1. A single-doped uranium lithium niobate crystal is characterized in that the preparation raw material comprises Li with the purity of 99.99 wt%₂CO₃、99.99wt％Nb₂O₅And UO with purity ≧ 99.99%₂Wherein, UO₂The doping amount of [ Li ] is 0.6 to 2.0 mol%]And [ Nb ]]Is 0.937.

2. The method for preparing the single-doped lithium uranium niobate crystal of claim 1, comprising the steps of:

step 1: mixing Nb with₂O₅Heating the powder to remove fluorine, and then adding Li₂CO₃And Nb after defluorination₂O₅Powder materialAnd UO₂After fully grinding and mixing, placing the mixture in a muffle furnace for sintering treatment to obtain uranium-doped lithium niobate powder;

step 2: grinding the uranium-doped lithium niobate powder obtained in the step 1, then loading the powder into a Pt crucible, and performing crystal growth by adopting a Bridgman method; grows a brown crystal without cracks and obvious growth stripes;

and step 3: and (3) under the heating condition, carrying out current polarization treatment on the crystal obtained in the step (2) to enable the crystal to form a single-domain structure, so as to obtain the single-doped uranium lithium niobate crystal.

3. The preparation method of the singly doped lithium uranium niobate crystal according to claim 2, wherein the temperature of the defluorination treatment in the step 1 is 700-900 ℃ and the time is 4-6 h; the sintering treatment specifically comprises the following steps: firstly, raising the temperature of a muffle furnace to 700-900 ℃, preserving heat for 4-6 h, then raising the temperature to 1000-1200 ℃ for 2-4 h, preserving heat for 6-8 h, and finally cooling to room temperature.

4. The method for preparing the single-doped lithium uranium niobate crystal according to claim 2, wherein the crucible descent method in the step 2 comprises the following specific steps: controlling the temperature of the upper furnace body to be 1300-1500 ℃; after the furnace body is balanced for 12-24 h, inoculating seed crystals, and starting a descending device to slowly descend the crucible; the crystal grows along the c-axis direction, the process is completed in a constant temperature section, the shouldering speed is 0.2-0.3 mm/h, and the constant-diameter growth speed is 0.3-0.4 mm/h; and finally, cooling according to the program segment, and naturally cooling to room temperature.

5. The method for preparing the single-doped lithium uranium niobate crystal according to claim 2, wherein the heating temperature in the step 3 is 1100-1200 ℃; the current density of the polarization treatment is 6-8 mA/cm²The time is 10-30 min.

Background

Lithium niobate (LiNbO3, LN) crystal is an important multifunctional and multipurpose artificial material with integrated physical properties of electro-optic, acousto-optic, piezoelectric, photorefractive and the like. The silicon material has a plurality of excellent performances, so that the silicon material is highly praised as silicon in photonics, is widely applied to a plurality of fields such as holographic storage, three-dimensional holographic display, integrated optical devices, optical communication modulators and the like, and is the most important multifunctional material. In recent years, with the development of holographic data storage technology, LN crystals are considered one of the most competitive candidates for the new generation of holographic storage applications due to their excellent photorefractive properties. Doping is an important technique for tuning the photorefractive properties of LN crystals. Particularly, variable metal ions with multiple valence states are doped, and corresponding impurity defect energy levels are introduced by doping impurity ions, so that the photorefractive property of the LN crystal is greatly improved, and the method has a vital effect on successfully realizing holographic storage.

To date, LN crystals, as one of the important holographic media materials, have low diffraction efficiency and sensitivity and long response time, which limits its application in the commercialization of holographic storage, and if three or more kinds of variable valence dopant ions can be successfully doped into LN, it can realize holography at different wavelengths simultaneously, which can be called "full-color holographic storage". Therefore, the search for new photorefractive doped ions and the improvement of the photorefractive response speed of the LN crystal become one of the hot points of research of researchers.

Based on the above analysis, uranium ions having various valence states and good stability can be used as suitable dopant ions. Which generally includes the +3, +4, +5, +6 valence state, and the like. Especially U⁴⁺Radius of (2) and Zr⁴⁺Similarly, UO₂Has a melting point similar to that of ZrO₂Close. Through research, reports on exploring the photorefractive performance of the uranium-doped lithium niobate crystal are not found at present.

Disclosure of Invention

The technical problem to be solved by the invention is as follows: LN crystals, one of the important holographic media materials, low diffraction efficiency and sensitivity, and long response time, limit its application to the commercialization of holographic storage.

In order to solve the technical problem, the invention provides a single-doped uranium lithium niobate crystal, and the preparation raw material comprises 99.99 wt% of Li₂CO₃、99.99wt％Nb₂O₅And UO with purity ≧ 99.99%₂Wherein, UO₂The doping amount of [ Li ] is 0.6 to 2.0 mol%]And [ Nb ]]Is 0.937.

The invention also provides a preparation method of the single-doped lithium uranium niobate crystal, which comprises the following steps:

step 1: mixing Nb with₂O₅Heating the powder to remove fluorine, and then adding Li₂CO₃And Nb after defluorination₂O₅Powder and UO₂After fully grinding and mixing, placing the mixture in a muffle furnace for sintering treatment to obtain uranium-doped lithium niobate powder;

step 2: grinding the uranium-doped lithium niobate powder obtained in the step 1, then loading the powder into a Pt crucible, and performing crystal growth by adopting a Bridgman method; grows a brown crystal without cracks and obvious growth stripes;

and step 3: and (3) under the heating condition, carrying out current polarization treatment on the crystal obtained in the step (2) to enable the crystal to form a single-domain structure, so as to obtain the single-doped uranium lithium niobate crystal.

Preferably, the temperature of the defluorination treatment in the step 1 is 700-900 ℃ and the time is 4-6 h; the sintering treatment specifically comprises the following steps: firstly, raising the temperature of a muffle furnace to 700-900 ℃, preserving heat for 4-6 h, then raising the temperature to 1000-1200 ℃ for 2-4 h, preserving heat for 6-8 h, and finally cooling to room temperature.

Preferably, the specific process of the crucible descending method in the step 2 is as follows: controlling the temperature of the upper furnace body to be 1300-1500 ℃; after the furnace body is balanced for 12-24 h, inoculating seed crystals, and starting a descending device to slowly descend the crucible; the crystal grows along the c-axis direction, the process is completed in a constant temperature section, the shouldering speed is 0.2-0.3 mm/h, and the constant-diameter growth speed is 0.3-0.4 mm/h; and finally, cooling according to the program segment, and naturally cooling to room temperature.

Preferably, the heating temperature in the step 3 is 1100-1200 ℃; the current density of the polarization treatment is 6-8 mA/cm²The time is 10-30 min.

Compared with the prior art, the invention has the beneficial effects that:

1. the photorefractive effect of the single-doped uranium lithium niobate crystal is remarkably enhanced, the photorefractive response time is remarkably shortened, the sensitivity is greatly improved, the saturation diffraction efficiency of the crystal is as high as 65.35%, the response time is only 1.87s, and meanwhile, the sensitivity of the crystal is 2.52cm/J, which means that the crystal is expected to realize full-color holographic storage in the future. (ii) a

2. The single-doped uranium lithium niobate crystal grown by the Bridgman-Stockbarge method has high crystallization quality and uniformity, and the preparation process is simple, is beneficial to large-scale production and has good industrial application prospect.

Drawings

FIG. 1 is a graph showing the double swing of the LN: U crystal in example 1;

FIG. 2 shows the variation of photorefractive diffraction efficiency and photorefractive response time of LN-U crystal with doping concentration, the light intensity of two writing lights is 400mW/cm²。

Detailed Description

In order to make the invention more comprehensible, preferred embodiments are described in detail below with reference to the accompanying drawings.

Example 1

A preparation method of a single-doped uranium lithium niobate crystal comprises the following steps:

step 1: with a purity of 99.99 wt.% Li₂CO₃、99.99wt％Nb₂O₅And UO with purity ≧ 99.99%₂As a base material, UO₂In which [ Li ] is 0.6 mol%]/[Nb]The molar ratio of (A) to (B) is 0.937, and 300g of the total weight of each raw material is weighed. Respectively weighing Li according to the metering ratio of the elements₂CO₃、Nb₂O₅、UO₂Starting with Nb₂O₅Placing the powder into a crucible, then placing the crucible in a muffle furnace to heat to 800 ℃, and then keeping the temperature for 5 hours to perform Nb reaction₂O₅And (4) carrying out defluorination treatment on the powder. Then Li is added₂CO₃Nb after preliminary sintering₂O₅And high purity UO₂The raw materials are fully ground and mixed, then are put into an alumina crucible and are sintered in a high-temperature muffle furnace, and the highest temperature is set to be 1100 ℃. Firstly, raising the temperature to 800 ℃, preserving heat for 5h, then raising the temperature to 1100 ℃ for 3h, preserving heat for 7h, and finally cooling to obtain the mixtureLithium uranium niobate powder;

step 2: taking the prepared polycrystalline powder out of the alumina crucible, grinding for 2h, putting the powder into a Pt crucible, and performing crystal growth by adopting a Bridgman method, wherein the process parameters are as follows: the highest temperature of the upper furnace body is controlled to be about 1400 ℃. And (4) inoculating seed crystals after the furnace body is balanced for about 12-24 h, and starting a descending device to slowly descend the crucible. The growth of the crystal along the c-axis direction is completed in a constant temperature section, the shouldering speed is 0.2-0.3 mm/h, and the constant-diameter growth speed is 0.3-0.4 mm/h. And finally, cooling according to the program segment, and naturally cooling to room temperature. Grows a crystal which is tan, has the diameter of 1 inch, has no crack and has no obvious growth stripe;

and step 3: the obtained crystal is at 1100-1200 ℃ and 7mA/cm²The current density is polarized for 20min, and then the solution is naturally cooled to room temperature to obtain a single domain crystal;

and 4, step 4: and (3) carrying out the procedures of orientation, cutting, grinding, polishing and the like on the prepared crystal to prepare an optical-grade single-doped uranium lithium niobate wafer by cutting and polishing in the Y direction with the thickness of 1 mm.

The X-ray double swing curve of the single doped lithium niobate wafer prepared as described above is shown in fig. 1, and it can be seen from fig. 1 that the peak shape is sharp, the symmetry is good, and the full width at half maximum is small, about 9 ". As the swing curves of the LN U crystal are basically similar, the LN U crystal is selected in the experiment_0.6A wafer is representative and sample uniformity is evaluated by testing the full width at half maximum value of 9 different locations on the wafer. The results show that the FWHM values are all in the range of 9-12 ″. This means that the LN: U crystals grown by the modified Bridgman method have higher crystal quality and uniformity.

Using 400mW/cm²The 488nm continuous laser carries out the photorefractive performance test on the uranium-doped lithium niobate crystal, as shown in fig. 2, the result shows that: the saturation diffraction efficiency of the crystal is 67.15%, the photorefractive response time is 1.98s, and the photorefractive sensitivity is 2.24 cm/J. Compared with lithium niobate crystal with the same component, the photorefractive effect is obviously improved, the response time is improved by 2 orders of magnitude, and the sensitivity is improved by 1 order of magnitude.

Example 2

A preparation method of a single-doped uranium lithium niobate crystal comprises the following steps:

step 1: with a purity of 99.99 wt.% Li₂CO₃、99.99wt％Nb₂O₅And UO with purity ≧ 99.99%₂As a base material, UO₂In which [ Li ] is 1 mol%]/[Nb]The molar ratio of (A) to (B) is 0.937, and 300g of the total weight of each raw material is weighed. Respectively weighing Li according to the metering ratio of the elements₂CO₃、Nb₂O₅、UO₂Starting with Nb₂O₅Placing the powder into a crucible, then placing the crucible in a muffle furnace to heat to 800 ℃, and then keeping the temperature for 5 hours to perform Nb reaction₂O₅And (4) carrying out defluorination treatment on the powder. Then Li is added₂CO₃Nb after preliminary sintering₂O₅And high purity UO₂The raw materials are fully ground and mixed, then are put into an alumina crucible and are sintered in a high-temperature muffle furnace, and the highest temperature is set to be 1100 ℃. Firstly, raising the temperature to 800 ℃, preserving heat for 5h, then raising the temperature to 1100 ℃ for 3h, preserving heat for 7h, and finally cooling to obtain uranium-doped lithium niobate powder;

step 2: taking the prepared polycrystalline powder out of the alumina crucible, grinding for 2h, putting the powder into a Pt crucible, and performing crystal growth by adopting a Bridgman method, wherein the process parameters are as follows: the highest temperature of the upper furnace body is controlled to be about 1400 ℃. And (4) inoculating seed crystals after the furnace body is balanced for about 12-24 h, and starting a descending device to slowly descend the crucible. The growth of the crystal along the c-axis direction is completed in a constant temperature section, the shouldering speed is 0.2-0.3 mm/h, and the constant-diameter growth speed is 0.3-0.4 mm/h. And finally, cooling according to the program segment, and naturally cooling to room temperature. Grows a crystal which is tan, has the diameter of 1 inch, has no crack and has no obvious growth stripe;

and step 3: the obtained crystal is at 1100-1200 ℃ and 7mA/cm²The current density is polarized for 20min, and then the solution is naturally cooled to room temperature to obtain a single domain crystal;

and 4, step 4: and (3) carrying out the procedures of orientation, cutting, grinding, polishing and the like on the prepared crystal to prepare an optical-grade single-doped uranium lithium niobate wafer by cutting and polishing in the Y direction with the thickness of 1 mm.

The X-ray double rocking curve result of the single-doped lithium niobate wafer prepared by the method shows that the single-doped lithium niobate wafer has a sharp peak shape, good symmetry and a half-height width value of 13'.

Using 400mW/cm²The 488nm continuous laser carries out the photorefractive performance test on the uranium-doped lithium niobate crystal, as shown in fig. 2, the result shows that the saturation diffraction efficiency of the crystal is 47.35%, the photorefractive response time is 94.94s, and the photorefractive sensitivity is 0.39 cm/J.

Example 3

A preparation method of a single-doped uranium lithium niobate crystal comprises the following steps:

step 1: with a purity of 99.99 wt.% Li₂CO₃、99.99wt％Nb₂O₅And UO with purity ≧ 99.99%₂As a base material, UO₂In which [ Li ] is 2.0 mol%]/[Nb]The molar ratio of (A) to (B) is 0.937, and 300g of the total weight of each raw material is weighed. Respectively weighing Li according to the metering ratio of the elements₂CO₃、Nb₂O₅、UO₂Starting with Nb₂O₅Placing the powder into a crucible, then placing the crucible in a muffle furnace to heat to 800 ℃, and then keeping the temperature for 5 hours to perform Nb reaction₂O₅And (4) carrying out defluorination treatment on the powder. Then Li is added₂CO₃Nb after preliminary sintering₂O₅And high purity UO₂The raw materials are fully ground and mixed, then are put into an alumina crucible and are sintered in a high-temperature muffle furnace, and the highest temperature is set to be 1100 ℃. Firstly, raising the temperature to 800 ℃, preserving heat for 5h, then raising the temperature to 1100 ℃ for 3h, preserving heat for 7h, and finally cooling to obtain uranium-doped lithium niobate powder;

step 2: taking the prepared polycrystalline powder out of the alumina crucible, grinding for 2h, putting the powder into a Pt crucible, and performing crystal growth by adopting a Bridgman method, wherein the process parameters are as follows: the highest temperature of the upper furnace body is controlled to be about 1400 ℃. And (4) inoculating seed crystals after the furnace body is balanced for about 12-24 h, and starting a descending device to slowly descend the crucible. The growth of the crystal along the c-axis direction is completed in a constant temperature section, the shouldering speed is 0.2-0.3 mm/h, and the constant-diameter growth speed is 0.3-0.4 mm/h. And finally, cooling according to the program segment, and naturally cooling to room temperature. Grows a crystal which is tan, has the diameter of 1 inch, has no crack and has no obvious growth stripe;

and step 3: the obtained crystal is at 1100-1200 ℃ and 7mA/cm²The current density is polarized for 20min, and then the solution is naturally cooled to room temperature to obtain a single domain crystal;

and 4, step 4: and (3) carrying out the procedures of orientation, cutting, grinding, polishing and the like on the prepared crystal to prepare an optical-grade single-doped uranium lithium niobate wafer by cutting and polishing in the Y direction with the thickness of 1 mm.

The X-ray double rocking curve result of the single-doped lithium niobate wafer prepared by the method shows that the single-doped lithium niobate wafer has a sharp peak shape, good symmetry and a half-height width value of 13'.

Using 400mW/cm²The 488nm continuous laser carries out the photorefractive performance test on the uranium-doped lithium niobate crystal, as shown in fig. 2, the result shows that the saturation diffraction efficiency of the crystal is 65.35%, the photorefractive response time is 1.87s, and the photorefractive sensitivity is 2.52 cm/J.

The above-described embodiments are only preferred embodiments of the present invention, and are not intended to limit the present invention in any way and substantially, it should be noted that those skilled in the art may make several modifications and additions without departing from the scope of the present invention, which should also be construed as a protection scope of the present invention.