Study on Rare Earth Doped Fluoride Multi-wavelength Infrared Display Materials

abstract

In this paper, the principle of rare earth luminescence, the development history of upconversion luminescent materials, the application of infrared upconversion luminescent materials and the current research status are briefly introduced. PbF2: Er, Yb upconversion luminescent materials were prepared by solid-state reaction at high temperature with PBF2 as matrix material, ErF3 as activator and YbF3 as sensitizer. The effects of sintering time and sintering temperature on the luminescent effect of infrared laser display materials were discussed emphatically. The fluorescence spectrum and upconversion luminescence characteristics of Er3+/Yb3+ luminescent system excited by 1064nm laser were studied. Experiments show that the material can emit green and red fluorescence under the excitation of 1064nm laser, and it is a new type of infrared laser display material.

Keywords: 1064nm upconversion infrared laser display Er3+/Yb3+

abstract

In this paper, the luminescence mechanism of rare earth is briefly introduced, and the development and application of upconversion materials are systematically expounded. The research status of conv conversion luminescence in infrared is also introduced. PbF2: er, Yb upconversion materials were synthesized by high-temperature solid-state reaction with pbf2 as matrix, ErY3 as activator and YbF3 as sensitizer. The effects of sintering temperature, sintering time and other factors on the luminescent properties of infrared laser display materials are emphatically discussed. The luminescence system, fluorescence spectrum and upconversion characteristics of Er3+/Yb3+ excited by 1064nm LD were studied. The experimental results show that strong green light and wedge-shaped upconversion emission are observed under the excitation of 1064nm LD, which is a new type of infrared laser display material.

Keywords: 1064nm upconversion infrared laser display material Er3+/Yb3+3

catalogue

abstract

abstract

Chapter 1 Introduction 1

1. 1 brief introduction to the spectral theory of rare earth elements

1. 1. 1 introduction of rare earth elements 1

1. 1.2 rare earth ion energy level 1

1. 1.3 crystal field theory II

The influence of 1. 1.4 matrix lattice 2

Development of 1.2 upconversion luminescent materials 3

Basic theory of 1.3 4 upconversion luminescence

1.3. 1 excited state absorption 4

1.3.2 photon avalanche upconversion 4

1.3.3 energy transfer upconversion 5

Sensitization mechanism and doping mode of 1.4 6

1.4. 1 sensitization mechanism 6

1.4.2 doping mode 7

1.5 application of upconversion luminescent materials 8

1.6 purpose and content of this paper 8

Chapter 2 Synthesis and Characterization of Infrared Laser Display Materials 10

2. Synthesis of1Infrared Laser Display Materials

2. 1. 1 experimental drug 10

2. 1.2 experimental instruments 10

2. 1.3 sample preparation 1 1

2.2 Characterization of Infrared Laser Display Materials 12

2.2. 1 XRD 12

2.2.2 fluorescence spectrum 12

Chapter III Results and Discussion 14

3. 1 Determination of matrix materials

3.2 the choice of flux 15

3.3 Determination of sintering time 15

3.4 Determination of sintering temperature 16

3.5 Determination of doping concentration 17

Conclusion 2 1

Reference 22

Thanks 23 Introduction to Chapter 1

1. 1 brief introduction to the spectral theory of rare earth elements

1. 1. 1 introduction of rare earth elements

Rare earth elements refer to group IIIB in the periodic table, scandium (SC) with atomic number 2 1: yttrium (Y) and lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (nd) and promethium in lanthanide elements with atomic numbers 57 to 7 1.

The atoms of rare earth elements have unfilled 4f and 5d electronic configurations, so they have rich electronic energy levels and long-lived excited states. There are more than 200,000 energy level transition channels, which can generate various radiation absorption and emission. The luminescence of rare earth compounds is based on the transition of their 4f electrons within the f-f configuration or between the f-d configurations.

Rare earth luminescent materials have many advantages:

(1) Compared with common elements, rare earth element 4f has various fluorescence characteristics due to its electron shell configuration.

(2) Rare earth elements are effectively shielded by the outer S and P orbitals because 4f electrons are in the memory orbit, and are not easily disturbed by the external environment. The 4f energy level difference is very small, and the f-f transition presents a sharp linear spectrum, so the luminescent color purity is high.

(3) The fluorescence lifetime spans 6 orders of magnitude from nanosecond to millisecond;

(4) Strong ability to absorb excitation energy and high conversion efficiency;

(5) The physical and chemical properties are stable, and it can withstand the effects of high-power electron beam, high-energy radiation and strong ultraviolet light.

1. 1.2 rare earth ion energy level

Rare earth ions have 4f electron shells, but in atomic and free ion states, f-f electron transition cannot occur due to parity prohibition [3&: 7]. In solid, the forbidden parity is lifted due to odd crystal field term, and f-f transition can occur. The principal quantum number of 4f orbit is 4, and the orbital quantum number is 3, which is larger than other S, P and D orbitals and has more energy levels. Besides the f-f transition, there are 4f-5d, 4f-6s and 4f-6p electronic transitions. Because the energy levels of 5d, 6s and 6p are at higher energy levels and the transition wavelength is short, most of them are in the vacuum ultraviolet region except a few ions. Because 4f shell is shielded by 5s2 and 5p6 shell, it is insensitive to external field, so its energy level and spectrum have the characteristics of atomic state in solid. Therefore, the spectrum of f-f transition is sharp, and the transition from 4f shell to other configurations is band spectrum, because other configurations are shells, which are greatly influenced by the environment.

Rare earth ions usually appear in trivalent form in compounds, and most of the spectra observed in visible and infrared regions belong to transitions within 4fN configuration. The general method to determine the spectral term after a given configuration is to select a reasonable spectral term by using angular momentum coupling and Pauli principle, but this method is quite troublesome and prone to errors when there are many electrons and quantum numbers. So it is not suitable for rare earth ions. By using the method of group theory, the branching rules of U7-GTR 7-GTG 2-GTR 3 group chains can conveniently give all the correct spectral terms of 4fN configuration. Generally, the quantum numbers of the total orbital angular momentum of spectral terms are expressed in uppercase English letters, such as S, P, D, F, G, H, I, K, L, M, N, O, Q ... The quantum numbers representing the total orbital angular momentum are 0, 1 respectively. In spectroscopy, the spectral term is represented by the symbol 2s+1l.

Crystal field theory of 1. 1.3

Crystal field theory holds that when rare earth ions are doped into crystals, their energy levels are different from those of free ions due to the influence of surrounding lattice ions. This influence mainly comes from the electrostatic field generated by surrounding ions, which is usually called crystal field [2]. The crystal field changes the energy level splitting and transition probability of ions. Rare earth ions form typical discrete luminescence centers in solids. In the discrete luminescence center, the electrons participating in the luminescence transition are the electrons forming the central ion itself, and the transition of electrons occurs between the energy levels of the ion itself. The luminescence properties of the center mainly depend on the ions themselves, while the influence of the matrix lattice is secondary.

The 4f electron energy of rare earth ions is higher than that of 5s and 5p orbitals, but 5s and 5p orbitals are outside 4f orbitals, so electrons on 5s and 5p orbitals can shield the crystal field, which greatly reduces the influence of 4f electrons on the crystal field. The influence of crystal field on 4f electrons of rare earth ions is much less than Coulomb interaction between electrons and spin-orbit interaction of 4f electrons. Considering the Coulomb interaction and spin-orbit interaction between electrons, the 4f electron energy level is expressed as 2J+ 1lj. The crystal field will split the energy level with the total angular momentum quantum number j, and the form and size of the split depend on the strength and symmetry of the crystal field. The 4f level splitting of rare earth ions is very sensitive to the surrounding environment (coordination, crystal field strength and symmetry), and it can be used as a probe to study the local environmental structure of rare earth ions in crystals, amorphous materials, organic molecules and biomolecules, while the center of gravity of 2J+I LJ energy levels is almost the same in different crystals, and the 4f electron luminescence of rare earth ions is characteristic, so it is easy to identify what rare earth ions are emitting according to the position of spectral lines.

Influence of 1. 1.4 matrix lattice

Matrix lattice has a great influence on the spectral position of f→d transition, and its influence on f→f transition is shown in three aspects:

(1) can change the symmetry of trivalent rare earth ions in crystal position, and make the spectral intensity of different transitions change obviously; (2) It can affect the splitting of some energy levels; (3) Anionic groups in some matrices can absorb excitation energy and transfer it to rare earth ions to make them emit light, that is, anionic groups in the matrices act as sensitizing centers. Especially, when the central ion (Me) of the anion group forms a straight line with the oxygen ion O2- in the middle and the rare earth ion (re) replacing the cation position in the matrix, that is, when Me-O-RE approaches 180, the matrix anion group is most effective for the energy transfer of the rare earth ion.

Development of 1.2 upconversion luminescent materials

Luminescence refers to the process that the energy absorbed in some way inside an object is converted into light radiation. The contents of luminescent optics include the conditions, processes and laws of light emission, the design principles, preparation methods and applications of luminescent materials and devices, and the interaction between light and matter. The application of luminescent physics and its materials science in the fields of information, energy, materials, aerospace, life science and environmental science and technology will certainly promote the rapid development of optoelectronic industry, and will play a decisive role in promoting the construction of global information superhighway and the development of national economy and science and technology. The electron energy spectrum of trivalent lanthanide rare earth ions is rich, because 4f orbitals exist in the electronic configuration of rare earth atoms, which creates conditions for various energy level transitions. Under the excitation of laser with appropriate wavelength, many laser lines can be generated, which can be extended from infrared spectrum to ultraviolet spectrum. Therefore, the study of rare earth ion luminescence has always been concerned by people.

In the late 1960s, Auzel accidentally discovered that rare earth ions such as Er3+, Ho3+ and Tm3+ could emit visible light under the excitation of infrared light when Yb3+ was doped into the matrix material in ytterbium sodium tungstate glass, and put forward the viewpoint of "up-conversion luminescence" [5&: 4]. The so-called up-conversion material refers to a material that can emit fluorescence shorter than the excitation wave under the excitation of light. Its characteristic is that the photon energy of excitation light is lower than that of emission light, which violates Stokes' law. Therefore, upconversion luminescence is also called "anti-Stokes luminescence".

Since 1970s, the research on up-conversion has turned to single-frequency laser up-conversion. In 1980s, due to the development of semiconductor laser pumping source and the demand of developing visible laser, it developed rapidly. Especially in recent years, with the further development of laser technology and laser materials, the great application potential of frequency upconversion in compact visible laser, fiber amplifier and other fields has aroused the interest of scientific workers, pushed the research of upconversion luminescence to a climax and made breakthrough practical progress. With the development of up-conversion materials and laser technology, people are considering expanding their application fields and transforming the existing research results into high-tech products. At the CLEO conference from 65438 to 0996, Downing cooperated with MacFarlane and others to put forward the method of three-color stereoscopic display. Dual-frequency up-conversion three-dimensional display was rated as one of the latest achievements in physics from 65438 to 0996. This display mode can not only reproduce the three-dimensional images of various objects, but also display various high-speed dynamic three-dimensional images processed by computers at will, with full solidification, materialization, high resolution, high reliability and running speed. Another significant application of upconversion luminescent materials is fluorescence anti-counterfeiting or security identification, which is a new research direction and has extremely broad application prospects. Under the excitation of infrared light, many visible spectral lines are emitted, and the relative intensity of each spectral line is sensitive to the matrix material and manufacturing process of the upconversion material, so it is not easy to forge, with strong confidentiality and very reliable anti-counterfeiting effect.

At present, rare earth ions are mainly concentrated in trivalent cations such as Nd3+, Er3+, Ho3+, Tm3+ and Pr3+. Yb3+ ion is the most commonly used sensitizing ion because of its unique energy level characteristics. Generally speaking, in order to prepare efficient upconversion materials, we must first find a suitable matrix material. At present, there are hundreds of up-conversion materials, including glass, ceramics, polycrystalline powder and single crystal. Its compounds can be divided into: (1) fluoride; (2) oxide; (3) oxyhalides; (4) Sulfur oxides; (5) Sulfide, etc.

Up to now, great progress has been made in the study of upconversion luminescence, and blue-green upconversion fluorescence of different rare earth ions has been obtained in fluoride glass, oxyfluoride glass and various crystals.

Basic theory of up-conversion luminescence in 1.3

Converting long-wave radiation into short-wave radiation through multiphoton mechanism is called up-conversion, which is characterized in that the energy of absorbed photons is lower than that of emitted photons [2&: 8]。 The upconversion luminescence of rare earth ions is based on the transition between 4f electron levels of rare earth ions. Due to the shielding effect of 4f shell electrons on 4f electrons, the transition between 4f electronic states is little influenced by the matrix, each rare earth ion has its determined energy level position, and the upconversion luminescence process of different rare earth ions is different. At present, the upconversion process can be summarized into three forms: excited state absorption, photon avalanche and energy transfer upconversion.

1.3. 1 excited state absorption

Excited state absorption (ESA) is the most basic process in upconversion luminescence, as shown in figure 1- 1. First, the electron whose emission center is in the ground state E0 absorbs a photon of ω 1 and transitions to the intermediate metastable state E 1. The electron on E 1 absorbs another photon of ω2 and jumps to the high energy level E2. When an electron at energy level E2 transitions to the ground state, it emits high-energy photons.

Figure 1- 1 Upconversion Excited State Absorption Process

1.3.2 photon avalanche upconversion

1979 was the first time to discover photon avalanche upconversion luminescence in LaCl3∶Pr3+ materials. In 1997, N. Rakov et al. reported that avalanche upconversion also occurred in fluoride glasses doped with Er3+. Because it can be used as the excitation mechanism of upconversion laser, it has attracted extensive attention. The process of "photon avalanche" is a combination of excited state absorption and energy transmission, as shown in figure 1-2. In a four-level system, Mo, M 1 and M2 are the ground state and intermediate metastable state, respectively, and E is the high energy level for emitting photons. The excitation light corresponds to the * * vibrational absorption of m1→ e. Although the photon energy of the excitation light does not oscillate with the ground state absorption, there will always be a small number of ground state electrons excited between e and M2, and then relaxed to M2. The electrons on M2 and the ground-state electrons of other ions have energy transfer I, resulting in two electrons located at M 1. An electron of M 1 is excited to a high energy level e after absorbing a photon of ω 1. Electrons at e level interact with the ground state of other ions to produce energy transfer II, and then three electrons at M 1 are produced. In this way, the number of electrons in the e level increases rapidly like an avalanche. When the electrons at the E level transition to the ground state, high-energy photons with energy ω are emitted. This process is an up-conversion "photon avalanche" process.

Figure 1-2 photon avalanche upconversion

1.3.3 energy transfer upconversion

Energy transfer (abbreviated as ET) refers to the coupling of two excited ions with similar energy through non-radiation process, one of which returns to a low energy state and transfers energy to the other ion, making it transition to a higher energy state. Figure 1-3 lists several possible energy transfer modes: (a) it is the most common energy transfer mode, in which the donor ion in the excited state transfers energy to the acceptor ion in the excited state, so that the acceptor ion transitions to a higher excited state; (b) This process is called multi-step continuous energy transfer. In this process, only donor ions can absorb the energy of incident photons. The acceptor ion is transferred to the intermediate state by the first energy transfer between the donor ion in the excited state and the acceptor ion in the ground state, and then the acceptor ion is excited to a higher excited state by the second energy transfer. (c) This process can be called Cross Relaxation Up-conversion (CR for short), which usually occurs between the same ions. In this process, two identical ions make one ion transition to a higher excited state and the other ion relax to a lower excited state or ground state through energy transfer. (d) The process is a schematic diagram of the synergistic luminescence process. The two excited rare earth ions directly emit light without the participation of the third ion. One of his obvious characteristics is that there is no energy level matching the emitted photon energy, which is a strange upconversion luminescence phenomenon; (e) The process is synergistic sensitization up-conversion, in which two rare earth ions in the excited state transition to the ground state at the same time, and the acceptor ion transitions to a higher energy state.

(a) General energy transfer (b) Multi-step continuous energy transfer

(c) cross relaxation energy transfer (d) cooperative luminescence energy transfer.

(e) cooperative sensitization up-conversion energy transfer

Figure 1-3 Schematic diagram of several energy transfer processes

The upconversion luminescence of rare earth ions is a multiphoton process. In the multiphoton process, the intensity of excitation light has the following relationship with the intensity of upconversion fluorescence:

Vitamin ∝ excitation

Where Itamin represents the intensity of upconversion fluorescence, Iexcitation represents the intensity of excitation light, and the curve between upconversion fluorescence intensity and excitation light intensity is a straight line in log-logarithmic coordinates, and its slope is the number n of photons required for upconversion process. This relationship is an effective method to judge whether the upconversion process is a multiphoton process.

Sensitization mechanism and doping mode of 1.4

Sensitization mechanism of 1.4

Sensitization is a common method to improve the upconversion luminescence efficiency of rare earth ions [9]. Its essence is that sensitized ions absorb excitation energy and transfer the energy to activated ions, so as to realize the population of high-energy particles of activated ions and improve the conversion efficiency of activated ions. This process can be expressed as follows:

Dexc+A→D+Aexc

D stands for donor ion, A stands for acceptor ion, and the subscript "exc" indicates that the ion is in excited state. Yb3+ ion has become the most commonly used and important sensitizing ion because of its unique energy level structure.

(1) direct up-conversion sensitization

It has strong absorption for rare earth-doped activation centers (such as Er3+, Tm3+, Ho3+) and sensitization centers Yb3+ * *, and the 2F5/2 energy level of Yb3+ is 9 10- 1000nm, and the absorption wavelength matches the wavelength of high-power infrared semiconductor laser. If the sensitizing center Yb3+ is directly excited by laser, the rare earth activation center can be excited to a high energy level by multi-step energy transfer of Yb3+ ions to the activation center, resulting in upconversion fluorescence. This process will lead to the obvious enhancement of upconversion fluorescence, which is called direct upconversion sensitization. Figure 1-4 illustrates the excitation process by taking Yb3+/Tm3+*** doping as an example.

Fig. 1-4 direct up-conversion sensitization

(2) Indirect up-conversion sensitization

Because Yb3+ ions absorb the pump laser in the range of 9 10- 1000 nm, and the penetration depth of the pump laser is very small, although direct up-conversion sensitization on the surface can greatly improve the up-conversion efficiency, it cannot be applied to up-conversion fiber systems. In view of this situation, IHO 1995- 1996 first proposed the method of "indirect up-conversion sensitization" [7]. A model of indirect up-conversion sensitization is proposed for the first time in the Tm3+/Yb3+ double doping system. When the activation center is Tm3+, if the excitation wavelength is absorbed by 3H6→3H4 of Tm3+, the activation center Tm3+ will be excited to 3H4 level, and then the Tm3+ion at 3H4 level will transfer energy with Yb3+ ion at 2F5/2 level. Then Yb3+ ions in the excited state 2F5/2 transfer energy with Tm3+ to realize Tm3+ population at 1G4 energy level, thus indirectly exciting Tm3+ ions to a higher energy level of 1G4 through the energy process of Tm3+→Yb3+→Tm3+. Resulting in blue upconversion fluorescence of Tm3+ ions. Fig. 1-5 is a schematic diagram of indirect up-conversion sensitization. Considering the sensitization of rare earth ions and the above up-conversion mechanism, the following points should be considered to realize up-conversion luminescence: (1) Sensitized ions have larger absorption cross section and higher doping concentration at excitation wavelength; (2) There is a great energy transfer probability between sensitized ions and activated ions; (3) The intermediate energy level of activated ions has a long lifetime.

Fig. 1-5 indirect up-conversion sensitization

1.4.2 doping mode

Table 1- 1 lists the doping systems that have been studied a lot at present, and also lists the excitation wavelength, matrix material and sensitization mechanism corresponding to a certain doping system.

Table 1- 1 Common doping systems

Sensitization mechanism of rare earth ion composite excitation wavelength matrix materials

Single doped Er3+980 nanometer zirconia nanocrystals—

Nd3+576 nanometer zinc oxide-silicon dioxide-B2O3-

Tm3+660 nm AlF3/CaF2/BaF2/YF3—

Direct Sensitization of Double-doped Yb3+:Er3+980 nm Ca3al2Ge3o12 Glass

Yb3+:Ho3+980 nm YVO4 directly sensitized

Indirect sensitization of Yb3+:TM3+800 nm oxyfluoride glass

Synergistic sensitization of Yb3+:TB3+ 1064 nm silica sol-gel glass.

Synergistic sensitization of Yb3+:Eu3+973 nm silica sol-gel glass

Yb3+:PR3+1064 nm lnf3/znf2/srf2baf2/gaf2/NaF directly sensitized.

Direct Sensitization of Nd3+:PR3+796 nm Zirconium F4-based Glass

Indirect Sensitization of Triple Doped Yb3+:Nd3Yb3+:Nd3+:TM3+800 nm Zr F4-based Glass

Indirect sensitization of Yb3+:Nd3Yb3+:Nd3+:Ho3+800 nm Zr F4 based glass.

Direct sensitization of Yb3+:Er3+Yb3+:Er3+:TM3+980 nm PBF2: CdF2 glass.

Application of 1.5 upconversion luminescent materials

The matrix material doped with rare earth can emit visible light with shorter wavelength such as red, green, blue and purple under the excitation of infrared light with longer wavelength. Generally, upconverted visible light contains multiple bands, each wave has multiple spectral lines, and different intensity combinations of these spectral lines can synthesize different colors of visible light [7]. The changes of doping ions, matrix materials and sample preparation conditions will cause the changes of the relative intensity of each fluorescence band. The spectral line intensity distribution of different samples has a unique relationship with color ratio (we define the relative intensity ratio of peaks in each fluorescence band in upconversion fluorescence spectrum as color ratio, which is usually based on the peak intensity of a certain band). Therefore, upconversion luminescent materials can be applied to fluorescent anti-counterfeiting or security identification. One of the research focuses of upconversion luminescent materials in the application of fluorescent anti-counterfeiting or security identification is to prepare anti-counterfeiting materials with high upconversion efficiency and characteristics, and the color ratio of upconversion fluorescent anti-counterfeiting materials can be controlled by proportion; That is, the color ratio relationship can be controlled by adjusting the type and concentration of rare earth ions and the type, structure and proportion of matrix materials.

1.6 the purpose and content of this article.

Nd:YAG laser emits 1064nm laser, which has wide application value in laser drilling, laser welding, laser nuclear fusion and other fields, and is the most commonly used laser band. However, because the infrared light of 1064nm is invisible to human eyes, it is necessary to align and correct the graphics card made of infrared laser display material with laser response of 1064nm.

In this paper, the infrared laser display material with response of 1064nm was prepared with fluoride as the matrix and doped with rare earth ions through formula and process research. The effects of proportioning, sintering temperature, atmosphere and time on powder properties were studied. The powder was characterized by XRD and fluorescence spectrum analysis. The optimum sintering temperature and ratio were determined, and finally the infrared laser display material with excellent infrared conversion performance at 1064nm was obtained.

The second chapter is the synthesis and characterization of infrared laser display materials.

After years of research, great progress has been made in infrared responsive luminescent materials, and blue-green upconversion fluorescence doped with different rare earth ions has been realized in fluoride glass, oxyfluoride glass and various crystals. But the efficiency of up-conversion fluorescence is far from practical, especially blue light, which is even lower. Therefore, the search for new infrared laser display materials is still under study. In this paper, the luminescent materials with response of 1064nm are mainly studied.

In this chapter, the blue-green upconversion fluorescence of Er ~ (3+)/Yb ~ (3+) dual-doped matrix materials is studied, and rare earth fluoride doped infrared laser display materials with good luminescence effect are obtained, and some meaningful research results are obtained.

2. Synthesis of1Infrared Laser Display Materials

2. 1. 1 experimental drug

(1) The main chemical reagents used in synthetic materials are: LaF3, BaF2, Na2SiF6, NaF, hydrofluoric acid, concentrated nitric acid, etc. Rare earth compounds are Er2O3 and Yb2O3, and their purity is above 4N.

(2) preparing 2)ErF3 and YbF3.

ErF3 and YbF3 used to prepare Yb3+/Er3+* * fluorine-doped infrared laser display materials were synthesized in the laboratory.

Rare earth oxides were used in the experiment. Weigh proper amount of Er2O3 and Yb2O3, put them in beaker 1 and beaker 2, drop a little excess nitric acid (concentration about 8mol/L), and stir them in a constant temperature magnetic stirrer until pink solution appears in beaker 1 and colorless solution appears in beaker 2. Its chemical reaction is as follows:

Er2O3+6HNO3→2Er(NO3)3+3H2O

Yb2O3+6HNO3→2Yb(NO3)3+3H2O

Then hydrofluoric acid was added into beaker 1 and beaker 2, respectively, and pink ErF3 precipitate was generated in beaker 1 and white flocculent YbF3 precipitate was generated in beaker 2. The chemical reaction is as follows:

Er(NO3)3+3HF→ErF3↓+3HNO3

Yb(NO3)3+3HF→YbF3↓+3HNO3

The generated ErF3 and YbF3 precipitates are separated with circulating water by vacuum pump and washed with distilled water for many times. Pour the precipitate separated from the solution into a beaker, put it into an electric heating constant-temperature drying oven, and keep it at 65438 000℃ for 65438 02 hours to obtain ErF3 and YbF3 needed by the experiment, and put them into a jar for later use.

2. 1.2 experimental instrument

SH23-2 Constant Temperature Heating Magnetic Agitator (Shanghai Meiyingpu Instrument Manufacturing Co., Ltd.)

PL 203 Electronic Analytical Balance (mettler toledo Instruments Shanghai Co., Ltd.)

202-0AB electrothermal constant temperature drying oven (Tianjin Test Instrument Co., Ltd.)

Shb-11/circulating water multipurpose vacuum pump (Zhengzhou Great Wall Science and Technology Co., Ltd.)

WGY- 10 Fluorescence Spectrophotometer (Tianjin Dong Gang Science and Technology Development Co., Ltd.)

DXJ-2000 Crystal Analyzer (Dandong Fiona Fang Instrument Co., Ltd.)

1064 nanometer semiconductor laser (Changchun new industry photoelectric technology co., ltd.)

4- 13 box resistance furnace (Shenyang energy-saving electric furnace factory)

2. 1.3 sample preparation

(1) experimental method

The sample preparation method of this experiment is: taking rare earth compounds YbF3, ErF3 and matrix fluoride as raw materials, introducing appropriate flux, and synthesizing infrared laser display materials by high-temperature solid-state method.

High-temperature solid-state method is to micronize high-purity luminescent matrix, activator, auxiliary activator and flux, mechanically mix them evenly, carry out solid-state reaction at a higher temperature, cool them, and then crush and sieve them to obtain a sample [8]. This solid-state reaction method, in which the mixture of solid raw materials directly participates in the reaction in solid form, is the most widely used method for preparing polycrystalline powder infrared laser display materials. At room temperature, solids generally do not react with each other. The high-temperature solid-state reaction process is divided into two parts: product nucleation and growth. The formation of crystal nucleus is generally difficult, because in the process of nucleation, the lattice structure and atomic arrangement of raw materials must be greatly adjusted or even rearranged. Obviously, this adjustment and rearrangement consumes a lot of energy. So the solid-state reaction can only be carried out at high temperature, and the reaction speed is usually very slow. According to Wagner reaction mechanism, there are three important factors affecting the reaction speed of solids: ① contact area and surface area between reacting solids; (2) Nucleation rate of product phase; (3) Diffusion speed of ions through each phase, especially through the product phase. However, the surface area of any solid increases sharply with the decrease of its particle size, so it is very necessary to fully grind the reactants in solid-state reaction [6]. At the same time, because the phase composition may be different at different interfaces between different reactants and product phases, the product composition may be uneven, so the solid-state reaction needs multiple grinding to make the product composition uniform. In addition, if the system has gas phase and liquid phase, it can often help the transport of substances and play an important role in solid-state reaction, so when preparing luminescent materials by solid-state reaction, an appropriate amount of flux is often added. In the presence of flux, the mass transfer process of high-temperature solid-state reaction can be carried out through various mechanisms such as evaporation-condensation, diffusion and viscous flow.

(2) Experimental steps

According to the mole percentage content of each component in the formula (table 3- 1, table 3-2 and table 3-3 give the composition of the main sample and the concentration of doped rare earth ions), accurately calculate the mass of each reagent, accurately weigh it with an electronic balance, put the raw materials into an agate mortar, grind them evenly, and put them into a ceramic crucible (solid powder accounts for about 1/3 of the crucible volume) After cooling, the infrared laser display material sample described in the experiment was obtained. Figure 2- 1 is the experimental flow chart:

Figure 2- 1 experimental flow chart

2.2 Characterization of Infrared Laser Display Materials

2.2. 1 XRD

X-ray diffraction analysis is one of the most effective methods to study the fine structure, phase analysis, grain assembly and orientation of crystals [10&; 9]。 X-ray diffraction analysis using powder crystals or polycrystals as samples is usually called powder X-ray diffraction analysis. In 1967, Hugo M.Rietveld proposed the least square fitting structure correction method for all powder diffraction patterns in powder neutron diffraction structure analysis, in view of the computer's ability to process a large number of data. 1977, Malmros and others introduced this method into X-ray powder diffraction analysis, and the research of Rietveld analysis began to develop rapidly [16&; 10]。

In this experiment, DXJ-2000 crystal analyzer produced by Dandong Fiona Fang Instrument Co., Ltd. was used to collect the data of powder samples. The main test parameters are: Cu target Kα line, pipe pressure 45kV, pipe flow 35Ma, slit DSlmm, RS0.3mm, SS 1 mm, scanning speed 10 degree/min (normal scanning), 0.02 degree/min. Through the test, it can be clear whether the prepared material has formed a crystal phase with a specific crystal structure, and it can also be simply judged whether there is a second phase in the matrix or whether the doping substance forms a solid solution with the matrix with the increase of doping amount.