Preparation of Er-Ytterbium-doped LaTa7O by a molten salt method 19 Method and application of upconversion phosphor

Abstract

The present invention discloses a method for preparing erbium-ytterbium-doped LaTa7O by a molten salt method. 19 Methods and applications of upconversion phosphors. One method is to prepare Er-Yb doped LaTa7O by molten salt method. 19 The method of up-conversion phosphor is based on the chemical composition La a Er b Yb c Ta7O 19 The stoichiometric ratio of each element in the mixture is 1, where a+b+c=1. Weigh the lanthanum ion La 3+ Compounds containing erbium ions Er 3+ Compounds containing ytterbium ions Yb 3+ Compounds and compounds containing tantalum ions Ta 5+ The compounds are mixed and ground, and then an excess of potassium chloride (KCl) is added to mix evenly. The material is sintered at 770°C or above for 2-168 hours. After sintering, the powder is cooled to room temperature and filtered with deionized water to obtain an upconversion luminescent material. LaTa7O prepared by the present invention 19 :Er 3+ / Yb 3+ Upconversion phosphor material, under 980nm excitation, the green light integral area reaches β-NaYF4:Er 3+ / Yb 3+ It can replace β-NaYF4:Er in the fields of fluorescence display, high corrosion environment with pH=0 or pH>12, high temperature environment above 450℃ and temperature sensing. 3+ / Yb 3+ Phosphor.

Description

Technical Field

[0001] The present invention relates to the technical field of up-conversion luminescent material preparation, and in particular to a method for preparing erbium-ytterbium-doped LaTa7O by a molten salt method. 19 Methods and applications of upconversion phosphors. Background Art

[0002] In recent years, rare earth doped fluorides have received extensive attention due to their good physical and chemical properties and excellent luminescence performance. This type of material has the advantages of high light transmittance, low phonon energy, and narrow emission spectrum band. Its application areas include anti-counterfeiting, lasers, three-dimensional flat panel displays, solar cells, photodynamic therapy, etc. As a rare earth doped matrix material, NaYF4 crystal has very low phonon energy and can obtain a very high luminescence quantum efficiency. NaYF4 has two crystal structures: cubic phase (α-) and hexagonal phase (β-). After doping with rare earth ions, the latter has relatively better luminescence performance. Among all rare earth ion doped fluorides, Er 3+ / Yb 3+ Co-doped β-NaYF4 is a material recognized to have high upconversion luminescence efficiency.

[0003] However, the chemical stability of fluoride is poor. In highly corrosive environments, high temperature environments, and high laser excitation, the structure of fluoride is easily destroyed and loses its excellent performance, thus limiting the development of β-NaYF4:Er 3+ / Yb 3+ Phosphors are used in special environments such as high corrosion, high temperature and high power excitation. If chemically stable oxides are used to replace fluorides, the upconversion fluorescence intensity of the oxides is lower than that of β-NaYF4:Er 3+ / Yb 3+ .

[0004] Therefore, it is urgent to propose an upconversion phosphor material that can replace β-NaYF4:Er 3+ / Yb 3+ Phosphors are used in special environments and maintain high upconversion fluorescence intensity. Summary of the Invention

[0005] In view of the above-mentioned shortcomings of the prior art, the purpose of the present invention is to provide a molten salt method for preparing erbium-ytterbium-doped LaTa7O 19 Upconversion phosphor method, prepared LaTa7O 19 :Er 3+ / Yb 3+ Up-conversion phosphor material, under 980nm excitation, the green light integral area reaches β-NaYF4:Er 3+ / Yb 3+It can replace β-NaYF4:Er in some special application environments. 3+ / Yb 3+ Phosphor.

[0006] In order to achieve the above object, the technical solution of the present invention is:

[0007] Preparation of Er-Ytterbium-doped LaTa7O by a molten salt method 19 The method for upconverting phosphor comprises the following steps:

[0008] According to chemical composition a Er b Yb c Ta7O 19 The stoichiometric ratio of each element in the mixture is 1, where a+b+c=1. Weigh the lanthanum ion La 3+ Compounds containing erbium ions Er 3+ Compounds containing ytterbium ions Yb 3+ Compounds and compounds containing tantalum ions Ta 5+ The compounds are mixed and ground, and then an excess of potassium chloride (KCl) is added and mixed until uniformly mixed. The material is sintered at a temperature above 770°C for 2-168 hours. After sintering, the powder is cooled to room temperature and filtered with deionized water to obtain an upconversion luminescent material. Preferably, the material is sintered at a temperature of 770-1150°C for 2-168 hours.

[0009] Furthermore, in the chemical formula, a=0.5, b=0.1, and c=0.4. Preferably, La:Er:Yb:Ta=0.5:0.1:0.4:7.

[0010] Furthermore, the lanthanum ion La 3+ Before mixing, bake the compound at 900℃ for 2 hours to dry out the moisture. La2O3 easily absorbs water and needs to be dried before use.

[0011] Furthermore, the molar ratio of the potassium chloride (KCl) to the up-conversion luminescent material is greater than 10: 1. Preferably, the amount of potassium chloride (KCl) added is 20 g.

[0012] Furthermore, the lanthanum ion La 3+ The compound is one of lanthanum oxide and lanthanum nitrate; the erbium ion Er 3+ The compound is one of erbium oxide and erbium nitrate; the compound containing ytterbium ion Yb 3+ The compound is one of ytterbium oxide and ytterbium nitrate; the compound containing tantalum ion Ta 5+The compound is tantalum oxide. Preferably, the purity of La2O3, Er2O3, Yb2O3, and Ta2O5 is 98.0-99.99%.

[0013] Furthermore, the material is sintered at 770-950°C (excluding 950°C) for 2-168 hours. After sintering, the powder is cooled to room temperature and filtered with deionized water to obtain pure LaTa7O 19 :0.1Er 3+ / 0.4Yb 3+ Preferably, the material is sintered at 770-825°C.

[0014] Further, the material is sintered at 950-1150°C, excluding 1150°C, for 2-168 hours. After sintering, the powder is cooled to room temperature and filtered with deionized water to obtain LaTa7O 19 :0.1Er 3+ / 0.4Yb 3+ and K2LaTa5O 15 :Er 3+ / Yb 3+ Mixed phase.

[0015] Furthermore, the material was sintered at a temperature above 1150°C for 2-168 hours. After sintering, the powder was cooled to room temperature and filtered with deionized water to obtain K2LaTa5O 15 :Er 3+ / Yb 3+ Pure phase, the K2LaTa5O 15 :Er 3+ / Yb 3+ It belongs to the tetragonal crystal system and its space group is P4 / mbm(127).

[0016] Furthermore, the LaTa7O 19 :0.1Er 3+ / 0.4Yb 3+ It belongs to the hexagonal crystal phase and its space group is P-6C2(188).

[0017] The Er-Yb-doped LaTa7O 19 Up-conversion phosphors are used in fluorescent displays, highly corrosive environments with pH = 0 or pH > 12, high-temperature environments above 450°C, and temperature sensing.

[0018] In summary, the present invention has the following beneficial effects:

[0019] First, this application uses LaTa7O 19 As a matrix, Er is doped into the matrix 3+ and Yb 3+, and using KCl as solvent, Er-Yb doped LaTa7O prepared by molten salt method 19 Upconversion phosphor, prepared by Er-Yb-doped LaTa7O 19 Upconversion phosphors have high brightness, pure color, and high chemical stability. They are expected to replace commercial β-NaYF4:Er in the fields of fluorescent display, high corrosion environment, high temperature environment and temperature sensing. 3+ / Yb 3+ The phosphor powder was experimentally determined to be LaTa7O 19 :0.1Er 3+ / 0.4Yb 3+ The green upconversion fluorescence integrated area of the phosphor is comparable to that of β-NaYF4:Er 3+ / Yb 3+ , reaching β-NaYF4:Er 3+ / Yb 3+ 60% of.

[0020] Second, pure phase LaTa7O was successfully prepared using the molten salt method at low temperature. 19 :Er 3+ / Yb 3+ Upconversion phosphor, while at high temperature, the product is pure phase K2LaTa5O 15 :Er 3+ / Yb 3+ ,This application can control the particle size from nano to micro scale by adjusting the sintering temperature and holding time, and the particle morphology is regular. It can be expected that further improvements in the experimental parameters, such as Er 3+ / Yb 3+ The concentration control, fine-tuning of the maximum molten salt temperature, and change of the holding time can further improve the LaTa7O 19 :Er 3+ / Yb 3+ Upconversion fluorescence intensity of phosphor. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following is a brief introduction to the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative labor.

[0022] Figure 1 The XRD results of the up-conversion luminescent materials synthesized in Examples 1-6 of the present invention are shown;

[0023] Figure 2This is a SEM morphology image of the upconversion luminescent material synthesized in Example 2 of the present invention;

[0024] Figure 3 The particle sizes of the a and b surfaces of the upconversion luminescent material synthesized in Example 2 of the present invention;

[0025] Figure 4 This is a SEM morphology image of the upconversion luminescent material synthesized in Example 1 of the present invention;

[0026] Figure 5 The particle sizes of the a and b surfaces of the upconversion luminescent material synthesized in Example 1 of the present invention;

[0027] Figure 6 The upconversion fluorescence spectra of the upconversion luminescent materials synthesized in Examples 1, 2, and 6 of the present invention under 980nm laser excitation;

[0028] Figure 7 The up-conversion luminescent material and β-NaYF4:Er synthesized in Example 1 of the present invention 3+ / Yb 3+ Upconversion fluorescence spectrum of phosphor under 980nm laser excitation;

[0029] Figure 8 This is a temperature-variable up-conversion spectrum diagram of Example 1 disclosed in the present invention;

[0030] Figure 9 Graph showing the relationship between the fluorescence intensity branching ratio (LIR value) and temperature in Example 1 disclosed in the present invention;

[0031] Figure 10 The absolute temperature sensitivity S of Example 1 disclosed in the present invention A The relationship graph with temperature;

[0032] Figure 11 is the relative temperature sensitivity S of Example 1 disclosed in the present invention R Graph of its relationship with temperature.

[0033] Figure 12 YTa7O 19 ,GdTa7O 19 and BiTa7O 19 XRD results of molten salt preparation. DETAILED DESCRIPTION

[0034] To make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the following will be combined with the appended drawings of the embodiments of the present invention. Figure 1-7The technical solutions in the embodiments of the present invention are clearly and completely described. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. All other embodiments derived 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.

[0035] The raw materials involved in this application are all commercially available.

[0036] Example

[0037] Example 1

[0038] Preparation of LaTa7O by a molten salt method 19 :0.1Er 3+ / 0.4Yb 3+ The method for upconverting phosphor comprises the following steps:

[0039] S1: Place 0.2 g of La2O3 in a muffle furnace and bake at 900°C for 2 hours to dry out the moisture;

[0040] S2: According to La 3+ :Er 3+ :Yb 3+ :Ta 5+ =0.5:0.1:0.4:7 molar ratio, weigh 0.1317g of La2O3, 0.0309g of Er2O3, 0.1274g of Yb2O3 and 2.5g of Ta2O5 respectively, mix them, grind the mixed raw materials, and after grinding them evenly, add a large amount of KCl (mass 20g) and continue to mix them evenly;

[0041] S3: The mixed raw materials are placed in a muffle furnace, sintered at 825°C for 24 hours, cooled to room temperature in the furnace, and filtered with deionized water to obtain an upconversion luminescent material.

[0042] Example 2

[0043] The only difference from Example 1 is that, S3: the mixed raw materials are placed in a muffle furnace, sintered at 825° C. for 2 hours, cooled to room temperature in the furnace, and filtered with deionized water to obtain an upconversion luminescent material.

[0044] Example 3

[0045] The only difference from Example 1 is that S3: the mixed raw materials are placed in a muffle furnace, sintered at 850° C. for 2 hours, cooled to room temperature in the furnace, and filtered with deionized water to obtain an upconversion luminescent material.

[0046] Example 4

[0047] The only difference from Example 1 is that S3: the mixed raw materials are placed in a muffle furnace, sintered at 950° C. for 2 hours, cooled to room temperature in the furnace, and filtered with deionized water to obtain an upconversion luminescent material.

[0048] Example 5

[0049] The only difference from Example 1 is that S3: the mixed raw materials are placed in a muffle furnace, sintered at 1050° C. for 2 hours, cooled to room temperature in the furnace, and filtered with deionized water to obtain an upconversion luminescent material.

[0050] Example 6

[0051] The only difference from Example 1 is that S3: the mixed raw materials are placed in a muffle furnace, sintered at 1150° C. for 2 hours, cooled to room temperature in the furnace, and filtered with deionized water to obtain an upconversion luminescent material.

[0052] Figure 1 The XRD test results of the up-conversion luminescent materials prepared in Example 1-6 are as follows: Cu target was used for the test, the equipment model was Rigaku D / MAX RE, and the incident wavelength λ was

[0053] Figure 1 It shows that hexagonal LaTa7O can be formed in molten salt at 825℃ 19 phase, and the structural space group is P-6C2(188). As the molten salt is kept at 825℃ for a longer time, the impurities in Ta2O5 will decrease, and LaTa7O 19 :Er 3+ / Yb 3+ The crystal grows more fully. At 950-1150℃ (excluding 1150℃) molten salt, LaTa7O 19 :Er 3+ / Yb 3+ and K2LaTa5O 15 :Er 3+ / Yb 3+ Mixed phase structure. In molten salt at 1150℃, K2LaTa5O 15 :Er 3+ / Yb 3+ The pure phase structure is tetragonal and the space group is P4 / mbm(127).

[0054] Figure 2 LaTa7O synthesized in Example 2 19 :0.1Er 3+ / 0.4Yb 3+ SEM morphology of phosphor.

[0055] Figure 2 It shows that LaTa7O 19 It is a layered structure similar to a hexagonal structure. This is consistent with the XRD results. There are some scattered small particles on the particle surface, which may be some impurities Ta2O5 or new grains that have not yet fully grown.

[0056] Figure 3 LaTa7O synthesized in Example 2 19 :0.1Er 3+ / 0.4Yb 3+ The a and b surface particle sizes of the phosphor.

[0057] Figure 3 It shows that the average size of the a and b surfaces is 0.98μm.

[0058] Figure 4 LaTa7O synthesized in Example 1 19 :0.1Er 3+ / 0.4Yb 3+ SEM morphology of phosphor.

[0059] Combine Figure 2 and Figure 4 Compared with the 2h heat preservation, the particle size of the phosphor synthesized in Example 1 increased and the scattered small particles decreased, indicating that the impurity Ta2O5 may be reduced or the newly nucleated grains have been further grown.

[0060] Figure 5 LaTa7O synthesized in Example 1 19 :0.1Er 3+ / 0.4Yb 3+ The a and b surface particle sizes of the phosphor.

[0061] Figure 5 It shows that the average size of the a and b surfaces is 1.67μm.

[0062] Figure 6 This is a comparison of upconversion fluorescence of Example 1, Example 2 and Example 6 under 980nm laser excitation.

[0063] Figure 6 It shows that the maximum upconversion fluorescence intensity is obtained when the temperature is kept at 825℃ for 24h. However, the upconversion fluorescence intensity of the molten salt sample at 1150℃ is very low. This is because the hexagonal LaTa7O 19 :Er 3+ / Yb 3+ The upconversion fluorescence efficiency is much higher than that of tetragonal K2LaTa5O 15 :Er 3+ / Yb 3+This upconversion fluorescence contrast image is also consistent with Figure 1 The XRD results are consistent with those of

[0064] For existing NaYF4:Er 3+ / Yb 3+ The luminescent material (Shenzhen Zhanwanglong Technology Co., Ltd., 980nm infrared up-conversion excited green NaYF4 anti-counterfeiting phosphor identification biological probe) was tested and compared with the fluorescence performance of the sample prepared in Example 1. The results are as follows Figure 7 .

[0065] from Figure 7 It can be seen that the LaTa7O 19 :0.1Er 3+ / 0.4Yb 3+ The upconversion green fluorescence integral area of the sample can reach β-NaYF4:Er 3+ / Yb 3+ 60% of.

[0066] Figure 8 The temperature-dependent up-conversion fluorescence spectrum of Example 1 under 980 nm laser excitation is shown. As the temperature increases, the fluorescence intensity decreases, which is a manifestation of thermal quenching. H with I S The relationship curve between the fluorescence intensity branching ratio (LIR value) and temperature, and the relationship curve between the LIR value and temperature T can be calculated by the following formula:

[0067]

[0068] I H For Er 3+ of 2 H 11 / 2 → 4 I 15 / 2 Emission fluorescence integrated intensity value;

[0069] I S For Er 3+ of 4 S 3 / 2 → 4 I 15 / 2 The integrated intensity of emitted fluorescence; B is a constant, k B is the Boltzmann constant, ΔE is 2 H 11 / 2 and 4 S 3 / 2 The band gap between energy levels.

[0070] The fitted function is LIR = 16.84exp(-794.56 / T), see Figure 9 , the fitting degree is 0.9920, Figure 9 It can be seen that I H / I S The value increases as the temperature increases, and there is a one-to-one correspondence.

[0071] The calculation formulas for absolute temperature sensitivity SA and relative temperature sensitivity SR are as follows:

[0072]

[0073]

[0074] The calculation results are shown in Figure 10 and Figure 11 The maximum absolute temperature sensitivity of this application is S A is 0.01147K -1 (at 398K), maximum S R It is 0.00869K -1 (at 303K). The currently reported β-NaYF4:Er 3+ / Yb 3+ At 363K, the maximum absolute sensitivity can be obtained to be 0.00368K -1 It can be seen that the LaTa7O 19 :Er 3+ / Yb 3+ Luminescent materials have certain application prospects in the field of photothermal sensing.

[0075] The mechanism involved in this application is: in the present invention, LaTa7O 19 The matrix is used as the main body of rare earth ion doping, and Er is doped in the matrix. 3+ and Yb 3+ , and use KCl as solvent, because K + The combination of ions and La-Ta-O requires high temperature. This application selects low temperature (less than or equal to 825℃) molten salt to obtain pure phase and avoid K + In addition, research has found that layered α-U3O8 tantalate is a metastable state and must be synthesized at a relatively low temperature. High temperatures will form other stable high-temperature phases. The LaTa7O 19 The structure is hexagonal P-6c2(188) crystal group, due to LaTa7O 19 The low phonon energy and layered structure of the matrix promote the 3+ Xiang Er 3+ The energy transfer occurs in a two-dimensional plane, which reduces the energy loss caused by cross relaxation and also improves the Yb 3+ Xiang Er 3+ The energy transfer efficiency is high, and outstanding upconversion fluorescence intensity is obtained.

[0076] Comparative Example

[0077] The only difference between Comparative Examples 1-3 and Example 1 is that Y2O3, Gd2O3 and Bi2O3 are used instead of La2O3. According to the ICSD database, BiTa7O 19 The space group is P-6c2(188);

[0078] Figure 12 The XRD test results of the up-conversion luminescent materials prepared in Comparative Examples 1-3 are as follows: Cu target was used for the test, the equipment model was Rigaku D / MAX RE, and the incident wavelength λ was

[0079] Figure 12 The XRD diffraction peaks of the molten salt product do not match the standard card, so these oxide preparation parameters are similar to those of LaTa7O 19 are different and require different experimental parameters for preparation.

[0080] Since GdTa7O 19 and BiTa7O 19 and P63 / mcm and YTa7O 19 The structure is similar. The space groups of each upconversion luminescent material measured by the above method are: GdTa7O 19 (P-6c2(188)) and BiTa7O 19 (P-6c2(188) and P63 / mcm(193)) with YTa7O 19 (P-6c2(188)). This shows that under similar structures, the chemical reaction activities of the raw materials Y2O3, Gd2O3, Bi2O3, and La2O3 are different due to the different elements. Therefore, compared with the upconversion luminescent materials prepared from the above materials, the present application successfully prepared pure phase LaTa7O using the molten salt method at low temperature (below 825°C). 19 :Er 3+ / Yb 3+ Upconversion phosphor with excellent upconversion fluorescence intensity.

[0081] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. Erbium-ytterbium doped LaTa7O 19 The application of up-conversion phosphor in the field of temperature sensing is characterized by: The Er-Yb-doped LaTa7O 19 The preparation method of upconversion phosphor comprises the following steps: According to chemical composition a Er b Yb c Ta7O 19 The stoichiometric ratio of each element in the mixture is 1, where a+b+c=1. Weigh the lanthanum ion La 3+ Compounds containing erbium ions Er 3+ Compounds containing ytterbium ions Yb 3+ Compounds and compounds containing tantalum ions Ta 5+ The compounds are mixed and ground, and after mixing and grinding, excess potassium chloride (KCl) is added and mixed evenly, and the materials are sintered at 770-950° C., excluding 950° C., for 2-168 hours. After the sintering is completed, the powder is cooled to room temperature and filtered with deionized water to obtain an upconversion luminescent material.

2. The Er-Yb-doped LaTa7O according to claim 1 19 The application of up-conversion phosphor in the field of temperature sensing is characterized by: In the chemical formula, a=0.5, b=0.1, and c=0.

4.

3. The Er-Yb-doped LaTa7O according to claim 1 19 The application of up-conversion phosphor in the field of temperature sensing is characterized by: Contains lanthanum ions La 3+ The compound was heated at 900 o C for 2 hours.

4. The Er-Yb-doped LaTa7O according to claim 1 19 The application of up-conversion phosphor in the field of temperature sensing is characterized by: The molar ratio of the potassium chloride (KCl) to the up-conversion luminescent material is greater than 10:

1.

5. The Er-Yb-doped LaTa7O according to claim 1 19 The application of up-conversion phosphor in the field of temperature sensing is characterized by: The lanthanum ion La 3+ The compound is one of lanthanum oxide and lanthanum nitrate; the erbium ion Er 3+ The compound is one of erbium oxide and erbium nitrate; the compound containing ytterbium ion Yb 3+ The compound is one of ytterbium oxide and ytterbium nitrate; the compound containing tantalum ion Ta 5+ The compound is tantalum oxide.

6. The Er-Yb-doped LaTa7O according to claim 2 19 The application of up-conversion phosphor in the field of temperature sensing is characterized by: Prepared LaTa7O 19 :0.1Er 3+ / 0.4Yb 3+ It belongs to the hexagonal crystal phase and its space group is P-6C2 (188).

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