A long-wavelength ultra-wideband sulfide near-infrared luminescent material, its preparation method and application

Abstract

The present invention is applicable to the technical field of luminescent materials, and provides a long-wavelength ultra-wideband sulfide near-infrared luminescent material and a preparation method and application thereof. The chemical formula of the luminescent material is Ca 1‑ x Cr x S, wherein 0≤x≤0.125%; the preparation method comprises the following steps: according to the chemical formula Ca 1‑x Cr x S, weigh the raw materials according to the molar ratio of each element in the raw material Ca:Cr=1-x:x, x is 0≤x≤0.125%, wherein the raw materials are compounds containing Ca and Cr elements respectively; add the weighed raw materials to a dispersant and grind them fully to obtain a uniform white powder, pre-sinter the ground white powder at 700-800°C for 2-3h, then introduce a sulfiding gas, and sinter for 2-3h in a sulfiding environment at 800-900°C to obtain the long-wavelength ultra-wideband sulfide near-infrared luminescent material. The luminescent material provided by the present invention has excellent performance, can effectively meet the needs of near-infrared LED devices, and has been widely used in modern food quality analysis, biological imaging, biomedicine and other fields.

Description

Technical Field

[0001] The present invention belongs to the technical field of luminescent materials, and particularly relates to a long-wavelength ultra-wideband sulfide near-infrared luminescent material, a preparation method thereof, and an application thereof. Background Art

[0002] The second near-infrared region (NIR-II) is between 1000 and 1700 nm, and has the advantages of low scattering, deep penetration, high signal-to-background ratio, etc., and can realize sensitive chemical bond detection, and is highly favored in sensing applications. Since NIR-II light has less scattering and absorption than NIR-I light, and can cover the vibration absorption of many functional groups, it has good application prospects in many fields such as information storage, optical imaging, biological imaging, optical switches, and non-destructive analysis. At the same time, its extensive application has led to an increasing demand for phosphor-converted light-emitting diodes (pc-LEDs) with NIR-II emission.

[0003] Transition metal ion Cr 3+ is the most ideal near-infrared activator reported so far. When it is located in a weak octahedral coordination crystal field, it usually produces broadband emission in the range of 650 - 1200 nm; in addition, due to its 4 A 2g → 4 T 1g spin-allowed transition, Cr 3+ ions usually have strong broadband absorption at about 460 nm and are compatible with commercial blue LED chips. However, the prior art with the publication number CN117070215A discloses a phosphate near-infrared luminescent material, a preparation method thereof, and an application thereof, which discloses that the emission peak wavelength of the near-infrared phosphor activated by Cr 3+ ions is shorter than 1000 nm, and the full width at half maximum (FWHM) is less than 200 nm, which will limit the detection range and accuracy of spectral applications. Therefore, it is urgently necessary to develop an ultra-wideband near-infrared second-region emission phosphor with excellent luminescent properties.

[0004] Alkaline earth sulfides such as zinc sulfide (ZnS), magnesium sulfide (MgS), calcium sulfide (CaS), strontium sulfide (SrS), barium sulfide (BaS), etc. usually have a wide optical band gap and have long been used as luminescent materials. When doped with certain activator ions, they can be effectively excited by ultraviolet or visible light to produce emission peaks in the ultraviolet to near-infrared region with a relatively wide full width at half maximum. The lower phonon energy in alkaline earth sulfides reduces the probability of non-radiative relaxation, and its strong covalency is expected to lower the center of gravity of the d orbital energy level of the luminescence center, thereby realizing long-wavelength near-infrared emission that is difficult to achieve in oxide materials. Therefore, alkaline earth sulfide luminescent materials have been widely used in the fields of photoluminescence, electroluminescence, cathode ray luminescence, etc. Lehmann first reported the results of a detailed systematic study on CaS doped with a large amount of activators and co-doped (Lehmann W. Activators and co-activators in calcium sulfide phosphors[J]. Journal of Luminescence, 1972, 5(2): 87-107.). However, the calcium sulfide phosphors disclosed in the above prior art do not have near-infrared luminescence.

[0005] Therefore, it is of great theoretical and application value to actively explore a new type of ultra-wideband near-infrared region II emission phosphor that can be effectively excited by blue light and has excellent performance. Summary of the Invention

[0006] The purpose of the embodiments of the present invention is to provide a long-wavelength ultra-wideband sulfide near-infrared luminescent material, aiming to solve the problems raised in the above background technology.

[0007] The embodiments of the present invention are implemented as follows. A long-wavelength ultra-wideband sulfide near-infrared luminescent material, the chemical general formula of the luminescent material is Ca 1-x Cr x S, where 0 ≤ x ≤ 0.125%.

[0008] Another purpose of the embodiments of the present invention is to provide a preparation method of a long-wavelength ultra-wideband sulfide near-infrared luminescent material, including the following steps:

[0009] According to the chemical general formula Ca 1-x Cr x S, weigh the raw materials according to the molar ratio of each element in the raw materials Ca:Cr = 1 - x:x, where x is 0 ≤ x ≤ 0.125%, and the raw materials are compounds containing Ca and Cr elements respectively;

[0010] The weighed raw materials are added with a dispersant and fully ground to obtain a uniform white powder. The ground white powder is pre-calcined at 700-800°C for 2-3 hours, and then a sulfiding gas is introduced and the powder is calcined at 800-900°C for 2-3 hours to obtain the long-wavelength ultra-wideband sulfide near-infrared luminescent material.

[0011] Preferably, the compound containing the Ca element is any one of CaO, CaCO3, CaCl2, CaSO4, and Ca(OH)2.

[0012] Preferably, the compound containing the Ca element is CaCO3.

[0013] Preferably, the compound containing Cr element is any one of Cr2O3, Cr(OH)3, and Cr2(SO4)3.

[0014] Preferably, the compound containing Cr element is Cr2O3.

[0015] Preferably, the dispersant is anhydrous ethanol.

[0016] Another object of an embodiment of the present invention is to provide an application of a long-wavelength ultra-wideband sulfide near-infrared luminescent material in preparing a near-infrared LED device excited by a blue light chip.

[0017] A long-wavelength ultra-wideband sulfide near-infrared luminescent material Ca 1-x Cr x S, Ca in the chemical formula 2+ ions can be Cr 3+ ion replacement, and with the Cr 3+ Concentration quenching occurs during the increase of ion doping concentration. The luminescent material can be effectively excited by blue light. Under 468nm excitation, broadband near-infrared emission covering 900~1650nm can be observed, with the strongest emission peak at 1170nm, which is attributed to Cr 3+ of 4 T2→ 4 A2's electronic transition, the maximum half-peak width of the emission spectrum can reach 310nm, with good physical and chemical stability, ideal fluorescence lifetime, green and pollution-free. It can be used as a broadband near-infrared sulfide luminescent material excited by a blue light chip to prepare near-infrared LED devices, which can be widely used in plant lighting and night vision imaging.

[0018] The preparation method provided in the embodiment of the present invention uses a gas-solid reaction method, the raw material resources used are abundant, the synthesis temperature is relatively low, the method is simple and easy to implement, the production process is simple, and it is convenient for large-scale production. The prepared product powder has excellent grain growth quality and few surface defects. The product is loose and easy to crush, easy to expand the scale for large-scale production, and will not affect its luminescence performance. Brief Description of the Drawings

[0019] Figure 1 XRD patterns of the samples prepared in Examples 1-5 and Comparative Example 1 of the present invention;

[0020] Figure 2 Excitation spectra of the samples prepared in Examples 1-5 of the present invention;

[0021] Figure 3 Emission spectra of the samples prepared in Examples 1-5 of the present invention;

[0022] Figure 4 Emission spectrum of the sample prepared in Example 2 of the present invention under 468 nm excitation;

[0023] Figure 5 Thermal quenching curve of the sample prepared in Example 2 of the present invention;

[0024] Figure 6 Normalized comparison chart of emission intensity of the sample prepared in Example 2 of the present invention at different temperatures;

[0025] Figure 7 Application comparison results between the LED device prepared with the sample of Example 2 of the present invention and the LED device prepared with a commercial blue chip. Detailed Description of the Invention

[0026] In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0027] A long-wavelength ultra-wideband sulfide near-infrared luminescent material, and its preparation method includes the following steps:

[0028] (1) According to the chemical formula Ca 1-x Cr x S, accurately weigh the corresponding raw materials with an electronic balance according to the molar ratio of each element in the raw materials Ca:Cr = 1 - x:x, where x is 0 ≤ x ≤ 0.125%, and the raw materials are Ca source and Cr source respectively;

[0029] The Ca source is an oxide, chloride, hydroxide, carbonate or sulfate containing Na;

[0030] The Cr source is an oxide, hydroxide or sulfate containing Cr;

[0031] (2) Put the weighed raw materials into an agate mortar, add absolute ethanol as a dispersant and grind them thoroughly. Grind until the alcohol volatilizes to obtain a uniform white powder. Put the ground white powder into an alumina crucible, place the crucible in a tube furnace at 800 °C for pre-sintering for 2 h, then introduce a sulfurizing gas, move the crucible to a tube furnace at 900 °C and sinter it in a sulfurizing environment for 3 h, and then slowly cool it to room temperature until it cools down, then the long-wavelength ultra-wideband sulfide near-infrared luminescent material can be obtained.

[0032] The following will describe the specific implementation of the present invention in detail with reference to specific embodiments.

[0033] Example 1. A long-wavelength ultra-wideband sulfide near-infrared luminescent material, and its preparation method includes the following steps:

[0034] (1) According to the chemical formula Ca 1-x Cr x S (x = 0.025%), the initial raw materials are selected as CaCO3 and Cr2O3, accurately weighed according to the stoichiometric ratio, and an appropriate amount of absolute ethanol is added as a dispersant and ground thoroughly for 30 min to make the raw materials evenly mixed to obtain a mixed powder;

[0035] (2) Put the mixed powder into an alumina crucible, place the crucible in a tube furnace at 800 °C for pre-sintering for 2 h, then introduce a sulfurizing gas, move the crucible to a tube furnace at 900 °C and sinter it in a sulfurizing environment for 3 h, and then slowly cool it to room temperature until it cools down.

[0036] Example 2. A long-wavelength ultra-wideband sulfide near-infrared luminescent material, and its preparation method includes the following steps:

[0037] (1) According to the chemical formula Ca 1-x Cr x S (x = 0.05%), the initial raw materials are selected as CaCO3 and Cr2O3, accurately weighed according to the stoichiometric ratio, and an appropriate amount of absolute ethanol is added as a dispersant and ground thoroughly for 30 min to make the raw materials evenly mixed to obtain a mixed powder;

[0038] (2) Put the mixed powder into an alumina crucible, place the crucible in a tube furnace at 800 °C for pre-sintering for 2 h, then introduce a sulfurizing gas, move the crucible to a tube furnace at 900 °C and sinter it in a sulfurizing environment for 3 h, and then slowly cool it to room temperature until it cools down.

[0039] Example 3. A long-wavelength ultra-wideband sulfide near-infrared luminescent material, and its preparation method includes the following steps:

[0040] (1) According to the chemical formula Ca 1-x Cr xS(x = 0.075%), select CaCO3 and Cr2O3 as the initial raw materials, accurately weigh them according to the stoichiometric ratio, add an appropriate amount of anhydrous ethanol as a dispersant and grind them thoroughly for 30 min to make the raw materials evenly mixed to obtain a mixed powder;

[0041] (2)Put the mixed powder into an alumina crucible, place the crucible in a tube furnace at 800 °C and pre-burn it for 2 h, then introduce a sulfurizing gas, move the crucible to a tube furnace at 900 °C and sinter it in a sulfurizing environment for 3 h, and then slowly cool it to room temperature until it cools down.

[0042] Example 4. A long-wavelength ultra-wideband sulfide near-infrared luminescent material, and its preparation method includes the following steps:

[0043] (1)According to the chemical formula Ca 1-x Cr x S(x = 0.1%), select CaCO3 and Cr2O3 as the initial raw materials, accurately weigh them according to the stoichiometric ratio, add an appropriate amount of anhydrous ethanol as a dispersant and grind them thoroughly for 30 min to make the raw materials evenly mixed to obtain a mixed powder;

[0044] (2)Put the mixed powder into an alumina crucible, place the crucible in a tube furnace at 800 °C and pre-burn it for 2 h, then introduce a sulfurizing gas, move the crucible to a tube furnace at 900 °C and sinter it in a sulfurizing environment for 3 h, and then slowly cool it to room temperature until it cools down.

[0045] Example 5. A long-wavelength ultra-wideband sulfide near-infrared luminescent material, and its preparation method includes the following steps:

[0046] (1)According to the chemical formula Ca 1-x Cr x S(x = 0.125%), select CaCO3 and Cr2O3 as the initial raw materials, accurately weigh them according to the stoichiometric ratio, add an appropriate amount of anhydrous ethanol as a dispersant and grind them thoroughly for 30 min to make the raw materials evenly mixed to obtain a mixed powder;

[0047] (2)Put the mixed powder into an alumina crucible, place the crucible in a tube furnace at 800 °C and pre-burn it for 2 h, then introduce a sulfurizing gas, move the crucible to a tube furnace at 900 °C and sinter it in a sulfurizing environment for 3 h, and then slowly cool it to room temperature until it cools down.

[0048] Comparative Example 1. A CaS, and its preparation method includes the following steps:

[0049] (1)According to the chemical formula Ca 1-x Cr x S(x = 0), that is, the composition of CaS, weigh CaCO3, add an appropriate amount of anhydrous ethanol as a dispersant and grind them thoroughly for 30 min to make the raw materials evenly mixed to obtain a powder;

[0050] (2) Put the powder into an alumina crucible, place the crucible in a tube furnace at 800 °C for pre-sintering for 2 h, then introduce a sulfide gas, move the crucible to a tube furnace at 900 °C and sinter it in a sulfide environment for 3 h, and then slowly cool it to room temperature until it cools down.

[0051] Performance test:

[0052] The samples prepared in Examples 1-5 and Comparative Example 1 were analyzed using powder X-ray diffraction (XRD) technology, and the XRD patterns obtained are as Figure 1 shown. Comparing the XRD data of all synthesized samples with the CaS standard card (PDF#08-0464), no impurity phases were found in all the prepared samples;

[0053] Figure 2 and Figure 3 The excitation and emission spectra of the samples prepared in Examples 1-5 are given. It can be seen that

[0054] The excitation spectrum consists of three broad peaks located near 260, 360, and 468 nm respectively. The absorption bands corresponding to the positions of the three excitation peaks are attributed to the 3+ ions of 4 A2( 4 F)→ 4 T1( 4 F), T1 ( 4 F), and 4 T2 ( 4 F) transitions. Under excitation at 450 nm, a broadband near-infrared emission covering 900 - 1650 nm can be observed, and the strongest emission peak is located at 1170 nm; while through spectral testing, the Ca 1-x Cr x S(x = 0), that is, CaS, prepared in Comparative Example 1 has no emission signal response under excitation at 468 nm, indicating that the sample has no near-infrared luminescence;

[0055] Figure 4 The best emission wavelength and full width at half maximum in the emission spectrum of the sample prepared in Example 2 are given. It can be seen that under excitation at 468 nm, the sample shows broadband emission in the second near-infrared region, with a full width at half maximum of 310 nm and the best emission wavelength of 1170 nm. The results show that the materials prepared in the examples of the present invention can be widely applied to the field of near-infrared spectroscopy technology.

[0056] Figure 5 The thermal quenching spectrum of the sample prepared in Example 2 is given. The results show that as the temperature increases, the emission intensity gradually decreases, and the sample exhibits relatively good thermal stability;

[0057] Figure 6 Figure 1 shows the normalized comparison chart of the emission intensity of the sample prepared in Example 2 at different temperatures. It can be seen that when the temperature rises to 150 °C, its emission intensity still remains 52.8% of the initial intensity;

[0058] The sample prepared in Example 2 was used to fabricate an LED device, and the LED device was compared and analyzed with the LED device fabricated with a commercial blue chip. The results are as Figure 7 shown. Figure 7 a and Figure 7 b are schematic diagrams of an ordinary camera in an indoor natural light environment without power supply. Figure 7 c and Figure 7 d are observation diagrams of a night vision camera in a dark environment with power supply. Under the irradiation of the powered NIRpc-LED device, the schematic diagrams of the items and the human hand behind the filter are clearly visible in the observation of the night vision camera. It is obvious that the NIR pc-LED fabricated with the material of the embodiment of the present invention can penetrate human tissues, indicating that this material has great application potential in the fields of biometric recognition, non-invasive monitoring, etc.

[0059] The above are only the preferred embodiments of the present invention, and are not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A long-wavelength ultra-wideband sulfide near-infrared luminescent material, characterized in that, The chemical general formula of the luminescent material is Ca 1-x Cr x S, where x = 0.05%; The preparation method comprises the following steps: (1) According to the chemical formula Ca 1-x Cr x S, where x = 0.05%, the initial raw materials are selected as CaCO3 and Cr2O3, accurately weighed according to the stoichiometric ratio, and an appropriate amount of anhydrous ethanol is added as a dispersant and ground thoroughly for 30 min to make the raw materials evenly mixed to obtain a mixed powder. (2) Put the mixed powder into an alumina crucible, place the crucible in a tube furnace at 800 °C for pre-sintering for 2 h, then introduce a sulfurizing gas, move the crucible to a tube furnace at 900 °C and sinter it for 3 h in a sulfurizing environment, and then slowly cool it to room temperature until it is cooled.

2. Application of a long-wavelength ultra-wideband sulfide near-infrared luminescent material as described in claim 1 in the preparation of a near-infrared LED device excited by a blue light chip.

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