Strontium aluminate long afterglow stress luminescence ceramic and method for preparing the same

Abstract

The application provides a strontium aluminate long-afterglow stress luminescence ceramic and a preparation method thereof. 2+ , x%Dy 3+ , y%Zr 4+ , wherein 0<=x<=2 and 0<=y<=3. The application can increase the afterglow duration and stress luminescence intensity of the material.

Description

Technical Field

[0001] This invention belongs to the field of long afterglow luminescent materials technology, and particularly relates to a strontium aluminate long afterglow stress luminescent ceramic and its preparation method. Background Technology

[0002] With the rapid development of structural health monitoring, intelligent sensors, optical information storage, and human-computer interaction, the demand for high-performance luminescent materials is increasing. In these applications, long-persistent luminescence (LPL) and mechanoluminescence (ML) materials have gradually become research hotspots due to their self-powered nature and lack of external power source. Long-persistent luminescent materials, also known as photoluminescent materials, operate on the principle of photoluminescence. Research on long-persistent luminescent materials began in 1866 when the Frenchman Sidot prepared Cu-doped ZnS luminescent materials, marking the start of the preparation and use of sulfide luminescent materials. However, the afterglow time of sulfide long-persistent materials is relatively short. To achieve long-term luminescence, radioactive elements are often added to the sulfides, which has adverse effects on the environment and health. From the 1960s onwards, research gradually shifted to aluminate matrix series, particularly Eu... 2+ Materials doped with strontium aluminate exhibit good luminescence properties; the main green-emitting, long-afterglow materials are SrAl₂O₄:Eu. 2+ (yellow-green light), Sr4Al 14 O 25 Eu 2+ (blue-green light), BaAl2O4:Eu 2+ Dy 3+ (Blue-green light), etc. Strontium aluminate materials are gradually entering commercial applications. Currently, strontium aluminate materials have long afterglow time, good brightness, relatively stable chemical and thermal properties, and are environmentally friendly and non-toxic. They have gradually replaced sulfide long afterglow materials and are widely used in the field of long afterglow luminescence from blue to green light emission.

[0003] Mechanoluminescence (ML) refers to the luminescence phenomenon produced by certain materials in response to mechanical stimulation. Currently, over 30 types of mechanoluminescent materials have been discovered, covering various systems including aluminates, sulfides, and titanates. Among them, zinc sulfide, zinc oxysulfide, and strontium aluminate are considered the three most promising materials due to their high brightness and low cost. Strontium aluminate, as a classic long-afterglow luminescent material, was extensively studied as early as the 1960s and 70s, but its mechanoluminescence properties have only gradually gained attention in the last two decades. As an important luminescent material, it possesses unique advantages, especially in both mechanoluminescence and long-afterglow luminescence.

[0004] However, these materials are susceptible to hydrolysis in complex environments, especially under humid or high-temperature conditions. Hydrolysis alters the crystal structure of strontium aluminate, significantly reducing its luminescent properties. To overcome this problem, researchers have employed various methods, such as coating, vitrification, and ceramization. Among these, ceramization, by transforming strontium aluminate into a ceramic sample, significantly improves the material's hydrolysis resistance and mechanical strength. Ceramized strontium aluminate not only maintains good luminescent properties but also possesses excellent mechanical properties and thermal stability, making it suitable for more demanding environmental conditions.

[0005] In recent years, researchers have significantly improved the luminescence properties of strontium aluminate by altering its doping system, particularly by incorporating rare earth ions. 2+ As a luminescent center, it can produce bright green light, originating from Eu 2+ 4f of ions 6 5d 1 →4f 7 (8S 7 / 2 Researchers discovered that electronic transitions between 1 mol% Eu... 2+ Strontium aluminate exhibits the strongest luminescence intensity, while europium is mainly present as Eu in most compounds. 3+ The luminescent material exists in a form that is not prone to valence changes in common synthetic environments. Furthermore, existing luminescent materials generally face challenges such as low luminous efficiency, short afterglow time, and difficulty in identifying stress states under complex stress conditions. These issues significantly restrict their practical engineering applications and make it difficult to meet the high-precision, long-duration application requirements of fields such as high-end industrial inspection and intelligent sensing. Therefore, developing a luminescent material with a longer afterglow duration, higher stress luminescence intensity, and excellent stability has become an urgent need for industry development. Summary of the Invention

[0006] The purpose of this invention is to provide a strontium aluminate long-afterglow stress-luminescent ceramic and its preparation method, which can increase the afterglow duration and stress-luminescence intensity of the material. The technical solution adopted is as follows: A strontium aluminate long-afterglow stress-luminescent ceramic with the general chemical formula SrAl2O4:1%Eu 2+ ,x%Dy 3+ y%Zr 4+ , where 0≤x≤2, 0≤y≤3.

[0007] Preferably, x=1, y=2.

[0008] A method for preparing a strontium aluminate long-afterglow stress-luminescent ceramic includes the following steps: Step 1, Preparation of precursors: Preparation of precursors for europium (Eu), dysprosium (Dy), and zirconium (Zr); Step 2, Ingredients and Mixing: Weigh out the Sr-containing compound, the Al-containing compound, and the precursor according to the stoichiometric ratio in the general chemical formula; The weighed raw materials are mixed to obtain raw material powder; Step 3: Preparation of ceramic blanks: After grinding and sieving the raw material powder, the ceramic blanks are statically pressed to obtain ceramic blanks; Step 4, Reduction Sintering: Place the ceramic blank in a pressureless hydrogen furnace and sinter it at 1450℃-1550℃ for 3-5 hours in a reducing atmosphere. After cooling, strontium aluminate long afterglow stress luminescent ceramic is obtained.

[0009] Preferably, the Sr-containing compound is strontium carbonate (SrCO3), and the Al-containing compound is Al2O3; The precursor of europium Eu is europium oxide Eu2O3; The precursor of dysprosium (Dy) is dysprosium oxide (Dy₂O₃); The precursor of zirconium Zr is zirconium oxide ZrO2.

[0010] Preferably, the reducing atmosphere is pure hydrogen or a mixture of gases; the mixture includes hydrogen and nitrogen.

[0011] The research and development process of this invention is as follows: A strontium aluminate long-afterglow stress-luminescent ceramic and its preparation method are disclosed. To increase the afterglow duration of the material, different amounts of Dy are incorporated. 3+ Exploring Dy 3+ Doping content of SrAl2O4:1%Eu 2+ The effect of adding 1% Dy on luminescence properties. Results showed that adding 1% Dy... 3+ Subsequently, the duration of the afterglow of strontium aluminate was significantly enhanced.

[0012] During the above process, it was discovered that the addition of Zr... 4+ At the same time, the stress luminescence intensity of strontium aluminate also changes to varying degrees. Therefore, fixing Dy 3+ The content is 1%, and different contents of Zr are added. 4+ Exploring Zr 4+ Doping content of SrAl2O4:1%Eu 2+ ,1%Dy 3+ The purpose of influencing luminescence performance is to increase its stress luminescence intensity and achieve afterglow synergistic stress luminescence.

[0013] Afterglow synergistic stress luminescence refers to the phenomenon that a ceramic material exhibits a persistent afterglow after being pre-irradiated.

[0014] Furthermore, after the material's afterglow properties have been fully utilized, mechanical force is applied to generate secondary luminescence, such as... Figures 10-11As shown, after the afterglow performance of the ceramic material has been basically exhausted, applying mechanical force (inscribing "ML" on the ceramic) at this time achieves secondary luminescence, thus realizing afterglow synergistic stress luminescence.

[0015] The results show that in SrAl2O4:1%Eu 2+ Add 1% Dy 3+ Subsequently, the afterglow duration of strontium aluminate was significantly enhanced; therefore, the material system was fixed at SrAl2O4:1%Eu. 2+ ,1%Dy 3+ After adding 2% Zr 4+ Stress luminescence is most pronounced at this time.

[0016] The ceramics of this invention can be prepared as inserts and pre-embedded on or inside the surface of key load-bearing structures such as engineering machinery (cranes, excavators), metallurgical equipment, chemical reactors, and large pumps; they can also be made into ceramic fibers and composited into the metal or composite matrix of the equipment.

[0017] When the equipment structure is subjected to loads that induce stress, deformation, or even microcracks, the ceramic emits 520nm green light under mechanical stimulation (pressure / impact). The greater the stress, the higher the light emission intensity. The microcrack propagation path forms a continuous emission band. By capturing the emission signal with high-speed optical imaging equipment, it is possible to achieve visualized quantitative detection of stress distribution, early identification of microcracks, and real-time tracking of their propagation trajectory. No external power supply is required, making it suitable for outdoor or harsh operating conditions. The ceramic is resistant to moisture and high temperatures, allowing for long-term operation in high-temperature and high-humidity chemical environments and complex outdoor environments for engineering machinery. The microcrack identification sensitivity is far higher than traditional mechanical testing methods, enabling early warning of structural failure risks.

[0018] The ceramic chip of this invention is manufactured into a standard-sized ceramic chip and integrated with an optical signal receiver and a signal conversion module to form a power-free stress sensor. The intensity of the green light generated by the ceramic chip under external pressure / impact / friction is linearly positively correlated with the stress magnitude. The optical receiver captures the light emission signal, which is then converted into an electrical / digital signal by the conversion module, enabling quantitative detection of mechanical quantities such as pressure, impact, and friction. Requiring no battery or external power supply, this self-powered sensor is suitable for detection scenarios in remote areas, enclosed spaces, and other environments without power supply. It features a fast response speed, with stress and light emission signals generated synchronously, resulting in low detection delay. Furthermore, the ceramic has stable chemical properties, is corrosion-resistant and wear-resistant, and has a long sensor lifespan.

[0019] The ceramic of this invention is made into ceramic patches and installed in parts such as robotic grippers, conveyor rollers, and workpiece fixtures on industrial production lines. When the robotic gripper picks up a workpiece, the conveyor belt transports a workpiece, or the fixture fixes a workpiece, contact stress is generated at the contact points. The ceramic patch emits green light synchronously. The light emission data is collected by the optical monitoring system of the production line to achieve real-time monitoring of contact stress, avoiding workpiece damage due to excessive contact stress or workpiece detachment or positioning deviation due to insufficient contact stress. Its advantages include wear resistance and impact resistance, adapting to the high-frequency working requirements of industrial production lines; no wiring required, allowing for flexible installation in various parts of the production line; and compatibility with the visual inspection system of the production line, making it easy to integrate.

[0020] The ceramic substrate of this invention is prepared as an optical storage substrate. Controllable mechanical stress is applied to the substrate surface using mechanical writing equipment (such as a precision engraving tool or a laser-induced mechanical stress device). By controlling the pressure and writing trajectory of the mechanical writing, green light emission patterns of different brightness and shapes are generated in corresponding areas on the ceramic substrate surface. The pressure corresponds to the brightness level, and the writing trajectory corresponds to the information pattern, thus realizing the optical storage of digital and image information. During retrieval, the emission pattern is acquired using an optical scanning device to restore the stored information. Its advantages include: mechanical writing involves no chemical reagents, making the storage process green and environmentally friendly; the ceramic substrate has high stability, and the stored optical information is not easily affected by temperature, humidity, or electromagnetic interference, resulting in a long information retention life; the long afterglow characteristic allows the stored information to continue emitting light after writing, facilitating information retrieval.

[0021] The ceramics of this invention are manufactured into road marking patches, traffic barrier reflective stickers, bridge crash barriers, etc., and applied to traffic facilities such as highways, rural roads, and bridges. During the day, the ceramics emit a long afterglow after being excited by sunlight, providing auxiliary guidance for nighttime driving. When a vehicle runs over road markings, collides with traffic barriers, or bridge crash barriers, the ceramics emit a stronger green light under mechanical stress, alerting drivers to driving safety. Simultaneously, the luminescent signal can pinpoint the location of a traffic accident. Its advantages include resistance to vehicle crushing and ultraviolet radiation, making it suitable for outdoor service requirements of traffic facilities; a power-free design, reducing maintenance costs for traffic signage; and stress-induced luminescence characteristics enabling real-time indication of traffic accidents.

[0022] Compared with the prior art, the advantages of the present invention are: 1. Three-tier trap system: When a material is irradiated with ultraviolet light, it generates charge carriers, Eu. 2+ As a luminescent center, after being doped with strontium aluminate, due to Eu 2+ and Sr 2+ With similar atomic radii, it replaced a portion of Sr. 2+In order to maintain electroneutrality, oxygen vacancies are generated to compensate for the lack of positive charge. This results in a certain amount of oxygen vacancies in strontium aluminate. Oxygen vacancies are intrinsic defects. In the band structure, they are usually introduced into defect energy levels within the band gap. They can serve as trap centers for electrons or holes, thus forming a first-order trap. By incorporating Dy 3+ The introduction of shallow traps increases carrier density, allowing more carriers to be absorbed by Dy. 3+ The captured objects formed a second-level trap, which, under room temperature thermal disturbances, were trapped by Dy. 3+ The captured charge carriers are slowly released, transitioning to europium (the luminescent center), and then returning to the ground state with accompanying light emission, thus greatly extending the afterglow duration. The addition of 1% Dy... 3+ This causes the charge carriers in these shallow traps to be nearly saturated, thus resulting in the longest-lasting afterglow phenomenon. Add Zr 4+ By introducing deep traps, it becomes difficult to release these charge carriers located in the deep traps under room temperature thermal disturbances. Greater thermal disturbances or mechanical forces are required to release these deep charge carriers, thus forming a third-level trap.

[0023] By introducing a three-stage trap system, afterglow synergistic stress luminescence was successfully achieved. That is, after the material is pre-radiated, it will exhibit a persistent afterglow phenomenon. Then, mechanical force is applied to release charge carriers deeper inside, generating secondary luminescence.

[0024] 2. Excellent stress luminescence properties: The material can emit bright green light under mechanical force (pressure, friction, impact), and the luminescence intensity is positively correlated with the stress magnitude. When fractured, a strong luminescence band is generated along the crack, which can realize the visualization of stress distribution and crack propagation.

[0025] 3. High stability: Through the ceramicization process, the material has high density, which fundamentally solves the problem of easy hydrolysis of strontium aluminate materials, making it suitable for harsh environments such as humidity and high temperature. Attached Figure Description

[0026] Figure 1 XRD spectra of the strontium aluminate long afterglow stress luminescent ceramics prepared in Examples 1-7; Figure 2 The fluorescence emission spectra of the strontium aluminate long-afterglow stress-luminescent ceramics prepared in Examples 1-4 are composed of fluorescence emission spectra. Figure 3 The afterglow attenuation spectrum is composed of the afterglow attenuation spectra of the strontium aluminate long-afterglow stress-luminescent ceramics prepared in Examples 1-4. Figure 4The stress-luminescent ceramic images are formed from the stress-luminescent ceramic images of the strontium aluminate long afterglow stress-luminescent ceramics prepared in Examples 1-4; Figure 5 The fluorescence emission spectra are composed of the fluorescence emission spectra of the strontium aluminate long afterglow stress luminescent ceramics prepared in Examples 3 and 5-7; Figure 6 The afterglow attenuation spectrum is composed of the afterglow attenuation spectra of the strontium aluminate long afterglow stress luminescent ceramics prepared in Examples 3 and 5-7. Figure 7 The stress-luminescent ceramic images are formed from the stress-luminescent ceramic images of the strontium aluminate long afterglow stress-luminescent ceramics prepared in Examples 3 and 5-7; Figure 8 Images showing the afterglow duration of the strontium aluminate long-afterglow stress-luminescent ceramics prepared in Example 6 and the comparative example; Figure 9 SAOE prepared for embodiments of the present invention: 1% Dy 3+ 2%Zr 4+ Stress-luminescent cracks generated when fractured under mechanical stress; Figure 10 After the afterglow performance has been largely utilized, SAOE: 1%Dy 3+ 2%Zr 4+ Diagram of afterglow synergistic stress luminescence process; Figure 11 for Figure 10 A magnified view of a portion of the image; Figure 12 SrAl2O4: 1%Eu 2+ ,x%Dy 3+ y%Zr 4+ Diagram of the afterglow synergistic stress luminescence mechanism. Detailed Implementation

[0027] The following will describe in more detail the strontium aluminate long-afterglow stress-luminescent ceramic and its preparation method of the present invention with reference to schematic diagrams, which illustrate preferred embodiments of the invention. It should be understood that those skilled in the art can modify the invention described herein while still achieving the advantageous effects of the invention. Therefore, the following description should be understood as being of general knowledge to those skilled in the art and is not intended to limit the invention.

[0028] SAOE: Strontium aluminate (SrAl2O4): 1% Eu 2+ .

[0029] LPL: Long-Persistent Luminescence; ML: Mechanoluminescence; XRD: X-ray diffraction; UV: Sunlight; Example 1 A strontium aluminate long-afterglow stress-luminescent ceramic with the chemical formula SrAl2O4:1%Eu 2+ 0%Dy 3+ 0%Zr 4+ .

[0030] All the above proportions are molar percentages.

[0031] The preparation method of strontium aluminate long afterglow stress luminescent ceramics includes the following steps: Step 1: Preparation of precursors: Preparation of precursors for europium (Eu), dysprosium (Dy), and zirconium (Zr).

[0032] Using ammonium bicarbonate as a precipitant, europium nitrate, dysprosium nitrate, and zirconium nitrate were added dropwise to the precipitant while controlling the pH value. The reaction generated a precursor precipitate, which was then filtered, washed, dried, and calcined to obtain a nanoscale oxide precursor.

[0033] The specific chemical reaction equation is as follows: 2Eu(NO3)3+6NH4HCO3→Eu2 (CO3)3↓+6NH4NO3+3CO2↑+3H2O 2Dy(NO3)3+6NH4HCO3→Dy2 (CO3)3↓+6NH4NO3+3CO2↑+3H2O Zr(NO3)4+4NH4HCO3→ZrOCO3↓+4NH4NO3+3CO2↑+H2O Eu2(CO3)3 Eu2O3 + 3CO2↑ Dy2 (CO3)3 Dy₂O₃ + 3CO₂↑ ZrOCO3 ZrO2 + CO2↑ Step 2, Ingredients and Mixing: Weigh out the precursors of SrCO3, Al2O3, Europium (Eu), Dysprosium (Dy), and Zirconium (Zr) according to the proportions of each element in the chemical formula.

[0034] The weighed raw materials are mixed to obtain raw material powder; Step 3, Molding: After grinding and sieving the raw material powder, it is statically pressed to obtain a ceramic blank.

[0035] Static pressing, specifically includes: The powder is placed into a circular mold and first dry-pressed at 1.5 MPa. Then it is placed in a cold isostatic press and pressed into a dense ceramic blank at 120 MPa.

[0036] Step 4, reduction sintering: A gas reduction method was employed: the ceramic green body was placed in a pressureless hydrogen furnace and sintered at 1450℃-1550℃ for 3-5 hours in a reducing atmosphere. After cooling, strontium aluminate long afterglow stress luminescent ceramics were obtained. Hydrogen gas ensured the Eu... 3+ To Eu 2+ Highly efficient restoration.

[0037] The specific chemical reaction equation is as follows: SrCO3 + Al2O3 + Eu2O3 + Dy2O3 + ZrO2 SrAl2O4:Eu 2+ ,Dy 3+ ,Zr 4+ +CO2↑ Unpressurized hydrogen furnace: The pressure inside the furnace is usually maintained at a level slightly higher than atmospheric pressure (e.g., 0.01~0.05 MPa) to prevent outside air from being drawn into the furnace and causing an explosion, which is different from a high-pressure furnace.

[0038] Example 2 Unlike Example 1, the strontium aluminate long afterglow stress luminescent ceramic has the chemical composition of SrAl2O4:1%Eu 2+ 0.5% Dy 3+ 0%Zr 4+ .

[0039] The preparation method of strontium aluminate long afterglow stress luminescent ceramic is the same as in Example 1.

[0040] Example 3 Unlike Example 1, the strontium aluminate long afterglow stress luminescent ceramic has the following chemical composition: SrAl2O4: 1%Eu 2+ 1%Dy 3+ 0%Zr 4+ .

[0041] The preparation method of strontium aluminate long afterglow stress luminescent ceramic is the same as in Example 1.

[0042] Example 4 Unlike Example 1, the strontium aluminate long afterglow stress luminescent ceramic has the chemical composition of SrAl2O4:1%Eu 2+ 2%Dy 3+ 0%Zr 4+ .

[0043] The preparation method of strontium aluminate long afterglow stress luminescent ceramic is the same as in Example 1.

[0044] Example 5 Unlike Example 1, the strontium aluminate long afterglow stress luminescent ceramic has the chemical composition of SrAl2O4:1%Eu 2+ 1%Dy 3+ 1%Zr 4+ .

[0045] The preparation method of strontium aluminate long afterglow stress luminescent ceramic is the same as in Example 1.

[0046] Example 6 Unlike Example 1, the strontium aluminate long afterglow stress luminescent ceramic has the chemical composition of SrAl2O4:1%Eu 2+ 1%Dy 3+ 2%Zr 4+ .

[0047] The preparation method of strontium aluminate long afterglow stress luminescent ceramic is the same as in Example 1.

[0048] Comparative Example Unlike Example 6, the reduction sintering in step 4 adopts the carbothermic reduction method: the ceramic blank is placed in an alumina crucible and sintered in a muffle furnace at 1450℃-1550℃ for 3-5 hours by carbon powder embedding. After cooling, strontium aluminate long afterglow stress luminescent ceramic is obtained.

[0049] Toner ensures Eu 3+ To Eu 2+ The restoration.

[0050] The chemical composition of the strontium aluminate long afterglow stress luminescent ceramic is the same as that in Example 6.

[0051] Example 7 Unlike Example 1, the strontium aluminate long afterglow stress luminescent ceramic has the chemical composition of SrAl2O4:1%Eu. 2+ 1%Dy 3 + 3% Zr 4+ .

[0052] The preparation method of strontium aluminate long afterglow stress luminescent ceramic is the same as in Example 1.

[0053] Figure 1 The curves in the figure correspond, from bottom to top, to the standard X-ray diffraction spectrum of strontium aluminate crystals and the X-ray diffraction spectra of the strontium aluminate long afterglow stress luminescent ceramics prepared in Examples 1-7.

[0054] Figure 1 In the diagram: the horizontal axis represents the diffraction angle, and the vertical axis represents the diffraction intensity.

[0055] Depend on Figure 1 It can be known that: By changing Dy 3+ Zr 4+ In SAOE:x%Dy 3+ y%Zr 4+ The proportion of doping concentration improves the long afterglow stress luminescence intensity and overall performance of ceramics. It can be seen that the diffraction peak positions of ceramic materials prepared under different doping concentrations are the same and can match the standard diffraction peaks of strontium aluminate crystals.

[0056] The above indicates that Dy 3+ Zr 4+ The doping does not affect the crystal structure of the material.

[0057] Figure 2 The images show the fluorescence emission spectra of ceramics, including those from Examples 1 to 4.

[0058] Figure 2 middle: The horizontal axis represents wavelength, usually measured in nanometers (nm). This indicates the primary color of light emitted by the ceramic material (520nm corresponds to green light). The vertical axis represents fluorescence intensity, usually expressed in arbitrary units (au). That is, how strong the light emitted at this wavelength is.

[0059] The wavelength corresponding to the peak in the figure is the maximum emission wavelength of the ceramic material. The fluorescence intensity corresponding to the maximum emission wavelength is taken as the normalized fluorescence intensity.

[0060] This is important optical information about the ceramic material, reflecting the color of the fluorescence.

[0061] Figure 2 In the partial diagram: The horizontal axis represents the value of x, and the vertical axis represents the normalized fluorescence intensity.

[0062] like Figure 2 The image shows the fluorescence emission spectra of ceramics prepared with different doping concentrations under light excitation. The emission band is 450nm~650nm, with an emission peak around 520nm, and the overall emission is green.

[0063] Sunlight UV, most indoor LED light sources, and portable light sources such as mobile phone flashlights and flashlights have light emission ranges concentrated in the 400nm~750nm range, while the absorption range of SAOE is 250nm-500nm. Their emission range partially overlaps with the absorption range of SAOE, indicating that these common household light sources can be used as absorption sources for SAOE.

[0064] With Dy 3+ As the concentration increases, the fluorescence intensity of the sample gradually decreases.

[0065] That is, Dy 3+ Ions typically exist as trap centers and play a key role in extending the afterglow duration of long-afterglow luminescent materials (LPLs). Charge carriers can be trapped, leading to a significant reduction in initial fluorescence intensity.

[0066] As x increases from 0 to 1, the fluorescence intensity drops rapidly from 100% to 55%. The decline then slows, and when x increases from 1 to 2, the fluorescence intensity shows only a 5% difference (from 55% to 45%). This means that the concentration of trapped carriers is close to saturation.

[0067] Figure 3 The images show the afterglow decay spectra of ceramics, including the afterglow decay spectra of Examples 1 to 4.

[0068] Figure 3 In the graph: the horizontal axis represents the duration of afterglow, and the vertical axis represents the fluorescence intensity.

[0069] "Afterglow duration" refers to the luminescence time after the light excitation is removed. It should be noted that this invention only recorded the afterglow decay trend of strontium aluminate within 10 minutes. In fact, the afterglow duration of strontium aluminate is much longer than 10 minutes.

[0070] Depend on Figure 3 Know: When Dy 3+ When the concentration reaches 1%, its decay curve becomes nearly flat, thus extending the afterglow duration.

[0071] Figures 2-3 , y=0.

[0072] In summary, combining Figures 2-3 The optimal value of x is determined to be 1.

[0073] Figure 4 This refers to the stress-luminescent ceramic image formed when the letter ML is engraved on the ceramic end face under the condition of afterglow.

[0074] Figure 4 In the middle: the green part represents ceramic. The engraving process is equivalent to applying mechanical stress to the ceramic.

[0075] Figure 4 (a) in the text: Undoped Dy 3+ The sample with x=0 showed almost no trace of stress luminescence, indicating that Eu alone could not elicit any significant luminescence. 2+ The generated oxygen vacancies act as traps, but they are not able to capture charge carriers. Instead, they are accompanied by light emission, making it difficult to observe stress luminescence.

[0076] Figure 4 (b) in: When Dy 3+When the concentration increased to 0.5% (x=0.5), the luminescence brightness increased slightly, and the "ML" lettering became slightly diffused, but remained clearly discernible, indicating that Dy 3+ The incorporation introduces some shallow traps, where charge carriers are released through stress, resulting in initial stress luminescence.

[0077] Figure 4 In (c): when x=1.0%, the stress luminescence intensity is further improved, and the luminescence area is more uniform, further proving that Dy 3+ The incorporation of [a substance] has a certain effect on improving stress luminescence.

[0078] Figure 4 (d) in: when Dy 3+ When the concentration increased to 2.0% (x=2.0), the stress luminescence intensity remained basically unchanged, indicating that the concentration of carriers trapped in the trap was close to saturation.

[0079] Figure 5 The images show the fluorescence emission spectra of ceramics under light excitation, including the fluorescence emission spectra of Examples 1 and 5-7.

[0080] Figure 5 In the partial diagram: The horizontal axis represents the value of y, and the vertical axis represents the normalized fluorescence intensity.

[0081] Normalized fluorescence intensity, its definition is the same as Figure 2 Same as above.

[0082] Figure 6 The images show the afterglow decay spectra of ceramics, including the afterglow decay spectra of Examples 1 and 5-7.

[0083] Figure 6 In the photograph of the ceramic afterglow, the value corresponds to y=2.

[0084] Figure 5 In the middle, when Zr 4+ When the concentration was increased from 0 to 2%, the fluorescence intensity increased. Figure 6 The afterglow decay curve (spectrum) in the image gradually flattens out.

[0085] That is, Zr 4+ The introduction of [a specific substance] will optimize the crystal structure of SrAl2O4, stabilize the trap energy level, and enhance the electron trapping ability.

[0086] And when Zr 4+ At a concentration of 3%, the afterglow decay curve is steeper than that at 2%. This is because Zr 4+ Excessive doping introduces too many structural defects, interfering with the traps' normal capture and release of electrons, leading to a decrease in afterglow performance (afterglow duration).

[0087] Combination Figures 5-6 The optimal value of y is determined to be 2.

[0088] Figure 7 This refers to the stress-luminescent ceramic image formed when the letter ML is engraved on the ceramic end face under the condition of afterglow.

[0089] Figure 7 In the middle: the green part represents ceramic. The engraving process is equivalent to applying stress to the ceramic.

[0090] Figure 7 (a) in the text: undoped Zr 4+ The sample with (y=0) already exhibits a certain stress luminescence intensity, but compared to the doped Zr... 4+ The sample showed slightly insufficient stress luminescence intensity.

[0091] Figure 7 (b) in the text: When Zr is doped 4+ At a concentration of 1%, the stress luminescence intensity is significantly improved compared to undoped Zr. 4+ The stress luminescence effect of the sample was significantly improved.

[0092] Figure 7 (c) in the text: When Zr is doped 4+ At a concentration of 2%, the stress luminescence intensity was most pronounced, with the "ML" markings exhibiting uniform illumination and the highest brightness, displaying clear luminescent traces. This indicates a sufficient amount of Zr. 4+ Doping allows almost all charge carriers in the deep traps to be released, resulting in optimal stress luminescence performance.

[0093] Figure 7 (d) in: while when Zr 4+ When the concentration reached 3%, the luminescence intensity decreased and some areas showed a lack of luminescence. The reason for this may be that the excessive doping concentration caused structural defects to become disordered, which interfered with the trap's normal capture and release of electrons.

[0094] contrast Figure 4 and Figure 7 It can be known that: Zr 4+ It can improve stress luminescence intensity. The specific comparison process is as follows: Figure 4 To dop different Dy 3+ Stress luminescence images of strontium aluminate concentrations Figure 7 To fix Dy 3+ At a concentration of 1%, different Zr doping 4+ Stress luminescence image of strontium aluminate at a certain concentration.

[0095] Figure 4 Compared to Figure 7 It is clearly visible to the eye. Figure 4 The overall stress luminescence is relatively weak, and the edges of the engraved "ML" lettering are blurred and diffused. Figure 7 It is doped with Zr 4+ Afterwards, compared to Figure 4 The light emitted was clearly visible, and the edges of the characters did not appear blurry or diffused, further proving that Zr... 4+ It can improve stress luminescence intensity, and the addition of 2% Zr can enhance this effect. 4+ The lettering "ML" is the clearest, indicating the strongest stress luminescence intensity.

[0096] Figure 8 Ceramics prepared using gas reduction and carbothermal reduction methods respectively (optimal doped sample: 1% Dy) 3+ 2%Zr 4+ Image of the afterglow duration.

[0097] Figure 8 The red dashed circle indicates that the ceramic sample still exists but is not visible to the naked eye.

[0098] Carbothermic reduction refers to a redox reaction carried out at a specific high temperature using inorganic carbon as a reducing agent. This method has advantages such as low cost and high safety, and is widely used in the chemical and metallurgical industries.

[0099] from Figure 8 As can be seen, the disadvantage of using carbon as a reducing atmosphere is that the reducing atmosphere is easily insufficient and the sample is contaminated. Compared with the gas reduction method, it can be observed that the black marks on the surface of ceramic samples prepared by the carbothermic reduction method are deeper. This may be because during the high-temperature sintering process, carbon powder adheres to the surface or even penetrates into the ceramic, severely contaminating the sample and causing the ceramic material to exhibit black contamination, thus affecting the Eu. 2+ The restoration led to Eu 3+ Not fully restored to Eu 2+ This results in a reduction in the duration of the ceramic's afterglow. The gas reduction method refers to introducing a corresponding reducing gas into a high-temperature furnace and placing the sample to be sintered into the high-temperature reduction furnace.

[0100] from Figure 8 As can be seen, the samples obtained by the gas reduction method have better performance; the gaseous reducing agent can uniformly penetrate the reaction system and quickly reduce Eu. 3+ Eu required to reduce to light emission 2+ It has a high reduction efficiency, so the afterglow lasts for a long time and the sample is uncontaminated.

[0101] Figure 9 In the diagram, the white arrows represent the direction in which mechanical stress is applied.

[0102] Figure 9 The optimal doped sample (1% Dy) is shown. 3+ 2% Zr 4+ (i.e., ceramics), during the fracture process, a continuous bright green luminescent band appears along the crack propagation path, confirming the synchronicity between stress luminescence and material deformation and fracture behavior, and providing the possibility for visualization of stress distribution.

[0103] Figure 10 An image of ceramics exhibiting afterglow-co-stress luminescence.

[0104] Figure 10 Optimal doped sample: 1% Dy 3+ 2% Zr 4+ Images of the afterglow duration of ceramics and images of secondary emission produced by applying stress (inscribing "ML" on the ceramics) after the afterglow duration has ended; Figure 11 for Figure 10 A magnified view of the medium-stress luminescence image.

[0105] Depend on Figures 10-11 It can be seen that the ceramic material has successfully achieved afterglow synergistic stress luminescence, that is, after the material is pre-radiated (photo-excited), it will exhibit a phenomenon of persistent afterglow. After the afterglow performance of the material is exhausted, mechanical force is applied to release charge carriers deeper inside, generating secondary luminescence.

[0106] Figure 12 middle: The orange circles represent electrons, or charge carriers; like Figure 12 The image shows SrAl2O4:1%Eu 2+ ,x%Dy 3+ y%Zr 4+ Diagram of the afterglow synergistic stress luminescence mechanism in ceramics: When the material is irradiated with ultraviolet light, charge carriers are generated, and valence band electrons absorb energy and transition to the conduction band. This is achieved by incorporating Dy. 3+ The introduction of shallow traps increases carrier density, allowing more carriers to be absorbed by Dy. 3+ The captured, under room temperature thermal perturbations, were controlled by Dy 3+ The captured charge carriers are slowly released, transitioning to europium (the luminescent center), and then returning to the ground state with accompanying light emission, thus greatly extending the afterglow duration; further doping with Zr... 4+ When deep traps are introduced, it is difficult to release these charge carriers located in the deep traps under room temperature thermal disturbances. Greater thermal disturbances or mechanical forces are required to release these deep charge carriers.

[0107] When a ceramic material is subjected to mechanical stress, the stress is converted into energy through lattice vibration and transferred to the trap energy level, breaking the binding effect between the charge carriers and the trap. At this time, the electrons in the deep trap are released, jump to europium (the luminescent center), and then return to the ground state to emit light, thus achieving luminescence.

[0108] By introducing Dy 3+ and Zr 4+ The study successfully achieved afterglow-co-stress luminescence, which means that after the material is pre-radiated, it will exhibit a persistent afterglow phenomenon. After the afterglow performance of the material is exhausted, mechanical force is applied to release charge carriers deeper inside, generating secondary luminescence.

[0109] The above are merely preferred embodiments of the present invention and do not constitute any limitation on the present invention. Any equivalent substitutions or modifications made by those skilled in the art to the technical solutions and content disclosed in the present invention without departing from the scope of the present invention shall be deemed to have remained within the protection scope of the present invention.

Claims

1. A strontium aluminate long afterglow stress-luminescent ceramic, characterized in that, Its general chemical formula is SrAl2O4:1%Eu 2+ ,x%Dy 3 + y%Zr 4+ , where 0≤x≤2, 0≤y≤3.

2. The strontium aluminate long afterglow stress-luminescent ceramic according to claim 1, characterized in that, x=1, y=2.

3. A method for preparing strontium aluminate long afterglow stress-luminescent ceramic according to any one of claims 1-2, characterized in that, Includes the following steps: Step 1, Preparation of precursors: Preparation of precursors for europium (Eu), dysprosium (Dy), and zirconium (Zr); Step 2, Ingredients and Mixing: Weigh out the Sr-containing compound, the Al-containing compound, and the precursor according to the stoichiometric ratio in the general chemical formula; The weighed raw materials are mixed to obtain raw material powder; Step 3: Preparation of ceramic blanks: After grinding and sieving the raw material powder, the ceramic blanks are statically pressed to obtain ceramic blanks; Step 4, Reduction Sintering: Place the ceramic blank in a pressureless hydrogen furnace and sinter it at 1450℃-1550℃ for 3-5 hours in a reducing atmosphere. After cooling, strontium aluminate long afterglow stress luminescent ceramic is obtained.

4. The method for preparing strontium aluminate long-afterglow stress-luminescent ceramic according to claim 3, characterized in that, The Sr-containing compound is strontium carbonate (SrCO3), and the Al-containing compound is Al2O3. The precursor of europium Eu is europium oxide Eu2O3; The precursor of dysprosium (Dy) is dysprosium oxide (Dy₂O₃); The precursor of zirconium Zr is zirconium oxide ZrO2.

5. The method for preparing strontium aluminate long afterglow stress-luminescent ceramic according to claim 3, characterized in that, The reducing atmosphere is pure hydrogen or a mixture of gases; the mixture includes hydrogen and nitrogen.

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