An up-conversion down-conversion near-infrared fluorescent powder and a preparation method thereof

Abstract

This invention relates to the field of luminescent materials technology, specifically to an upconversion / downconversion near-infrared phosphor and its preparation method. The near-infrared phosphor uses MgO as a matrix and Cr... 3+ Yb 3+ As a doping sensitizer, Er 3+ As a doping activator, it was prepared by a high-temperature solid-state method. The prepared phosphor contained MgO and Cr. 3+ Yb 3+ and Er 3+ The molar ratio of the components is (91.5–99):(0.5–8):(0.35–0.475):(0.025–0.15). The prepared near-infrared phosphor possesses independent emission and luminescence functions in multiple modes, including upconversion and downconversion. In a single material system, it emits bright near-infrared light upon excitation by visible light, and simultaneously emits visible light upon excitation by near-infrared light, making it undetectable by the naked eye or ordinary equipment. This significantly increases the difficulty for counterfeiters to detect and replicate, providing a physical basis for achieving multiple anti-counterfeiting verifications. Furthermore, the prepared near-infrared phosphor exhibits high luminous efficiency and stability, and the preparation method is simple and easy to implement, facilitating large-scale production.

Description

Technical Field

[0001] This invention relates to the field of luminescent materials technology, specifically to an upconversion / downconversion near-infrared phosphor and its preparation method. Background Technology

[0002] Compared to traditional ultraviolet luminescent powders, near-infrared luminescent powders possess the core advantages of superior concealment and high anti-counterfeiting barriers. Their emission is invisible to the human eye and requires specialized equipment for detection, significantly increasing the difficulty of counterfeiting and identification. Simultaneously, their rich spectral characteristics serve as unique "fingerprints," easily integrating with machine identification and digital traceability systems. To address the urgent needs of the current high-end anti-counterfeiting field for high concealment, multi-mode verification, and difficulty in replication, multi-mode near-infrared luminescent materials capable of up-conversion and down-conversion have significant application prospects in advanced anti-counterfeiting, information security, and biomedical instruments. However, obtaining high-performance multi-mode near-infrared luminescent materials faces a series of severe and profound challenges on the road to large-scale application: the primary pain point lies in the bottleneck of material performance. Many near-infrared luminescent materials suffer from low luminous efficiency, resulting in weak signals and requiring high-performance excitation and detection equipment, thus hindering rapid on-site identification. Secondly, cost and process constraints are particularly prominent. High-performance luminescent materials often rely on expensive rare earth elements or complex nano-synthesis processes (such as thermal injection and hydrothermal methods), leading to high production costs and making large-scale application difficult for cost-sensitive products. In addition, the long-term stability of the material is a key test, which directly determines the effective lifespan and reliability of the anti-counterfeiting label.

[0003] Therefore, there is an urgent need to provide a near-infrared phosphor with multi-mode emission that combines upconversion and downconversion, and its preparation method, to solve the above-mentioned problems in the prior art. Summary of the Invention

[0004] To address the shortcomings of existing technologies, the present invention aims to provide an upconversion and downconversion near-infrared phosphor and its preparation method. The prepared near-infrared phosphor has independent emission and luminescence functions in multiple modes of upconversion and downconversion, and also has high luminous efficiency and stability. The preparation method is simple and easy to implement, and can be easily mass-produced.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: This invention provides a method for preparing a near-infrared phosphor with upconversion and downconversion luminescence, wherein the near-infrared phosphor uses MgO as a matrix and Cr as a component. 3+ Yb 3+ As a doping sensitizer, Er 3+ As a doping activator, it was prepared by a high-temperature solid-state method. The prepared phosphor contained MgO and Cr. 3+ Yb3+ and Er 3+ The molar ratio is (91.5-99):(0.5-8):(0.35-0.475):(0.025-0.15).

[0006] The near-infrared phosphor provided by this invention uses MgO as a matrix and adds a specific amount of Cr. 3+ Yb 3+ Er 3+ The near-infrared phosphor prepared by co-doping via a high-temperature solid-state method has been experimentally proven to possess high crystallinity, luminescence intensity, quantum efficiency, and stability, while also exhibiting independent emission and luminescence capabilities in multiple modes, including upconversion and downconversion. Utilizing inexpensive excitation sources of different wavelengths (a red laser pointer and a 980nm infrared laser), two completely independent near-infrared emission signals are triggered to achieve multi-mode luminescence with upconversion and downconversion. All excitation and emission lights are within the invisible wavelength range, achieving a completely "invisible" operation that cannot be detected by the naked eye or ordinary equipment, greatly increasing the difficulty for counterfeiters to detect and replicate, and providing a physical basis for multi-layered anti-counterfeiting verification. Furthermore, the high-temperature solid-state method is simple and easy to implement, facilitating large-scale production, indicating that the near-infrared phosphor prepared by this invention has significant application value in high-level, precision security and anti-counterfeiting materials.

[0007] Specifically, this invention selects MgO as the matrix, which has stable chemical properties, high mechanical strength, and good weather resistance. This endows the prepared near-infrared phosphor with good stability, chemical inertness, and resistance to photobleaching, ensuring that its performance does not degrade during long-term use in complex environments and meeting the durability requirements of various commodity packaging. In addition, MgO is inexpensive, which is conducive to industrial production and application.

[0008] Co-doped Yb³ + and Cr³ + As a dual sensitizer, and through doping Er 3+ As the core activator, Er 3+ Acceptable from Yb 3+ and Cr 3+ The energy, when excited by ~650nm red light, Cr 3+ Ions absorb light energy and efficiently transfer it to neighboring Er. 3+ Ions, promoting Er 3+ The ion transitions to an excited state and then relaxes, emitting near-infrared light with a center wavelength of ~1550 nm (downconversion emission mode); when excited with a ~980 nm near-infrared laser, Yb 3+ Ions, acting as efficient energy antennas, absorb photons and transfer energy to Er. 3+ Ions, through a two-photon or multi-photon energy accumulation process, ultimately cause Er to...3+ The ions emit green or red light (upconversion emission mode) with center wavelengths of ~540nm and ~660nm, and the emission intensity is relatively high.

[0009] Furthermore, the near-infrared phosphor contains MgO and Cr. 3+ Yb 3+ and Er 3+ The molar ratio is 98.5:(0.5-8):(0.35-0.475):(0.025-0.15).

[0010] Furthermore, the near-infrared phosphor contains MgO and Cr. 3+ Yb 3+ and Er 3+ The molar ratio is 98.5:1:(0.35-0.475):(0.025-0.15).

[0011] Furthermore, the near-infrared phosphor contains MgO and Cr. 3+ Yb 3+ and Er 3+ The molar ratio is 98.5:1:0.45-0.0475:0.025-0.05.

[0012] Furthermore, the near-infrared phosphor contains MgO and Cr. 3+ Yb 3+ and Er 3+ The molar ratio is 98.5:1:0.0475:0.025.

[0013] Furthermore, the method for preparing the upconversion-downconversion luminescent near-infrared phosphor includes the following steps: S1. Weigh magnesium oxide, chromium oxide, ytterbium oxide and erbium oxide as powder raw materials according to the molar ratio of (91.5-99):(0.5-8):(0.35-0.475):(0.025-0.15); S2. Grind and mix the powdered raw material from S1 with ethanol thoroughly to obtain a mixed powder; S3. The mixed powder from S2 is calcined at 1000-1500℃ for 10-20 hours, cooled to room temperature, and then ground to obtain the near-infrared luminescent powder.

[0014] Further, in step S2, ethanol is added at a weight-volume ratio of 1g:1-2ml for the powdered raw material; preferably, in step S2, ethanol is added at a weight-volume ratio of 1g:1.5ml for the powdered raw material.

[0015] Further, the specific method of S3 is as follows: the mixed powder is transferred to a corundum crucible, covered and placed in a high-temperature reaction furnace, and heated to 1000-1500℃ at a heating rate of 3-7℃ / min for 10-20 hours. After natural cooling to room temperature, the sample is taken out and ground to obtain the near-infrared luminescent powder. Preferably, the heating rate is 5℃ / min; preferably, the high-temperature calcination temperature is 1300-1500℃; preferably, the high-temperature calcination time is 17 hours.

[0016] Further, the specific method of S3 is as follows: the mixed powder is transferred to a corundum crucible, covered and placed in a high-temperature reaction furnace, heated to 1300-1500℃ at a heating rate of 5℃ / min for 17h, and then naturally cooled to room temperature. The sample is then taken out and ground to obtain the near-infrared luminescent powder.

[0017] This invention also provides a near-infrared phosphor with upconversion and downconversion luminescence, prepared according to the above method. This near-infrared phosphor can be used in anti-counterfeiting inks. The phosphor is mixed with transparent printing ink and then applied to product labels, packaging, or certificates using screen printing or inkjet printing technology to form invisible patterns or QR codes. In specific applications, one or both upconversion and downconversion luminescence modes can be used. For example, red light excitation (downconversion) mode can be used for first-line general inspection, while 980nm excitation (upconversion) mode can be used for second-line or expert-level precision inspection. The spectra emitted by both modes together constitute the material's unique and difficult-to-clone "spectral fingerprint."

[0018] Compared with the prior art, the beneficial effects of the present invention are: 1. The near-infrared phosphor provided by this invention uses MgO as a matrix and adds a specific amount of Cr. 3+ Yb 3+ Er 3+ The near-infrared phosphor prepared by this invention through precise co-doping and high-temperature solid-state method has been proven by experiments to have high crystallinity, luminescence intensity, quantum efficiency and stability. The prepared near-infrared phosphor integrates downconversion luminescence and upconversion luminescence, and can realize two independent near-infrared light outputs in a single system. All excitation and emission light are in the invisible band of the human eye, which has extremely high safety and concealment.

[0019] 2. The near-infrared phosphor of the present invention is synthesized by a high-temperature solid-state reaction method. The high-temperature solid-state method is simple and easy to implement, and is easy to achieve large-scale production. It is suitable for batch production at the kilogram level and above, can effectively control costs, and has good prospects for industrial application. Attached Figure Description

[0020] Figure 1 The XRD pattern of the near-infrared phosphor in Example 1; Figure 2 The visible-near-infrared emission spectrum of the near-infrared phosphor in Example 2; Figure 3 The upconversion emission spectrum of the near-infrared phosphor in Example 3; Figure 4 The visible-near-infrared emission spectrum of the near-infrared phosphor in Example 4; Figure 5 The visible-near-infrared emission spectrum of the near-infrared phosphor in Example 5; Figure 6 The luminescence stability test of the near-infrared phosphor in Example 5; Figure 7 The quantum yield spectrum of the near-infrared fluorescent powder in Example 5; Figure 8 Quantum yield spectra of near-infrared fluorescent powders in Example 6 and Controls 1-3; Figure 9 The luminescence stability test of the near-infrared phosphor in Example 6; Figure 10 This is a luminescence image of the near-infrared phosphor in Example 7. Detailed Implementation

[0021] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. The described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0022] Unless otherwise specified, all methods described herein are conventional methods, and all raw materials described herein are available from publicly available commercial sources.

[0023] Example 1 This embodiment provides a matrix using MgO and Cr. 3+ Er 3+ and Yb 3+ Co-doped near-infrared phosphor material Mg 0.985 Cr 0.01 Yb 0.00475 Er 0.00025 O, that is, the molar ratio of each element is Mg:Cr:Yb:Er:O=0.985:0.01:0.00475:0.00025:1. According to the above material composition design, accurately weigh magnesium oxide (MgO), ytterbium oxide (Yb2O3), erbium oxide (Er2O3) and chromium oxide (Cr2O3).

[0024] The above raw materials were placed in an agate mortar, and a small amount of ethanol (2g raw material, 3mL ethanol) was added. The mixture was ground for about 1 hour to ensure thorough mixing. The mixture was then transferred to a corundum crucible, covered, and placed in a high-temperature furnace. The furnace was heated at a rate of 5 °C / min to 1000–1500 °C for 17 hours. Afterward, the mixture was allowed to cool naturally to room temperature. The sample was then removed from the crucible and ground for about 1 hour to obtain the near-infrared phosphor Mg. 0.985 Cr 0.01 Yb 0.00475 Er 0.00025 O.

[0025] The near-infrared phosphor prepared at 1000–1500 °C was scanned using an XRD diffractometer. Figure 1 Near-infrared phosphor Mg prepared at different temperatures 0.985 Cr 0.01 Yb 0.00475 Er 0.00025 The XRD patterns of O were obtained, and the XRD diffraction peaks of the near-infrared phosphor samples prepared above were matched one-to-one with the ICSD cards of MgO.

[0026] from Figure 1 It can be seen that the prepared near-infrared phosphor samples have high crystallinity, and the diffraction peaks of the prepared samples show an increasing trend with increasing temperature. The near-infrared phosphor prepared at 1300-1500℃ has better crystallinity, and the near-infrared phosphor prepared at 1400℃ has the best crystallinity.

[0027] Example 2 This embodiment provides a matrix using MgO and Cr. 3+ Er 3+ and Yb 3+ Co-doped near-infrared phosphor material Mg 0.995- m Cr m Yb 0.00475 Er 0.00025 O, where Er 3+ and Yb 3+ The molar percentages remain constant, meaning the molar ratio of each element is Mg:Cr:Yb:Er:O = 0.995-m:m:0.00475:0.00025:1, where m represents 0.005, 0.01, 0.03, 0.05, and 0.08, respectively. Based on the above material composition design, accurately weigh magnesium oxide (MgO), ytterbium oxide (Yb₂O₃), erbium oxide (Er₂O₃), and chromium oxide (Cr₂O₃).

[0028] The above raw materials were placed in an agate mortar, and a small amount of ethanol (2g raw material, 3mL ethanol) was added. The mixture was ground for about 1 hour to ensure thorough mixing. The mixture was then transferred to a corundum crucible, covered, and placed in a high-temperature furnace. The temperature was increased to 1500℃ at a heating rate of 5℃ / min and calcined for 17 hours. Afterward, the mixture was allowed to cool naturally to room temperature. The samples were then removed from the crucible and ground for about 1 hour to obtain different Cr... 3+ The proportion of near-infrared phosphor Mg 0.995-m Cr m Yb 0.00475 Er 0.00025 O.

[0029] Different Cr values ​​were determined using an FLS980 steady-state / transient fluorescence spectrometer. 3+ The proportion of near-infrared phosphor Mg 0.985 Cr 0.01 Yb 0.005-x Er x The visible-near-infrared emission spectrum of O was obtained, with an excitation wavelength of 455 nm and a test wavelength range of 600-1600 nm. The results are as follows: Figure 2 As shown.

[0030] Depend on Figure 2 It can be seen that maintaining Yb and Er ions in MgO:Cr 3+ ,Yb 3+ Er 3+ With the proportion of Cr ions remaining constant, adjusting the doping concentration (0.5%, 1%, 3%, 5%, 8%) revealed a pattern where the overall intensity of the luminescent powder first increased and then decreased as the Cr ion concentration increased. When the Cr ion concentration... 3+ The phosphor exhibits the strongest luminescence intensity when the ion concentration is 1%. When Cr... 3+ When the proportion further increases, the increase in its concentration triggers Cr 3+ Nonradiative relaxation between these phases leads to fluorescence quenching.

[0031] Example 3 This embodiment provides a matrix using MgO and Cr. 3+ Er 3+ and Yb 3+ Co-doped near-infrared phosphor material Mg 0.985 Cr 0.01 Yb 0.005-x Er x O, of which Cr 3+ With the molar percentage remaining constant, Er 3+The proportions are 5%, 10%, 20%, and 30%, respectively, while ensuring that the total molar amount of Yb and Er ions remains constant at 0.005. That is, the molar ratio of each element is Mg:Cr:Yb:Er:O = 0.985:0.01:0.005-x:x:1, where x is 0.00025, 0.0005, 0.001, and 0.0015, respectively. Based on the above material composition design, accurately weigh magnesium oxide (MgO), ytterbium oxide (Yb₂O₃), erbium oxide (Er₂O₃), and chromium oxide (Cr₂O₃).

[0032] The above raw materials were placed in an agate mortar, and a small amount of ethanol (2g raw material, 3mL ethanol) was added. The mixture was ground for about 1 hour to ensure thorough mixing. The mixture was then transferred to a corundum crucible, covered, and placed in a high-temperature reactor. The temperature was increased to 1400℃ at a heating rate of 5℃ / min and calcined for 17 hours. Afterward, the mixture was allowed to cool naturally to room temperature. The samples were then removed from the crucible and ground for about 1 hour to obtain different Er values. 3+ The proportion of near-infrared phosphor Mg 0.985 Cr 0.01 Yb 0.005-x Er x O.

[0033] The different Er values ​​prepared above were determined using an FLS980 steady-state / transient fluorescence spectrometer. 3+ The proportion of near-infrared phosphor Mg 0.985 Cr 0.01 Yb 0.005-x Er x The upconversion luminescence spectrum of O was obtained, with an excitation wavelength of 980 nm and a test wavelength range of 500-750 nm. The results are as follows: Figure 3 As shown.

[0034] from Figure 3 It can be seen that under continuous laser irradiation at 980nm, green light at 500-560nm and red light at 620-700nm were obtained. The red light peak is slightly lower than the green light peak, thus giving the powder a yellowish luminescence. Simultaneously, as the doping ratio of Er ions increases, the MgO:Cr... 3+ ,Yb 3+ Er 3+ The overall luminescence intensity first increases and then decreases. The luminescence is stronger when the Er ion doping ratio is 5%-10%, and strongest when the Er ion doping ratio is 10%. When Er... 3+ When the proportion increases further, Er is triggered due to the increase in its concentration. 3+ Nonradiative relaxation between these phases leads to fluorescence quenching.

[0035] Example 4 This embodiment provides a matrix using MgO and Cr. 3+ Er 3+and Yb 3+ Co-doped near-infrared phosphor material Mg 0.985 Cr 0.01 Yb 0.005-x Er x O, of which Cr 3+ With the molar percentage remaining constant, Er 3+ The proportions are 5%, 10%, 20%, and 30%, respectively, while ensuring that the total molar amount of Yb and Er ions remains constant at 0.005. That is, the molar ratio of each element is Mg:Cr:Yb:Er:O = 0.985:0.01:0.005-x:x:1, where x is 0.00025, 0.0005, 0.001, and 0.0015, respectively. Based on the above material composition design, accurately weigh magnesium oxide (MgO), ytterbium oxide (Yb₂O₃), erbium oxide (Er₂O₃), and chromium oxide (Cr₂O₃).

[0036] The above raw materials were placed in an agate mortar, and a small amount of ethanol (2g raw material, 3mL ethanol) was added. The mixture was ground for about 1 hour to ensure thorough mixing. The mixture was then transferred to a corundum crucible, covered, and placed in a high-temperature furnace. The temperature was increased to 1500℃ at a heating rate of 5℃ / min and calcined for 17 hours. Afterward, the mixture was allowed to cool naturally to room temperature. The samples were then removed from the crucible and ground for about 1 hour to obtain different Er values. 3+ The proportion of near-infrared phosphor Mg 0.985 Cr 0.01 Yb 0.005-x Er x O.

[0037] Different Er values ​​were determined using an FLS980 steady-state / transient fluorescence spectrometer. 3+ The proportion of near-infrared phosphor Mg 0.985 Cr 0.01 Yb 0.005-x Er x The downconversion emission spectrum of O was obtained, with an excitation wavelength of 455 nm and a test wavelength range of 600-1100 nm. The results are as follows: Figure 4 As shown.

[0038] from Figure 4 It can be seen that the broad emission peak of 600nm~1050nm obtained under 455nm excitation corresponds to Cr 3+ The 4T2→4A2 energy level transition was observed. Additionally, two sharp emission peaks were found near 980 nm, corresponding to the 2F5 / 2-2F7 / 2 energy level transition of the Yb ion. Small emission peaks near 1150 nm, 1250 nm, 1380 nm, and 1540 nm correspond to Er. 3+ Emission peak in the near-red region. When Cr 3+ The amount remains constant, despite the change in Er 3+The proportion of MgO and Cr showed subtle changes in the spectrum, but the ratio of MgO to Cr... 3+ ,Yb 3 + Er 3+ The overall luminous intensity remains unchanged.

[0039] Example 5 This embodiment provides a matrix using MgO and Cr. 3+ Er 3+ and Yb 3+ Co-doped near-infrared phosphor material Mg 0.985 Cr 0.01 Yb 0.0045 Er 0.0005 O, that is, the molar ratio of each element is Mg:Cr:Yb:Er:O=0.985:0.01:0.0045:0.0005:1. According to the above material composition design, accurately weigh magnesium oxide (MgO), ytterbium oxide (Yb2O3), erbium oxide (Er2O3) and chromium oxide (Cr2O3).

[0040] The above raw materials were placed in an agate mortar, and a small amount of ethanol (2g raw material, 3mL ethanol) was added. The mixture was ground for about 1 hour to ensure thorough mixing. The mixture was then transferred to a corundum crucible, covered, and placed in a high-temperature furnace. The temperature was increased to 1300℃ at a heating rate of 5℃ / min and calcined for 15 hours. Afterward, the mixture was allowed to cool naturally to room temperature. The sample was then removed from the crucible and ground for about 1 hour to obtain the near-infrared phosphor Mg. 0.985 Cr 0.01 Yb 0.0045 Er 0.0005 O.

[0041] The near-infrared phosphor Mg was determined using an FLS980 steady-state / transient fluorescence spectrometer. 0.985 Cr 0.01 Yb 0.0045 Er 0.0005 The upconversion luminescence spectrum of O was obtained, with an excitation wavelength of 980 nm and a test wavelength range of 300-700 nm. The results are as follows: Figure 5 As shown. Figure 6 The prepared Mg 0.985 Cr 0.01 Yb 0.0045 Er 0.0005 The luminescence stability test data of O-phosphorus powder, where I0 represents the luminescence intensity at room temperature (25℃), and I represents the actual luminescence intensity at different temperatures. Figure 7 The quantum yield spectrum of the prepared near-infrared fluorescent powder under 455nm blue light excitation.

[0042] from Figure 5 It can be seen that the prepared Mg0.985 Cr 0.01 Yb 0.0045 Er 0.0005 The excitation spectrum of the O phosphor at the emission peak of 980 nm has an excitation bandwidth covering the visible light region (390~780 nm), and there are two strong excitation peaks corresponding to blue light around 455 nm and red light around 660 nm.

[0043] from Figure 6 It can be seen that the luminescence intensity gradually decreases as the temperature rises. When the temperature rises to 65℃, the luminescence intensity is still above 90%. Even at a temperature as high as 150℃, the luminescence intensity still reaches 60%, indicating that the material has good luminescence stability.

[0044] from Figure 7 It can be seen that the quantum yield spectrum of the prepared near-infrared phosphor under 455nm blue light excitation, based on MgO:Cr 3+ ,Yb 3+ Er 3+ The quantum yield of the phosphor was 25.31% when the integral area of ​​the emission peak in the 600-1600 nm range was divided by the integral area of ​​the excitation peak in the 440-460 nm range.

[0045] Example 6 This embodiment provides a matrix using MgO and Cr. 3+ Er 3+ and Yb 3+ Co-doped near-infrared phosphor material Mg 0.985 Cr 0.01 Yb 0.00475 Er 0.00025 O, that is, the molar ratio of each element is Mg:Cr:Yb:Er:O=0.985:0.01:0.00475:0.00025:1. According to the above material composition design, accurately weigh magnesium oxide (MgO), ytterbium oxide (Yb2O3), erbium oxide (Er2O3) and chromium oxide (Cr2O3).

[0046] The above raw materials were placed in an agate mortar, and a small amount of ethanol (2g raw material, 3mL ethanol) was added. The mixture was ground for about 1 hour to ensure thorough mixing. The mixture was then transferred to a corundum crucible, covered, and placed in a high-temperature furnace. The furnace was heated to 1400℃ at a rate of 5℃ / min for 17 hours. Afterward, the mixture was allowed to cool naturally to room temperature. The sample was then removed from the crucible and ground for about 1 hour to obtain the near-infrared phosphor Mg. 0.985 Cr 0.01 Yb 0.00475 Er 0.00025 O.

[0047] Simultaneously, luminescent materials of controls 1, 2, and 3 were prepared, wherein control 1 was prepared using MgO as a matrix and Cr... 3+ Er 3+ and Yb 3+ Co-doped phosphor material Mg 0.965 Cr 0.03 Yb 0.00475 Er 0.00025 O, i.e., the molar ratio of each element is Mg:Cr:Yb:Er:O = 0.965:0.03:0.00475:0.00025:1. Based on the above material composition design, accurately weigh magnesium oxide (MgO), ytterbium oxide (Yb₂O₃), erbium oxide (Er₂O₃), and chromium oxide (Cr₂O₃). Place the above raw materials in an agate mortar, then add a small amount of ethanol (2g raw material, 3mL ethanol), and grind for about 1 hour to ensure thorough mixing. Transfer the mixture to a corundum crucible, cover, and place in a high-temperature reactor. Heat to 1400℃ at a heating rate of 5℃ / min for 17 hours, then allow to cool naturally to room temperature. Remove the sample from the crucible and grind for about 1 hour to obtain the fluorescent powder MgO (control 1). 0.965 Cr 0.03 Yb 0.00475 Er 0.00025 O.

[0048] The preparation method of the luminescent material in control 2 uses MgO as the matrix and Cr... 3+ Er 3+ Co-doped phosphor material Mg 0.985 Cr 0.01 Er 0.005 O, i.e., the molar ratio of each element is Mg:Cr:Er:O = 0.985:0.01:0.005:1. Based on the above material composition design, accurately weigh magnesium oxide (MgO), ytterbium oxide (Yb₂O₃), erbium oxide (Er₂O₃), and chromium oxide (Cr₂O₃). Place the above raw materials in an agate mortar, then add a small amount of ethanol (2g raw material, 3mL ethanol), and grind for about 1 hour to ensure thorough mixing. Transfer the mixture to a corundum crucible, cover, and place in a high-temperature reactor. Heat to 1400℃ at a heating rate of 5℃ / min for 17 hours, then allow to cool naturally to room temperature. Remove the sample from the crucible and grind for about 1 hour to obtain the phosphor MgO of control 2. 0.985 Cr 0.01 Er 0.005 O.

[0049] The preparation method of the luminescent material in control 3 uses MgO as the matrix and Cr... 3+ Er 3+ and Yb 3+ Co-doped phosphor material Mg 0.985 Cr 0.01Yb 0.005 O, i.e., the molar ratio of each element is Mg:Cr:Yb:O = 0.985:0.01:0.005:1. Based on the above material composition design, accurately weigh magnesium oxide (MgO), ytterbium oxide (Yb₂O₃), and chromium oxide (Cr₂O₃). Place the above raw materials in an agate mortar, then add a small amount of ethanol (2g raw material, 3mL ethanol) and grind for about 1 hour to ensure thorough mixing. Transfer the mixture to a corundum crucible, cover, and place in a high-temperature reactor. Heat to 1400℃ at a heating rate of 5℃ / min for 17 hours, then allow to cool naturally to room temperature. Remove the sample from the crucible and grind for about 1 hour to obtain the near-infrared phosphor MgO (reference 3). 0.985 Cr 0.01 Yb 0.005 O.

[0050] Figure 8 The near-infrared fluorescent powder Mg prepared 0.985 Cr 0.01 Yb 0.00475 Er 0.00025 Quantum yield spectra of O and control 1-3 phosphors under 455nm blue light excitation, based on MgO:Cr 3+ ,Yb 3+ Er 3+ The quantum yield of the phosphor was 50.12% when the integrated area of ​​the emission peak (600–1600 nm) was divided by the integrated area of ​​the excitation peak (440–460 nm). The quantum yield of the phosphor prepared in Control 1 was 25.89%. The quantum yield of the phosphor prepared in Control 2 was 45.18%. The quantum yield of the phosphor prepared in Control 3 was 28.61%.

[0051] Furthermore, Figure 9 The prepared Mg 0.985 Cr 0.01 Yb 0.00475 Er 0.00025 The luminescence stability test data of the O-phosphorus powder is shown, where I0 represents the luminescence intensity at room temperature (25℃), and I represents the actual luminescence intensity at different temperatures. As can be seen from the graph, the luminescence intensity gradually decreases with increasing temperature. When the temperature rises to 60℃, the luminescence intensity is still above 95%, and even at a temperature as high as 150℃, the luminescence intensity still reaches 64%, indicating that the prepared Mg... 0.985 Cr 0.01 Yb 0.00475 Er 0.00025 O-phosphorescent powder has good luminescence stability.

[0052] Example 7 This embodiment provides a matrix using MgO and Cr. 3+ Er3+ and Yb 3+ Co-doped near-infrared phosphor material Mg 0.985 Cr 0.01 Yb 0.00475 Er 0.00025 O, that is, the molar ratio of each element is Mg:Cr:Yb:Er:O=0.985:0.01:0.00475:0.00025:1. According to the above material composition design, accurately weigh magnesium oxide (MgO), ytterbium oxide (Yb2O3), erbium oxide (Er2O3) and chromium oxide (Cr2O3).

[0053] The above raw materials were placed in an agate mortar and then a small amount of ethanol (2g of raw material, 3mL of ethanol) was added and ground for about 1 hour to ensure thorough mixing. The mixture was then transferred to a corundum crucible, covered, and placed in a high-temperature furnace. The furnace was heated to 1500℃ at a rate of 5℃ / min for 17 hours. Afterward, the mixture was allowed to cool naturally to room temperature. The sample was then removed from the crucible and ground for about 1 hour to obtain the near-infrared phosphor Mg. 0.985 Cr 0.01 Yb 0.00475 Er 0.00025 O.

[0054] Figure 10 To determine the properties of MgO:Cr under natural light, blue light, red light, and near-infrared light irradiation. 3+ ,Yb 3+ Er 3+ Images of luminescent powder.

[0055] Depend on Figure 10 It is known that the fluorescent powder synthesized in this application exhibits different colors under different excitation light irradiation. Under natural light, the powder's original color is grayish-green. When illuminated with 394nm light, the powder emits red light. Under continuous 980nm laser irradiation, the grayish-green powder emits a yellowish light. Finally, under 660nm red light irradiation, an infrared camera reveals that the powder emits extremely bright infrared light. This indicates that MgO:Cr 3+ ,Yb 3+ Er 3+ Fluorescent powder has important application value in security and anti-counterfeiting.

[0056] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application and not to limit them; although this application has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications can still be made to the specific implementation of this application or equivalent substitutions can be made to some technical features, all of which should be covered within the scope of the technical solutions claimed in this application.

Claims

1. A method for preparing upconversion / downconversion near-infrared phosphors, characterized in that, The near-infrared phosphor is based on MgO and contains Cr. 3+ Yb 3+ As a doping sensitizer, Er 3+ As a doping activator, it was prepared by a high-temperature solid-state method. The prepared phosphor contained MgO and Cr. 3+ Yb 3+ and Er 3+ The molar ratio is (91.5-99):(0.5-8):(0.35-0.475):(0.025-0.15). The preparation method includes the following steps: S1. According to the composition of the prepared phosphor, MgO, Cr 3+ Yb 3+ and Er 3+ The molar ratio is (91.5-99):(0.5-8):(0.35-0.475):(0.025-0.15). Magnesium oxide, chromium oxide, ytterbium oxide and erbium oxide are weighed as powder raw materials. S2. Grind and mix the powdered raw material from S1 with ethanol thoroughly to obtain a mixed powder; S3. The mixed powder from S2 is calcined at 1000-1500℃ for 10-20 hours, cooled to room temperature, and then ground to obtain the near-infrared luminescent powder.

2. The method for preparing an upconversion / downconversion near-infrared phosphor according to claim 1, characterized in that, The near-infrared phosphor contains MgO and Cr. 3+ Yb 3+ and Er 3+ The molar ratio is 98.5:(0.5-8):(0.35-0.475):(0.025-0.15).

3. The method for preparing an upconversion / downconversion near-infrared phosphor according to claim 1, characterized in that, The near-infrared phosphor contains MgO and Cr. 3+ Yb 3+ and Er 3+ The molar ratio is 98.5:1:(0.35-0.475):(0.025-0.15).

4. The method for preparing an upconversion / downconversion near-infrared phosphor according to claim 1, characterized in that, The near-infrared phosphor contains MgO and Cr. 3+ Yb 3+ and Er 3+ The molar ratio is 98.5:1:0.45-0.0475:0.025-0.

05.

5. The method for preparing an upconversion / downconversion near-infrared phosphor according to claim 1, characterized in that, The near-infrared phosphor contains MgO and Cr. 3+ Yb 3+ and Er 3+ The molar ratio is 98.5:1:0.0475:0.

025.

6. The method for preparing an upconversion / downconversion near-infrared phosphor according to claim 1, characterized in that, In S2, ethanol is added at a weight-volume ratio of 1g:1-2ml for the powdered raw material.

7. The method for preparing an upconversion / downconversion near-infrared phosphor according to claim 6, characterized in that, In S2, ethanol is added at a weight-volume ratio of 1g:1.5ml for the powdered raw material.

8. The method for preparing an upconversion / downconversion near-infrared phosphor according to claim 1, characterized in that, The specific method for S3 is as follows: the mixed powder is transferred to a corundum crucible, covered and placed in a high-temperature reaction furnace, heated to 1000-1500℃ at a heating rate of 3-7℃ / min for 10-20 hours, and then naturally cooled to room temperature. The sample is then taken out and ground to obtain the near-infrared luminescent powder.

9. A method for preparing an upconversion / downconversion near-infrared phosphor according to claim 8, characterized in that, The heating rate is 5°C / min.

10. A method for preparing an upconversion / downconversion near-infrared phosphor according to claim 8, characterized in that, The high-temperature burning temperature is 1300-1500℃.

11. A method for preparing an upconversion / downconversion near-infrared phosphor according to claim 8, characterized in that, The high-temperature burning time is 17 hours.

12. The method for preparing an upconversion / downconversion near-infrared phosphor according to claim 1, characterized in that, The specific method for S3 is as follows: the mixed powder is transferred to a corundum crucible, covered and placed in a high-temperature reaction furnace, heated to 1300-1500℃ at a heating rate of 5℃ / min and calcined for 17 hours, and then naturally cooled to room temperature. The sample is then taken out and ground to obtain the near-infrared luminescent powder.

13. An upconversion / downconversion near-infrared phosphor, characterized in that, It is prepared by the method according to any one of claims 1-12.

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