A single-mode excitation color-changing luminescence upconversion material and its preparation method and its application in security and anti-counterfeiting

Abstract

The present invention discloses a single-mode excitation color-changing luminescence up-conversion material and a preparation method thereof and its application in security anti-counterfeiting, belonging to the technical field of optical anti-counterfeiting. The molecular formula of the single-mode excitation color-changing luminescence up-conversion material is A x MOCl y‑1 :Yb / Ln, where A is Li + 、Na + , K + , Cs + At least one of; M is La 3+ , Y 3+ , Gd 3+ 、Lu 3+ At least one of; Ln is Er 3+ 、Ho 3+ 、Tm 3+ At least one of 1≤x≤4, 4≤y≤7. The excitation wavelength range of the single-mode excitation color-changing luminescence upconversion material is 950nm-11000nm, and the emission wavelength range is 400nm-800nm. Under the excitation of single-mode near-infrared light, the material exhibits color-changing upconversion luminescence. The upconversion material has a fast-response color-changing luminescence function, can be used as a high-level security anti-counterfeiting strategy, and the identification method is simple and convenient.

Description

Technical Field

[0001] The present invention relates to the technical field of optical anti-counterfeiting, and in particular to a single-mode excitation color-changing luminescent up-conversion material, a preparation method thereof, and an application thereof in security anti-counterfeiting. Background Art

[0002] Globally, the counterfeit and shoddy goods business causes economic losses of more than $1.7 trillion each year. Counterfeiting in the fields of medicines, high-value goods and currency seriously threatens the physical health of consumers, the interests of enterprises and social and economic security. Anti-counterfeiting strategies can make genuine goods difficult to be copied and effectively prevent counterfeit goods from circulating in the market. As one of the anti-counterfeiting strategies, rare earth-doped upconversion crystal materials have the advantages of low background fluorescence and strong resistance to photobleaching. At present, the upconverter materials used in currency and high-value goods have a single green light emission. These anti-counterfeiting materials emit light with almost no change in color when excited by near-infrared light. Anti-counterfeiting patterns constructed with such materials may still be imitated by counterfeiters using other materials with similar luminescence.

[0003] The security level of upconversion anti-counterfeiting materials can be improved by regulating the luminescence color. In recent years, a lot of research has been done on multicolor fluorescent materials. For example, multicolor fluorescence is produced by multimode fluorescence, adjusting laser power, or using pulsed lasers. These strategies have greatly improved the security level of anti-counterfeiting technology, but relatively complex identification equipment is required to trigger the multicolor luminescence of these new upconversion materials. First, upconversion and downconversion co-luminescence require multiple excitation sources; second, power-dependent multicolor luminescence requires adjustable ultra-high power lasers; finally, adjustable lifetime multiplexing requires time gate decoding equipment. The complexity of the material structure and the special identification method limit the commercial application of these anti-counterfeiting materials. Therefore, it is necessary to develop an anti-counterfeiting material with convenient identification and high security level.

[0004] Therefore, based on the above technical problems, there is an urgent need to provide an anti-counterfeiting material with convenient identification method and high security level. Summary of the invention

[0005] In order to solve the above technical problems, the present invention provides a single-mode excitation color-changing luminescent upconversion material and its preparation method and its application in security and anti-counterfeiting. The present invention adopts anion doping strategy and uses solid phase reaction method to prepare A x MOCl y-1 :Yb / Ln upconversion material. Under the excitation of a single near-infrared light, a variety of different paths of color-changing upconversion luminescence are realized. This color-changing luminescence upconversion material is not only simple and convenient to identify, but also has a high level of security and anti-counterfeiting, and has potential applications in the field of anti-counterfeiting.

[0006] The first object of the present invention is to provide a single-mode excitation color-changing luminescence up-conversion material, the molecular formula of the single-mode excitation color-changing luminescence up-conversion material is A x MOCl y-1 :Yb / Ln,

[0007] Where A is Li + 、Na + , K + , Cs + At least one of;

[0008] M is La 3+ , Y 3+ , Gd 3+ 、Lu 3+ At least one of;

[0009] Ln = Er 3+ 、Ho 3+ 、Tm 3+ At least one of;

[0010] 1≤x≤4, 4≤y≤7.

[0011] In some embodiments of the present invention, the A x MOCl y-1 :Yb / Ln in Yb 3+ As a sensitizer, it occupies the M position, Yb 3+ The doping amount is 1%-30%.

[0012] In some embodiments of the present invention, the A x MOCl y-1 :Ln in Yb / Ln 3+ As an activator, it occupies the M position, Ln 3+ The doping amount is 0.1%-5%.

[0013] In some embodiments of the present invention, the A x MOCl y-1 :O in Yb / Ln 2- It is the doped anion, occupying the Cl site.

[0014] In some embodiments of the present invention, the excitation wavelength of the single-mode excitation color-changing luminescence upconversion material is 950nm-1100nm.

[0015] In some embodiments of the present invention, the emission wavelength of the single-mode excitation color-changing luminescence upconversion material is 400nm-800nm.

[0016] The color change of the single-mode excitation color-changing luminescent up-conversion material includes but is not limited to red to green, green to cyan, and green to blue.

[0017] The second object of the present invention is to provide a method for preparing the single-mode excitation color-changing luminescence upconversion material, comprising the following steps: using the chloride of A, the chloride of M, a sensitizer and an activator to prepare the single-mode excitation color-changing luminescence upconversion material by a solid phase reaction method.

[0018] In some embodiments of the present invention, the chloride of A is selected from one or more of LiCl, NaCl, KCl, and CsCl;

[0019] The chloride of M is selected from one or more of LaCl3, YCl3, GdCl3, and LuCl3;

[0020] The sensitizer is selected from YbCl3;

[0021] The activator is selected from one or more of ErCl3, HoCl3, and TmCl3.

[0022] In some embodiments of the present invention, the heat treatment temperature in the solid phase reaction method is 100° C.-500° C., and the heat treatment time is 2-48 hours.

[0023] In some embodiments of the present invention, the specific preparation method is:

[0024] The chloride of A, the chloride of M, the sensitizer and the activator are prepared according to the molecular formula A x MOCl y-1 :Yb / Ln are mixed in a ratio of 50:1 and then ground evenly, and a muffle furnace, a tube furnace or an oven is used for heating to carry out a solid phase reaction to obtain the single-mode excitation color-changing luminescent upconversion material.

[0025] The third object of the present invention is to provide an application of the single-mode excitation color-changing luminescence upconversion material in security and anti-counterfeiting.

[0026] The above technical solution of the present invention has the following advantages compared with the prior art:

[0027] (1) Anion O 2- Doping, O occupies the Cl position and the crystal field symmetry is reduced; the low-symmetry crystal field is conducive to the Stark splitting of the 4f energy level of small-radius rare earth ions under the action of laser thermal effect, changing the upconversion luminescence dynamics; the upconversion luminescence mechanism is transformed from energy transfer upconversion to excited state absorption, thereby realizing thermally responsive color-changing upconversion luminescence.

[0028] (2) The solid phase reaction method is used in the preparation process, and the optical properties are stable;

[0029] (3) Single-mode excitation triggers color-changing luminescence, and the identification method is simple and convenient;

[0030] (4) The color-changing luminescence paths are diversified and the anti-counterfeiting technology level is high. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to make the content of the present invention more clearly understood, the present invention is further described in detail below according to specific embodiments of the present invention in conjunction with the accompanying drawings, wherein:

[0032] Figure 1 is the XRD spectrum of Cs2GdOCl4:Yb / Er of Example 1 of the present invention;

[0033] Figure 2 The upconversion emission spectra of the color-changing luminescent upconversion material Cs2GdOCl4:Yb / Er of Example 1 of the present invention at different times under the excitation of 975nm;

[0034] Figure 3 The emission spectrum of the color-changing luminescent upconversion material Cs2GdOCl4:Yb / Er of Example 1 of the present invention is an integrated intensity diagram at 525nm (Green) and 660nm (Red) emission bands;

[0035] Figure 4 This is a photograph of the color change of the luminescent color of the color-changing luminescent upconversion material Cs2GdOCl4:Yb / Er solid powder in Example 1 of the present invention within 4 seconds;

[0036] Figure 5 is the XRD spectrum of CsGdOCl3:Yb / Ho of Example 2 of the present invention;

[0037] Figure 6 The upconversion emission spectra of the color-changing luminescent upconversion material CsGdOCl3:Yb / Ho of Example 2 of the present invention at different times under the excitation of 975nm;

[0038] Figure 7 The emission spectrum of the color-changing luminescent upconversion material CsGdOCl3:Yb / Ho of Example 2 of the present invention is an integrated intensity diagram of the emission bands at 475nm (Blue), 530nm (Green), 590nm (Orange) and 650nm (Red);

[0039] Figure 8 This is a photograph of the color change of the luminescent color of the color-changing luminescent upconversion material CsGdOCl3:Yb / Ho solid powder in Example 2 of the present invention within 4 seconds;

[0040] Fig. 9 is the XRD spectrum of K3YOCl5:Yb / Tm of Example 3 of the present invention;

[0041] Fig.10The upconversion emission spectra of the color-changing luminescent upconversion material K3YOCl5:Yb / Tm in Example 3 of the present invention at different times under the excitation of 975nm;

[0042] Fig.11 This is a photograph of the luminescent color change of the color-changing luminescent upconversion material K3YOCl5:Yb / Tm solid powder in Example 3 of the present invention within 6 seconds. DETAILED DESCRIPTION

[0043] The present invention is further described below in conjunction with the accompanying drawings and specific embodiments so that those skilled in the art can better understand the present invention and implement it, but the embodiments are not intended to limit the present invention.

[0044] Example 1 (Cs2GdOCl4:Yb / Er)

[0045] This embodiment provides a method for preparing a single-mode excitation color-changing luminescent upconversion material (Cs2GdOCl4:Yb / Er), which is specifically as follows:

[0046] Weigh 2mmol CsCl, 0.78mmol GdCl3, 0.2mmol YbCl3, and 0.02mmol ErCl3, mix them evenly in a mortar, and calcine the mixture in a tube furnace at a temperature of 450°C for 24 hours to obtain Cs2GdOCl4:Yb / Er. Its XRD spectrum is as follows: Figure 1 shown.

[0047] The obtained Cs2GdOCl4:Yb / Er was excited at 975nm and the emission spectrum of the sample was continuously captured. From the emission spectrum and the integrated intensity of the emission band at different times, it can be seen that ( Figure 2 , 3 ), the initial red light emission band (~660nm) intensity is greater than the green light emission band (~525nm) intensity, and the sample emits red light; as the excitation time increases, the red light emission band intensity gradually weakens, while the green light emission intensity gradually increases, and the sample emits green light in the later stage; Figure 4 It can be seen that within a short time (4s), Cs2GdOCl4:Yb / Er undergoes a red→green color change when excited at 975nm.

[0048] Example 2 (CsGdOCl3:Yb / Ho)

[0049] This embodiment provides a method for preparing a single-mode excitation color-changing luminescent upconversion material (CsGdOCl3:Yb / Ho), which is specifically as follows:

[0050] Weigh 1mmol CsCl, 0.78mmol GdCl3, 0.2mmol YbCl3, and 0.02mmol HoCl3, mix them evenly in a mortar, and calcine the mixture in a muffle furnace at a temperature of 300°C for 2 hours to obtain CsGdOCl3:Yb / Ho. Its XRD spectrum is shown below: Figure 5 shown.

[0051] The obtained CsGdOCl3:Yb / Ho was excited at 975nm, and the emission spectra at different excitation times were measured. The emission bands of the emission spectra were integrated. The results are as follows: Figure 6 and Figure 7 As shown. Figure 6 It can be seen that at the beginning of 975nm excitation, the green light emission intensity (~540nm) of the sample is dominant, and its red light emission intensity (~660nm) is relatively weak, so the sample initially emits green light; as the excitation time increases, the blue light emission intensity (~475nm) of the sample gradually increases, and its intensity exceeds the green and red light emission intensities ( Figure 7 ).Depend on Figure 8 It can be seen that CsGdOCl3:Yb / Ho undergoes a color change from green to blue within 4s under 975nm excitation.

[0052] Example 3 (K3YOCl5:Yb / Tm)

[0053] This embodiment provides a method for preparing a single-mode excitation color-changing luminescent upconversion material (K3YOCl5:Yb / Tm), which is specifically as follows:

[0054] Weigh 3mmol KCl, 0.79mmol YCl3, 0.2mmol YbCl3, and 0.01mmol TmCl3, mix them evenly in a mortar, and place the mixture in an oven for heat treatment at 120°C for 48 hours to obtain K3YOCl5:Yb / Tm. Its XRD spectrum is as follows: Fig. 9 As shown.

[0055] The obtained K3YOCl5:Yb / Tm sample was continuously excited at 975nm to obtain the emission spectra at different times ( Fig.10 ). In the early stage of the emission spectrum, there is a strong green light emission peak at ~525nm, while the blue light emission peak at ~475nm is weak, so the sample shows green light emission at the initial stage of excitation; as the excitation time increases, although the green light emission band is enhanced, the blue light emission band is enhanced more significantly, so the sample shows blue light emission in the later stage of excitation. The color-changing luminescence photos of the solid powder in a short period of time confirm this single-mode excitation color-changing (green→blue) upconversion luminescence phenomenon ( Fig.11 ).

[0056] Obviously, the above embodiments are merely examples for clear explanation and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived from these are still within the protection scope of the invention.

Claims

1. A single-mode excitation color-changing luminescence upconversion material, characterized in that: The single-mode excitation color-changing luminescent up-conversion material is prepared by the following method: chloride of A, chloride of M, sensitizer and activator are prepared according to the formula A. x MOCl y-1 : Yb / Ln are mixed in a solid phase reaction to obtain the single-mode excitation color-changing luminescent upconversion material; Among them, A is Li + 、Na + , K + , Cs + At least one of; M is La 3+ , Y 3+ , Gd 3+ 、Lu 3+ At least one of; Ln = Er 3+ 、Ho 3+ 、Tm 3+ At least one of; x=1, y=4; or x=2, y=5, or x=3, y=6; The A x MOCl y-1 :O in Yb / Ln 2- It is the doped anion, occupying the Cl site.

2. The single-mode excitation color-changing luminescence upconversion material according to claim 1, characterized in that: The excitation wavelength of the single-mode excitation color-changing luminescence upconversion material is 950 nm-1100 nm; The emission wavelength of the single-mode excitation color-changing luminescence up-conversion material is 400 nm-800 nm.

3. The single-mode excitation color-changing luminescence upconversion material according to claim 1, characterized in that: The color change of the single-mode excitation color-changing luminescent up-conversion material includes red to green, green to cyan, or green to blue.

4. The single-mode excitation color-changing luminescence upconversion material according to claim 1, characterized in that: The chloride of A is selected from one or more of LiCl, NaCl, KCl, and CsCl; The chloride of M is selected from one or more of LaCl3, YCl3, GdCl3, and LuCl3; The sensitizer is selected from YbCl3; The activator is selected from one or more of ErCl3, HoCl3, and TmCl3.

5. The single-mode excitation color-changing luminescence upconversion material according to claim 1, characterized in that: In the solid phase reaction method, the heat treatment temperature is 100°C-500°C, and the heat treatment time is 2-48h.

6. Use of the single-mode excitation color-changing luminescence upconversion material according to any one of claims 1 to 5 in security and anti-counterfeiting.

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