A Ho 3+ Preparation method of Cs2NaYbCl6 doped microcrystals and their application in anti-counterfeiting and temperature sensors

Abstract

This invention relates to the field of luminescent materials technology, specifically a Ho 3+ A method for preparing Cs₂NaYbCl₆ microcrystals and their application in anti-counterfeiting and temperature sensors. The preparation method includes: Step 1, according to the stoichiometric ratio of Cs₂NaYbCl₆... x Ho y Weigh the raw materials CsCl, NaCl, YbCl3·6H2O, and HoCl3·6H2O, where x + y = 1, and x ∈ (0, 1), y ∈ (0, 1); Step 2, add the above raw materials to deionized water and stir to dissolve to obtain a clear solution; Step 3, dry the clear solution until the solution evaporates and white crystals precipitate; Step 4, grind the white crystals to obtain HoCl3·6H2O. 3+ This invention relates to the preparation of high-purity, high-performance Cs₂NaYbCl₆:Ho microcrystals via a simple dissolution-drying method. 3+ Microcrystals enable multi-color tunable upconversion luminescence, and an optical anti-counterfeiting / information encryption system and a high-sensitivity temperature sensing system based on this material are constructed.

Description

Technical Field

[0001] This invention relates to the field of luminescent materials technology, specifically a Ho 3+ Preparation method of Cs2NaYbCl6 doped microcrystals and their application in anti-counterfeiting and temperature sensors. Background Technology

[0002] Upconversion luminescent (UCL) materials can convert low-energy near-infrared photons into high-energy visible light photons through energy migration. Their anti-Stokes luminescence properties effectively avoid background autofluorescence interference, making them valuable for applications in optical anti-counterfeiting, information encryption, and optical temperature measurement.

[0003] Traditional upconversion luminescent matrix materials such as fluorides and oxides suffer from insufficient physicochemical stability, while lead-based perovskite materials, containing toxic lead, severely limit their practical industrial applications. Meanwhile, traditional single-mode fluorescent anti-counterfeiting technologies have limitations in coding capacity and are easily counterfeited, failing to meet the demands for high-security anti-counterfeiting. Existing optical temperature sensing materials are mostly based on fluorescence intensity ratio (FIR) technology of thermally coupled energy levels, which suffers from low sensing sensitivity, poor temperature resolution, and large relative measurement errors, failing to meet the requirements of high-precision temperature measurement applications.

[0004] Lead-free metal halide double perovskites Cs₂B₁B₃X₆ (B₁ = Na, K, Ag; B₃ = Bi, Sb, In; X = Cl, Br, I) have become an ideal alternative matrix to traditional lead-based perovskites due to their low toxicity, excellent photothermal stability, and highly designable crystal structure. Among them, Cs₂NaYbCl₆ intrinsically contains a high concentration of Yb in its lattice. 3+ Ions can serve as a "self-sensitized" matrix platform, efficiently absorbing 980nm near-infrared light without additional doping of sensitizers, and transferring energy to activator ions through energy transfer, providing favorable conditions for constructing an efficient upconversion luminescence system.

[0005] Holmium ion (Ho) 3+ Because it has a rich stepped energy level structure, it is similar to Yb 3+ High energy transfer efficiency between them, its green light ( 5 F4 / 5 S2→ 5 I8) and red light ( 5 F5 → 5 I8) emission intensity is highly sensitive to crystal field environment and temperature, making it an ideal upconversion luminescence activator ion. Theoretically, Ho 3+ The Cs2NaYbCl6 doped system can achieve multicolor tunable upconversion luminescence by adjusting the doping concentration, and at the same time, it can achieve high-sensitivity temperature sensing based on the temperature dependence of its emission intensity, and has the potential to build a single-matrix dual-function optical platform.

[0006] But currently, regarding Ho 3+ Research on the Cs₂NaYbCl₆ doped system still has significant shortcomings: First, the concentration-dependent microscopic mechanism of red-green light emission tuning has not been systematically elucidated; second, the dynamic modulation effect of temperature on the emission color of this system lacks in-depth study; third, the integrated application of this material in optical anti-counterfeiting and temperature sensing has not yet been explored, and there is a lack of a Cs₂NaYbCl₆:Ho doped system that can be scalably prepared and possesses both multi-color tunable emission and high-sensitivity temperature measurement performance. 3+ Microcrystal preparation method, and integrated anti-counterfeiting and temperature measurement application scheme based on this material. Summary of the Invention

[0007] To address the problems of poor physicochemical stability, low anti-counterfeiting security, and insufficient temperature measurement accuracy of existing materials in the prior art, this invention provides a Ho 3+ The preparation method of Cs2NaYbCl6 doped microcrystals and their application in anti-counterfeiting and temperature sensors can realize the integrated application of single matrix materials in multicolor optical anti-counterfeiting, information encryption and high-precision temperature sensing. At the same time, the preparation method has the characteristics of simple operation, readily available raw materials and large-scale production.

[0008] This invention is achieved through the following technical solution: A Ho 3+ Methods for preparing Cs₂NaYbCl₆ doped microcrystals include: Step 1: Weigh the raw materials CsCl, NaCl, and YbCl3 in a ratio of Cs:Na:Yb:Ho = 2:1:(0.9~0.1):(0.1~0.9). 6H2O, HoCl3 6H2O, where x+y=1, and x∈(0,1), y∈(0,1); Step 2: Add the above raw materials to deionized water and stir to dissolve to obtain a clear solution; Step 3: Dry the clear solution until the solution evaporates and white crystals precipitate out; Step 4: Grind the white crystals to obtain Ho. 3+ Cs2NaYbCl6 doped microcrystals.

[0009] Preferably, in step 2, the ratio of CsCl to deionized water is 2 mmol: 2 mL.

[0010] Preferably, in step 3, the drying temperature is 60~120℃.

[0011] A method according to the Ho 3+ Ho obtained by the preparation method of Cs2NaYbCl6 doped microcrystals3+ Cs2NaYbCl6 doped microcrystals.

[0012] Preferably, when Ho 3+ When the doping concentration is 0.3, the Cs₂NaYbCl₆: 0.3Ho 3+ The microcrystals exhibit a green light emission intensity of 2.5 × 10⁻⁶ at 549 nm. 6 au.

[0013] Preferably, when Ho 3+ When the doping concentration is 0.3, the Cs₂NaYbCl₆: 0.3Ho 3+ The microcrystals exhibit a relative sensitivity of 1.6% K at 298 K. -1 The temperature resolution is 0.32K.

[0014] Preferably, when Ho 3+ When the doping concentration is 0.7, the Cs₂NaYbCl₆: 0.7Ho 3+ The microcrystals exhibit a red light emission intensity of 2.1 × 10⁻⁶ at 657 nm. 6 au.

[0015] Preferably, when Ho 3+ When the doping concentration is 0.9, the Cs₂NaYbCl₆: 0.9Ho 3+ The red-green light emission intensity ratio of the microcrystal is 3.5.

[0016] A Ho 3+ Application of Cs2NaYbCl6 doped microcrystals in the field of anti-counterfeiting.

[0017] A Ho 3+ Application of Cs2NaYbCl6 doped microcrystals in the field of temperature sensors.

[0018] Compared with the prior art, the present invention has the following beneficial effects: This invention provides a Ho 3+ In the preparation method of doped Cs₂NaYbCl₆ microcrystals, Ho is doped... 3+ Furthermore, the luminescence intensity of the microcrystalline powder was adjusted by controlling its doping concentration, and high-purity, high-performance Cs2NaYbCl6:Ho was prepared by the dissolution-drying method. 3+ Microcrystals enable multi-color tunable upconversion luminescence, and an optical anti-counterfeiting, information encryption, and high-sensitivity temperature sensing system based on this material are constructed, thereby solving the technical problems of poor physical and chemical stability, low anti-counterfeiting security, and insufficient temperature measurement accuracy of existing materials.

[0019] In terms of process, the dissolution-drying method adopted in this application does not require complex processes such as high-temperature sintering, hydrothermal / solvothermal processes. The reaction conditions are mild, the operation steps are simple, and the raw materials are all commercially available high-purity reagents that are readily available, making it suitable for industrial-scale preparation. At the same time, the resulting microcrystalline powder has high purity and uniform particle size, making it easy to process and apply in subsequent applications.

[0020] This invention provides a Ho 3+ Ho obtained by the preparation method of Cs2NaYbCl6 doped microcrystals 3+ Doped Cs₂NaYbCl₆ microcrystals are lead-free double perovskite materials, exhibiting low toxicity, environmental friendliness, and excellent photothermal and chemical stability; Ho 3+ Ions were successfully incorporated into the matrix lattice through isomorphic substitution without altering the cubic crystal structure of the matrix. The material exhibits good crystallinity, weak concentration quenching and thermal quenching effects, and excellent luminescence stability. Attached Figure Description

[0021] Figure 1 The Cs2NaYbCl6:xHo component in this invention 3+ XRD patterns and crystal structure diagrams of microcrystals (x=0.1, 0.3, 0.5, 0.7, 0.9), where (a) is a comparison diagram of the XRD pattern and the standard card, (b) is a magnified view of the (220) crystal plane, (c) is the crystal structure diagram of the Cs2NaYbCl6 matrix, and (d) is the crystal structure diagram of Ho. 3+ Crystal structure diagram of doped Cs₂NaYbCl₆; Figure 2 The solution is Cs₂NaYbCl₆: 0.3Ho 3+ Microstructure and elemental analysis diagrams of microcrystals, where (a) and (b) are SEM images at different magnifications, (c) is an EDS energy spectrum and elemental content table, and (d)-(h) are mapping distribution diagrams of Na, Cl, Cs, Ho, and Yb elements; Figure 3 Cs2NaYbCl6:xHo 3+ The upconversion luminescence properties of the microcrystals are shown in the diagram, where (a) is the upconversion emission spectrum under 980 nm excitation, and (b) is the green-red light emission intensity as a function of Ho³. + The concentration change curves, (c) and (d) are the fluorescence lifetime decay curves for 549nm green light and 657nm red light, respectively; Figure 4 The solution is Cs₂NaYbCl₆: 0.3Ho 3+ Ho in microcrystals 3+ / Yb 3+ Schematic diagram of energy transfer and upconversion luminescence mechanism; Figure 5 Cs2NaYbCl6:xHo3+ CIE chromaticity coordinate diagram and luminescence images of microcrystals, where the left image shows the CIE1931 chromaticity coordinate distribution, and the right image shows the luminescence images of samples with x=0.3, 0.7, and 0.9 under 980nm excitation; Figure 6 Comparison of anti-counterfeiting patterns prepared for fluorescent ink under natural light and 980nm excitation, where (a)-(d) are glass-based patterns and weighing paper-based screen-printed patterns under natural light, and (e)-(h) are the luminescence patterns of the corresponding patterns under 980nm LD excitation; Figure 7 Comparison images of binary information encryption patterns, where (a) is the pattern under natural light and (b) is the light emission decoding pattern under 980nm excitation; Figure 8 The solution is Cs₂NaYbCl₆: 0.3Ho 3+ The temperature-dependent upconversion luminescence properties of the microcrystals are shown in the figure, where (a) is the upconversion emission spectrum at different temperatures, (b) is the contour plot of the emission spectrum, (c) is the curve of green and red light emission intensity as a function of temperature, and (d) is the curve of red and green light intensity ratio as a function of temperature. Figure 9 The solution is Cs₂NaYbCl₆: 0.3Ho 3+ A schematic diagram of temperature-dependent CIE chromaticity coordinates and thermochromic effects of microcrystals, where the left figure shows the CIE chromaticity coordinate distribution at different temperatures, and the right figure shows a schematic diagram of the thermochromic process; Figure 10 shows Cs₂NaYbCl₆: 0.3Ho 3+ The temperature sensing performance of the microcrystal is shown in the figure, where (a) is the fitting curve of FIR with temperature, (b) is the curve of absolute sensitivity and relative sensitivity with temperature, (c) is the curve of temperature resolution with temperature, and (d) is the FIR repeatability curve of 4 heating-cooling cycles. Figure 11 The solution is Cs2NaYbCl6:0.3Ho. 3+ Test chart evaluating the temperature sensing performance of phosphor. Detailed Implementation

[0022] The following specific embodiments illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification.

[0023] Exemplary embodiments of the present invention will now be described with reference to the accompanying drawings. However, the present invention may be embodied in many different forms and is not limited to the embodiments described herein. These embodiments are provided to fully and completely disclose the invention and to fully convey its scope to those skilled in the art. The terminology used in the exemplary embodiments illustrated in the drawings is not intended to limit the invention. In the drawings, the same units / elements are referred to by the same reference numerals.

[0024] Unless otherwise stated, the terms used herein (including technical terms) have their common meaning as understood by one of ordinary skill in the art. Furthermore, it is understood that terms defined in commonly used dictionaries should be understood to have a meaning consistent with the context of their relevant field, and not to be interpreted as having an idealized or overly formal meaning.

[0025] The present invention will be further described in detail below with reference to specific embodiments. These descriptions are for explanation purposes only and are not intended to limit the scope of the invention.

[0026] All raw materials used in this invention are commercially available products, including CsCl, NaCl, and YbCl3. 6H2O, HoCl3 The purity of 6H2O was 99.99%. The silane coupling agent, anhydrous ethanol, ethyl acetate, and PMMA were all of analytical grade. The deionized water was prepared in the laboratory.

[0027] The testing instruments used included: a Bruker D8 X-ray diffractometer (XRD), a JEOL JSM6701F field emission scanning electron microscope (FESEM) and its matching energy dispersive spectrometer (EDS), a HORIBA FluoroLog-3 fluorescence spectrophotometer, a temperature control console, an infrared thermometer, a centrifuge, a magnetic stirrer, and a forced-air drying oven.

[0028] This invention discloses a Ho 3+ Methods for preparing Cs₂NaYbCl₆ doped microcrystals include: Step 1: Weigh the raw materials CsCl, NaCl, and YbCl3 in a ratio of Cs:Na:Yb:Ho = 2:1:(0.9~0.1):(0.1~0.9). 6H2O, HoCl3 6H2O, where x+y=1, and x∈(0,1), y∈(0,1).

[0029] Step 2: Add the above raw materials to deionized water and stir to dissolve to obtain a clear solution. The ratio of CsCl to deionized water is 2 mmol: 2 mL.

[0030] Step 3: Dry the clear solution at 60~120℃ until the solution evaporates and white crystals precipitate.

[0031] Step 4: Grind the white crystals to obtain Ho. 3+ Cs2NaYbCl6 doped microcrystals.

[0032] This invention also discloses a HO 3+ The preparation method of doped CS2NAYBCL6 microcrystals involves controlling Ho 3+ With doping concentrations (x=0.1~0.9), continuous upconversion emission color tuning from green (x=0.3), yellow (x=0.7) to red (x=0.9) can be achieved under 980nm near-infrared excitation. The emission intensity is high, the color purity is good, and the CIE chromaticity coordinates change regularly with the doping concentration, which can provide a basis for multi-mode anti-counterfeiting.

[0033] The present invention also discloses a method according to the Ho described above. 3+ Ho obtained by the preparation method of Cs2NaYbCl6 doped microcrystals 3+ Cs2NaYbCl6 doped microcrystals.

[0034] When Ho 3+ When the doping concentration is 0.3, the Cs₂NaYbCl₆: 0.3 Ho 3+ The microcrystals exhibit a green light emission intensity of 2.5 × 10⁻⁶ at 549 nm. 6 au, with a relative sensitivity of 1.6% K at 298 K. -1 The temperature resolution is 0.32K.

[0035] When Ho 3+ When the doping concentration is 0.7, the Cs₂NaYbCl₆: 0.7Ho 3+ The microcrystals exhibit a red light emission intensity of 2.1 × 10⁻⁶ at 657 nm. 6 au.

[0036] When Ho 3+ When the doping concentration is 0.9, the Cs₂NaYbCl₆: 0.9Ho 3+ The red-green light emission intensity ratio of the microcrystal is 3.5.

[0037] Example 1 According to the stoichiometric ratio Cs2NaYb0.9Ho 0.1 Cl6, accurately weigh 4.12g of CsCl, 0.58g of NaCl, and YbCl3. 3.72g of 6H₂O and HoCl₃ 0.41g of 6H₂O; Pour the above raw materials into 20 mL of deionized water, place on a magnetic stirrer and stir at 300 r / min until the solution is completely clear; Transfer the clear solution to a forced-air drying oven and dry at 60°C for 24 hours until the solution evaporates and white crystals precipitate. The white crystals were transferred to an agate mortar and ground thoroughly for 10 minutes to obtain Cs₂NaYbCl₆: 0.1Ho. 3+ Microcrystalline powder.

[0038] The microcrystal, excited by a 980nm LD, has CIE chromaticity coordinates of (0.533, 0.478), exhibits yellow-green upconversion luminescence, and has a green light emission intensity of 1.2 × 10⁻⁶ at 549nm. 6 The red light emission intensity at 657nm is 0.8 × 10⁻⁶. 6 au.

[0039] Example 2 According to the stoichiometric ratio Cs2NaYb 0.7 Ho 0.3 Cl6, accurately weigh 4.12g of CsCl, 0.58g of NaCl, and YbCl3. 6H2O 3.08g, HoCl3 6H₂O 1.24g; Pour the above raw materials into 20 mL of deionized water and place them on a magnetic stirrer. Stir at 400 r / min until the solution is completely clear. Transfer the clear solution to a forced-air drying oven and dry at 60°C for 18 hours until the solution evaporates and white crystals precipitate. The white crystals were transferred to an agate mortar and ground thoroughly for 12 minutes to obtain Cs₂NaYbCl₆: 0.3Ho. 3+ Microcrystalline powder.

[0040] The microcrystal, excited by a 980nm LD, has CIE chromaticity coordinates of (0.306, 0.683) and exhibits bright green upconversion luminescence, with a green light emission intensity of 2.5 × 10⁻⁶ at 549nm. 6 au is the maximum value among all doping concentrations; as a temperature sensing material, its relative sensitivity at 298 K reaches 1.6% K. -1 The temperature resolution is 0.32K.

[0041] Example 3 According to the stoichiometric ratio Cs2NaYb 0.3 Ho 0.7 Cl6, accurately weigh 4.12g of CsCl, 0.58g of NaCl, and YbCl3. 6H2O 1.59g, HoCl3 6H2O 2.89g; Pour the above raw materials into 20 mL of deionized water and place them on a magnetic stirrer. Stir at 500 r / min until the solution is completely clear. Transfer the clear solution to a forced-air drying oven and dry at 60°C for 12 hours until the solution evaporates and white crystals precipitate. The white crystals were transferred to an agate mortar and ground thoroughly for 15 minutes to obtain Cs₂NaYbCl₆: 0.7Ho. 3+ Microcrystalline powder.

[0042] The microcrystal, under 980nm LD excitation, has CIE chromaticity coordinates of (0.415, 0.573), exhibits bright yellow upconversion luminescence, and its 657nm red light emission intensity reaches 2.1 × 10⁻⁶. 6 au is the maximum value among all doping concentrations.

[0043] Example 4 According to the stoichiometric ratio Cs2NaYb 0.1 Ho 0.9 Cl6, accurately weigh 4.12g of CsCl, 0.58g of NaCl, and YbCl3. 0.85g of 6H₂O and HoCl₃ 6H2O 3.73g; Pour the above raw materials into 20 mL of deionized water and place them on a magnetic stirrer. Stir at 400 r / min until the solution is completely clear. Transfer the clear solution to a forced-air drying oven and dry at 60°C for 15 hours until the solution evaporates and white crystals precipitate. The white crystals were transferred to an agate mortar and ground thoroughly for 12 minutes to obtain Cs₂NaYbCl₆: 0.9Ho. 3+ Microcrystalline powder.

[0044] The microcrystal has CIE chromaticity coordinates of (0.582, 0.409) under 980nm LD excitation, exhibiting a distinct red upconversion luminescence with a red-green light emission intensity ratio of 3.5, which is the highest among all doping concentrations.

[0045] Reference Figure 1 Cs2NaYbCl6:xHo 3+ XRD diffraction patterns of phosphors (x=0.15, 0.3, 0.5, 0.7, 0.9). Figure 1(a) shows that the diffraction peaks of all samples are consistent with those of the standard card Cs₂NaYbCl₆ (PDF#89-0054), and no impurity peaks were observed, indicating that the synthesized samples have good purity. Furthermore, Ho 3+ Doping does not change the crystal structure; all samples retain a cubic crystal structure with the Fm-3m space group. With Ho 3+ With increasing doping concentration, the XRD diffraction patterns show a significant shift of the diffraction peaks to lower angles, which is particularly pronounced on the (220) crystal plane. Figure 1 As shown in (b), this is because the Ho ion has a smaller radius. 3+ Replaced Yb³ in the matrix + The peak shift is more pronounced with increasing doping concentration, consistent with Bragg's law, further confirming the Ho... 3+ The ions have been effectively integrated into the host lattice.

[0046] Figure 1 (c) is the crystal structure diagram of the Cs2NaYbCl6 matrix. Figure 1 (d)Ho 3+ The unit cell structure diagram of the crystal structure model, where Na + and Yb 3+ The ions selectively occupy octahedral sites and coordinate with Cl ions at the corners to form [NaCl6]. 5 and [YbCl6] 3 The octahedron is formed by the Cs ion, which is located at the center of the surrounding octahedral cavity. Based on considerations of effective ionic radius and charge balance, Ho... 3+ It is expected to replace Yb ​​in the host lattice 3+ Site.

[0047] Reference Figure 2 As shown in 2(a) and (b), the obtained Cs2NaYbCl6: 0.3Ho 3+ It appears as irregular, aggregated particles with a wide size distribution and lacking a clear crystal plane. The EDS spectrum in 2(c) confirmed the presence of Cs, Na, Yb, Ho and Cl, and no impurity elements were detected, verifying the high phase purity of the sample.

[0048] Reference Figure 3 , Figure 3 (a) Demonstrates Cs2NaYbCl6:xHo under 980 nm LD excitation at room temperature. 3+The UC emission spectra of the phosphors (x = 0.1, 0.2, 0.3, 0.5, 0.7, 0.9) are shown. Two distinct emission bands are clearly visible: a green emission band in the 525-575 nm range (centered at 549 nm) and a red emission band in the 625-700 nm range (peak at 657 nm), corresponding to Ho... 3+ Characteristic electronic transitions: 5 F4 / 5 S2→ 5 I8 and 5 F5 → 5 I8. The peak locations of green and red emissions are in different Ho... 3+ Its emission intensity remains almost constant at different doping concentrations, while it varies significantly with the doping level. For example... Figure 3 As shown in (b), (c), and (d), with Ho 3+ As the concentration increased from 0.1 to 0.9, the intensity of the green emission at 549 nm initially increased, then decreased. At low Ho... 3+ At doping levels, Yb 3+ To Ho 3+ Energy transfer is the dominant process: Yb 3+ (Sensitizer) absorbs 980 nm photons and transfers energy to Ho. 3+ (Activator), promote 5 I6→ 5 F4 / 5 S2 or 5 I7→ 5 The shift in F5 level. With Ho 3+ Increased content leads to improved energy transfer efficiency, resulting in enhanced green emissions. 3+ The concentration reached its peak. When Ho 3+ When the doping concentration exceeds 0.3%, concentration quenching becomes the dominant factor: adjacent Ho 3+ The reduction in interion distance will trigger Ho 3+ The cross-relaxation (CR) process between the two states leads to a reduction in the number of green emission excited states, resulting in a decrease in green emission intensity. In contrast, the red emission intensity at 657 nm increases with Ho. 3+ The concentration increases monotonically, reaching its maximum at a doping level of 0.7. When the doping level further increases to 0.9, Yb... 3+ The decrease in mole fraction significantly weakened Yb 3 + To Ho 3+ Energy transfer efficiency. Meanwhile, Ho 3+ The enhanced CR and increased nonradiative transition probability in ions lead to a sharp decrease in the overall emission intensity of the UC.

[0049] Reference Figure 4Under 980 nm light irradiation, Yb 3+ Absorbing photons from the ground state 2 F7 / 2 transitions to the excited state²F5 / 2, and transfers energy to Ho through three energy transfer upconversion (ETU) processes. 3+ First, the ETU1 process will... 3+ From the ground state 5 I8 stimulated to 5 The I6 intermediate energy level; subsequently, the ETU2 process further... 3+ from 5 I6 energy level increased to 5 The F4 luminescent energy level produces green light emission. 5 F4→ 5 I8). In 5 Ho at the I6 level 3+ It can also be achieved through non-radiative relaxation (NRT1) to 5 The I7 level is then populated through the ETU3 process. 5 The F5 energy level emits red light. 5 F5 → 5 I8). Furthermore, in 5 Ho at the F4 energy level 3+ It can be achieved through non-radiative relaxation (NRT2) to 5 The F5 energy level contributes to the red light emission channel.

[0050] Reference Figure 5 In Cs2NaYbCl6:Ho³ + Within the system, with Ho 3+ With increasing doping concentration, the relative intensities of the green and red upconversion emission peaks change significantly. Therefore, for different Ho... 3+ Cs₂NaYbCl₆ samples with varying doping concentrations were subjected to CIE 1931 chromaticity coordinate analysis. The corresponding chromaticity parameters are listed in Table 1, and the chromaticity coordinate distribution is as follows: Figure 5 As shown, it can be clearly observed that all samples emit visible light under 980 nm excitation. With Ho... 3+ As the concentration increases, the emission color gradually shifts from the green region to the red region. It is worth noting that Cs₂NaYbCl₆:0.7Ho 3+ The sample primarily emits red light, achieving significant modulation of the emission color. Furthermore, photographs of the sample taken under 980 nm laser irradiation visually demonstrate the distinct color evolution process of the upconversion emission.

[0051] The present invention also discloses a Ho described above. 3+ Application of Cs2NaYbCl6 doped microcrystals in the field of anti-counterfeiting.

[0052] Example 5 Cs₂NaYbCl₆ prepared in Example 2: 0.3Ho 3+ Green fluorescent ink was prepared using microcrystals as raw materials. Add 20 mL of anhydrous ethanol to a 50 mL beaker, then add 50 μL of silane coupling agent and 5 μL of deionized water dropwise. Sonicate at 100 W for 15 min, then place the beaker in an 80 °C water bath and stir for 30 min to allow the silane coupling agent to be completely hydrolyzed. Add 1g of Cs₂NaYbCl₆: 0.3Ho to the hydrolyzed silane coupling agent solution. 3+ Microcrystalline powder was stirred in an 80℃ water bath for 2 hours to complete surface modification; the modified suspension was centrifuged at 8000 r / min for 5 min, the precipitate was collected and washed twice with anhydrous ethanol, dried at 60℃ for 6 hours and then ground to obtain hydrolysis-resistant microcrystalline powder. Weigh 0.5g of PMMA powder and slowly add it to 10mL of ethyl acetate while stirring with a glass rod. Heat in a 40℃ water bath and stir until the PMMA is completely dissolved to obtain a transparent PMMA film-forming solution. The above hydrolysis-resistant microcrystalline powder was slowly added to the PMMA film-forming solution and magnetically stirred at 300 r / min for 1 h to ensure uniform dispersion of the microcrystalline powder. Then, it was allowed to stand for 3 h to remove air bubbles, resulting in green upconversion fluorescent ink.

[0053] The ink exhibits a bright green luminescence under 980nm LD excitation, with no hydrolysis or luminescence quenching, good film-forming properties, and no cracks after drying.

[0054] In summary, the fluorescent ink prepared based on the microcrystals of this invention is completely invisible under natural light, but exhibits vivid multicolor luminescence only under 980nm near-infrared excitation. It can construct multi-mode anti-counterfeiting patterns, binary information encryption patterns, and encrypted barcodes, thereby increasing the difficulty of anti-counterfeiting and the level of information encryption, and thus solving the problem of easy counterfeiting of traditional single-mode fluorescent anti-counterfeiting.

[0055] Example 6 Cs₂NaYbCl₆ prepared in Example 4: 0.9Ho 3+ Red fluorescent ink was prepared using microcrystals as raw materials. Add 20 mL of anhydrous ethanol to a 50 mL beaker, then add 50 μL of silane coupling agent and 5 μL of deionized water dropwise. Sonicate at 200 W for 20 min, then place the beaker in an 80 °C water bath and stir for 60 min to allow the silane coupling agent to be completely hydrolyzed. Add 1g of Cs₂NaYbCl₆: 0.9Ho to the hydrolyzed silane coupling agent solution. 3+ Microcrystalline powder was stirred in an 80℃ water bath for 3 hours to complete surface modification; the modified suspension was centrifuged at 10000 r / min for 10 min, the precipitate was collected and washed 3 times with anhydrous ethanol, dried at 60℃ for 12 hours and then ground to obtain hydrolysis-resistant microcrystalline powder. Weigh 0.5g of PMMA powder and slowly add it to 10mL of ethyl acetate while stirring with a glass rod. Heat in a 40℃ water bath and stir until the PMMA is completely dissolved to obtain a transparent PMMA film-forming solution. The above hydrolysis-resistant microcrystalline powder was slowly added to the PMMA film-forming solution and magnetically stirred at 300 r / min for 2 h to ensure uniform dispersion of the microcrystalline powder. Then, it was allowed to stand for 4 h to remove air bubbles, resulting in red upconversion fluorescent ink.

[0056] This ink exhibits a bright red glow under 980nm LD excitation, has good hydrolysis resistance and excellent film-forming properties, and can be used for screen printing.

[0057] Example 7 The green fluorescent ink from Example 5 and Cs2NaYbCl6:0.7Ho were used respectively. 3+ Yellow fluorescent ink and red fluorescent ink from Example 6 were used to coat square, circular, and triangular patterns onto a glass slide. The slide was then left to air dry in a ventilated place for 24 hours to obtain a glass-based multicolor anti-counterfeiting pattern.

[0058] The anti-counterfeiting pattern is completely invisible under natural light. Under 980nm LD near-infrared excitation, the square pattern emits green light, the circle emits yellow light, and the triangle emits red light. (Refer to...) Figure 6 The square "□" emits a bright green light, corresponding to Cs2NaYbCl6: 0.3Ho 3+ It exhibits a characteristic green emission; the circular mark "○" emits yellow light, originating from Cs2NaYbCl6: 0.7Ho 3+ The triangular marker "△" glows red and can be attributed to Cs₂NaYbCl₆: 0.9Ho 3+ The patterns are clear, the colors are highly contrasting, and there are no distracting colors, giving it excellent anti-counterfeiting effects. It can be used for anti-counterfeiting labels on food, medicine, cosmetics and other products.

[0059] Example 8 The green fluorescent ink of Example 5 was defined as binary code "1", and the red fluorescent ink of Example 6 was defined as binary code "0". Based on the ASCII code of the letter "CHU", a circular array of binary information encryption patterns was prepared on weighing paper by screen printing. After printing, the paper was placed in a 60°C forced-air drying oven for 3 hours to dry.

[0060] Reference Figure 7 Under natural light, the encrypted pattern is only visible as a regular circular array, and no information can be identified. Under 980nm LD near-infrared excitation, the circular array emits green and red light, and the letters "CHU" can be decoded according to the encoding rules. The information encryption effect is significant and can be used for high-security information storage and transmission.

[0061] Example 9 Barcodes were printed on PVC plastic sheets using the green fluorescent ink of Example 5 and dried in a 60°C forced-air drying oven for 2 hours to obtain encrypted barcodes.

[0062] The barcode is invisible to the naked eye and cannot be recognized by mobile phone scanners without 980nm near-infrared excitation; however, under 980nm LD excitation, the barcode emits a bright green light and can be clearly recognized by a scanner, which can read the encrypted information "CHU", and can be used for product traceability and anti-counterfeiting.

[0063] The present invention also discloses a Ho described above. 3+ Application of Cs2NaYbCl6 doped microcrystals in the field of temperature sensors.

[0064] Cs₂NaYbCl₆:0.3Ho was tested in the temperature range of 298 K to 573 K. 3+ The temperature-dependent upconversion emission spectrum of the phosphor is shown in the following results. Figure 8 As shown in (a), the characteristic peak positions of green and red light emission remain essentially unchanged throughout the entire temperature range. However, due to Figure 8 As shown in (b) and (c), the integrated intensity of the 549 nm green light emission generally decreases with increasing temperature, while the intensity of the 657 nm red light emission continuously increases. This phenomenon can be explained by a temperature-dependent multiphonon relaxation process: 5 F4 / 5 S2 energy level and lower 5 The band gap between F5 levels is relatively small (approximately 1500–2000 cm). - ¹), making 5 F4 / 5 S2 direction 5Nonradiative relaxation of F5 occurs readily via multiphonon emission. As temperature increases, the phonon density increases, accelerating the multiphonon relaxation rate, leading to… 5 F4 / 5 The decrease in the population of the S2 luminescent level leads to a reduction in the green light emission intensity. Simultaneously, the enhanced relaxation process shifts the population to... 5 F5 energy level, thereby enhancing 5 F5 → 5 The red light emission intensity corresponding to the I8 transition.

[0065] Reference Figure 9 When the temperature increases from 298 K to 573 K, the phosphor's emission color gradually changes from green (color coordinates (0.326, 0.647)) to cyan (color coordinates (0.072, 0.731)). Table 3.1 lists the emission colors of Cs₂NaYbCl₆:0.3Ho. 3+ Chromaticity coordinates of phosphor at different temperatures. Yb³ at room temperature. + Ions absorb near-infrared light and efficiently transfer energy to Ho. 3+ The ions excite their electrons to higher excited states. These electrons then undergo rapid nonradiative relaxation via phonon emission, populating to lower energies. 5 F4 / 5 The S2 energy level produces strong green emission. However, with increasing temperature, lattice vibrations are significantly enhanced (accompanied by an increase in phonon density). Under these conditions, Ho³ + In ions 5 F4 / 5 Electrons in the S2 level can absorb the energy of thermophonons, causing them to be re-excited to a higher energy level (e.g., ...). 5 F3 / 5 The probability of G6 increases significantly, a process known as thermally activated upconversion. Once these high energy levels are populated, electrons can relax to the ground state via radiative transitions, producing cyan-blue emission. Furthermore, Ho at higher energy levels... 3+ Ions may also migrate to neighboring Yb 3+ Ions undergo reverse energy transfer, effectively reducing Ho 3+ The population of the luminescent energy level further weakens green emission. The combined effect of enhanced cyan emission and weakened green emission leads to the observed change in emission color with increasing temperature.

[0066] Example 10 The Cs2NaYbCl6 prepared in Example 2: 0.3Ho 3+ The microcrystalline powder is evenly spread on the temperature control panel to a thickness of 0.5 mm to ensure no agglomeration. The temperature control console was set to 573K and held at that temperature for 10 minutes. Then, using a 980nm LD as the excitation source (1W power), the upconversion emission spectrum at that temperature was collected by a fluorescence spectrophotometer.

[0067] Calculate the integrated intensities of the emission peaks at 549 nm and 657 nm in the spectrum to obtain FIR=I. 657 / I 549 =3.82; the calculated theoretical temperature is 575.1K; simultaneously, the actual temperature of the sample surface was measured using an infrared thermometer, and the actual temperature was found to be 573K. The relative error of this measurement was 0.4%, proving that the microcrystalline material of this invention maintains extremely high temperature measurement accuracy in the high-temperature region and has no significant performance degradation.

[0068] Among them, the experimental data were fitted using an exponential equation, and the pre-fitted FIR-T relationship equation was used.

[0069] In the formula, T is the thermodynamic temperature, and A, B, and C are fitting parameters

[30] . The fluorescence intensity ratio (FIR) data were fitted using this formula, and the results are as follows: Figure 10 As shown in (a). The fitting results show that in the temperature range of 298 K to 573 K, the ratio of fluorescence intensity between the two transitions increases monotonically with increasing temperature, and the experimental data and the fitting curve are in good agreement.

[0070] As shown in Figure 10(b), in the range of 298 K to 573 K, Cs2NaYbCl6:0.3Ho 3+ S A With S R All values ​​gradually decrease with increasing temperature, with a maximum absolute sensitivity of 0.0384 K. - ¹, The maximum relative sensitivity is 0.0157 K. - ¹, both of which occur at 298 K.

[0071] Temperature resolution (δT) is another important performance parameter used to characterize the smallest detectable temperature change, expressed as:

[0072] δFIR / FIR represents the relative error of the temperature detection parameter relative to the acquisition settings, typically taken as 0.5%. As shown in Figure 10(c), within the test temperature range of 298–573 K, Cs₂NaYbCl₆: 0.3Ho 3+The temperature resolution δT of the phosphor is between 0.31806 K and 0.53687 K, indicating that the material has high temperature measurement accuracy.

[0073] The repeatability (R) of the FIR signal was evaluated through four consecutive heating and cooling cycles, and the results are shown in Figure 10(d). The R value can be calculated using the following formula:

[0074] In the formula, Δm is the fluorescence intensity ratio (FIR) value, and Δi is the average FIR value over four cycles. The R values ​​calculated at 298 K and 573 K both exceed 99%, and the FIR values ​​show almost no significant drift during cycling, indicating that the material has excellent signal stability and reliability in actual temperature measurements.

[0075] Reference Figure 11 The testing system was used to test Cs2NaYbCl6:Ho 3+ The temperature sensing performance of the phosphor was evaluated by placing the sample on a heating stage and exciting it with a 980 nm laser diode (LD). The resulting upconversion emission spectrum was acquired via fiber optic cable and analyzed by a computer, as shown in Figure 11(a). The theoretical temperature value was calculated from the spectral data as follows: Figure 11 (b)-(d), and compared with the temperatures measured in real time by the infrared thermometer 11(f)-(i). The results show that the theoretical prediction values ​​and the measured values ​​are in good agreement, and the relative errors are all less than 3% within the test temperature range, confirming the theoretical prediction of Cs2NaYbCl6:0.3Ho. 3+ The reliability and practical feasibility of applying phosphors in the field of fluorescence thermometry.

[0076] In summary, the Cs2NaYbCl6:Ho prepared by this invention... 3+ Microcrystals are a single-matrix dual-function optical platform with multi-color tunable upconversion luminescence and high-sensitivity temperature sensing performance. They can be used simultaneously for optical anti-counterfeiting / information encryption and high-precision temperature sensing, breaking the limitation of traditional luminescent materials with single function. They have a wide range of applications and can be made into fluorescent inks for optical anti-counterfeiting and information encryption. They can also be used directly as temperature sensing materials for industrial temperature measurement, biological temperature measurement, and environmental temperature measurement, and have broad industrial application prospects and market value.

[0077] The above description is merely a preferred embodiment of the present invention and is not intended to limit the technical solution of the present invention in any way. Those skilled in the art should understand that, without departing from the spirit and principles of the present invention, the technical solution can be modified and replaced in several simple ways, and these modifications and replacements are all within the scope of protection covered by the claims.

Claims

1. A Ho 3+ A method for preparing Cs₂NaYbCl₆ doped microcrystals, characterized in that, include: Step 1: Weigh the raw materials CsCl, NaCl, and YbCl3 in a ratio of Cs:Na:Yb:Ho = 2:1:(0.9~0.1):(0.1~0.9). 6H2O, HoCl3 6H2O, where x+y=1, and x∈(0,1), y∈(0,1); Step 2: Add the above raw materials to deionized water and stir to dissolve to obtain a clear solution; Step 3: Dry the clear solution until the solution evaporates and white crystals precipitate out; Step 4: Grind the white crystals to obtain Ho. 3+ Cs2NaYbCl6 doped microcrystals.

2. The Ho according to claim 1 3+ A method for preparing Cs₂NaYbCl₆ doped microcrystals, characterized in that, In step 2, the ratio of CsCl to deionized water is 2 mmol: 2 mL.

3. The Ho according to claim 1 3+ A method for preparing Cs₂NaYbCl₆ doped microcrystals, characterized in that, In step 3, the drying temperature is 60~120℃.

4. A Ho according to any one of claims 1 to 3 3+ Ho³ obtained by the preparation method of Cs₂NaYbCl₆ microcrystals + Cs2NaYbCl6 doped microcrystals.

5. The Ho according to claim 4 3+ Doped Cs₂NaYbCl₆ microcrystals, characterized in that, When Ho 3+ When the doping concentration is 0.3, the Cs₂NaYbCl₆: 0.3Ho 3+ The microcrystals exhibit a green light emission intensity of 2.5 × 10⁻⁶ at 549 nm. 6 au.

6. The Ho according to claim 4 3+ Doped Cs₂NaYbCl₆ microcrystals, characterized in that, When Ho 3+ When the doping concentration is 0.3, the Cs₂NaYbCl₆: 0.3Ho 3+ The microcrystals exhibit a relative sensitivity of 1.6% K at 298 K. -1 The temperature resolution is 0.32K.

7. The Ho according to claim 4 3+ Doped Cs₂NaYbCl₆ microcrystals, characterized in that, When Ho 3+ When the doping concentration is 0.7, the Cs₂NaYbCl₆: 0.7Ho 3+ The microcrystals exhibit a red light emission intensity of 2.1 × 10⁻⁶ at 657 nm. 6 au.

8. The Ho according to claim 4 3+ Doped Cs₂NaYbCl₆ microcrystals, characterized in that, When Ho 3+ When the doping concentration is 0.9, the Cs₂NaYbCl₆: 0.9Ho 3+ The red-green light emission intensity ratio of the microcrystal is 3.

5.

9. A Ho as described in claim 4 3+ Application of Cs2NaYbCl6 doped microcrystals in the field of anti-counterfeiting.

10. A Ho as described in claim 4 3+ Application of Cs2NaYbCl6 doped microcrystals in the field of temperature sensors.

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