedral configuration. These two basic configurations can form a wide variety of Boron oxyanion clusters, which make the borate structure very diverse, the configuration available for selection is rich, and the melting point of boronic acid is low, the synthesis method is simple and effective, and the cost is relatively cheap, which makes it can be combined with various types of cations, For example, organic cations, alkali or alkaline earth metal ions, etc., to form a variety of functional materials. Rare earth has a special 4f orbital electron and is shielded by the outer 5s ² 5p ⁶ orbital electron, so it has high luminescence purity and can be used as a luminescence center. When a rare earth compound is used as a luminescent material, its luminescence intensity and luminescence wavelength are affected by the matrix combined with it. Choosing a suitable matrix will enhance the luminescence intensity and adjust the luminescence wavelength. Combining rare earth cations with structurally rich clusters of borate anions can yield materials with good luminescence properties.

The high temperature solid-phase synthesis method is the main method to obtain rare earth borates, and the hydrothermal synthesis method with relatively low temperature is difficult to obtain rare earth borate crystals. The reason is that according to the Lux-Flood acid-base theory, the rare earth ions have high charge, When combined with polyboronic acid ion clusters, the charge is relatively concentrated, and it is difficult to form a stable structure, so it is difficult to crystallize (Chem. Mater. 2003, 15, 2253-2260). In addition, because the reaction environment of borate crystals obtained under hydrothermal conditions is between alkaline and weakly acidic, rare earth ions are easily hydrolyzed into precipitation under such conditions, and it is difficult to form rare earth borate crystals.

SUMMARY OF THE INVENTION

In view of the problems existing in the prior art, the present invention provides a rare earth praseodymium borate crystal material and a preparation method thereof. The rare earth borate crystal is obtained by a hydrothermal synthesis method at a lower temperature, the energy consumption of the synthesis process is low, and the raw materials used are Easy to get and cheap. The obtained rare earth borate compound has the characteristic luminescence properties of Pr.

In order to solve the above-mentioned technical problems, the present invention adopts the following technical solutions:

A rare earth praseodymium borate crystal material, the rare earth metal borate crystal material is Pr[B ₅ O ₈ (OH)]NO ₃ ·2H ₂ O crystal, Pr[B ₅ O ₈ (OH)]NO ₃ · The 2H ₂ O crystal belongs to the P2 ₁ /c space group.

Further, the Pr[B ₅ O ₈ (OH)]NO ₃ ·2H ₂ O crystal contains one trivalent rare earth Pr ion, 5 crystallographically independent trivalent B ions, 9 O ions connected to B, 1 nitrate ion, two crystal water molecules, 5 B ions and 9 O ions are connected to form a [B ₅ O ₈ (OH)] polyanion cluster, which can be seen as three BO ₃ triangles and Formed by two BO _tetrahedra sharing the top corner oxygen, this anion cluster can be used as a basic building unit, each unit connects another 4 units to form a two-dimensional layered BO structure on the ac plane, and the rare earth Pr is filled in the two-dimensional layered BO within the structure window.

The preparation method of the rare earth praseodymium borate crystal material of the present invention includes the following steps: mixing 15 mmol of boric acid, 1 mmol of praseodymium nitrate hexahydrate, 1 mmol of alumina, and 3 mL of deionized water in a polytetrafluoroethylene liner with a volume of 23 mL After homogeneous, the reaction was carried out at 260 °C for one day, and then cooled to 240 °C for 4 days to obtain light green regular flaky crystal rare earth praseodymium borate Pr[B ₅ O ₈ (OH)]NO ₃ ·2H ₂ O crystal material.

Preferably, the molar ratio of boric acid, praseodymium nitrate hexahydrate, and alumina is 15:1:1.

Preferably, based on 1 mmol of praseodymium nitrate hexahydrate, 2-4 mL of deionized water is required.

Further, based on 1 mmol of praseodymium nitrate hexahydrate, 3 mL of deionized water is required.

The typical preparation steps of the rare earth neodymium borate near-infrared luminescent crystal material of the present invention are as follows: mix 15 mmol of boric acid, 1 mmol of praseodymium nitrate hexahydrate, 1 mmol of alumina, and 3 mL of deionized water in a polytetrafluoroethylene liner with a volume of 23 mL. Then, the reaction was carried out at 260 °C for one day under the condition of autogenous pressure (the pressure generated by internal air and water vapor), and then the temperature was lowered to 240 °C for 4 days to obtain light green regular flaky crystal rare earth praseodymium borate Pr[ B ₅ O ₈ (OH)]NO ₃ ·2H ₂ O crystalline material.

Beneficial effects of the invention: There are many rare earth borate compounds that have been reported, but most of them have powder morphology. The reported crystal morphology products have completely different crystallographic parameters and completely different physical and chemical properties due to different connection methods. During the hydrothermal reaction, both boric acid and praseodymium nitrate hexahydrate were melted at 260 °C to form a molten state. After the molten boric acid was combined with alumina, the form of the boric acid ion cluster was changed, so that the boric acid was combined with the molten rare earth. The added 3ml of water, these waters make the reaction raw materials finally form a homogeneous mixture in the reactor, react at a set temperature and autogenous pressure, and after the reaction finishes cooling to room temperature, natural crystallization obtains Pr[B ₅ O ₈ (OH) ]NO ₃ ·2H ₂ O crystalline material.

The compound in the present invention is synthesized by hydrothermal at medium temperature, the synthesis steps are simple, the obtained crystal quality is high, it is not deliquescent in the air, and it is insoluble in water, and the specific structure can be obtained by single crystal diffraction test, and the synthesis process consumes energy Low, the raw materials used are readily available and cheap. The obtained rare earth borate compound has the characteristic luminescence properties of Pr.

Description of drawings

Fig. 1 is the asymmetric unit of compound Pr[B ₅ O ₈ (OH)]NO ₃ ·2H ₂ O;

Figure 2 shows the two-dimensional BO layer structure of the compound Pr[B ₅ O ₈ (OH)]NO ₃ ·2H ₂ O;

Figure 3 is a unit cell stacking diagram of the compound Pr[B ₅ O ₈ (OH)]NO ₃ ·2H ₂ O;

Fig. 4 is the powder diffraction pattern of compound Pr[B ₅ O ₈ (OH)]NO ₃ ·2H ₂ O (the upper curve is the experimental value, and the lower curve is the simulated value);

Fig. 5 is the fluorescence spectrum of the compound Pr[B ₅ O ₈ (OH)]NO ₃ ·2H ₂ O (excitation wavelength 400 nm).

Detailed ways

The present invention will be further described below with reference to specific embodiments. It should be understood that the following examples are only used to illustrate the present invention rather than to limit the scope of the present invention, and those skilled in the art can make some non-essential improvements and adjustments according to the content of the above invention.

Example 1

The preparation method of the rare earth praseodymium borate crystal material of the present embodiment is as follows: after mixing 15 mmol of boric acid, 1 mmol of praseodymium nitrate hexahydrate, 1 mmol of alumina, and 3 mL of deionized water in a polytetrafluoroethylene liner with a volume of 23 mL, at 260 The reaction was carried out at ℃ for one day, and then cooled to 240℃ for 4 days to obtain a pale green regular flaky crystal rare earth praseodymium borate Pr[B ₅ O ₈ (OH)]NO ₃ ·2H ₂ O crystal material.

During the hydrothermal reaction, both boric acid and praseodymium nitrate hexahydrate were melted at 260 °C to form a molten state. After the molten boric acid was combined with alumina, the form of the boric acid ion cluster was changed, so that the boric acid was combined with the molten rare earth. The added 3ml of water, these waters make the reaction raw materials finally form a homogeneous mixture in the reactor, and the reaction is carried out at a set temperature and autogenous pressure. After the reaction is completed and cooled to room temperature, natural crystallization forms the product of this example. When other conditions remain unchanged, it is found that the rare earth praseodymium borate crystal material can be obtained between 2 and 4 mL of water when the amount of water added is changed.

In the present invention, a new rare earth metal borate Pr[B ₅ O ₈ (OH)]NO ₃ ·2H ₂ O crystal is synthesized by a medium-temperature hydrothermal method through specific reaction conditions, and its main crystallographic parameters are shown in Table 1. The compound Pr[B ₅ O ₈ (OH)]NO ₃ ·2H ₂ O crystal belongs to the P2 ₁ /c space group, and its asymmetric unit structure is shown in Figure 1. It contains a trivalent rare earth Pr ion, and five crystallographically independent The trivalent B ion, 9 O ions connected to B, 1 nitrate ion, and two crystal water molecules. Five B ions are linked with nine O ions to form a [B ₅ O ₈ (OH)] polyanion cluster, which can be regarded as formed by three BO ₃ triangles and two BO ₄ tetrahedra sharing the top corner oxygen. The anion cluster can be used as a basic building unit, each unit connects four other units to form a two-dimensional layered BO structure on the ac plane, and the rare earth Pr is filled within the window of the two-dimensional layered BO structure (Fig. 2). As shown in the unit cell stacking diagram (Fig. 3), the layered BO structures are filled with nitrate ions and crystal water.

之间，另一类B与四个氧形成的BO₄四面体结构中，B-O键的键长范围在

之间。硝酸根离子中N-O键键长范围在

之间，Pr与10个氧原子配位，其Pr-O键的键长范围在

之间。这些键长数值与已报道过的稀土硼酸盐晶体数据中相符。The BO bond length in the compound is divided into two categories, one is the BO ₃ triangular structure, and the bond length of the BO bond is in the range of

In the BO _tetrahedral structure formed by another type of B and four oxygens, the bond length of the BO bond is in the range of

between. The bond length of NO bond in nitrate ion is in the range of

In between, Pr is coordinated with 10 oxygen atoms, and the bond length of the Pr-O bond is in the range of

between. These bond length values are consistent with reported rare earth borate crystal data.

The crystal of compound Pr[B ₅ O ₈ (OH)]NO ₃ ·2H ₂ O was tested by powder XRD, as shown in Figure 4, in the range of 9-50°, the peak positions of its powder experimental diffraction peak and theoretical diffraction peak A one-to-one correspondence can be obtained, which proves that the obtained compound is a pure phase. The visible light luminescence properties of the compound are shown in Figure 5. Under the condition of excitation wavelength of 400nm, the characteristic emission peaks of Pr appear in the range of 450-850nm, which are respectively 461nm, 476nm, 493nm and 611nm, 694nm. These five characteristic emission peaks correspond to Characteristic emission peaks generated by ³ H ₄ → ³ P ₂ , ³ H ₄ → ³ P ₁ , ³ H ₄ → ³ P ₀ and ¹ D ₂ → ³ H ₄ , ³ P ₀ → ³ F ₃ transitions of rare earth Pr ions , indicating that the compounds can act as potential photoluminescent materials.

Table 1 Compound Pr[B ₅ O ₈ (OH)]NO ₃ ·2H ₂ O crystallographic data table

In the present invention, rare earth borate crystals are obtained by a hydrothermal synthesis method at a lower temperature, and alumina or zinc oxide is selected to be used. The purpose of the combination of boron-oxygen cluster framework is to add aluminum-zinc oxide as a reaction raw material to boric acid and rare earth to change the inherent reaction environment of rare earth and boric acid, thereby obtaining rare earth borate crystals in hydrothermal synthesis.

In the present invention, alumina, zinc oxide, boric acid and praseodymium nitrate are selected as reaction raw materials, and an appropriate amount of deionized water is added as a medium to carry out hydrothermal reaction. Experiments, see Table 2 for specific experiments.

Table 2 series of comparative tests

It can be seen from Table 2 that the No. 6 experiment successfully obtained the crystal of the compound Pr[B ₅ O ₈ (OH)]NO ₃ ·2H ₂ O of the present invention, which was obtained by a one-step hydrothermal synthesis method, and the crystal morphology was pale. Green flakes, small crystals and many surface cracks, the unit cell parameters were determined by single crystal experiments, but the analysis was difficult. Based on the conditions for successfully obtaining crystals, 15 mmol of boric acid, 1 mmol of praseodymium nitrate hexahydrate, 1 mmol of alumina, and 3 mL of deionized water were mixed uniformly in a 23 mL polytetrafluoroethylene liner at 260° C., autogenous pressure ( The reaction was carried out under the conditions of the pressure generated by the internal air and water vapor for one day, and then the temperature was lowered to 240° C. to continue the reaction for 4 days, and a light green regular flaky crystal with higher quality was obtained. During the hydrothermal reaction, both boric acid and praseodymium nitrate hexahydrate were melted at 260 °C to form a molten state. After the molten boric acid was combined with alumina, the form of the boric acid ion cluster was changed, so that the boric acid was combined with the molten rare earth. The added 3ml of water, these waters make the reaction raw materials finally form a homogeneous mixture in the reactor, and the reaction is carried out at a set temperature and autogenous pressure. After the reaction is completed and cooled to room temperature, natural crystallization forms the product of this example. Under the condition that other conditions remain unchanged, when changing the amount of water, it is found that the crystals of the product of the present invention can be obtained between 2-4 mL of water.

Many rare earth borate compounds have been reported, but most of them have powder morphology. The reported crystal morphology products have completely different crystallographic parameters and completely different physical and chemical properties due to different connection methods. The compound in the present invention is synthesized by medium-temperature hydrothermal, the synthesis steps are simple, the obtained crystals are of high quality, do not deliquesce in air, and are insoluble in water. The specific structure can be obtained by single crystal diffraction test. The synthesis process can The consumption is low, and the raw materials used are easily available and cheap. The obtained rare earth borate compound has the characteristic luminescence properties of Pr.

The foregoing has shown and described the basic principles and main features of the present invention, as well as the advantages of the present invention. It should be understood by those skilled in the art that the present invention is not limited by the above-mentioned embodiments. What is described in the above-mentioned embodiments and the description is only to illustrate the principle of the present invention. Without departing from the spirit and scope of the present invention, the present invention will also have Various changes and modifications fall within the scope of the claimed invention. The claimed scope of the present invention is defined by the appended claims and their equivalents.

Claims (7)

1. A rare earth praseodymium borate crystal material, characterized in that: the rare earth metal borate crystal material is Pr[B ₅ O ₈ (OH)]NO ₃ ·2H ₂ O crystal, Pr[B ₅ O ₈ The (OH)]NO ₃ ·2H ₂ O crystal belongs to the P2 ₁ /c space group. 2 . The rare earth praseodymium borate crystal material according to claim 1 , wherein the Pr[B ₅ O ₈ (OH)]NO ₃ ·2H ₂ O crystal contains one trivalent rare earth Pr ion and five Crystallographically independent trivalent B ions, 9 O ions linked to B, 1 nitrate ion, two crystal water molecules, 5 B ions linked to 9 O ions to form a [B ₅ O ₈ (OH )] polyanion cluster, the anion cluster can be regarded as formed by 3 BO ₃ triangles and two BO ₄ tetrahedra sharing the top corner oxygen, this anion cluster can be used as a basic building unit, each unit connects another 4 units to form ac The two-dimensional layered BO structure on the plane, the rare earth Pr is filled within the window of the two-dimensional layered BO structure. 3. The preparation method of the rare earth praseodymium borate crystal material according to claim 1 or 2, characterized in that it comprises the following steps: adding boric acid, praseodymium nitrate hexahydrate, alumina and deionized water into the polytetrafluoroethylene lining After mixing uniformly, the reaction was carried out at 260 °C for one day, and then the temperature was lowered to 240 °C for 4 days to obtain light green regular flaky crystal rare earth praseodymium borate Pr[B ₅ O ₈ (OH)]NO ₃ ·2H ₂ O crystal material. 4 . The method for preparing a rare earth neodymium borate near-infrared luminescent crystal material according to claim 3 , wherein the molar ratio of the boric acid, praseodymium nitrate hexahydrate and alumina is 15:1:1. 5 . 5. The preparation method of the rare earth neodymium borate near-infrared luminescent crystal material according to claim 3, characterized in that: taking 1 mmol of praseodymium nitrate hexahydrate as a benchmark, 2 to 4 mL of deionized water is required. 6 . The preparation method of the rare earth neodymium borate near-infrared luminescent crystal material according to claim 5 , characterized in that: taking 1 mmol of praseodymium nitrate hexahydrate as a benchmark, 3 mL of deionized water is required. 7 . 7. the preparation method of rare earth neodymium borate near-infrared luminescent crystal material according to claim 5, is characterized in that typical preparation step is as follows: with boric acid 15mmol, praseodymium nitrate hexahydrate 1mmol, alumina 1mmol, 3mL deionized water in The volume of 23mL polytetrafluoroethylene liner was mixed evenly, reacted at 260 °C for one day, and then cooled to 240 °C and continued to react for 4 days to obtain light green regular flaky crystal rare earth praseodymium borate Pr[B ₅ O ₈ (OH)]NO ₃ ·2H ₂ O crystalline material.

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