Erbium and ytterbium co-doped calcium bismuth titanate dual-mode excitation up-conversion fluorescent anti-counterfeiting material and preparation method thereof

Abstract

The invention discloses an erbium and ytterbium co-doped calcium bismuth titanate dual-mode excitation up-conversion fluorescent anti-counterfeiting material and a preparation method thereof, the dual-mode excitation up-conversion fluorescent anti-counterfeiting material comprises an erbium and ytterbium co-doped calcium bismuth titanate light storage luminescent material, the chemical formula of the erbium and ytterbium co-doped calcium bismuth titanate light storage luminescent material is CaBi4 (0.97-x) Ti4O15: xEr < 3 + >, yYb < 3 + >, x is more than or equal to 0.005 and less than or equal to 0.1, and y is more than or equal to 0.1 and less than or equal to 0.4. The preparation method comprises the following steps: S1, weighing Bi2O3, Er2O3, Yb2O3, CaCO3 and TiO2 according to a stoichiometric ratio, and mixing and grinding the weighed materials into powder; and S2, sintering the powdery material obtained by grinding in the step S1 in a reducing atmosphere at the sintering temperature of 500-850 DEG C for 5-10 hours, then cooling to room temperature, and grinding the cooled material to obtain the erbium and ytterbium co-doped calcium bismuth titanate fluorescent powder CaBi4Ti4O15: Yb < 3 + > and Er < 3 + >. According to the calcium bismuth titanate dual-mode excitation up-conversion fluorescence anti-counterfeiting material disclosed by the invention, CaBi4Ti4O15 titanate is taken as a matrix to be double-doped with Yb < 3 + > and Er < 3 + >, so that the up-conversion luminescence performance and the fluorescence luminescence anti-counterfeiting performance are improved.

Description

Technical Field

[0001] The invention relates to the technical field of rare earth luminescent materials, and in particular to an erbium- and ytterbium-co-doped bismuth calcium titanate dual-mode excitation up-conversion fluorescent anti-counterfeiting material and a preparation method thereof. Background Art

[0002] In recent years, there has been a significant surge in interest in rare earth (RE) upconversion (UC) luminescent materials due to their great potential in a variety of applications. These materials have a wide range of applications, including solid-state lasers, three-dimensional stereoscopic displays, biomedical systems, and anti-counterfeiting technologies. Upconversion luminescence (UCL) is a special radiation process by which two or more low-energy (long-wavelength) photons are converted into one high-energy (short-wavelength) photon. This energy conversion property has led to widespread attention and application of fluorescent materials in a variety of fields such as bio-markers, data storage technology, laser anti-counterfeiting, and three-dimensional displays.

[0003] Among these fluorescent materials, calcium bismuth titanate has attracted much attention due to its unique optical properties. This material can not only convert low-energy light into high-energy light, but also has many significant advantages, such as narrow-band emission, extended fluorescence duration, and the ability to produce a variety of fluorescent outputs. It is these characteristics that make calcium bismuth titanate widely used in various anti-counterfeiting technologies.

[0004] However, currently calcium bismuth titanate used as upconversion luminescent materials all have single-mode photoluminescence, which is easy to be forged and copied, which will greatly reduce the credibility of anti-counterfeiting measures and cannot effectively meet the increasingly complex requirements of contemporary anti-counterfeiting measures. Summary of the invention

[0005] The present invention provides an erbium-ytterbium co-doped bismuth-calcium titanate dual-mode excitation up-conversion fluorescent anti-counterfeiting material and a preparation method thereof, in order to solve the above problems.

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

[0007] On the one hand, the present invention provides a dual-mode excitation up-conversion fluorescent anti-counterfeiting material of calcium bismuth titanate co-doped with erbium and ytterbium, the chemical formula of which is: CaBi 4(0.97-y) Ti 4 O 15 :xEr 3+ ,yYb 3+

[0008] Among them, 0.005≤x≤0.1, 0.1≤y≤0.4.

[0009] Furthermore, when the value of y is 0.2 and the value of x is 0.03, the chemical formula of the erbium-ytterbium co-doped calcium bismuth titanate dual-mode excitation up-conversion fluorescent anti-counterfeiting material is: CaBi 3.08 Ti 4 O 15 :0.03Er 3+ , 0.2Yb 3+ .

[0010] Another aspect of the present invention provides a method for preparing the erbium-ytterbium co-doped bismuth-calcium titanate dual-mode excitation up-conversion fluorescent anti-counterfeiting material, comprising the following steps:

[0011] S1: According to the stoichiometric ratio n Ca :n Bi :n Ti :n Er :n Yb =1:4(0.97-y):4:x:yWeigh CaCO 3 、Bi 2 O 3 、TiO 2 , Er 2 O 3 and Yb 2 O 3 , and mix and grind the weighed materials into powder, wherein 0.005≤x≤0.1, 0.1≤y≤0.4;

[0012] S2: Sinter the powdered material obtained by grinding in step S1 under a reducing atmosphere at a sintering temperature of 500-850°C for 5-10 hours, then cool to room temperature, grind the cooled material to obtain erbium and ytterbium co-doped powdered calcium bismuth titanate up-conversion fluorescent anti-counterfeiting material CaBi 4 Ti 4 O 15 :Yb 3+ , Er 3+ .

[0013] Furthermore, in S1, the grinding method is to place the material in an agate mortar and grind it for 30-60 minutes.

[0014] Furthermore, in S2, the specific method of sintering is: sintering the powdered material obtained by grinding in a carbon powder reducing atmosphere or a nitrogen-hydrogen mixed gas reducing atmosphere at 500°C for 5 hours, and then at 850°C for 10 hours.

[0015] Furthermore, the prepared erbium and ytterbium co-doped bismuth calcium titanate up-conversion fluorescent anti-counterfeiting material has an emission peak near 663nm when the monitoring wavelength is 980nm, and emits red light; under the excitation of 1550nm, the emission peak is located near 548nm, and emits green light.

[0016] Furthermore, the CaCO 3 、Bi 2 O 3 、TiO 2 , Er 2 O 3 and Yb 2 O 3 The purity is not less than 99.99%.

[0017] The beneficial effects of the present invention are:

[0018] The present invention uses CaBi 4 Ti 4 O 15 Titanate as a matrix for Yb dual doping 3+ , Er 3+ , prepared the Er-Yb co-doped calcium bismuth titanate dual-mode excitation upconversion fluorescent anti-counterfeiting material CaBi 4 Ti 4 O 15 :Er 3+ / Yb 3+ When excited at 980nm and 1550nm, the fluorescent material exhibits main green and red photoluminescence (PL) colors, respectively, showing multimodal conversion, improving the up-conversion luminescence performance and fluorescent luminescence anti-counterfeiting performance; and compared with traditional single-mode materials, since the multimodal material can produce different luminescence colors under the excitation of light of different wavelengths, the complexity and diversity of anti-counterfeiting identification are greatly increased, avoiding the problem that traditional single-mode materials have only one luminescence mode and are easily imitated or copied. Therefore, the multimodal material described in the present invention improves the concealment and security of anti-counterfeiting. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces 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 creative work.

[0020] Figure 1 The fluorescent CaBi disclosed in the present invention 4(0.97-y) Ti 4 O 15 :x Er 3+ / y Yb 3+ XRD patterns of (x=1%, 3%; y=20%, 30%);

[0021] Figure 2 The fluorescence emission spectrum of the phosphor disclosed in Comparative Examples 1-4 of the present invention with the comprehensive emission intensity of 665nm red light under 980nm laser and 548nm green light under 1550nm laser;

[0022] Figure 3 The up-conversion luminescence spectra of the phosphors disclosed in Examples 1-4 of the present invention (excitation wavelengths are 980 nm ( Figure 3 a) and 1550nm( Figure 3 b));

[0023] Figure 4 The up-conversion current luminescence spectrum of the phosphor disclosed in Example 1 of the present invention;

[0024] Figure 5 It is a fitting diagram of the variable current of the phosphor disclosed in Example 1 of the present invention;

[0025] Figure 6 is the up-conversion luminescence spectrum of the phosphor disclosed in Example 2 of the present invention;

[0026] Figure 7 It is a fitting diagram of the variable current of the phosphor disclosed in Comparative Example 2 of the present invention;

[0027] Figure 8 For the present invention Yb 3+ and Er 3+ Energy level diagram of ions, Figure 8 a is the energy level diagram at 980nm wavelength, Figure 8 b is the energy level diagram at a wavelength of 1550nm;

[0028] Fig. 9 The up-conversion variable temperature luminescence spectrum and the variable temperature fitting diagram of the phosphor disclosed in Example 2 of the present invention;

[0029] Fig.10 This is a fitting diagram of the up-conversion temperature sensitivity of the phosphor disclosed in Example 2 of the present invention;

[0030] Fig.11 The up-conversion variable temperature luminescence spectrum and the variable temperature fitting diagram of the phosphor disclosed in Example 3 of the present invention;

[0031] Fig.12 This is a fitting diagram of the up-conversion temperature sensitivity of the phosphor disclosed in Example 3 of the present invention. DETAILED DESCRIPTION

[0032] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0033] The sources of raw materials used in this application are as follows:

[0034] Table 1 Source of raw materials

[0035] Raw material name source <![CDATA[Er 2 THE 3 ]]> Tianjin Jinke Fine Chemical Research Institute <![CDATA[Yb 2 THE 3 ]]> Tianjin Jinke Fine Chemical Research Institute <![CDATA[TiO 2 ]]> Sinopharm Chemical Reagent Co., Ltd. <![CDATA[Bi 2 THE 3 ]]> Tianjin Jinke Chemical Reagent Co., Ltd. CaCO3 Sinopharm Chemical Reagent Co., Ltd.

[0036] Example

[0037] Example 1

[0038] CaBi 3.48 Ti 4 O 15 : 3% Er 3+ , 10% Yb 3+ The method for preparing the fluorescent anti-counterfeiting material comprises the following steps:

[0039] S1: weigh 0.0556g of 99.99% pure CaCO 3 , 0.1775g purity 99.99% TiO 2 , 0.4504g purity 99.99% Bi 2 O 3 , 0.0128g purity 99.99% Er 2 O 3 and 0.0438 g Yb with a purity of 99.99% 2 O 3 Place in an agate mortar and grind with alcohol for 30 minutes to obtain a powdered material;

[0040] S2: The powdery material obtained after grinding in step S1 is fired at 500°C for 5 hours in a carbon powder reducing atmosphere, and then fired at 850°C for 10 hours. After the sample is cooled to room temperature with the furnace, it is taken out, the powder is finely collected, and ground in an agate mortar to obtain erbium and ytterbium co-doped calcium bismuth titanate phosphor powder (CaBi 3.48 Ti 4 O 15 : 3% Er 3+ , 10% Yb 3+ ).

[0041] Example 2

[0042] CaBi3.08 Ti 4 O 15 : 3% Er 3+ , 20% Yb 3+ The preparation method of fluorescent luminescent material is different from that of Example 1 in that 0.3987 g of Bi with a purity of 99.99% is weighed. 2 O 3 .

[0043] Example 3

[0044] CaBi 2.68 Ti 4 O 15 : 3% Er 3+ , 30% Yb 3+ The preparation method of fluorescent anti-counterfeiting material is different from that of Example 1 in that 0.3469 g of 99.99% Bi 2 O 3 .

[0045] Example 4

[0046] CaBi 2.28 Ti 4 O 15 : 3% Er 3+ , 40% Yb 3+ The preparation method of fluorescent anti-counterfeiting material is different from that of Example 1 in that 0.2951 g of 99.99% Bi 2 O 3 .

[0047] Comparative Example

[0048] Comparative Example 1

[0049] CaBi 3.96 Ti 4 O 15 : 1% Er 3+ The method for preparing the anti-counterfeiting luminescent material is different from that in Example 1 except that Yb is not added. 2 O 3 , weighing 0.5126g purity 99.99% Bi 2 O 3 .

[0050] Comparative Example 2

[0051] CaBi 3.88 Ti 4 O 15 : 3% Er 3+ The method for preparing the anti-counterfeiting luminescent material is different from that in Example 1 except that Yb is not added. 2 O 3, weighing 0.5022g purity 99.99% Bi 2 O 3 .

[0052] Comparative Example 3

[0053] CaBi 3.8 Ti 4 O 15 : 5% Er 3+ The method for preparing the anti-counterfeiting luminescent material is different from that in Example 1 except that Yb is not added. 2 O 3 , weighing 0.4918g purity 99.99% Bi 2 O 3 .

[0054] Comparative Example 4

[0055] CaBi 3.68 Ti 4 O 15 : 8% Er 3+ The method for preparing the anti-counterfeiting luminescent material is different from that in Example 1 except that Yb is not added. 2 O 3 , weighing 0.4763g purity 99.99% Bi 2 O 3 .

[0056] Performance Testing

[0057] Test Example 1

[0058] The up-conversion fluorescent anti-counterfeiting materials obtained in Examples 2-3 and Comparative Examples 1-2 were subjected to X-ray diffraction analysis. The instrument used was Shimadzu XRD-6000, Japan. The irradiation source was Cu target Kα radiation. The scanning range was 10-70° and the scanning speed was 2° / min. The XRD diffraction pattern of the prepared light storage luminescent material was compared with the standard card JCPDS#43-0973. The comparison results are shown in Figure 1 .

[0059] Depend on Figure 1 It can be seen that the change of the doping concentration of the sample will not change its own crystal structure properties, and the prepared samples are all pure phase.

[0060] Test Example 2

[0061] The up-conversion fluorescent anti-counterfeiting materials prepared in Comparative Examples 1-4 were subjected to spectrum tests under 980nm laser and 1550nm laser. The test results are shown in Figure 2 , Figure 2 (a) and Figure 2 (b) Spectra at 980 and 1550 respectively; Figure 2It can be seen that under 980nm excitation, the main emission is in the green region, accompanied by weak red emission. On the contrary, under 1550nm excitation, the main emission peak falls in the red spectral range, especially in the range of 640-695nm. And it can be observed that Er 3+ The change in concentration does not significantly affect the color of the phosphor. At the same time, under 1550nm excitation, the emission color can be effectively tuned by changing the dopant concentration, while under 980nm excitation, this tuning effect is not obvious.

[0062] Test Example 3

[0063] The dual-mode excitation up-conversion fluorescent anti-counterfeiting materials obtained in Examples 1-4 were subjected to spectral testing under 980nm and 1550nm lasers. The testing method was as follows: first, the sample was fixed on a bracket to ensure accurate irradiation of the light beam, then the laser power was adjusted to the required level, and the luminescence spectrum was recorded using a spectrometer. This process was repeated, and the tests were performed under 980nm and 1550nm lasers, respectively, to obtain the luminescence characteristic data of the material at different wavelengths;

[0064] Test results see Figure 3 , Figure 3 (a) and Figure 3 (b) Luminescence spectra under 980nm and 1550nm lasers, respectively. Figure 3 It can be seen that the test results are as follows Figure 3 As shown in (a) and 3(b), the green emission under 1550nm laser excitation is significantly weaker than the red emission. 3+ and Yb 3+ Ion co-doping into CaBi 4 Ti 4 O 15 The relative emission intensity is significantly increased in the phosphor matrix, and this enhancement is mainly due to the Yb 3+ The absorption cross section of the ions is larger.

[0065] Test Example 4

[0066] The dual-mode excitation up-conversion fluorescent anti-counterfeiting materials obtained in Example 1 and Example 2 were respectively subjected to variable current and variable temperature tests, and the test method was as follows:

[0067] Place the sample on the sample holder, turn on the 980nm laser, and set the current to 2A to excite the sample. At each current value, use a spectrometer to record the luminescence spectrum of the upconversion fluorescent material, pay attention to recording parameters such as the peak position and intensity, then gradually reduce the current from 2A to 0.8A, reducing it by 0.1A each time (i.e. 2A, 1.9A, 1.8A, 1.7A, 1.6A, 1.5A, 1.4A, 1.3A, 1.2A, 1.1A, 1.0A, 0.9A, 0.8A), and repeat recording the spectral data at each current value;

[0068] After completing the test of the 980nm laser, turn off the 980nm laser, turn on the 1550nm laser, and set the current to 2A to excite the sample. At each current value, use a spectrometer to record the luminescence spectrum of the up-conversion fluorescent material, paying attention to recording parameters such as peak position and intensity. Then, gradually reduce the current from 2A to 0.8A, reducing it by 0.1A each time (i.e. 2A, 1.9A, 1.8A, 1.7A, 1.6A, 1.5A, 1.4A, 1.3A, 1.2A, 1.1A, 1.0A, 0.9A, 0.8A), and repeat recording the spectral data at each current value;

[0069] Test results see Figure 4-12 ,Depend on Figure 4-5 It can be seen that the emission intensity of the phosphor prepared in Example 1 at 549nm and 662nm under the excitation of 980nm laser is linearly fitted with slopes of 1.8 and 1.9, respectively, which indicates that the green and red UC emissions are the products of the two-photon absorption process; in addition, Figure 6-7 It can be seen that the slopes of the phosphor prepared in Example 2 under 1550 nm laser excitation are 2.6 and 2.7, respectively, which is consistent with the three-photon absorption process.

[0070] In summary, the present invention specifically describes CaBi 4 Ti 4 O 15 :Er 3+ / Yb 3+ The phosphor exhibits green and red emission when excited by 980nm and 1550nm lasers, respectively. In addition, the CaBi 4 Ti 4 O 15 :Er 3+ Therefore, these phosphors played a role in demonstrating their ability to hide critical information and act as security personnel.

[0071] The upconversion luminescence mechanism is as follows:

[0072] Upconversion luminescence refers to the phenomenon that some materials emit high-energy light (such as visible light) under the excitation of low-energy light (such as near-infrared light). This phenomenon mainly depends on the energy transfer process between rare earth ions (such as Er3+, Yb3+) in upconversion luminescent materials. In the upconversion process, near-infrared light (NIR) is usually used to excite rare earth ions. Rare earth ions have a unique electronic energy level structure and can absorb multiple low-energy photons and be excited to a higher energy level through a multi-photon process. In upconversion materials, two different types of rare earth ions are usually doped, such as Yb3+ and Er3+. Under the excitation of near-infrared light, Yb3+ ions are first excited to a high energy level, and then transfer energy to Er3+ ions through an energy transfer process. After receiving energy, Er3+ ions eventually return to the ground state through non-radiative transitions and radiative transitions, releasing high-energy visible light. This process realizes energy upconversion, that is, converting low-energy light into high-energy light.

[0073] In order to verify the above conclusion, Er-doped 3+ / Yb 3+ The upconversion luminescence energy level diagram of the ion under 980nm and 1550nm laser excitation is drawn, see Figure 8 .

[0074] According to the fluorescence intensity ratio-temperature change, the Sa curve reaches a maximum value as the temperature increases, while the Sr value gradually decreases, and Sa increases steadily as the temperature increases; Table 1 shows the maximum values ​​of the absolute sensitivity (Sa) of different materials under 980nm and 1550nm laser excitation.

[0075] Table 1 Maximum absolute sensitivity of different materials

[0076]

[0077] By comparing the data in Table 1, it can be seen that the CaBi prepared in the present invention 4(0.97-y) Ti 4 O 15 :3mol%Er 3+ / y mol% Yb 3+ (y=20 and 30) phosphors show higher maximum Sa values ​​than other materials. 4(0.97-y) Ti 4 O 15 :3mol%Er 3+ / y mol% Yb 3+ The potential of (y=20 and 30) phosphors as special optical temperature sensors provides a range of upconversion emission colors for various applications. Figure 9-12 , Fig. 9The up-conversion variable temperature luminescence spectrum and the variable temperature fitting diagram of the phosphor prepared in Example 2 are shown in FIG. Fig.10 This is a fitting diagram of the up-conversion temperature sensitivity of the phosphor prepared in Example 2; Fig.11 The up-conversion variable temperature luminescence spectrum and variable temperature fitting diagram of the phosphor prepared in Example 3 are shown in FIG. Fig.12 This is a fitting diagram of the up-conversion temperature sensitivity of the phosphor prepared in Example 3.

[0078] 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 aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein by 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. An Erbium- and Ytterbium-co-doped bismuth-calcium titanate dual-mode excitation up-conversion fluorescent anti-counterfeiting material, characterized in that: Its chemical formula is: CaBi 4(0.97-y) Ti4O 15 :xEr 3+ ,yYb 3+ Among them, 0.005≤x≤0.1, 0.1≤y≤0.

4.

2. The Erbium-Ytterbium co-doped bismuth-calcium titanate dual-mode excitation up-conversion fluorescent anti-counterfeiting material according to claim 1, characterized in that: When the value of y is 0.2 and the value of x is 0.03, the chemical formula of the erbium-ytterbium co-doped calcium bismuth titanate dual-mode excitation up-conversion fluorescent anti-counterfeiting material is: CaBi 3.08 Ti4O 15 :0.03Er 3+ , 0.2Yb 3+ .

3. A method for preparing the erbium and ytterbium co-doped bismuth calcium titanate dual-mode excitation up-conversion fluorescent anti-counterfeiting material as claimed in claim 1, characterized in that: The following steps are included: S1: According to the stoichiometric ratio n Ca :n Bi :n Ti :n Er :n Yb =1:4(0.97-y):4:x:y Weigh CaCO3, Bi2O3, TiO2, Er2O3 and Yb2O3, and mix and grind the weighed materials into powder, wherein 0.005≤x≤0.1, 0.1≤y≤0.4; S2: The powdered material obtained by grinding in step S1 is sintered in a reducing atmosphere at a sintering temperature of 500-850°C for 5-10 hours, and then cooled to room temperature. The cooled material is ground to obtain erbium and ytterbium co-doped powdered calcium bismuth titanate up-conversion fluorescent anti-counterfeiting material CaBi4Ti4O 15 :Yb 3+ , Er 3+ .

4. The preparation method according to claim 3, characterized in that: In S1, the grinding method is to place the material in an agate mortar and grind it for 30-60 minutes.

5. The preparation method according to claim 3, characterized in that: In S2, the specific method of sintering is: sintering the powdered material obtained by grinding in a carbon powder reducing atmosphere or a nitrogen-hydrogen mixed gas reducing atmosphere at 500° C. for 5 hours, and then at 850° C. for 10 hours.

6. The preparation method according to claim 3, characterized in that: The prepared erbium and ytterbium co-doped bismuth calcium titanate up-conversion fluorescent anti-counterfeiting material has an emission peak near 663nm when the monitoring wavelength is 980nm, and emits red light; under the excitation of 1550nm, the emission peak is near 548nm, and emits green light.

7. The preparation method according to claim 3, characterized in that: The purity of the CaCO3, Bi2O3, TiO2, Er2O3 and Yb2O3 is not less than 99.99%.

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