Preparation method and application of holmium-based red-near-infrared phosphor

Abstract

The present invention relates to the technical field of phosphors, and discloses a preparation method and application of a holmium-based red-near-infrared phosphor. The preparation method comprises the following steps: sealing CsCl, NaCl, HoCl3·6H2O, SbCl3 and concentrated hydrochloric acid in a reactor, and then placing the reactor in a blast drying oven for sufficient reaction to obtain a reactant; cooling the reactant naturally to room temperature, and then washing it with ethanol several times to obtain micron crystals; the present invention realizes efficient, wide-range and thermally stable red-near-infrared light emission; in addition, by Sb 3+ Ion doping expands the excitation center of the phosphor into the ultraviolet region, avoiding the blue light hazard in the lighting field and further improving the light quality. Finally, the phosphor is combined with a 365nm chip to produce an LED, which shows good prospects in medical light sources, night vision, non-destructive testing and optical communications.

Description

Technical Field

[0001] The present invention relates to the technical field of phosphors, and in particular to a preparation method and application of a holmium-based red-near-infrared phosphor. Background Art

[0002] Lighting accounts for 20% of global electricity consumption annually. Light-emitting diodes (LEDs) have become the next-generation lighting technology due to their compact size, high energy efficiency, and excellent color quality. Recently, emerging lead-free metal halides, with their large absorption cross-sections, easily tunable band gaps, high fluorescence quantum yields, and strong chemical stability, have shown promising applications in lighting and displays. However, current research focuses on the visible light region, while the development of red-near-infrared light sources holds significant demand for applications in healthcare, night vision, and optical communications.

[0003] Rare earth ions possess a rich array of electronic energy levels and excellent photostability. Their narrowband emission, in particular, spans the ultraviolet, visible, and infrared regions. Therefore, they can be doped into lead-free metal halides to expand the emission range of phosphors. However, as the doping level of rare earth ions increases, the luminescence intensity is limited by concentration quenching. We note that the varying octahedral spacing in double perovskite metal halides is well-suited for high-concentration rare earth ion doping, potentially overcoming this bottleneck. Summary of the Invention

[0004] The purpose of the present invention is to solve the shortcomings of the prior art and to propose a preparation method and application of a holmium-based red-near-infrared phosphor.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions:

[0006] A method for preparing a holmium-based red-near-infrared phosphor comprises the following steps:

[0007] CsCl, NaCl, HoCl3·6H2O, SbCl3 and concentrated hydrochloric acid were sealed in a reaction vessel, and then placed in a forced air drying oven for sufficient reaction to obtain a reactant;

[0008] After the reactant is naturally cooled to room temperature, the reactant is washed with ethanol several times to obtain micron crystals, which are the holmium-based red-near infrared phosphor;

[0009] The molar ratio of CsCl, NaCl, HoCl3·6H2O and SbCl3 is 2:1:(1-x):x; x includes 5%, 10%, 15% and 20%.

[0010] Preferably, the reaction temperature in the blast drying oven is 180° C., and the reaction time is 12 hours.

[0011] Preferably, the concentration of the concentrated hydrochloric acid is 38%.

[0012] Preferably, the reactant is washed 4 times with ethanol.

[0013] The above-mentioned method for preparing a holmium-based red-near-infrared phosphor is used to prepare the phosphor in the preparation of LEDs.

[0014] A method for preparing an LED comprises the following steps:

[0015] Step 1: Grind the micron crystals prepared above thoroughly, then mix and stir with epoxy resin A to obtain a mixture;

[0016] Step 2: Place the mixture obtained in step 1 into a vacuum chamber to remove air bubbles;

[0017] Step 3: Apply the mixture obtained in step 2 on a 365nm chip, and then place the coated chip in a vacuum drying oven for curing to obtain the LED.

[0018] The temperature in the vacuum drying oven is 120°C, and the curing time is 1 hour.

[0019] The beneficial effects of the present invention are:

[0020] The present invention utilizes the characteristics of the octahedral spacing arrangement in the double perovskite structure and the Ho 3+ The cross-relaxation phenomenon between Sb and Br can overcome the concentration quenching effect of traditional rare earth phosphors, and achieve high-efficiency, wide-range and thermally stable red-near-infrared light emission; In addition, by 3+ Ion doping expands the excitation center of the phosphor into the ultraviolet region, avoiding the blue light hazard in the lighting field and further improving the light quality. Finally, the phosphor is combined with a 365nm chip to produce an LED, which shows good prospects in medical light sources, night vision, non-destructive testing and optical communications. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is a schematic diagram of the luminescence mechanism of the phosphor prepared by the present invention;

[0022] Figure 2 Cs2NaHoCl6:xSb 3+ XRD spectrum of

[0023] Figure 3 Cs2NaHoCl6:15%Sb 3+ SEM and elemental mapping images;

[0024] Figure 4 Cs2NaHoCl6:15%Sb3+ Schematic diagram of energy spectrum analysis;

[0025] Figure 5 Cs2NaHoCl6:xSb 3+ XPS spectra and high-resolution spectra;

[0026] Figure 6 Cs2NaHoCl6:15%Sb 3+ Thermogravimetric analysis of

[0027] Figure 7 Cs2NaHoCl6:xSb 3+ Absorption spectrum of

[0028] Figure 8 Cs2NaHoCl6:xSb 3+ (a) Excitation and (b) emission spectra of

[0029] Figure 9 (a) is an LED photo taken by a visible light camera; (b) is an LED photo taken by a near-infrared camera; (c) is a fruit photo taken by a visible light camera under natural light; (d) is a fruit photo taken by a near-infrared camera under near-infrared light radiation in dark conditions. DETAILED DESCRIPTION

[0030] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments.

[0031] Example 1: 2 mmol of CsCl, 1 mmol of NaCl, 95% mmol of HoCl3·6H2O, 5% mmol of SbCl3, and 5 mL of 38% concentrated hydrochloric acid were sealed in a reaction vessel, and then placed in a forced air drying oven at 180°C for 12 hours to obtain a reactant; after the reactant was naturally cooled to room temperature, it was washed with ethanol four times to obtain micron crystals;

[0032] The micron crystals are fully ground, then mixed with epoxy resin A glue and stirred evenly to obtain a mixture; the mixture is placed in a vacuum chamber to remove bubbles therein; the mixture is coated on a 365nm chip, and the coated chip is placed in a vacuum drying oven and cured at 120°C for 1 hour to obtain the LED.

[0033] Example 2: 2 mmol of CsCl, 1 mmol of NaCl, 90% mmol of HoCl3·6H2O, 10% mmol of SbCl3, and 5 mL of 38% concentrated hydrochloric acid were sealed in a reaction vessel, and then placed in a forced air drying oven at 180°C for 12 hours to obtain a reactant; after the reactant was naturally cooled to room temperature, it was washed four times with ethanol to obtain micron crystals;

[0034] The micron crystals are fully ground, then mixed with epoxy resin A glue and stirred evenly to obtain a mixture; the mixture is placed in a vacuum chamber to remove bubbles therein; the mixture is coated on a 365nm chip, and the coated chip is placed in a vacuum drying oven and cured at 120°C for 1 hour to obtain the LED.

[0035] Example 3: 2 mmol of CsCl, 1 mmol of NaCl, 85% mmol of HoCl3·6H2O, 15% mmol of SbCl3, and 5 mL of 38% concentrated hydrochloric acid were sealed in a reaction vessel, and then placed in a forced air drying oven at 180°C for 12 hours to obtain a reactant. After the reactant was naturally cooled to room temperature, it was washed four times with ethanol to obtain micron crystals.

[0036] The micron crystals are fully ground, then mixed with epoxy resin A glue and stirred evenly to obtain a mixture; the mixture is placed in a vacuum chamber to remove bubbles therein; the mixture is coated on a 365nm chip, and the coated chip is placed in a vacuum drying oven and cured at 120°C for 1 hour to obtain the LED.

[0037] Example 4: 2 mmol of CsCl, 1 mmol of NaCl, 80% mmol of HoCl3·6H2O, 20% mmol of SbCl3, and 5 mL of 38% concentrated hydrochloric acid were sealed in a reaction vessel, and then placed in a forced air drying oven at 180°C for 12 hours to obtain a reactant. After the reactant was naturally cooled to room temperature, it was washed with ethanol four times to obtain micron crystals.

[0038] The micron crystals are fully ground, then mixed with epoxy resin A glue and stirred evenly to obtain a mixture; the mixture is placed in a vacuum chamber to remove bubbles therein; the mixture is coated on a 365nm chip, and the coated chip is placed in a vacuum drying oven and cured at 120°C for 1 hour to obtain the LED.

[0039] Under 365nm chip excitation, Sb 3+ Ion absorption energy (5s 2 →5s 1 p 1 ) and pass it to Ho 3+ ion( Figure 1). Due to the high content of Ho 3+ The ions induce a cross-relaxation process. 5 F4 / 5 The electrons in the S2 level will relax to 5 F5 energy level, and 5 The electrons at the I7 level will be pumped to 5 I6 energy level, which in turn causes Ho 3+ The green emission of the ions disappears, and the red and near-infrared luminescence are enhanced.

[0040] The X-ray diffraction (XRD) peaks of the phosphor prepared by the above invention are completely consistent with the standard chart of cubic phase Cs2NaHoCl6 ( Figure 2 ), indicating that the sample is pure phase and does not contain other impurities. 3+ The ionic radius is smaller than Ho 3+ Ionic radius, Sb 3+ The increase in ion doping will cause the lattice to shrink, which in turn causes the XRD peak to shift to a larger angle. Scanning electron microscopy (SEM) can be used to observe that the sample morphology is a micron-scale octahedron. The corresponding element mapping image and energy spectrum analysis show that Cs, Na, Ho, Cl and Sb elements are present and evenly distributed ( Figure 3 and Figure 4 ). X-ray photoelectron spectroscopy (XPS) showed the characteristic peaks of Cs 3d, Na 1s, Ho 4d, Cl 2p and Sb 3d, and Sb 3+ After ion doping, the characteristic peak of Cs 3d shifts to a lower binding energy, which further proves that Sb 3+ Successful doping of ions ( Figure 5 In addition, the thermogravimetric analysis results show that the sample has good thermal stability ( Figure 6 ).

[0041] Sb 3+ After ion doping, the sample showed a new absorption peak between 200-380nm ( Figure 7 ), which comes from Sb 3+ Ionic 5s 2 →5s 1 p 1 Correspondingly, the broad peak at 250-400 nm in the excitation spectrum is attributed to Sb 3+ Ion absorption ( Figure 8 ). Under 350nm excitation, Sb 3+ The ions absorb energy and transfer it to Ho 3+ ions, whose emission peaks are located at 650nm, 980nm, 1200nm and 1450nm, which are much higher than the luminescence intensity of the undoped sample under 362nm excitation. 3+The emission peak intensity gradually increased with the increase of the doping concentration of ions, and the optimal doping concentration was determined to be 15%. Then the phosphor was combined with a 365nm chip to prepare an LED, which emitted strong red and near-infrared light ( Figure 9 a and 9b), which can cover three biological windows. Finally, after filtering out the red light with an optical filter, an ideal near-infrared light source can be obtained, which shows good prospects in night vision, non-destructive testing and optical communications ( Figure 9 c and 9d).

[0042] The present invention will Ho 3+ The combination of ions and double perovskites expands the near-infrared luminescence of lead-free metal halides; holmium-based double perovskites are constructed using rare earth as the matrix element, in which the high content of Ho 3+ ions cause cross-relaxation, overcoming the concentration quenching effect; the introduction of Sb 3+ Ion doping extends the effective excitation center into the ultraviolet region.

[0043] The present invention realizes strong pure red (650nm) and near-infrared luminescence (980nm, 1200nm and 1450nm); the effective excitation center extends from blue light (450nm) to the ultraviolet light region (365nm).

[0044] The above description is only a preferred specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any technician familiar with the technical field, within the technical scope disclosed by the present invention, who makes equivalent replacements or changes based on the technical solution and inventive concept of the present invention, should be covered by the scope of protection of the present invention.

Claims

1. A method for preparing a holmium-based red-near infrared phosphor, characterized in that: The following steps are involved: CsCl, NaCl, HoCl3·6H2O, SbCl3 and concentrated hydrochloric acid were sealed in a reactor, wherein the concentration of the concentrated hydrochloric acid was 38%, and then placed in a blast drying oven for sufficient reaction to obtain a reactant. The reaction temperature in the blast drying oven was 180°C and the reaction time was 12 hours; After the reactant was naturally cooled to room temperature, the reactant was washed with ethanol four times to obtain micron crystals, which are the holmium-based red-near infrared phosphor; The molar ratio of CsCl, NaCl, HoCl3·6H2O, and SbCl3 is 2:1:(1-x):x, where x is 15%.

2. A method for preparing an LED, characterized in that: The following steps are involved: Step 1: Grind the holmium-based red-near infrared phosphor prepared in claim 1 thoroughly, then mix and stir with epoxy resin A to obtain a mixture; Step 2: Place the mixture obtained in step 1 into a vacuum chamber to remove air bubbles; Step 3: Apply the mixture obtained in step 2 on a 365nm chip, then place the coated chip in a vacuum drying oven and cure it at 120° C. for 1 hour to obtain the LED.

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