CN115353877A

CN115353877A - Up-conversion/long afterglow multi-mode luminescent material and preparation and application thereof

Info

Publication number: CN115353877A
Application number: CN202210726170.2A
Authority: CN
Inventors: 陈硕然; 赵鑫; 叶常青; 李琳; 王筱梅; 宋延林
Original assignee: Suzhou University of Science and Technology
Current assignee: Suzhou University of Science and Technology
Priority date: 2022-06-24
Filing date: 2022-06-24
Publication date: 2022-11-18

Abstract

The invention belongs to the technical field of luminescent materials, and particularly relates to an up-conversion/long-afterglow multi-mode luminescent material and preparation and application thereof. The invention realizes a novel multimode luminescent system by combining TTA-UC organic luminescent molecule pairs (a sensitizer and an annihilator) with lanthanide doped fluorescent powder with different afterglow colors, and can realize luminescence including Fluorescence (FL), up-conversion (UC) and afterglow through a double excitation mode (365/532 nm). The prepared luminescent material can be patterned by a direct writing technology, and the application of multi-dimensional anti-counterfeiting and information coding is finally realized.

Description

Up-conversion/long afterglow multi-mode luminescent material and preparation and application thereof

Technical Field

The invention belongs to the technical field of luminescent materials, and particularly relates to an up-conversion/long-afterglow multi-mode luminescent material as well as preparation and application thereof.

Background

In recent years, with the rapid development of economy, the problem of counterfeit products has become increasingly serious and urgent on a global scale. Therefore, various anti-counterfeiting technologies such as bar codes, two-dimensional codes, digital watermarks, radio frequency identification, holographic technologies, and recently developed luminescent anti-counterfeiting technologies have been developed to ensure the security and reliability of products. Because of its advantages of being recognizable by naked eyes, strong secrecy, difficult to copy, etc., anti-counterfeiting technologies based on various light-emitting materials have attracted extensive research interest and have been practically applied. The working mode of the early luminescent anti-counterfeiting material is to emit light with specific wavelength under the fixed and unchangeable excitation wavelength, and the single mode is easy to crack and copy, so that the luminescent anti-counterfeiting material is greatly limited in practical application. In order to cope with the continuously developed counterfeit technology, more advanced materials containing multiple light-emitting modes are needed to be applied to the anti-counterfeiting technology, so that the system can be excited by exciting light with different wavelengths, and the light-emitting modes different from the traditional fluorescence, such as up-conversion light-emitting, long-afterglow light-emitting, stimulus-responsive light-emitting and the like, are presented, and then the multi-dimensional light-emitting anti-counterfeiting technology with higher safety factor is developed.

The long afterglow material has good application prospect in the fields of biological imaging, sensing detection, emergency lighting, information storage and the like due to the special self-sustaining luminescence property. Among different kinds of afterglow materials, lanthanide doped inorganic afterglow phosphors have been commercialized due to their stable properties. However, most phosphors can only be excited by short wavelength light sources such as uv light, which is the most used excitation light source in anti-counterfeiting applications, and this is why anti-counterfeiting technologies based on uv excitation are relatively easy to imitate or crack. On the other hand, photon up-conversion (UC) is a special Photoluminescence (PL) process that converts low-energy photons into high-energy photons. Due to the special anti-Stokes displacement, the up-conversion has been applied to the fields of photovoltaic energy, biological imaging, sensing detection, anti-counterfeiting coding and the like. The characteristic of long wavelength excitation of up-conversion is applied to anti-counterfeiting, and flexible and changeable excitation modes can be realized, so that anti-counterfeiting safety and concealment are improved. Therefore, if a combination of afterglow and upconversion luminescent materials is used, a multimode luminescent system with long/short wavelength excitation and long/short lifetime PL emission can be obtained.

At present, the literature reports that the two light-emitting modes are combined mainly in the following two ways: one is that a certain material has both afterglow and upconversion luminescence properties, and is usually a lanthanide doped nanomaterial (for example, the invention patent with application number 201710336902.6 adopts two materials for compounding, one is for emitting upconversion light, the other is for absorbing the upconversion light to emit afterglow light, the material in the invention patent with application number 201610875520.6 has both the characteristics of upconversion luminescence and afterglow luminescence, and is also an inorganic material doped with rare earth elements); and secondly, through an energy transfer process, the up-conversion luminescence energy can be used for exciting the afterglow material, namely, the up-conversion energy can charge energy for the afterglow. The latter is comparatively simple to synthesize and prepare and allows tuning of excitation and emission wavelengths by selecting different afterglow and upconversion luminescent material pairs, thus also providing a controllable luminescence mode and performance for anti-counterfeiting.

Up-conversion materials reported in the literature for applications in anti-counterfeiting and coding so far mostly belong to the lanthanide up-conversion mechanism, usually excited by Near Infrared (NIR) laser. The larger anti-stokes shift of lanthanide up-conversion nanoparticles (UCNPs) can realize visible light emission, i.e. an anti-counterfeiting visual effect which can be recognized by naked eyes. However, the up-conversion luminescence mode of lanthanide UCNPs is still limited by a fixed excitation wavelength (typically 980 or 808 nm), making it inflexible with respect to anti-counterfeiting performance and easy to crack or copy. In addition, high-power near-infrared laser invisible to naked eyes is easy to cause potential damage to human eyes in the daily use process.

Among other up-conversion mechanisms, triplet-triplet annihilation up-conversion (TTA-UC) has the advantages of high up-conversion efficiency, flexible and adjustable excitation and emission wavelength positions, and low excitation power threshold, and is also called weak light up-conversion. The TTA upconversion mechanism provides a very promising alternative to existing upconversion related applications, especially in the solar cell and rate sensing areas. Moreover, only a few researches are focused on the anti-counterfeiting application of TTA-UC at present, which also makes the TTA-UC a new idea for updating and iterating the anti-counterfeiting technology.

Disclosure of Invention

The invention aims to solve the problems and provides an up-conversion/long-afterglow multi-mode luminescent material and a preparation method and an application thereof, wherein a novel multi-mode luminescent system is realized by combining a TTA-UC organic luminescent molecule pair (a sensitizer and an annihilator) with lanthanide doped fluorescent powder with different afterglow colors, fluorescence (FL), up-conversion (UC) and afterglow luminescence can be realized in a double excitation mode (365/532 nm), and the prepared luminescent material can be patterned by a direct writing technology, so that the application of multi-dimensional anti-counterfeiting and information coding is finally realized.

According to the technical scheme of the invention, the preparation method of the up-conversion/long afterglow multi-mode luminescent material is characterized by comprising the following steps,

s1: dissolving poly alpha pinene (P alpha P) and Polyisobutylene (PIB) in an organic solvent to obtain an ink matrix;

s2: adding rare earth long afterglow fluorescent powder (afterglow fluorescent powder) into the ink matrix to obtain an ink semi-finished product;

s3: adding a sensitizing agent and an annihilating agent into the ink semi-finished product to obtain ink;

s4: and printing or coating the ink according to a design pattern to obtain the up-conversion/long-afterglow multi-mode luminescent material.

The invention constructs a multi-mode luminescent material combining 'up-conversion' + 'long afterglow', one printing point can realize at most four different luminescent modes, namely ultraviolet-excited fluorescence emission, ultraviolet energy-charged afterglow emission, up-conversion emission excited by 532nm laser and afterglow luminescence charged by up-conversion.

Further, the specific operation of step S1 is as follows: grinding the poly alpha pinene into powder, dissolving the powder in an organic solvent, adding polyisobutylene, and uniformly mixing to obtain the ink matrix.

Further, the organic solvent is selected from one or more of tetrahydrofuran, toluene, dichloromethane, chloroform and dimethyl sulfoxide.

Further, the mass fraction of the poly alpha pinene in the ink is 3-15%, preferably 9-15%; the mass fraction of the polyisobutene is 53-60%.

Further, the mass fraction of the rare earth long afterglow fluorescent powder in the ink is 2-16%.

The TTA-UC organic luminescent molecule pair (a sensitizer and an annihilator) is combined with the lanthanide doped fluorescent powder with different afterglow colors, wherein the triplet state-triplet state annihilation up-conversion luminescence mechanism has high luminous efficiency and low excitation energy threshold value of non-optical up-conversion luminescence, and the types of the photosensitizer and the annihilator are changed, so that the wavelength positions of excitation and up-conversion luminescence can be conveniently adjusted, and the anti-counterfeiting technology is more flexible; meanwhile, the wavelength of the excitation light is flexible and adjustable, and even when a proper photosensitizer/annihilator pair is selected, the excitation light can be excited by a high-power red or green laser pen, so that the near-infrared laser light source is simpler and more convenient to operate, and the safety coefficient is higher.

Further, the sensitizer is octaethylporphyrin platinum (PtOEP), octaethylporphyrin palladium, tetraphenylporphyrin palladium, tetraphenylphosphonoplatin or octabutoxyphthalocyanine palladium; the annihilation agent is anthracene, anthracene derivatives, perylene derivatives, pyrene or pyrene derivatives; specifically, the anthracene derivative may be 9, 10-Diphenylanthracene (DPA) or 9, 10-bis (phenylethynyl) anthracene.

Further, the concentration of the sensitizer in the ink is 8 × 10 ^-6 mol/L-1.5×10 ^-5 mol/L, concentration of annihilator is 5X 10 ^-4 mol/L-2.5×10 ^-3 mol/L。

Further, the molar ratio of the sensitizer to the annihilator in the ink is 1:50-250, preferably 1: 150-250.

Further, in the step S4, the printing mode includes inkjet printing, a dispenser, screen printing, transfer printing, and the like, and the coating mode includes spraying, blade coating, and the like; the parameters (viscosity, surface tension, etc.) of the ink can be adjusted according to the requirements of the processing method, and after printing or coating, the solvent can be naturally volatilized or can be heated to be quickly volatilized.

The invention provides an up-conversion/long-afterglow multi-mode luminescent material prepared by the preparation method.

The third aspect of the invention provides the application of the up-conversion/long-afterglow multi-mode luminescent material in multi-dimensional anti-counterfeiting and information coding.

The present invention prepares the multimode luminescent material as an ink and prints it in a pattern or array (fig. 20 a); one printed dot can realize at most four different light emitting modes, namely ultraviolet excited fluorescence emission, ultraviolet energy-charged afterglow emission, up-conversion emission excited by 532nm laser and up-conversion energy-charged afterglow emission (fig. 20 b); in the process of preparing the ink, a resin network constructed by two polymers of poly alpha-pinene (P alpha P) and Polyisobutylene (PIB) is used as a solid matrix, so that organic dye molecules and afterglow fluorescent powder can be well dispersed in the solid matrix (figure 20 c); because the P α P can chemically react with high-energy singlet oxygen in the system, and meanwhile, the low gas permeability of the PIB can prevent external oxygen molecules from entering the system, and the two polymers respectively have synergistic effects from the chemical and physical layers, the inhibition of oxygen molecules on the triplet-triplet energy transfer (TTET) process between the photosensitizer and the annihilator and the quenching of the up-conversion luminescence can be effectively prevented, so that stable TTA up-conversion luminescence can be realized in the air (fig. 20 d); the mechanism of the four light emission modes can be demonstrated by energy level diagrams (FIG. 20e, f). For the TTA-UC process, a photosensitizer absorbs incident 532nm laser and is excited to a singlet state, then the incident 532nm laser is converted into a triplet state through intersystem crossing (ISC), after TTET, the triplet state of an annihilator receives energy, and then the TTA process is carried out between two triplet annihilator molecules to form an annihilator with a singlet state and a ground state. Eventually, the radiation transition from the singlet state to the ground state of the annihilator emits up-converted light. Further, the singlet state of the annihilator can be obtained by direct ultraviolet excitation, and fluorescence emission of the annihilator can be realized (fig. 20 e). For persistent phosphors, the energy transfer process occurs when there is an overlap between the excitation wavelength range and the upconversion emission wavelength range. Under irradiation of ultraviolet light or up-conversion light, electrons are excited from the 4f level of the activator Eu2+ to the 5d level, and some of the excited electrons are easily trapped by oxygen vacancies. When the excitation light is turned off, the captured electrons can be released back to the 5d level by heat and then relax to the lowest 5d level. Finally, radiative transitions from 5d to 4f levels produce afterglow luminescence (FIG. 20 f). Multiple luminescent patterns can subsequently be obtained from the same printed pattern under different activation conditions by careful design of the composition and corresponding luminescent properties of each portion of the printed pattern (fig. 15). The method has the advantages of simple manufacture, low cost, flexible coding mode and difficult simulation, and provides a new idea for the development of multi-dimensional anti-counterfeiting and information coding application.

Compared with the prior art, the technical scheme of the invention has the following advantages:

1. the invention adopts a double polymer network of poly alpha pinene and polyisobutylene as the solid dispersion medium of the luminescent material, on one hand, the two polymers can effectively remove dissolved oxygen molecules in the system, so that TTA up-conversion luminescence which is easily quenched by the oxygen molecules can be efficiently and stably used in the air atmosphere; in addition, the biopolymer substrate can also adjust the properties of the ink during printing;

2. the invention combines an up-conversion system of a triplet-triplet annihilation (TTA) mechanism with an afterglow material to construct a multi-mode luminescent material combining up-conversion and long afterglow, so that the material can present at most four different patterns under different excitation modes and luminescent modes, and can be applied to the fields of multi-dimensional anti-counterfeiting, information coding and the like;

3. the method has great potential, different excitation and up-conversion emission modes can be obtained by replacing TTA dye pair combinations of different photosensitizers/annihilators, and flexible and variable luminescence effects (including luminescence mode, luminescence color, luminescence intensity and the like) can be obtained by replacing different afterglow luminescent materials matched with up-conversion luminescence.

Drawings

Figure 1 is a normalized absorption spectrum and PL spectrum of PtOEP and DPA in a pp/PIB polymer matrix (top) and THF solution (bottom).

FIG. 2 is a normalized excitation and emission spectra of four inorganic phosphors with different afterglow colors (a blue b cyan c green d orange).

FIG. 3 is an up-conversion emission spectrum for different photosensitizer/annihilator ratios; (b) The trend of the integrated intensity of the up-converted peak with increasing DPA concentration.

FIG. 4 (a) shows UC spectra of PtOEP/DPA in P alpha P/PIB matrix under 532nm laser excitation at different power densities; (b) a log-log graph of UC intensity based on excitation power in a.

FIG. 5 (a) is a PL spectrum before and after adding P.alpha.P to a THF solution of PtOEP/DPA in an air atmosphere (inset: corresponding to a sample photograph); (b) Phosphorescence decay curves for PtOEP in THF under nitrogen bubbling and nitrogen protected oxygen-free atmosphere (red) and exposure to air atmosphere (black), respectively; (c) Corresponding phosphorescence decay curves of PtOEP in P.alpha.P-containing THF solutions after different irradiation times (0-25 s) of 532nm continuous laser.

FIG. 6 (a) is a dynamic PL spectrum based on time after cessation of bubbling with 532nm laser irradiation of a PtOEP/DPA THF solution containing P.alpha.P; (b) a plot of up-conversion peak intensity based on recovery time; illustration is shown: photographs of the samples during bubbling (left) and after complete recovery of up-conversion (right); (c) The bubbling process was repeated, subjecting the sample to an up-conversion intensity change at ten "quench-recovery" cycles.

FIG. 7 (a) is a plot of upconversion relative emission intensity over time in THF solutions of PtOEP/DPA at various P.alpha.P contents; (b) The relative strength of the P.alpha.P/PIB in the bipolymer matrix was plotted against time, and all samples were stored and measured at room temperature.

FIG. 8 (a) is a photograph of ink viscosity at different mass fractions of PIB (inset: photograph of drop wetting behavior of corresponding viscosity on a paper substrate); (b) And (3) the dispersion behavior of the fluorescent powder in the inks with different PIB contents after different settling times.

Fig. 9 shows the optical properties of the multimode luminescent ink: (a) absorption, (b) FL, and (c) UC spectra of inks having four different afterglow colors.

FIG. 10 shows the excitation spectra (dashed lines) of the four phosphors and the upconversion spectra (solid lines) of PtOEP/DPA.

FIG. 11 is (a) an up-conversion spectrum of a multimode luminescent ink with different afterglow phosphor contents; (b) The calculated energy transfer from TTA up-conversion to phosphor; (c) normalizing the upconverted spectrum; (d) Strength of ratio (I) ₄₅₅ /I ₄₃₀ )。

Fig. 12 light transmittance of the bipolymer matrix (P α P to PIB mass ratio of 3.

FIG. 13 (a) is a schematic diagram of a process of directly "writing" a high power 532nm laser pen on a multimode luminescent film; (b) Afterglow luminescence pattern (scale bar: 5 mm) drawn by the method in a; (c) variation of the luminous intensity of the pattern in b with time.

Fig. 14 is a method of "drop on demand" patterning based on the direct write technique. (a) printer photo (Sonoplot, microplotter II); (b) A pattern drawn on printer software, wherein each color represents ink corresponding to an afterglow color; (c) actual print pattern based on b (scale: 2 mm); (d) an afterglow luminescent pattern after ultraviolet irradiation; (e) afterglow luminescent patterns obtained after irradiation with a 532nm laser beam.

Fig. 15 shows the multi-dimensional anti-counterfeiting application realized by patterning the multi-mode luminescent material. (a) Preparing a schematic diagram of a multi-dimensional luminous pattern based on a direct writing method, and carefully designing and arranging luminous performance of each position of the pattern by controlling components and deposition positions of ink; (b) The printed pattern (left side, scale: 2 mm) on the white paper is excited by 365nm ultraviolet light and 532nm laser light respectively, the fluorescent pattern shows background fluorescent interference from the base material, and the corresponding ultraviolet energy-filled afterglow pattern shows misleading information of 76; the up-conversion transmit mode presents clear and non-interfering information "49", while the corresponding up-conversion energy-charged afterglow mode displays true hidden information "15".

FIG. 16 is a normalized PL spectrum (excitation: 365 nm) of commercial white printing paper (black) and DPA (red).

Fig. 17 is a coding strategy based on multimode lighting regime inspired by binary codes: (a) All the printed points in the 8 x 4 array show blue afterglow luminescence (scale bar: 1 mm) after being irradiated by ultraviolet light, and show misleading signals; (b) After 532nm laser irradiation, part of printed points display afterglow and luminescence, and display a hidden encrypted signal; (c) The on/off states of the persistence of the printing dots represent

binary codes

1 and 0, respectively; (d) Based on the algorithm in c, the afterglow pattern in b can be translated into the information "USTS".

Fig. 18 is a coding strategy for a multimode lighting system based on morse code heuristic: (a) a printed array in daylight (scale: 1 mm); (b) a print dot scanning order for reading the light emission signal; printing afterglow signals of the array after ultraviolet irradiation; printing afterglow signals of the array after 532nm laser irradiation; (e) Printing an afterglow signal of the array after ultraviolet light and 532nm laser are simultaneously irradiated; (f) the weak green dot represents the code "-; the strong green dot represents the code "·"; a single white dot represents a space; the double white dots represent the end of the message; (g) Based on the algorithm in f, the light signal in e can be translated into the message "USTS".

FIG. 19 (a) is an excitation spectrum and PL spectrum of a white afterglow phosphor (mixed by blue and orange phosphors); (b) CIE coordinates of all afterglow phosphors.

FIG. 20 is a schematic view of a multimode light emitting system.

Detailed Description

The present invention is further described below in conjunction with the drawings and the embodiments so that those skilled in the art can better understand the present invention and can carry out the present invention, but the embodiments are not to be construed as limiting the present invention.

The main experimental drugs and instruments in the following examples are shown in tables 1 and 2, respectively:

TABLE 1

TABLE 2

Wherein PtOEP and DPA are the classical sensitizer and annihilator pair of TTA-UC. Figure 1 shows normalized absorption and PL spectra of DPA and PtOEP in a matrix of a biopolymer and in THF solution of tetrahydrofuran, respectively. When dispersed in a solid polymer matrix, the pi-pi vibration absorption peaks (357, 374.5 and 394 nm) of DPA and the Soret absorption peaks (380 nm) of PtOEP are slightly broadened and red-shifted compared to those in THF solution (DPA: 355, 373.5 and 394nm PtOEP 382nm), which is due to the weaker interactions between chromophores. In the PL spectrum, however, the PL peak at 410nm in THF disappeared in the polymer matrix due to the internal filtering effect, which is affected by the thickness and concentration of the solid sample. In contrast, the peak shape and peak position of the emission spectrum of PtOEP were not changed. Since the subsequent experiment TTA-UC selects 532nm laser excitation, the requirement that the Q band of PtOEP in the solid matrix still covers 532nm and does not coincide with the absorption band of DPA is the premise of the subsequent TTA up-conversion luminescence experiment. Through subsequent experiments, all of these small changes in the optical physical properties of PtOEP/DPA in the polymer matrix do not affect the achievement of TTA up-conversion luminescence.

The afterglow luminescent materials used are four lanthanide doped inorganic afterglow phosphors, which are commercially available products, the basic information of which is shown in table 3, and the excitation and PL spectra of which are shown in fig. 2.

TABLE 3

EXAMPLE 1 preparation of Up-converting/Long persistence Multi-mode luminescent Material

0.9g of P.alpha.P was weighed out, ground to a powder and then dissolved in 30mL of THF, then 6g of PIB was added and shaken through a homogenizer until the mixture was homogeneous. Then 1g of afterglow fluorescent powder is added into the solution and mixed for standby. Respectively preparing mother liquor of PtOEP and DPA, THF is used as solvent, and the concentration is respectively 1X 10 ^-4 M and 1X 10 ^-2 And M. And finally, adding the two mother solutions of the TTA upconversion system into the previous mixed solution according to the required amount, thereby completing the preparation of the ink. The other inks of different compositions used were prepared with reference to the above procedure.

Patterning preparation of the multimode luminescent material was carried out using a direct writing device (Sonoplot, micropolotter II). The ink is deposited on the substrate through a capillary tube mounted on an X-Y-Z three-dimensional moving stage. The print pattern is designed and drawn on the instrument software.

The PtOEP and the DPA are replaced by other TTA-UC organic luminescent molecule pairs, and the corresponding up-conversion/long-afterglow multi-mode luminescent material can be prepared.

Analysis of results

1. TTA upconversion luminescence property in polymer matrix

The upconversion luminescence spectra of different photosensitizer/annihilator ratios in a pp/PIB matrix are shown in fig. 3. Maintaining the concentration of photosensitizer constant (1X 10) ^-5 mol/L), the concentration of the annihilator is increased continuously (from 5X 10) ^-4 mol/L to 2.5X 10 ^-3 mol/L), the up-conversion intensity gradually increases and reaches the maximum value at 1 ^-3 mol/L。

Calculating the up-conversion quantum yield of the system according to the optimal proportion, taking an ethanol solution (fluorescence quantum yield is 0.95) of rhodamine 6G as a reference sample, and calculating the formula as follows

Where φ, A, I and η represent the quantum yield, absorbance at the excitation wavelength (532 nm), PL integrated intensity and medium refractive index (1.36 for ethanol and 1.53 for polymer matrix), respectively, and the coefficient 2 is because 2 photons are absorbed to generate 1 upconverted photon under the TTA mechanism. The final calculated up-conversion quantum yield was 2.4%.

Under the optimal mixture ratio, the upconversion spectrum of PtOEP/DPA in a polymer solid matrix under different laser powers is tested, and linear fitting under a log-log coordinate system is carried out to measure the excitation energy threshold. By adjusting the intensity of the laser, a luminescence spectrum at different excitation powers was obtained (fig. 4 a). The laser power is increased from 47.77mW/cm along with the increase of the excitation light intensity ² The concentration is increased to 2331.21mW/cm ² . As can be seen from the log-log relationship curve of the integrated area of the up-conversion emission peak and the laser power density (FIG. 4 b), through linear fitting, the slope of the curve is reduced from 1.91 to 1.26, and the abscissa of the intersection point of the two fitting lines is the excitation power threshold value of 615mW/cm ² 。

2. Chemical oxygen removal capability of poly-alpha-pinene

The photochemical deoxygenation capacity of P.alpha.P was investigated and the results are shown in FIGS. 5 and 6, where both samples in FIG. 5a are PtOEP/DPA in THF, and they are exposed directly to air. All parameters were the same for both samples, only one of which contained a certain amount of P α P. The results show that the sample containing P α P, although exposed to air, still exhibits a bright blue up-conversion emission under 532nm laser excitation, indicating that dissolved oxygen in the solution has been substantially removed. In contrast, the sample without P α P had no up-conversion emission peak in the PL spectrum (black curve) due to quenching by oxygen, whereas the faint red emission from the sensitizer PtOEP was seen in the inset.

To further verify the deoxygenation effect of P α P, the effect on the phosphorescence lifetime of PtOEP was investigated (fig. 5b, c). First, both samples in fig. 5b were THF solutions of the photosensitizer PtOEP without pa, wherein one sample (right side) was treated by nitrogen bubbling to remove oxygen and measured under nitrogen atmosphere, so that an approximately oxygen-free environment was simulated to obtain measurement results in the oxygen-free environment; while the other sample (left) was simply exposed to air without any pretreatment. As a result, under oxygen-free and oxygen-free conditions, the phosphorescence lifetime of PtOEP at 645nm was 18.71 and 4.27. Mu.s, respectively (excitation light source was 532nm pulsed light). The lifetime degradation is due to quenching of the triplet state of the photosensitizer by oxygen, which in turn indicates that a longer lifetime represents a low oxygen concentration and a shorter lifetime represents a relatively high oxygen concentration if the phosphorescence lifetime of the photosensitizer is taken as an indicator of the oxygen content. Based on this conclusion, the increased lifetime of the photosensitizer in fig. 5c also implies a decrease in oxygen concentration. The phosphorescence lifetimes were measured after 532nm continuous laser irradiation of photosensitizer THF solutions containing pp, the results of which are shown in figure 5 c. The photosensitizer lifetime (left most) before laser irradiation was 4.46 μ s, similar to the lifetime results of the sample exposed to air atmosphere in fig. 5b, demonstrating that the oxygen concentration is higher, near saturation. When PtOEP is excited to a triplet state by a high power laser, a photochemical deoxidation process based on P α P occurs. As the laser irradiation time increased, the photosensitizer lifetime also gradually increased, indicating that the oxygen concentration in the system gradually decreased. When irradiated for 25s, the lifetime reached a maximum of 16.18. Mu.s, which is close to the lifetime of the sample after nitrogen treatment in FIG. 5b, indicating that the deoxygenation effect of the photochemical deoxygenation method based on P.alpha.P has reached substantially the level of the nitrogen bubbling method. The phosphorescence lifetime results for the photosensitizers at different laser irradiation times are shown in table 4.

TABLE 4 change of the lifetime of PtOEP in the P-. Alpha.P-containing solution with laser irradiation time

Fig. 6 demonstrates the deoxygenation ability of P α P from another perspective. As shown, the samples were PtOEP/DPA in P.alpha.P-containing THF placed in an open cuvette. The results of the previous experiments have demonstrated that with the aid of P α P, the samples can exhibit strong blue up-conversion luminescence under laser excitation, even when exposed to air. At this point, the blue upconversion light disappears immediately when air is bubbled into the solution using a dropper, and the upconversion light recovers rapidly after bubbling ceases (fig. 6b inset). The up-conversion emission spectrum based on the recovery time was measured throughout the up-conversion recovery process (fig. 6 a), and the up-conversion emission intensity curve is shown in fig. 6 b. From the results, it is clear that the up-conversion emission of blue can be completely recovered within 2.4 seconds. Furthermore, as long as the P α P in the system is not completely consumed, the entire "quench-recovery" process can be repeated, and fig. 6c records the results for ten cycles, with up-conversion being able to recover quickly after multiple quenches.

The stability of the up-converted luminescence of the ink samples and the solid samples in air was also investigated. Figure 7a shows the upconversion luminescence stability during 24 hours of exposure of samples (inks) of PtOEP/DPA solutions with different P α P content in air. The result shows that the increase of the content of the P alpha P can obviously slow down the reduction of the up-conversion strength, and the stability of the product in the air is obviously improved. Theoretically, the stability of upconversion luminescence in air depends on the content of P α P in the system, which sacrifices itself to eliminate oxygen by chemical reaction. However, as an industrial tackifier, too much P α P content increases the viscosity of the system to restrict the fluidity of the dye molecules and thus decrease the upconversion efficiency. Therefore, simply increasing the P α P content is not an optimal strategy in order to improve the stability of the up-converted luminescence without sacrificing efficiency as much as possible. PIB is a typical linear saturated polymer that is commonly used in the literature as a solid medium for the upconversion on TTA due to its good gas barrier properties. When the PIB is introduced into the polymer matrix of the P alpha P, the PIB can be used as an isolation barrier to prevent external oxygen from permeating into the matrix, so that the oxidation process of the P alpha P naturally occurring in the air is slowed down, and the service life of the P alpha P as an oxygen scavenger in a system is prolonged. Fig. 7b measures the upconversion luminescence stability in a ppap/PIB bipolymer matrix, with the upconversion luminescence intensity remaining above 30% of the initial intensity even after one month of standing. In addition, because of having an alicyclic structure, the molecular chain of P α P is relatively rigid, which is not favorable for the fluidity of the dye molecules dispersed therein. The introduction of PIB, a flexible chain polymer, can achieve a plasticizing effect, thereby improving TTA-UC performance in a solid matrix.

2. Performance testing of multimode luminescent inks

The ink viscosities for different PIB contents were measured in fig. 8a (both solvents were THF, and both printing substrates were white commercial printing paper). The results show that as the PIB content increases, the ink viscosity increases significantly. The inset shows the wetting behavior of ink drops with corresponding viscosity on the substrate surface, and the result shows that when the mass fraction of PIB is lower than 53%, the spreading degree of the ink on the substrate is larger, which is not beneficial to the stability of the pattern in the printing process, and is also not beneficial to the concentration of luminescent materials, which affects the luminescent effect. When the mass fraction of PIB is more than 60%, it is found that the ink may not be printed smoothly since it becomes too viscous. Furthermore, FIG. 8b compares the dispersion of the persistent phosphor in inks of different PIB content and shows that the dispersibility of the phosphor increases with increasing PIB content, i.e., increasing viscosity. The phosphor can maintain good dispersibility after standing in ink with PIB content of more than 60% for 3 hours. The best mass fraction of PIB in the ink was finally determined to be 60% by a comprehensive evaluation of the results in fig. 8.

The optical properties of the prepared multimode luminescent ink (luminophor: ptOEP/DPA/fluorescent powder; polymer: P alpha P/PIB; solvent: THF) were measured. In FIG. 9, the absorption, FL (365 nm excitation) and UC (532 nm excitation) spectra for four different afterglow color inks are shown, and the results in FIGS. 9a and b show that both the absorption and down-converted emission spectra can be viewed as a superposition of the individual phosphor spectra. Since the annihilator DPA exhibits an emission intensity that is relatively superior to the other two luminescent materials, the spectrum exhibits mainly the peak shape of DPA. In addition, the four inks also measured UC spectra under 532nm laser excitation (fig. 9 c). The results show that the addition of the phosphor causes a slight red shift of the up-conversion emission peak because the energy transfer from TTA-UC to the phosphor occurs, and the emission peak of the phosphor coincides with the up-conversion peak, resulting in a red shift of the overall peak shape.

The energy transfer between the up-converted emission and the phosphor can also be visualized by comparing the up-converted emission spectrum of the PtOEP/DPA system with the excitation spectrum of the phosphor, with the results shown in fig. 10. The excitation spectra of the four phosphors are overlapped with the up-conversion emission spectra to a certain extent, which indicates that each phosphor can be excited and charged by the up-conversion energy. Therefore, afterglow luminescence can be realized through an excitation mode of 532nm as long as a TTA-UC system exists; the excitation spectrum result of the fluorescent powder can also be obtained, and if no TTA-UC system exists, 532nm can not directly excite the four fluorescent powders.

When the blue afterglow ink is selected as an example and the addition amount of the phosphor therein is quantitatively analyzed, the result is shown in fig. 11. As shown in fig. 11a, the up-conversion emission intensity decreased with increasing phosphor content because some of the photons emitted by TTA-UC were absorbed by the phosphor. Some of the energy absorbed by the phosphor is immediately and directly emitted by the phosphor in the form of transition radiation, which is also the cause of the change of the emission peak shape in the emission spectrum; and a part of the energy is stored in a trap energy level, and the excitation light is gradually released after being removed to form afterglow luminescence. For this process, the energy transfer efficiency from TTA luminescence to afterglow luminescence can be estimated, and the calculation formula is as follows:

in the formula (I), the compound is shown in the specification,

and

respectively represent the number of photons absorbed by the fluorescent powder and emitted by TTA-UC,

and

respectively representing the integrated intensity of the up-converted emission of the whole system before and after the addition of the phosphor. Therefore, the calculated energy transfer efficiency is shown in FIG. 11b, and the maximum energy transfer efficiency from TTA-UC to the phosphor can reach 52.3%. From the normalized up-conversion spectrum, it can be seen that the degree of red shift of the emission peak increases with the increase of the phosphor content (fig. 11 c), and the ratio of the intensity at the optimum emission wavelength of the phosphor to the intensity at the up-conversion optimum emission wavelength is obtained, and the signal intensity of the ratio increases with the increase of the phosphor content (fig. 11 d). Both the red shift and the change in the ratio signal indicate laterally the occurrence of energy transfer, and as the fluorescence content increases, the extent of energy transfer also increases.

Application example

The bi-polymer matrix shows good optical transparency (fig. 12) and is very suitable as a dispersion medium for luminescent materials.

The prepared luminescent ink can be used for printing and other processing and manufacturing methods based on solution. For example, a multimode luminescent film can be prepared by a doctor blade method, and then an afterglow pattern can be directly drawn on the film by using a high power 532nm laser pen (FIG. 13). The position irradiated by the light spot emits upconversion light due to the absorption of the energy of the laser pen, and the upconversion energy charges the afterglow fluorescent powder, and finally, even if the light spot is removed, afterglow luminous handwriting can still be left.

Compared with other solution processing techniques, the direct writing method can realize the preparation of complex multi-dimensional patterns by accurately regulating and controlling the ink components and the deposition positions thereof (fig. 14). The results show that the same printed pattern can emit different polychromatic afterglow patterns when energized at different excitation wavelengths.

To further show the application of the TTA-UC/afterglow illuminant system in multi-dimensional anti-counterfeiting, four inks based on different luminescent material (photosensitizer, annihilator and phosphor) combinations are prepared for the printing preparation of multi-mode luminescent patterns (fig. 15 a). A simple "double-digit" pattern is designed, and the selection of the corresponding ink at each location on the pattern is also carefully designed. The print pattern and the corresponding light emission patterns in the four light emission modes are shown in fig. 15 b. Because the printing substrate that uses in this application is white commercial printing paper, the fluorescent whitening agent that contains in the paper can send stronger blue light fluorescence under the excitation of 365nm ultraviolet ray. These background fluorescence interfere with the luminescence of the printed pattern, and as shown in fig. 16, the fluorescence peak of the white printing paper and the fluorescence peak of the DPA overlap to a large extent under the excitation of 365nm ultraviolet light. Since optical brighteners are commonly used in the paper industry, and paper is the most commonly used substrate in security applications, interference of background fluorescence caused thereby has become an inevitable problem in security methods based on uv excitation patterns. The results in fig. 15b show that under uv excitation, although the pattern locations containing DPA can be excited to emit blue fluorescence, information cannot be clearly read from the pattern due to the strong noise interference of the substrate paper. However, from another point of view, the corresponding result of the fluorescence pattern under the excitation of ultraviolet light can also be considered as a protection or misleading for the truly hidden information. After the pattern is fully irradiated by 365nm ultraviolet light, a green afterglow pattern can be displayed after the light source is removed, which shows that afterglow fluorescent powder is contained at the corresponding light-emitting position and is excited by the ultraviolet light to be charged and emit light. The information "76" is clearly read from the afterglow luminescence pattern, which is the first important information read from this pattern. So far, TTA up-conversion luminescence does not occur in the above process, and fluorescence and afterglow emission are directly excited and charged by ultraviolet light.

By switching the excitation mode, under the excitation of 532nm laser, a clear blue up-conversion luminescence pattern without background fluorescence interference can be obtained through the cut-off filter, which indicates that the position corresponding to the luminescence pattern contains a TTA up-conversion double-dye system PtOEP and DPA. The purpose of adding a short-pass cut-off filter is to filter out the green excitation light. The absence of background fluorescence interference in this mode is due to the inability of the paper substrate to be excited by the 532nm laser. At this time, the second duplicate information "49" can be read by the blue up-conversion luminescence pattern. Finally, the printed pattern, after being sufficiently irradiated with the 532nm laser, can similarly exhibit a green afterglow pattern after the light source is removed, but the afterglow pattern at this time is different from the afterglow pattern obtained by ultraviolet excitation. This is because 532nm excitation cannot directly excite the phosphor to obtain afterglow, and only the pattern position containing both PtOEP, DPA and phosphor will glow in this mode. The afterglow light at this time is excited and charged by the just-mentioned up-conversion light, and information "15" can be read from the afterglow pattern, which is also the third information obtained from this pattern.

In summary, the multi-dimensional anti-counterfeiting pattern prepared by the application has four light-emitting modes: (1) fluorescence, (2) uv-excited afterglow, (3) upconversion, (4) upconversion excited afterglow, and each mode shows a different luminescence pattern. The fluorescent mode can be considered as a mask mode because of the signal being read indistinctly by the interference, and the information read in the other three modes can be considered as valid information. Of course, according to the specific anti-counterfeiting use requirement, only the information obtained in the up-conversion energy-filling afterglow mode can be used as the true hidden information, because the light-emitting mode is the most complex and involves all the light-emitting materials in the system, that is, the other three modes become the shielding and misleading information, which provides higher safety for the multi-dimensional anti-counterfeiting application.

The multimode luminescent system combining TTA up-conversion and afterglow luminescence can also be applied to information coding technology. The basic principle in designing new lighting coding systems is to construct a coding relationship between the lighting signal and the digital signal. Fig. 17c shows that a simple mechanism for the coding strategy based on the multimode lighting regime of the present invention is established, i.e. to mark the on/off state of the lighting signal. Specifically, a binary system is constructed by using the on-off state of afterglow luminescence (the 'on' state is a signal '1', and the 'off' state is a signal '0'). Therefore, the afterglow luminous signal of the printed dot matrix can be easily translated into a binary digital code and then translated into the information of English letters. In addition, the multi-mode luminous system provides a protection mechanism for real hidden information, and the information safety level is improved. In short, all printed dots were set to contain an afterglow phosphor, so that after UV irradiation the entire array glows with a afterglow, showing misleading information (FIG. 17 a). Only the printed dots associated with the actual hidden message contain the TTA upconversion system and the corresponding afterglow luminescent array after 532nm laser irradiation can be converted to a binary digital code representing the hidden message "USTS" (fig. 17b, d).

In order to further improve the information security level of the multi-mode light-emitting coding system, information such as signal reading sequence, afterglow intensity, light-emitting color and the like can be additionally encrypted through a specific algorithm. Inspired by morse code, a cryptographic algorithm based on multimode lighting system was developed (fig. 18). A specially tailored encryption algorithm will certainly be more secure in practical applications than known encryption algorithms. Here, the information unit is encrypted using the afterglow luminescence intensity (strong green afterglow signal is code "·"; weak green afterglow signal is code "-), the single white afterglow point is information" space ", and the double white afterglow point is the end of the message (fig. 18 f). A white afterglow can be obtained by mixing blue and orange phosphors (fig. 19). Fig. 18a shows a printing array based on a multimode light-emitting system, and the design lacking a dot in the lower left corner can make the coding array easier to locate and identify, and the reading process more reliable, which is of great significance to the practical application of multimode light-emitting coding technology. After irradiation with ultraviolet light, the afterglow luminescence array in fig. 18c can be obtained. According to the signal reading sequence in fig. 18b, four information unit regions separated by three single white points can be clearly identified, but only misleading information can be read. Unlike the binary code-based encoding strategy in fig. 17, the afterglow luminescence signal corresponding to the true hidden information is not directly obtained after 532nm laser excitation and energy charging. Since only the printed dot containing the TTA up-conversion scheme is lit (fig. 18 d), no valid information can even be read at this time. In fact, the key to decoding is hidden in the excitation mode, i.e. two light sources, uv and 532nm laser, are required to excite the print array simultaneously. In this special mode, the printed dots containing the TTA upconversion system can take more energy from both excitation modes, so they will show stronger afterglow luminescence (fig. 18 e). According to the algorithm decoding, the hidden information can be acquired as "USTS".

It should be understood that the above examples are only for clarity of illustration and are not intended to limit the embodiments. Various other modifications and alterations will occur to those skilled in the art upon reading the foregoing description. And are neither required nor exhaustive of all embodiments. And obvious variations or modifications of the invention may be made without departing from the spirit or scope of the invention.

Claims

1. A preparation method of an up-conversion/long afterglow multi-mode luminescent material is characterized by comprising the following steps,

s1: dissolving poly alpha pinene and polyisobutylene in an organic solvent to obtain an ink matrix;

s2: adding rare earth long afterglow fluorescent powder into the ink matrix to obtain an ink semi-finished product;

2. The method for preparing an upconversion/long afterglow multimode luminescent material according to claim 1, wherein the step S1 comprises the following steps: grinding the poly alpha pinene into powder, dissolving the powder in an organic solvent, adding polyisobutylene, and uniformly mixing to obtain the ink matrix.

3. The method for preparing an upconversion/long afterglow multimode luminescent material according to claim 1 or 2, wherein the organic solvent is one or more selected from the group consisting of tetrahydrofuran, toluene, dichloromethane, chloroform and dimethylsulfoxide.

4. The method for preparing up-conversion/long-afterglow multi-mode luminescent material as claimed in claim 1, wherein the mass fraction of poly alpha pinene in the ink is 3-15%, and the mass fraction of polyisobutylene is 53-60%.

5. The method for preparing up-conversion/long-afterglow multi-mode luminescent material as claimed in claim 1, wherein the mass fraction of the rare earth long-afterglow fluorescent powder in the ink is 2-16%.

6. The method of claim 1, wherein the sensitizer is octaethylporphyrin platinum, octaethylporphyrin palladium, tetraphenylporphyrin platinum, or octabutoxyphthalocyanine palladium; the annihilation agent is anthracene, anthracene derivatives, perylene derivatives, pyrene or pyrene derivatives.

7. The method for preparing up-conversion/long-afterglow multi-mode luminescent material according to claim 1, wherein the concentration of the sensitizer in the ink is 8 x 10 ^-6 mol/L-1.5×10 ^-5 mol/L, concentration of annihilating agent is 5X 10 ^-4 mol/L-2.5×10 ^-3 mol/L。

8. The method for preparing an upconversion/long afterglow multi-mode luminescent material according to claim 1, wherein a molar ratio of the sensitizer to the annihilating agent in the ink is 1:50-250.

9. An up-conversion/long-afterglow multi-mode luminescent material prepared by the preparation method of any one of claims 1 to 8.

10. The use of the up-conversion/long persistence multi-mode luminescent material of claim 9 in multi-dimensional anti-counterfeiting and information encoding.