A niobate phosphate nonlinear optical crystal and preparation and application thereof

Abstract

The application provides a niobium phosphate nonlinear optical crystal and preparation and application thereof. 12 Nb3P7O 31 , belongs to an orthorhombic system, a space group is Pna21, is a non-central symmetric structure, cell parameters are: a=0.5 nm, b=1.0 nm, c=0.5 nm, and Z=4, has a large nonlinear optical effect (3xKDP), is phase-matched, a theoretical indirect band gap is 5.11 eV, has a large laser damage threshold, a wide transmission range, stable physical and chemical properties, good mechanical properties, is not easy to deliquesce, and is easy to preserve, and can be used as a ferroelectric crystal, a pyroelectric crystal or a laser substrate material, and is widely applied in preparation of middle infrared laser nonlinear optical composite functional devices, piezoelectric devices, laser frequency conversion devices and the like.

Description

Technical Field

[0001] The present invention belongs to the technical field of crystal materials, and specifically comprises a niobium phosphate nonlinear optical crystal and its preparation and application. Background Art

[0002] In the past 40 years, nonlinear optical crystals have made rapid progress in the field of laser technology and have become indispensable materials in technologies such as laser frequency conversion, electro-optical modulation, and photorefractive refraction. For example, AgGaS2 (AGS), KH2PO4 (KDP), LiNbO3, BaTiO3, and KNbO3 have been mass-produced. Excellent nonlinear optical crystals should not only have a non-centrosymmetric structure, but also have large nonlinear optical coefficients, phase matching, high laser damage threshold, wide transmission range, high transmittance, and high laser conversion efficiency. By introducing octahedral coordinated d 0 Transition metal ions (Mo 6+ 、W 6 + 、Nb 5+ etc.) and main group cations with lone pair electrons (I 5+ 、Te 4+ 、Se 4+ etc.) and π-conjugated systems [(BO3) 3- 、(B3O6) 3- 、(B3O7) 5- etc.], which can increase the probability of obtaining non-centrosymmetric structures. And d 0 The second-order Jahn-Teller distortion order of transition metal ions is: Mo 6+ ≈V 5+ >W 6+ ≈Ti 4+ ≈Nb 5+ >Ta 5+ >Zr 4+ ≈Hf 4+ , indicating that Nb 5+ The introduction of ions is conducive to the distortion of the crystal structure, which is found in LiNbO3(LN), KNbO3(KN), Ba2NaNb5O 15 (BNN), Sr 1-x Ba xIt can be observed in Nb2O6 (SBN) crystals that the Nb atoms in the NbO6 octahedron shift from the central position, resulting in different lengths of the Nb-O bonds, increased polarizability, and thus increased second harmonic response. In addition, phosphates have become another system suitable for exploring nonlinear optical crystals due to their diverse structures, low melting points, and short UV cutoff edges. And related scientific research work to explore the niobium phosphate system has been ongoing. Previous studies by our research group have found that the nonlinear optical effect of NaNb2PO8 crystals is approximately 2.03×KDP, and it has a large theoretical birefringence value (Δn=0.1169), a wide transmission range (0.4-4.2μm), and excellent resistance to laser damage (2.8GW / cm 2 ), how to further obtain niobium phosphate crystals with greater nonlinear optical effects remains the focus of future work. Summary of the Invention

[0003] To address the aforementioned issues with the existing technology, the first objective of the present invention is to provide a niobium phosphate nonlinear optical crystal. This crystal exhibits a significant nonlinear optical effect (3×KDP), a theoretical indirect band gap of 5.11 eV, a high laser damage threshold, a wide transmission range, stable physical and chemical properties, good mechanical properties, resistance to deliquesce, and ease of storage.

[0004] The second object of the present invention is to provide a method for preparing the niobium phosphate nonlinear optical crystal as described above.

[0005] The third object of the present invention is to provide an application of the niobium phosphate nonlinear optical crystal as described above as a ferroelectric crystal, a pyroelectric crystal, or a laser matrix material.

[0006] A fourth object of the present invention is to provide an application of the niobium phosphate nonlinear optical crystal described above in the preparation of mid-infrared laser nonlinear optical composite functional devices, piezoelectric devices, and laser frequency conversion devices.

[0007] To achieve the above first object, the technical solution adopted by the present invention includes:

[0008] The present invention discloses a niobium phosphate nonlinear optical crystal, the chemical formula of which is Na 12 Nb3P7O 31 , belongs to the orthorhombic crystal system, the space group is Pna21, it is a non-centrosymmetric structure, and the unit cell parameters are: And Z=4.

[0009] To achieve the above second purpose, the technical solutions adopted by the present invention include:

[0010] The present invention discloses a method for preparing the nonlinear optical crystal as described above, which is prepared by a conventional preparation method in the art, such as a Czochralski method or a flux method.

[0011] Furthermore, the specific steps of the Czochralski method are:

[0012] After the raw materials are melted, they are placed in a crystal growth furnace, heated to 700-750°C, stirred at a constant temperature, cooled to 3-5°C above the saturation point temperature, and a seed crystal rod is used to introduce the seed crystal. The temperature is lowered to the crystallization temperature at a rate of 0.1-0.5°C / h, and the seed crystal rod is rotated at a rate of 20-30r / min. At the same time, the crystal is pulled at a pulling speed of 6-15mm / h. After the crystal growth is completed, the crystal is lifted from the liquid surface.

[0013] Furthermore, the raw material is a mixture of a Na compound, a P compound, and a Nb compound, or a pure phase polycrystalline powder Na 12 Nb3P7O 31 .

[0014] Furthermore, the mixture is prepared according to the following steps:

[0015] The Na-containing compound, the P-containing compound and the Nb-containing compound are mixed according to a Na:Nb:P molar ratio of 12:3:7 to obtain the product.

[0016] Furthermore, the pure phase polycrystalline powder Na 12 Nb3P7O 31 Prepared according to the following steps:

[0017] The Na-containing compound, the P-containing compound, and the Nb-containing compound are mixed in a Na:Nb:P molar ratio of 12:3:7, heated to 200-300°C and kept at this temperature for 12-24 hours, and then heated to 700-720°C and kept at this temperature for 24-36 hours to obtain a pure phase polycrystalline powder Na 12 Nb3P7O 31 .

[0018] Furthermore, the Na-containing compound includes but is not limited to one or more of NaH2PO4, Na2HPO4, and Na2CO3.

[0019] Furthermore, the P-containing compound includes but is not limited to one or more of NaH2PO4, Na2HPO4, and NH4H2PO4.

[0020] Furthermore, the Nb-containing compound is Nb2O5.

[0021] Furthermore, the growth temperature range of the nonlinear optical crystal is 650-680°C.

[0022] Further, the specific steps of the flux method are:

[0023] The raw materials are mixed with flux, melted and placed in a crystal growth furnace, heated to 740-780°C, stirred at a constant temperature, cooled to 3-5°C above the saturation point of the mixed melt, and a seed crystal is introduced using a seed crystal rod. The temperature is lowered at a rate of 0.1-0.5°C / d, and the seed crystal rod is rotated at a rate of 20-30r / min. After the crystal growth is completed, the crystal is lifted from the liquid surface and then cooled to room temperature at a cooling rate of 1-5°C / h.

[0024] Furthermore, the co-solvent is NaF.

[0025] Furthermore, the raw material is a mixture of a Na compound, a P compound, and a Nb compound, or a pure phase polycrystalline powder Na 12 Nb3P7O 31 .

[0026] Furthermore, the mixture is prepared according to the following steps:

[0027] The Na-containing compound, the P-containing compound and the Nb-containing compound are mixed according to a Na:Nb:P molar ratio of 12:3:7 to obtain the product.

[0028] Furthermore, the pure phase polycrystalline powder Na 12 Nb3P7O 31 Prepared according to the following steps:

[0029] The Na-containing compound, the P-containing compound, and the Nb-containing compound are mixed in a Na:Nb:P molar ratio of 12:3:7, heated to 200-300°C and kept at this temperature for 12-24 hours, and then heated to 700-720°C and kept at this temperature for 24-36 hours to obtain a pure phase polycrystalline powder Na 12 Nb3P7O 31 .

[0030] Furthermore, the Na-containing compound includes but is not limited to one or more of NaH2PO4, Na2HPO4, and Na2CO3.

[0031] Furthermore, the P-containing compound includes but is not limited to one or more of NaH2PO4, Na2HPO4, and NH4H2PO4.

[0032] Furthermore, the Nb-containing compound is Nb2O5.

[0033] Furthermore, the growth temperature range of the nonlinear optical crystal is 650-680°C.

[0034] To achieve the third objective, the present invention employs the following technical solutions:

[0035] The present invention discloses an application of the nonlinear optical crystal as described above as a ferroelectric crystal, a pyroelectric crystal, or a laser matrix material.

[0036] To achieve the fourth objective, the present invention employs the following technical solutions:

[0037] The present invention discloses an application of the nonlinear optical crystal described above in a mid-infrared laser nonlinear optical composite function device, a piezoelectric device, and a laser frequency conversion device.

[0038] Furthermore, the piezoelectric device includes but is not limited to one of a piezoelectric oscillator, a filter, a piezoelectric transducer, a piezoelectric pressure sensor, an electroacoustic transducer, and an ultrasonic sensor.

[0039] Furthermore, the laser frequency conversion device includes but is not limited to one of a frequency doubling device, a sum frequency device, and a difference frequency device.

[0040] Beneficial effects of the present invention:

[0041] The chemical formula of the nonlinear optical crystal is Na 12 Nb3P7O 31 , belongs to the orthorhombic crystal system, the space group is Pna21, it is a non-centrosymmetric structure, and the unit cell parameters are: and Z=4, has a large nonlinear optical effect (3×KDP), and is phase-matched. The theoretical indirect band gap is 5.11eV. It has the advantages of a large laser damage threshold, a wide transmission range, stable physical and chemical properties, good mechanical properties, not easy to deliquesce, and easy to preserve. It can be used as a ferroelectric crystal, pyroelectric crystal or laser matrix material, and is widely used in the preparation of mid-infrared laser nonlinear optical composite functional devices, piezoelectric devices, laser frequency conversion devices and other devices. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] The specific embodiments of the present invention will be further described in detail below with reference to the accompanying drawings.

[0043] Figure 1 The niobium phosphate compound Na prepared in Example 1 is shown. 12 Nb3P7O 31 The powder X-ray diffraction (PXRD) spectrum of the product was compared with the standard spectrum.

[0044] Figure 2 The UV-visible-near infrared transmission spectrum and mid-infrared transmission spectrum of the niobium phosphate powder prepared in Example 1 are shown.

[0045] Figure 3 A schematic diagram of the niobium phosphate crystal structure prepared in Example 2 is shown.

[0046] Figure 4 The Na prepared in Example 2 is shown 12 Nb3P7O 31 Schematic diagram of the optical path system of a crystal as a nonlinear optical device;

[0047] Among them, a is laser, b is lens, c is crystal, d is prism, e is frequency-doubled light, and f is fundamental frequency light. DETAILED DESCRIPTION

[0048] To more clearly illustrate the present invention, the present invention is further described below in conjunction with preferred embodiments and accompanying drawings. It should be understood that the embodiments described are only some embodiments of the present invention, not all embodiments. All other embodiments obtained by persons of ordinary skill in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0049] Example 1: Preparation of pure phase polycrystalline powder niobium phosphate compound Na by solid phase reaction method 12 Nb3P7O 31

[0050] NaH2PO4, Na2HPO4 and Nb2O5 were weighed according to the molar ratio of Na:Nb:P of 12:3:7, mixed and fully ground, and placed in a muffle furnace; the temperature was raised to 200℃ at a rate of 50℃ / h and kept at this temperature for 12h to remove H2O; the temperature was then raised to 700℃ at the same rate and kept at this temperature for 24h, during which time the temperature was repeatedly ground to obtain pure phase polycrystalline powder Na 12 Nb3P7O 31 The powder X-ray diffraction test (PXRD) was performed on it, and the results were as follows Figure 1 As shown in the figure, the XRD pattern of the prepared polycrystalline powder is basically consistent with the XRD pattern of the standard card, proving that the target niobium phosphate compound Na 12 Nb3P7O 31 of polycrystalline powder.

[0051] Figure 2 The UV-visible-near infrared transmission spectrum and mid-infrared transmission spectrum of the prepared niobium phosphate powder are shown, which show that the niobium phosphate has a high transmittance in the wavelength range of 400-2500 nm.

[0052] Example 2: Growth of Na by Czochralski method 12 Nb3P7O 31 crystals

[0053] The Na prepared in Example 1 12 Nb3P7O 31 The polycrystalline powder (600.8 g) was added in batches Melt in a platinum crucible to obtain a melt; place the crucible containing the melt in a crystal growth furnace, heat it to 720°C, and stir at a constant temperature for 48 hours; cool it down to 680°C at a rate of 0.5°C / h, place a seed crystal rod in the crucible, and place a seed crystal on the rod so that the lower end of the seed crystal is immersed in the melt. Then cool it to the crystallization temperature, rotate the lifting rod at a rate of 20r / min, and pull it upward at a pulling speed of 6mm / h. After the crystal growth is completed, lift the crystal from the liquid surface to obtain a colorless single crystal with a size of 5.3cm×6.2cm×5.4cm. The obtained crystal was structurally analyzed and the analysis results confirmed that it was the target substance, Na niobium phosphate. 12 Nb3P7O 31 , see the crystal structure diagram Figure 3 .

[0054] The results of the powder frequency doubling test show that the crystal has a large nonlinear optical effect (3×KDP), which is the largest nonlinear optical effect among niobium phosphate crystals reported so far, and has been verified by theoretical calculations (d 15 =-1.00pm / V,d 24 =-0.59pm / V and d 33 =-1.56pm / V); theoretical calculations show that the indirect band gap of this compound is 5.11eV.

[0055] Example 3: Flux method for growing Na 12 Nb3P7O 31 crystals

[0056] NaF was selected as flux, and NaH2PO4 (71.99 g), Na2HPO4 (212.94 g), Nb2O5 (239.22 g) and NaF (150.12 g) were weighed and put into a mortar for mixing and grinding. The mixed melt was melted in a platinum crucible to obtain a mixed melt; the crucible containing the mixed melt was placed in a crystal growth furnace, heated to 750°C, and stirred at a constant temperature for 24 hours; when the temperature was cooled to 5°C above the saturation temperature of the mixed melt, a preheated seed crystal was slowly lowered into the crystal furnace through a platinum wire so that it contacted the melt surface. After the seed crystal was introduced, the temperature was lowered at a rate of 0.1°C / d, while the seed crystal rod was rotated at a speed of 20 r / min to observe the growth of the crystal; the growth cycle was 25-30 days, and a transparent Na niobium phosphate crystal with a size of 2.1 cm × 3.3 cm × 2.5 cm was obtained. 12 Nb3P7O 31 crystal.

[0057] Example 4: Flux method for growing Na 12 Nb3P7O 31 crystals

[0058] NaF is selected as flux, and Na 12 Nb3P7O 31 The polycrystalline powder (500.4 g) and flux NaF (150.12 g) were mixed and ground in a mortar, and then added in batches. Melt in a platinum crucible to obtain a mixed melt; place the crucible containing the mixed melt in a crystal growth furnace, heat it to 750°C, stir it at a constant temperature for 24 hours, and then cool it to 5°C above the saturation temperature of the mixed melt; slowly lower the preheated seed crystal into the crystal furnace through a platinum wire so that it contacts the surface of the melt. After the seed crystal is introduced, the temperature is lowered at a rate of 0.1°C / d, while the seed crystal rod is rotated at a speed of 26r / min to observe the growth of the crystal; the growth cycle is 25-30 days, and a transparent Na niobium phosphate crystal with a size of 2.4cm×2.3cm×3.4cm is obtained. 12 Nb3P7O 31 crystal.

[0059] Example 5: Application of infrared laser nonlinear optical composite functional devices

[0060] The Na prepared in Example 2 12 Nb3P7O 31 The crystal is cut in a directional manner to obtain a crystal device with a cross-sectional size of 4×4mm and a length of 6mm in the light-transmitting direction; the light-transmitting surfaces at both ends of the crystal device are precisely polished and coated. Figure 4 As shown in the optical system diagram, the infrared light with a wavelength of 1064nm generated by laser a is converged by lens b and incident on crystal device c. After that, it passes through dispersion prism d to obtain frequency-doubled light e (532nm) and unconverted fundamental frequency light f (1064nm).

[0061] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not limitations on the implementation methods of the present invention. For ordinary technicians in the relevant field, other different forms of changes or modifications can be made based on the above description. It is impossible to list all the implementation methods here. All obvious changes or modifications derived from the technical solution of the present invention are still within the scope of protection of the present invention.

Claims

1. A niobium phosphate nonlinear optical crystal, characterized in that: The chemical formula of the nonlinear optical crystal is Na 12 Nb3P7O 31 , belongs to the orthorhombic crystal system, the space group is Pna21, and the unit cell parameters are: a=18.1661(9)Å, b=21.1437(10)Å, c=6.9515(3)Å and Z=4.

2. The method for preparing a nonlinear optical crystal according to claim 1, wherein: The nonlinear optical crystal is grown by adopting a Czochralski method or a flux method.

3. The preparation method according to claim 2, characterized in that The specific steps of the Czochralski method are: After the raw materials are melted, they are placed in a crystal growth furnace, heated to 700-750°C, stirred at a constant temperature, cooled to 3-5°C above the saturation point temperature, and a seed crystal rod is used to introduce the seed crystal. The temperature is lowered to the crystallization temperature at a rate of 0.1-0.5°C / h, and the seed crystal rod is rotated at a rate of 20-30r / min. At the same time, the crystal is pulled at a pulling speed of 6-15mm / h. After the crystal growth is completed, the crystal is lifted from the liquid surface.

4. The preparation method according to claim 2, characterized in that The specific steps of the flux method are: The raw materials are mixed with flux, melted and placed in a crystal growth furnace, heated to 740-780°C, stirred at a constant temperature, cooled to 3-5°C above the saturation point of the mixed melt, and a seed crystal is introduced using a seed crystal rod. The temperature is lowered at a rate of 0.1-0.5°C / d, and the seed crystal rod is rotated at a rate of 20-30r / min. After the crystal growth is completed, the crystal is lifted from the liquid surface and then cooled to room temperature at a cooling rate of 1-5°C / h.

5. The preparation method according to claim 4, characterized in that The flux is NaF.

6. The preparation method according to claim 3 or 4, characterized in that The raw material is a mixture of Na compounds, P compounds and Nb compounds, or a pure phase polycrystalline powder Na 12 Nb3P7O 31 .

7. The preparation method according to claim 6, characterized in that The mixture is prepared according to the following steps: The Na-containing compound, the P-containing compound and the Nb-containing compound are mixed according to a Na:Nb:P molar ratio of 12:3:7 to obtain the product.

8. The preparation method according to claim 6, characterized in that The pure phase polycrystalline powder Na 12 Nb3P7O 31 Prepared according to the following steps: The Na-containing compound, the P-containing compound, and the Nb-containing compound are mixed in a Na:Nb:P molar ratio of 12:3:7, heated to 200-300°C and kept at this temperature for 12-24 hours, and then heated to 700-720°C and kept at this temperature for 24-36 hours to obtain a pure phase polycrystalline powder Na 12 Nb3P7O 31 .

9. Use of the nonlinear optical crystal according to claim 1 in mid-infrared laser nonlinear optical composite functional devices and laser frequency conversion devices.

10. The use according to claim 9, characterized in that The laser frequency conversion device includes one of a frequency doubling device, a sum frequency device, and a difference frequency device.

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