Brief introduction of the first author: Hao Qinglong, the second member and the third deputy director of insurance association of china Artificial Products Professional Committee, and the general manager of Beijing Hualong Yang Ya Science and Technology Development Co., Ltd.
I. Introduction
The natural night pearl is a very precious wealth. In ancient China, there were many beautiful legends about it, which gave it a mysterious color. In modern times, people have discovered many kinds of natural luminous pearls, such as fluorite luminous pearls, diamond luminous pearls and crystal luminous pearls. (Luan Bingzhen, 2003) has aroused widespread concern in the collection field. The natural luminous pearl is very rare, so it is very precious and cannot be owned and enjoyed by more people.
Beijing Hualong Technology Development Co., Ltd. makes full use of China's advanced science and technology (how, in 2004) and rich rare earth resources. On the basis of repeated experiments and practice for several years, the synthetic luminous gem (classified as artificial gem according to the national standard GB/T 16552-2003 Jewelry and Jade Name) has been successfully realized, and it is still called "synthetic luminous gem" or "hereinafter referred to as".
As early as the early 1960s, people artificially synthesized luminous powder and its plastic products based on zinc sulfide, but its phosphorescence intensity was low and its luminous time was short. At the end of 1980s, with the development of science and technology, the traditional luminous powder can no longer meet people's needs. The research on the production of luminescent materials by rare earth element activation method began internationally, and it was first developed by Germans. As we all know, the reserves of rare earth elements in China are far ahead in the world, and the separation technology of individual rare earth elements by Chinese researchers is second to none in the world. Therefore, Chinese jewelry enterprises have great resource advantages and technical advantages in synthesizing luminescent gems by rare earth element activation method. Beijing Hualong Yang Ya Science and Technology Development Co., Ltd. is ahead of the industry in the research and development of luminescent gems synthesized by activating rare earth elements. By studying the phosphorescence phenomenon, its luminous principle, the composition and structure of mineral materials, using alkaline earth metal aluminate as matrix, adding boron element and adding rare earth element as activator, they grew luminous gems with high initial phosphorescence afterglow intensity, stable luminescence and long luminous time. 1996 On March 28th, the company applied for an invention patent named "Long-afterglow high-brightness luminescent material and its preparation method" in China Patent Office, and obtained the patent certificate on February 28th, 2000, and then applied for patents in the United States and South Korea. 1996 applied for the invention patent of "synthetic luminescent gem and its manufacturing method" in China Patent Office on June 7th, and was awarded the invention patent certificate on May 4th, 2003. Beijing Hualong Yang Ya Science and Technology Development Co., Ltd. named the luminous gem invented by them as "Qinglong luminous synthetic luminous gem", referred to as "Qinglong luminous gem", which was appraised by experts and put into mass production in Beijing in July 20001year.
Secondly, the synthesis method of "Qinglong luminous gem" is briefly described.
The synthesis method of "Qinglong luminous gem" includes two processes: preparation of luminous powder and preparation of luminous gem.
Preparation of luminous powder
The raw materials used to prepare luminescent powder are SrCO3, Al2O3 and H3BO3, and the activators and auxiliary activators added in the raw materials are Eu2O3, Nd2O3 and Dy2O3.
1) raw material preparation: respectively weigh SRCO37 1.6g, Al2O3 350.5g and h3bo30.3g; Weigh 0.88 g of activator and auxiliary activator, 0.84 g of Nd2O3 and 0.93 g of Dy2O3, pulverize the above raw materials and activator, mix them thoroughly, and put them into a crucible.
2) Sintering raw materials: putting the crucible filled with the mixture into an electric furnace. Under the reducing condition, it is heated to 800 ~ 65438 0400℃ for 3h, then it is kept at 65438 0300℃ for 2h, and then it is naturally cooled to 200℃ and taken out from the electric furnace to obtain luminescent materials, which are used as raw materials for artificial synthesis of luminescent gems.
By changing some components and their proportions in luminescent materials, luminescent materials with different colors can be produced, and noctilucent powders with different colors can be produced by using these materials.
2. Preparation of luminescent gems
1) Put the prepared luminous powder into the crucible. Luminous powder can be powder (screened by 300 mesh or 400 mesh) or sintered body without crushing.
2) Bury the crucible in carbon powder (as reducing atmosphere) in a pressure electric furnace and heat it. After 5 ~ 8h, the furnace temperature is slowly raised to 1550 ~ 1700℃ and pressurized to 2 atmlatm =10/325 Pa.
Above, after constant temperature and pressure for 2 ~ 3h, naturally cool to 200℃.
3) taking the sintered body out of the pressure electric furnace and cooling it to room temperature.
4) grinding (or carving) and polishing the sintered body to make luminous gem ring or handicraft carving.
Third, the characteristics of synthesizing "Qinglong Luminous Gem"
1. Luminescence characteristics
Figure 1 X-ray powder diffraction pattern of synthetic "Qinglong Luminous Gem"
The luminescent properties of "Qinglong Luminous Gem" synthesized with rare earth elements as activators are nearly 30 times higher than those based on zinc sulfide in the early 1960s. This luminescent material is protected from light for 24 hours, and then irradiated at a distance of 60cm from a 27W fluorescent lamp for 30 minutes. After turning off the light source, the residual brightness of "Qinglong Luminous Gem" 5s is 1 1570mcd/m2, the luminous time can reach more than 10h, and the longest visible afterglow time can reach 60-70h.
2. Radioactivity characteristics
The luminescence of the synthetic "Qinglong noctilucent stone" is due to the excitation of rare earth elements and is not radioactive. In order to dispel people's doubts, we specially went to the national authority-China Institute of Metrology for testing. The test results show that its specific activity is only 0.024~0.055Bq/g/g, which is far lower than the specific activity exemption limit issued by China's State Environmental Protection Agency (natural radioactive material is 350 bq/g; Artificial radioactive substance is 70 Bq/g), which can be considered as non-radioactive, so it will not cause any harm to human body and can be used safely.
3. Gemmological nature
The synthesized "Qinglong Luminous Gem" has a monoclinic matrix with Mohs hardness of 6.5, density of 3.54g/cm3 and refractive index of 1.65.
4. Study on the crystal structure of the synthetic "Qinglong Luminous Gem"
The crystal of "Qinglong Luminous Gem" is synthesized with boron-containing alkaline earth metal aluminate as matrix and rare earth elements as activator and auxiliary activator, and its chemical formula is M N Al2-XBXO4. Where m represents alkaline earth metals (mainly Sr), n represents rare earth elements (mainly Eu), and the content of X is 0. 1≤x≤ 1. In this luminous gem structure, aluminum and oxygen form a tetrahedron structure, and the tetrahedrons are connected in the form of * * * to form a hexagonal ring, and a wide hexagonal pore channel is formed in the direction perpendicular to the hexagonal ring. The internal space is enough to accommodate alkaline earth metal cations with a larger radius, such as Sr (which can be partially replaced by at least one element among Mg, Ca and Ba), and rare earth elements, such as Eu (which can be La, ce, PR, etc.) ) is allowed to enter. The cation arrangement entering the channel is not as tightly connected as the aluminum-oxygen tetrahedron, but there are some vacancies.
The synthesized "Qinglong Luminous Gem" is analyzed by X-ray powder diffraction, and the result is shown in figure 1.
The phase attribution of diffraction pattern is retrieved by JCPDS card. It is found that the diffraction data of the synthesized "Qinglong Luminous Gem" is similar to that of 34-0379(SrAl2O4) of JCPDS card. The d value of the strongest diffraction peak is roughly equivalent to the intensity. However, as long as we carefully analyze the diffraction data of the synthesized "Qinglong Luminous Gem", we can find that there are many differences between the diffraction data of the synthesized "Qinglong Luminous Gem" and the powder diffraction data of JCPDS card 34-0379. These differences can be summarized as follows:
1) at an angle of 2θ from 3 to 100. In this range, 143 diffraction peaks were collected in the synthesized "Qinglong Luminous Gem", among which the 2θ angle (CuKa) was 3 ~ 67. It can be compared with 34-0379 of JCPDS card. In this interval, 1 18 diffraction peaks were collected from the synthesized "Qinglong Luminous Gem" sample, 77 diffraction peaks were consistent with 34-0379, and 45 diffraction peaks did not exist on the diffraction diagram of 34-0379. Especially, the 2θ of the synthesized "Qinglong Luminous Gem" sample is 7.1(d =12.451=10m.
),14.26 (d = 6.21), 18. 12 (d = 4.89), 21.48 (d = 4. This shows that the X-ray powder diffraction patterns of the synthesized "Qinglong Luminous Gemstone" are obviously different from those of 34-0379 phase.
2) In each pair of diffraction peaks that can be compared between the synthesized "Qinglong Luminous Gem" and 34-0379, there is a systematic difference in the D value between them. After eliminating the systematic error of the instrument, it can be seen that the D value of the artificially synthesized "Qinglong Luminous Gem" in each pair of data is slightly larger than that of the 34-0379 period. According to the cell parameters provided by card 34-0379 {A = 8.4424 (8), B = 8.822 (1), c=5. 1607(6), β = 93.4 15 (6)). The range of unit parameters is as follows:
Man-made products, China
It can be seen that the cell parameters of the synthesized "Qinglong Luminous Gem" are obviously different from those of 34-0379. This difference in cell parameters can be thought to be caused by the change of chemical composition in crystal structure.
The existence of a large number of redundant diffraction peaks may be due to the existence of another new phase in the synthesized "Qinglong Luminous Gem". After data retrieval, most of these redundant diffraction peaks can be compared with one called Sr4Al4O2[Al 10O23]. The crystal structure of this phase has been clarified (how, 2005). The unit cell parameters are a=24.785( 1), b=8.487(2), c=4.886( 1), and the space group is Pmma.
It is proved that the synthesized "Qinglong Luminous Gem" has at least two phases. The first phase is a compound similar to 34-0379 (SrAl2O4), and the second phase is a compound similar to Sr4Al4O2[Al 10O23]. Hereinafter, these two stages will be referred to as the first stage and the second stage respectively.
After a lot of microscopic observation and analysis of the second phase by optical microscope and electron probe analysis technology, it is found that the second phase exists widely in the synthetic "Qinglong Luminous Gemstone" sample. It is often distributed at the edge of the first phase particles, and has obvious orange-yellow interference color under orthogonal polarization, and the grain size is coarse, which is about 3 ~ 5 times that of the first phase. According to the polarizing microscope, the second object accounts for 8% ~ 12% of the whole particle area. Micro-analysis technology proves that the second phase has a strong luminescent function, and a lot of tests and identification have been done on the luminescent characteristics of the second phase.
Due to the precise control of batching process and sintering process, the synthesized "Qinglong Luminous Gem" has a multiphase structure, which is one of the development directions of modern materials science. As a multiphase material, the synthesized "Qinglong Luminous Gem" shows better performance than single-phase material, and greatly improves the afterglow time.
Professor Shi Nicheng of China Geo University studied the structure of the synthesized "Qinglong Luminous Gemstone" and obtained the first phase structure diagram as shown in Figure 2, in which purple represents aluminum-oxygen tetrahedron and green balls represent alkaline earth metals or rare earth elements in pores.
Fig. 2 Crystal structure of the first phase of artificial "Qinglong Luminous Gem"
In addition, a certain amount of boron (B) was added to the synthesized "Qinglong Luminous Gemstone", and the infrared spectrum analysis showed that part of boron replaced aluminum to form a B-O triangle structure, which destroyed and unstable the Al-O tetrahedron structure.
5. Discussion on the luminous mechanism of artificial "Qinglong Luminous Gem"
1. alkaline earth boroaluminate matrix provides a suitable crystal structure for rare earth luminescence, and the addition of EU, Dy and nd has different contributions to luminescence.
After Eu is added to alkaline earth boroaluminate, because the radii of Eu2+ ions and Sr2+ ions are close, Eu2+ ions can easily replace part of Sr2+ ions in the lattice structure, forming a substituted solid solution (Nadeshina et al., 1976), thus forming the crystal field environment of Eu2+4f65d→4f7 transition.
After adding Dy element, Dy3+ ion acts as secondary activation ion, replacing part of SR2+ ions in the lattice. Because the radius of Dy3+ ion is larger than that of SR2+ ion, the crystal lattice of the product is distorted, and because Dy3+ ion is not equivalent to SR2+ ion, a "hole trap" is generated, which becomes a "color center". When excited by light, free electrons jump to the excited state with higher energy. When they fall back from the excited state, they may either return to the ground state or fall into a trap and be stored. After the excitation stops, the energy of free electrons is provided by thermal disturbance at room temperature (including the energy released by lattice distortion or distortion during recovery). Free electrons that gain energy will be excited and jump to high energy. Some free electrons may jump out of the trap and fall back and forth to the ground state. Others can't jump out of the trap, but jump and fall back into the trap. If the energy released when free electrons fall back is in the visible range, we can see color phosphorescence. One of the luminescence mechanisms is that the substitution of ions with different valence states leads to the formation of "hole traps". The effect of Nd element is similar to that of Dy element.
2. Boron (B) is added to the synthetic "Qinglong Luminous Gem".
This is an important part of the invention patent. With the addition of boron, a small amount of boron replaced aluminum, forming a triangle structure of B-O and a tetrahedron structure of Al- O. In this way, a small amount of B-O triangle replaced the tetrahedron of Al-(), making the crystal structure unbalanced and forming lattice defects, which contributed to the high brightness and long afterglow of Qinglong luminous gem. Therefore, the substitution of B- () triangle for Al-O tetrahedron is an important structural feature of synthesizing "Qinglong Luminous Gem". Artificially creating lattice defects and forming "color centers" are the second luminescence mechanism.
In addition, after boron enters the crystal structure, a small amount of B-O triangle replaces Al-O tetrahedron, which makes the lattice distortion, and the lattice distortion has a certain strengthening effect on luminescence.
As mentioned above, under the excitation of sunlight or other energy, free electrons can jump from the ground state to the excited state level, and then the energy released from the excited state level falls back to the ground state. If there are lattice defects, electron traps will be formed. This falling electron may not necessarily return to the ground state, but it may fall into this trap. The trapped electrons have two activities. First, electrons are excited by external energy, jump out of the trap and fall back to the ground state, and at the same time release energy. If this energy is in the visible range, we can see color. Secondly, electrons can't jump out of the trap after being excited by external energy, so they will fall into the trap bottom after jumping to the highest point in the trap, and still release energy when falling back from the highest point. If this energy is in the visible range, we can see color. This electron has repeated jumps in the trap. If the electron can see the color when it falls back, it will definitely stay for a long time. Of course, the repeated transitions of electrons need energy to supplement the excitation, and this energy may come from the twisted lattice. Due to its own instability, the twisted lattice produces slight changes under the excitation of energy and stores energy. After the excitation light source stops irradiating, this slight change produces energy conversion and releases energy during the reset process, so that free electrons can be continuously replenished with energy, thus making the material obtain long afterglow time. This is the third mechanism of luminescence.
3. There is a two-phase structure in the synthesized "Qinglong Luminous Gemstone" sample.
Synthesizing multiphase materials is a unique method to artificially synthesize "Qinglong Luminous Gem" to enhance afterglow. The formation of multiphase solid solution changes the field energy of the lattice and enhances the instability of the lattice.
In the structural study, we say that the second phase is distributed at the edge of the first phase particles, which has obvious orange-yellow interference color under orthogonal polarization, and the crystal particles are coarse, which is about 3 ~ 5 times that of the first phase. According to the polarizing microscope, the second object accounts for 8% ~ 12% of the whole particle area. Microscopic analysis technology proves that the second phase has strong luminescent function. Although we haven't done enough research on why the second phase has such a strong luminescence function, it is definitely the fourth luminescence mechanism.
4. The role of rare earth elements
The biggest feature of rare earth elements is that the electronic transition energy levels of rare earth elements in f-d configuration are many and the transition energy is very small. In this way, the energy released by the electron transition or rebound in the trap center formed by lattice defects and the energy released in the process of lattice distortion or distortion recovery can stimulate the electron transition of rare earth element f-d configuration, and these electrons can emit light when they jump back to the ground state from the excited state. The data show that in the 4f configuration of trivalent rare earth ions, * * has 65,438+0,639 energy levels, and the number of possible transitions between energy level pairs is as high as 65,438+0,996,5438+0,77 (Zhang Keli, 2005). Such a large number of energy levels and transitions will certainly make the luminescence time very long, but there are some synthetic "Qinglong Luminous Gems". This is the fifth mechanism of luminescence.
Conclusion of intransitive verbs
An artificial luminous gem with excellent luminous performance was synthesized artificially, and it was awarded a national invention patent, named "Qinglong luminous synthetic luminous gem".
The luminous mechanism of artificial "Qinglong Luminous Gem" is discussed. Firstly, there are macropores in the crystal structure, which make alkaline earth metal ions and rare earth ions enter the pores, creating conditions for luminescence. The inequality of rare earth elements replacing alkaline earth metals leads to "hole trap" to capture free electrons, which is one of the luminescence mechanisms; The addition of boron increases the defects of crystal structure, that is, the trap of capturing free electrons is the second luminescence mechanism; The addition of boron also increases the instability of the crystal, distorts the crystal, stores energy when excited, and releases energy to act on free electrons after excitation is cancelled, which is the guarantee of luminescence, which is the third luminescence mechanism; The formation of composite crystals, especially the formation of the second phase, becomes a special crystal structure of luminescence, which is the fourth luminescence mechanism; The electron transition energy of rare earth element f-d configuration is many and the transition energy is very small, which is the main factor for synthesizing "Qinglong Luminous Gem" with high brightness and long afterglow, and it is also the fifth luminescence mechanism.
Attachment: Some handicrafts made by Qinglong Luminous Gemstone are photos in visible light and dark environment.
Jewelry in visible and dark environment
Guanyin image in visible light and dark environment (purple phosphorescence)
Carve handicrafts (flowers) in visible light and dark environment
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