Latest ArticlesThe sol-gel technology is an interdisciplinary field combining materials science and chemistry. It utilizes highly active chemicals as precursors, taking part in chemical reactions and treatment such as hydrolysis, polymerization, gelation, etc.. Solid product are often achieved by specific drying, heat treatment, or other processes/conditions. As an advanced wet-chemical preparation method, sol-gel technology finds widespread applications in the fabrication of zero-dimensional to three-dimensional nanomaterials, bulk materials, thin film coatings, fiber materials, etc. Materials obtained through this method exhibit superior characteristics and properties compared to those obtained through traditional methods. Most sol-gel processes are conducted at low temperatures, resulting in lower reaction temperatures compared to traditional methods. Materials prepared using this method possess inherent advantages in terms of chemical homogeneity, doping uniformity, and product purity. Moreover, the design of the early-stage preparation process enables the synthesis of multi-component materials with multi-phase.
Over the past two decades, China has made great progress in the research and application of sol-gel technology. Scientists have developed a wide range of methods for preparing novel materials using sol-gel techniques. These materials have been applied across various domains including optics, electronics, sensing, catalysis, energy storage, pharmaceuticals, separation, and many others. These achievements typically involve the preparation of advanced materials with novel functionalities or enhanced performance using sol-gel processes. Through this overview of the latest developments in the sol-gel academic field, one can appreciate the comprehensive research and significant contributions made in China.
The development of sol-gel technology can be traced back to the mid-19th century. As the 20th century progressed, the method of using gelation to prepare solid materials began to receive increased attention from researchers. More and more scholars began to focus on sol-gel technology, proposing various methods for preparing materials in various forms. These methods have found applications in multiple domains such as electronic devices, catalysis, energy, metal corrosion protection, optics, and others. In 1981, the First International Workshop on Glasses and Glass Ceramics from Gels was held in Padova, Italy, marking the rapid development phase of sol-gel technology. Sol-gel research in China also began in the 1980s, when many research institutions started extensively to work on sol-gel technology during this period. In 1990, the inaugural "National Conference on Sol-Gel Science and Technology" was held at Zhejiang University, marking the beginning of the sol-gel era in China. Subsequently, this conference has been held every 2 to 3 years, providing a high-quality platform for academic exchange in the field of sol-gel technology in China. In 2008, the Sol-gel Committee of the Chinese Ceramic Society was established, signifying the formal establishment of a professional association for sol-gel technology in China. The Sol-gel Committee of the Chinese Ceramic Society not only actively organizes academic activities within China but strives to promote communication with the abroad academic society and to organize international conferences as well. From August 28 to September 2, 2011, the 16th International Sol-gel Conference was held in Hangzhou, China. This marked the first time that China hosted this prestigious academic conference in the sol-gel field, receiving high praise from the international sol-gel community.
In recent years, Chinese research institutions and scholars have published an avalanche of papers in the field of sol-gel. Over the past decade (2014-2023), there has been a steady increase in global publications related to the sol-gel field, with a total of 128 627 papers. Among these, articles authored by Chinese researchers accounted for 32.5% of the global output, with this proportion reaching 50% in the year 2022. This paper focuses on highlighting some research achievements in the preparation of nano-powder materials, fiber materials, and functional coatings using the sol-gel method. It also discusses the application in energy storage, catalysis, electromagnetic shielding, thermal conductivity, luminescence, and thermal insulation.
With the rapid development of sol-gel technology, the achievements of the Chinese sol-gel academic community have also propelled its industrial development. Many new materials developed through sol-gel processes have entered the industrial application stage and become part of people's daily lives. The mass production of nano oxides and ceramic powders using the sol-gel method is well developed in China. It is applied in various fields such as semiconductors, optical component polishing materials, functional coatings, reinforcement of polymer materials, and catalytic carrier materials. Sol-gel technology has also been widely applied in the production of functional coating materials, used in applications such as anti-corrosion coatings for metals, optical coatings, and more.
Since the concept of sol-gel was proposed, sol-gel technology has demonstrated tremendous potential in various fields, ranging from materials science to life sciences and environmental engineering. It is evident that China has made remarkable progress in both academic and industrial application of sol-gel technology, bringing it into a new stage of vigorous development. By reviewing and summarizing the development of sol-gel technology in China, one can clearly see the remarkable achievements and groundbreaking progress made in this field. Chinese researchers have played a key role in this process, driving the continuous evolution of this technology. China's successful experiences in sol-gel technology are not only evident in scientific research but also widely applied in industrial manufacturing and sectors. Looking ahead, sol-gel technology is expected to focus on several key development directions in the future. In fundamental research, the study of sol-gel technology can focus on the functional design and construction of precursors, their combination with functionalized ionic solvents, and the construction of micro-reactive zones. In terms of industrial technology, sol-gel technology shows promising prospects in the preparation of spherical powders at different scales, deep ultraviolet treatment, non-high-temperature treatment processes such as solvent thermal treatment, as well as aerogels/hydrogels. Sol-gel technology in China holds vast potential for development. We anticipate that sol-gel technology will be widely applied in more fields, especially playing a more crucial role in addressing major issues such as energy, environment, and health. In the future, it will continue to make outstanding contributions to human well-being and technological advancement.
The typical all-inorganic metal halide perovskite CsPbX3 (X=Cl, Br, I) is widely used in the field of optoelectronics due to its advantages such as tunable spectra, good monochromaticity, and high photoluminescence quantum efficiency. However, the structural instability of perovskite crystals is one of the inevitable problems affecting their practical applications.
Perovskite nanocrystal glass, with its unique advantages such as tunable emission wavelength in the visible light spectrum, ultra-high stability, high photoluminescence quantum efficiency, and good monochromaticity, is widely used in frontier areas such as optical storage, Micro-LEDs, and ultra-high-resolution displays. However, there are still some issues with perovskite nanocrystal glass in applications. For example, the dense glass network structure limits the migration and growth of nanocrystals, resulting in lower quantum efficiency compared to nanocrystals in colloids. To optimize quantum efficiency, appropriate B-site substitution ions can be selected to reduce the toxicity of Pb and to improve the stability of perovskite nanocrystals. The heat treatment process reduces the energy barrier of the glass network, promotes the migration and enrichment of perovskite ions, and regulates the glass network structure to affect the migration and aggregation of ions, thereby affecting the nucleation and growth of perovskites. Additionally, self-crystallizing glass has relatively low energy barriers and reduces energy consumption during the heat treatment process. These methods of controlling crystal quality provide opportunities for improving the quantum efficiency of perovskite nanocrystal glass.
Furthermore, controlling the size and composition of perovskite nanocrystals can achieve tunable emission wavelengths. In addition to the above methods, ultrafast lasers, with features such as energy accumulation due to multiphoton absorption, micro-explosions induced by plasma thermal expansion, and rearrangement of glass frameworks, can induce local crystallization of glass, enabling direct redistribution of regional elements and design of localized chemical compositions. These optimization measures make full-spectrum coverage possible, which benefits significantly for color rendering, lighting efficiency, and energy savings.
Perovskite nanocrystal glass exhibits excellent stability while maintaining its excellent optical properties, demonstrating tremendous potential in the field of optics. Through encapsulation in a glass matrix, the stability of perovskite nanocrystals is enhanced, ensuring long-term stability and high efficiency performance in harsh environments. The fundamental mechanisms of controlling the composition of perovskite crystals and emission wavelengths through heat treatment, ultrafast laser writing, and other methods are analyzed thoroughly. Finally, the potential applications and development prospects of perovskite nanocrystal glass in fields such as LEDs and optical storage are summarized and forecasted.
Encapsulating CsPbX3 NCs within a glass matrix has enhanced the stability of nanocrystals, enabling efficient and long-term luminescence in optical applications. To improve the PLQY and to tune the emission wavelength of CsPbX3 NCs@glass, methods such as B-site substitution, modification of glass components, optimization of heat treatment processes, and improvement of laser processing parameters can be employed to regulate their luminescent properties. The resulting materials have been widely used in fields such as optical storage, LED displays, photocatalysis, and X-ray detection. However, the quantum efficiency of CsPbX3 NCs@glass reported in most literatures is generally lower than that in colloidal nanocrystals since the dense glass network hinders the diffusion of CS+, Pb2+, X-, making direct modification and surface passivation of perovskite nanocrystals challenging. To unlock the potential applications of CsPbX3 NCs@glass in optical fields, the other considerations are suggested to keep in mind, that is, to reduce the toxicity of Pb and to enhance the quantum efficiency of blue-band of CsPbX3 NCs@glass. The strategies are hopeful to achieve technological leap in this area.
Extracted Titanium slag is a type of industrial solid waste produced when titanium is recovered from titanium-containing blast furnace slag using the high-temperature carbonization-low-temperature selective chlorination method. Currently, it can only be disposed of through simple stockpiling and burial, which endangers both the environment and human health. The use of titanium slag to prepare microcrystalline glass with excellent physical and chemical properties is of great significance for the utilization of solid waste resources and the improvement of environmental pollution.
Raw material components and heat treatment systems have a significant impact on the microstructure and mechanical properties of glass ceramics. The current work is based on the chemical composition of titanium slag. high-performance glass-ceramics were prepared by melting sintering method by adding quartz tailings to increase SiO2 content. Our study examines how the acidity coefficient (Mk) and sintering temperature affect the crystallization, microstructure, physical and chemical properties of microcrystalline glass. Additionally, we reveal the composition of the physical phase of glass ceramics made from titanium slag and the evolution of crystallization. These findings provide a technical foundation for the synergistic treatment of various solid wastes in the preparation of glass ceramics.
Titanium slag and quartz tailings were prepared, combined, ball milled, and sieved accordingly. The required raw materials were weighed exactly, put into a corundum crucible, heated untill the glass liquid melted and clarified. The liquid was then quickly dumped into water, to form glass particles, following a procedure of drying, ball milling, and sieving. The basic glass powder and PVA solution were uniformly mixed before being placed in a press-bar mold and pressed into blank samples, which were then sintered to produce glass ceramics sheet samples.
The chemical composition of the raw materials was evaluated using X-ray fluorescence spectrometry. A thermal analyzer was used to perform the DSC analysis simultaneously. An X-ray diffractometer was used to conduct physical phase analysis on raw materials and glass ceramics samples. The microstructure of the glass ceramics samples was observed using a scanning electron microscope (SEM), and their microscopic composition was analyzed using an energy dispersive-X-ray spectrometer (EDS).
According to the principle of Archimedes, the bulk density and water absorption of each glass-ceramic sample were measured. The bending strength of glass-ceramics was tested by GB/T4741—1999 three-point bending method. JC/T 2097—2011 industrial microcrystalline plate was used to test the acid etching amount of microcrystalline glass.
The morphology investigation reveals that the samples' sintering or fusing steadily improves with an increase in Mk under the same temperature settings. At point of Mk=2.4, the sample begins to soften and distort, whereas at Mk =2.7, it looks to froth.
The XRD spectra of the glass ceramics samples demonstrate that the type and amount of the early crystalline phases vary when the Mand sintering temperature increases. Increasing the heat treatment temperature enhances the intensity of the diffraction peaks of the crystalline phases in low Mk glass ceramics samples. At the same sintering temperature, the content of anorthite in glass ceramics samples rises with increasing Mk, while the content of diopside increases in low Mk and decreases in high Mk.
The surface and cross-section micro-morphology of the glass ceramics samples demonstrates that the sintering temperature is too low and the materials do not attain the sintered state at lower temperature. With the same Mk, the number of holes in the samples decreases with increasing sintering temperature. As the sintering temperature rises, big closed holes become easier to develop.
The features of the glass ceramics samples, together with the results of XRD spectra and SEM analysis, show that Flexural strength and bulk density are mainly related to the type of crystalline phase, crystal content, and appropriately increase the sintering temperature. Mk is conducive to the growth of tremolite and calcium feldspar crystals in the billet, and it also benefits exclusion of porosity, so that the glass ceramics can form a flatter surface, and show higher mechanical-strength, thus to improve the sample's densification, flexural strength, acid resistance, and reduce water absorption as well. At higher acidity coefficients, increasing the SiO2 content in the base glass causes an increase of the liquid phase, which is beneficial for filling pores, reducing the water absorption capacity of glass ceramics, and improving corrosion resistance under acidic conditions.
With the increase of Mk and sintering temperature, the type and quantity of crystalline phases of glass ceramics samples will undergo high-temperature physical phase reconstruction. Within a certain temperature range, the increase of sintering temperature can promote the growth of crystals in glass ceramics and the intensity of the diffraction peaks of crystalline phases. However, there exists a moderate temperature, above which the transformation of the crystalline phase shows different behavior, that is, low Mk favors the growth of diopside in glass ceramics, while high Mk promotes the formation of anorthite. When the Mk and the sintering temperature are both low, the glass ceramics samples are not completely sintered. This conditions for crystal growth and exclusion of pores are not sufficient. When the Mk and the sintering temperature increase simultaneously, the liquid phase appears in the matrix, which benefits the growth procedure of crystals to form a fixed crystal skeleton. When the sintering temperature is too high or the Mk is too high, the glass matrix begins to melt, and the phenomenon of overcooking occurs, which leads to an increase in the glassy phase and the expansion of pores, resulting in a strong and solid crystal skeleton. The expansion of pores makes the disjointed circular pores in the glass ceramics samples gradually increase. At Mk =1.5 and sintering temperature of 1 190 ℃, the produced material shows a water absorption rate of 0.07%, bulk density of 3.05 g/cm3, acid resistance of 96.6%, flexural strength of 144 MPa, which fully meet the requirements of industrial glass ceramics panels.
Metal-organic frameworks (MOFs) exhibit excellent tunability in structure, primarily due to the mutual substitution and doping of central ions and organic ligands. Changes in central ions and organic ligands could impact their glass-forming stability, pore size, catalytic ability, and other physicochemical properties. For example, the MIL-100 metal-organic framework materials, centered around chromium ions, exhibits high stability and catalytic activity in oxidation reactions. However, replacing chromium ions with aluminum ions will lead to decreased stability and catalytic activity in oxidation reactions. Therefore, exploring the mutual combinations of different metal ions and organic ligands is crucial for developing new MOFs. Fe-MOF, characterized by highly controllable pore structure, excellent catalytic performance, and magnetism, is widely applied in the fields of gas adsorption and separation, catalysis, drug delivery, and environmental protection. However, the activity of Fe ions induces a low thermal stability, which consequently leads to the decomposition of most Fe-MOF crystals prior to melting. This impedes the glass transition process through melt-quenching. In this study, a solvent-free method was utilized to prepare a Fe-MOF crystal, which was subsequently transformed into glass state via melt-quenching. The morphological and structural evolution of this Fe-MOF during heating, as well as the mechanism underlying its glass transition, were thoroughly investigated.
In a meticulously controlled environment within a glove box featuring extremely low levels of oxygen and water content (oxygen content ≤0.282 mg·m-3, water content ≤0.3 mg·L-1), the mass of 1.86 g ferrocene and 1.362 g imidazole were weighed, blended together within a polytetrafluoroethylene container and sealed within a sturdy steel outer casing. Subsequently, the reaction vessel was transferred to a high-temperature blast drying oven, following by a controlled reaction process at 150 ℃ for 96 h. After the reaction, the product was washed with dimethylformamide (DMF) until the washing out solution turned transparent. Ultimately the sample was dried within a vacuum drying oven operating at a pressure of -0.1 MPa and a temperature of 80 ℃ for 12 h, permitting the acquisition of the FCIR crystals. To further manipulate the FCIR material into a glassy state, a melt-quenching technique was employed. Approximately 15 mg FCIR crystal were transferred into a specialized platinum crucible, which was then positioned within the Differential Scanning Calorimeter (DSC). The sample undergoes a controlled heating process at 10 ℃·min-1 until 500 ℃ under an argon atmosphere flowing at 40 mL·min-1. Subsequently, the sample cooled to room temperature at 20 ℃·min-1.
The thermodynamic behavior characterizations of all the samples were conducted using a Netzsch STA449 F1 instrument. Room temperature powder XRD data (2θ=5° to 50°) were collected with a Bruker D8 Advance diffractometer using Cu Kα (λ=1.540 6 Å) radiation. The surface appearance were acquired by Olympus CX33 optical microscope and Zeiss sigma 500 field emission scanning electron microscope (3 kV). The structural changes were characterized through FT-IR and FT-Raman, which obtained by Bruker INVENIO-S Fourier infrared transform spectrometer with a spectral resolution of 4 cm-1 and Thermo Fisher DXR 2xi spectrometer with a laser of 1 064 rm, respectively.
FCIR go through three processes during the formation of glass: (ⅰ) the terminal imidazole molecules connected to Fe(II) release at 210-301 ℃ with a weight loss of 19.4%, corresponding to the first peak of DSC curve; (ⅱ) the crystal melting at 398-426 ℃ according to the second peak of DSC curve; (ⅲ) the liquid continues to be heated to 500 ℃ and then cooled to room temperature to form glass, which is certified by the absence of the Bragg in the XRD patterns and Tg appeared in the DSC curve. Remarkably, the loss of mass rapidly occurres at 535-575 ℃, which is relative to the thermal decomposition. In addition, the optical and SEM images of FCIR show morphological changes. The release of imidazole disrupts the surface structure of the crystal, leading to the formation of numerous micropores and irregular cracks. The molten sample exhibits a round periphery and the surface shows deformations and wrinkles, indicating that the molten state of FCIR possesses a very high viscosity. By combining FT-IR and FT-Raman spectroscopy, it can be demonstrated that during the process of heating at 210-301 ℃, the terminal imidazole in the Fe-IM6 octahedra disappeared. These findings provide insights into the structural evolution and thermal properties of FCIR at different temperatures, offering important clues for further research on the properties and applications of this material.
A Fe-MOF crystal (FCIR) was obtained using a solvent-free method and vitrified through melt-quenching. The release of terminal imidazole led to the transformation of the Fe-IM6 octahedral into Fe-IM4 tetrahedra, which were convinced by FT-IR and FT-Raman spectra. Subsequently, the crystal underwent melting, resulting in a disordered structure at high temperatures, which was retained through rapid cooling to room temperature.
Inorganic perovskite nanocrystals exhibit superior thermal stability and higher quantum yields compared to organic-inorganic hybrid perovskites. Additionally, perovskite nanocrystals have gained significant attention in fields such as solar cells, low-threshold lasers, light-emitting diodes (LEDs), and photodetectors, owing to their excellent tunable luminescent and optoelectronic properties.
As a kind of nanocrystal with excellent photoelectric properties, CsPbX3 can achieve tunable emission in the whole visible spectral region by means of compositional alloying and quantum size effect. However, all-inorganic CsPbX3 perovskite nanocrystal still faces challenges in terms of poor stability and the toxicity of lead, which limits its application. Various strategies have been proposed to improve its resistance against environmental erosion, including surface modification, polymer encapsulation, and in-situ crystallization within inert glass matrices. Among them, embedding nanocrystals into inert glass matrices has been proposed to enhance their stability and demonstrate excellent heat resistance and resistance to intense light irradiation. However, traditional oxide glass is prepared under high-temperature open environments, leading to the volatilization of some glass components and the decomposition of perovskite nanocrystals. It results in unclear composition of the prepared glass and poor sample reproducibility. On the other hand, in response to the environmental toxicity of lead-based perovskites, non-toxic metals such as Sn, Bi, and Ge were employed for the substitution for Pb. Tin-based perovskites, in particular, have similar crystal and electronic structures to lead-based perovskites and exhibit fascinating near-infrared luminescence. By controlling the composition and quantum size, the emission spectra of CsSnX3 perovskites can be tuned from visible light to approximately 1 μm in the near-infrared spectral region, which can not be achieved in lead-based perovskite materials. However, due to the high sensitivity and easy oxidation of metastable Sn2+, the synthesis of CsSnX3 perovskite usually requires more stringent conditions, making the preparation procedure more difficult.
Chalcogenide glassy flux method is introduced by using chalcogenide-based materials with good glass-forming ability, such as GeS2 and Sb2S3, as fluxes. Metal halides like CsX, SnX2, or PbX2 are dissolved in such chalcogenide fluxes, and the resulting mixture is melted and rapidly cooled to form glass. Subsequent heat treatment is applied to achieve controllable precipitation of the dissolved metal halides. This method allows for the formation of perovskite nanocrystals with arbitrary halide compositions within the transparent glass matrix, and meanwhile prevents the loss of metal halide precursors, therefore improving the reproducibility. The controllable crystallization mechanism of chalcogenide glass-ceramics with the composition of 79.2GeS2-15.8Sb2S3-5CsSnBr3 was investigated. The base samples were subjected to thermal treatments at 290 ℃ for 13, 20, 60 h, and 100 h. The variation of particle size and quantity of precipitated CsSnBr3 nanocrystals was observed by SEM and plotted as a function of the heat-treatment conditions. It was found that it exhibited power-law variations with time, following the Lifshitz-Slyozov-Wagner (LSW) theory. The phenomenon of increasing crystal size and decreasing crystal quantity during the heat treatment process was explained using Ostwald ripening theory. As the heat treatment progresses, the continuous growth of larger crystals consumes at the expense of smaller crystals. Eventually, when all crystal sizes became similar, this dissolution-growth behavior reach equilibrium.
Inorganic perovskite nanocrystals have attracted significant attention due to their tunable emission wavelength and excellent optoelectronic properties. By utilizing glass flux method, controlled precipitation of perovskite nanocrystals such as CsPbX3 and CsSnX3 has been successfully achieved in sulfur-based glass. Tunable photoluminescence ranging from visible to near-infrared has been realized. The crystallization behavior of these perovskite nanocrystals in sulfur-based glass was revealed to follow the Ostwald ripening mechanism, allowing for controllability of nanocrystal size, crystal phase, and crystallinity. However, further research is required to investigate the characteristics of perovskite nanocrystals in sulfur-based glass, e.g., the relationship between their size, luminescence intensity, composition variations, and luminescence efficiency. Additionally, as a semiconductor material, sulfur-based glass holds potential application in electroluminescence compared to other substrate materials.
Alumina ceramic continuous fiber is one of the most important materials because of its high strength and modulus, high temperature resistance, chemical inertness in both oxidizing and reducing atmospheres even at high temperature, resistance to attack from non-oxide materials, good electrical insulation and low thermal conductivity. The high strength and high-temperature resistance have allowed the development of metal and ceramic matrix composites with high tensile strength or high-temperature load-bearing capability. Thus, alumina ceramic continuous fiber is of great importance in aerospace, advanced manufacturing, and other fields.
The Al2O3 content in alumina ceramic fiber is usually more than 70% (mass fraction), and generally contains a small amount of other oxides, such as SiO2, B2O3, Fe2O3, ZrO2, and etc. Amorphous SiO2, transition phase alumina, α-Al2O3 and mullite are the common phases in alumina ceramic fibers, resulting in various phase compositions and microstructures. Chemical composition and the microstructure have great effects on the fibers' mechanical performance and temperature resistance. Depending on the chemical composition and the microstructure, the alumina ceramic fibers show the tensile strength from 1.5 GPa to 3.1 GPa, and a long-term using temperature varied from 1 000 ℃ to 1 300 ℃. The careful selection is necessary according to the unique circumstances and conditions involved in the use and processing of the alumina fibers. Furthermore, the preparation of alumina ceramic fibers with controlled composition and microstructure is critical.
Main methods for manufacturing alumina ceramic fibers can be classified as slurry process, melt-spinning process, prepolymerization process and sol-gel spinning process. The melt spinning method was limited in the length of the fibers, thus, it was not suitable for the preparation of the alumina continuous fibers. While it is difficult to prepare alumina fibers with high strength from the slurry method. Excellent alumina continuous fibers can be obtained through the pre-polymerization process and sol-gel spinning process, in which the sol-gel method shows the advantages of adjustable composition, uniform composition at the atomic level, relative moderate preparation conditions and low cost, becoming the most important preparation method for alumina ceramic continuous fibers.
In the past decades, a family of alumina fibers have been developed, typically as the commercial 3M NextelTM alumina ceramic fibers, which have been used in a variety of areas. However, its export to China is restricted by developed countries because of the application in military field, such as aerospace. To develop the local production, many researchers of China have devoted to the preparation of alumina continuous ceramic fibers, mainly by new sol, that is, how to transform from the gel fiber to ceramic fiber. Fortunately, significant progress has been made recently, so that commercialization of the ceramic fiber comes to be true. This further promotes the applications of alumina ceramic fibers. However, there is still a certain gap in performance between the local produced fibers and the fibers abroad. Continued technological innovation is still an important task in the future.
At present, the development of alumina based ceramic continuous fiber in China is mainly carried out under the national academic financial support. The main work at current stage mainly focuses on how to produce the fibers which could meet the basic properties. Most research and development usually rely on model products. Few attention is paid to the research on relevant scientific mechanism and theory, resulting in lack of theoretical support for new applications and in lack of independent innovation ability. Since most of the applications of alumina continuous fiber are based on its performance of high temperature resistance and high strength, it can be predicted that improving the tensile strength and thermal resistance of alumina continuous fiber is still the main goal in the future. Therefore, it is believed as important work to carry out key basic theoretical research, to clarify the intrinsic relationship between the composition-structure-processing-performance of alumina ceramic fibers, and to establish a theoretical model of high-performance alumina ceramic continuous fiber. These investigations can direct the design and preparation of the fibers, to achieve breakthroughs hopefully in the strength and temperature resistance of alumina ceramic continuous fiber, and to furtherly promote the application of fiber and the composite in aerospace and the related fields.
With the continuous development of laser technology, ultra-narrow linewidth lasers show important application prospects in many fields. However, the output linewidth of conventional semiconductor laser chips is usually large, which cannot meet the practical application requirements. Therefore, it is of great significance to study the key technologies for preparing ultra-narrow linewidth lasers. As a new type of optical component, volume Bragg grating, with the advantages of tunable diffraction wavelength, stable laser wavelength, and narrow linewidth, has become an effective way to solve this problem. This work tried to prepare 1.5 μm volume Bragg grating (VBG) based on chlorine-containing PTR glass to meet the demand for ultra-narrow linewidth lasers in the fields of new generation of coherent laser communication, LIDAR, and high-precision fiber sensing.
The glass samples were prepared as long strips with a diameter of 5 mm and a length of 28 mm. The thermal expansion was recorded by warming the glass samples from room temperature to 800 ℃ at a rate of 10 ℃/min using a DIL 402PC/4 high-temperature thermal expansion meter from NETZSCH, Germany. The samples of chlorine-containing PTR glass before and after exposure were also tested by differential thermal analysis using a Q600SDT integrated thermal analyser from TA Instruments, USA. This is an important parameter to understand the dimensional stability of the glass during temperature change. A D2 PHASER type X-ray diffractometer from Bruker, Germany was used to analyze the changes in crystal structure of chlorine containing PTR glass before and after exposure, nucleation and precipitation heat treatment to understand the structural evolution and property changes of the material.
A Lambda 750S UV-Vis-NIR spectrophotometer from Perkin Elmer, USA was used to study the optical absorption properties of chlorine-containing PTR glass before and after exposure, nucleation and decrystallisation heat treatments, and to understand its absorption capacity at different wavelengths.
The glass powder was mixed with high purity KBr and pressed into tablets, and then scanned by infrared spectroscopy with a scanning speed of 0.158 cm/s. A Nicolet iS50 Fourier infrared spectrometer from Thermo Fisher Scientific, USA was used. The samples were then analyzed for their infrared transmittance properties. The infrared transmission properties of the samples were analyzed to understand the transmission properties of the materials in the infrared band. An in Via-Peflex type Raman spectrometer from Renishaw, UK was used. The molecular vibration and vibrational information of the samples were further analyzed through Raman spectroscopy to further understand the structure and properties of the materials.
Firstly, the thermal properties of the new PTR glass were investigated. Its transition temperature (Tg) and softening temperature (Tf) were 446.2 ℃ and 499.4 ℃, respectively. These two parameters are important for glass processing and applications. The coefficient of thermal expansion was similar to that of bromine-containing PTR glass in the temperature range of 30-400 ℃, indicating that the substitution of Br- by Cl- has a small effect on the thermal expansion properties of PTR glass. Secondly, it was found that NaF nanocrystals were successfully precipitated from chlorine-containing PTR glass after the precipitation heat treatment by XRD (X-ray diffraction) and TEM (transmission electron microscopy) inspection. These nanocrystals were distributed as dark grey elliptical particles with a particle size of 5 nm in the glass. high-resolution transmission electron microscopy (HRTEM) further revealed the lattice structure of these nanocrystals, and the spacing of adjacent crystal planes corresponded to the (111) crystal planes of NaF crystals. In addition, the detection of absorption spectra of chlorine-containing PTR glasses showed a new broad and weak absorption peak at 413 nm, which was attributed to the absorption of plasma AgCl.
Compared with the plasma AgBr absorption peak precipitated in the conventional PTR glass, the plasma AgCl absorption peak of the chlorine-containing PTR glass blueshifted in the UV sepctrum, which supplied the possibility of developing short-wavelength VBG products. In terms of glass structure, Raman and Fourier infrared spectroscopy analyses showed that the structure of chlorine-containing PTR glasses did not change significantly after the precipitation heat treatment. Finally, the article explores the performance of chlorine-containing PTR glasses for VBG applications. The diffraction efficiency of VBG was found to be positively correlated with the refractive index modulation and grating thickness. Under the same conditions of exposure dose and heat treatment process, increasing the thickness of VBG can significantly improve its diffraction efficiency. The experimental results show that the centre wavelengths of VBGs with thicknesses of 10 mm and 16 mm are 1 549.44 nm and 1 549.48 nm, respectively, and the half-height full widths are 0.0611 nm and 0.0570 nm, respectively.
Novel chlorine-containing PTR glass components were designed and prepared using a two-step melting process to produce photothermally sensitive refractive glasses with a homogeneity of 10-6.325 nm UV irradiation led to a decrease in the transition temperature and the onset of precipitation of the PTR glass, and an increase in the precipitation properties, which is very favourable for the preparation of high-quality VBGs. XRD and TEM results confirmed that NaF nanocrystals of an average size of 5 nm were precipitated from the chlorine-containing PTR glass. NaF nanocrystals with an average particle size of 5 nm. Raman and FTIR spectra showed that holographic exposure and heat treatment further enhanced the glass network structure. A reflective volume Bragg grating with a centre wavelength of 1.5 μm was prepared, with a diffraction efficiency of 50% and a half-height full width of 0.0570 nm, which sets the foundation for the development of 1.5 μm ultra-narrow linewidth semiconductor lasers.
X-ray detectors could be divided into direct and indirect types, the latter has cheaper and more stable properties. As the key component of indirect detection, scintillators could convert high-energy photons into low-energy ultraviolet or visible photons. However, the preparation process of traditional scintillation single crystals is relatively complex and costly, and the hygroscopicity of materials also puts strict requirements on their working environment and packaging technology. Moreover, the Tl and Cd are toxic and not environmentally friendly. Therefore, it is very necessary to find new scintillators with simple preparation, low-cost, chemically stable, and environmentally stable properties. The glass-ceramics combines the excellent optical properties of nanocrystals with the high stability and transparency of inorganic glass. High-quality and large-area glass-ceramics could also be easily obtained. Rare earth ions have special energy level structures and luminescence characteristics. Under optical excitation, they can absorb energy and emit light of specific wavelengths, thereby enhancing their scintillation performance and luminescence characteristics, and are resistibility to radiation damage. When the scintillation glass is irradiated by external excitation light sources, the rare earth ions absorb the energy and transfer to high energy level state, and then release energy through radiation transitions. In this paper, rare earth ions are doped into glass-ceramics to introduce efficient luminescent centers. The luminescence performance of ZnGa2O4∶Tb3+ glass-ceramics under X-ray irradiation and its indirect imaging ability are studied.
To prepare ZnGa2O4 glass-ceramics composing of 52SiO2-10Na2CO3-22ZnO-16Ga2O3-x%Tb4O7 (mole fraction), the raw materials were weighed and ground in an agate mortar for 15 min. After uniformly mixing, the powder was transferred to a 30 ml alumina crucible and melted at 1 600 ℃ for 60 min. The sample was poured onto a preheated copper plate at 350 ℃, pressed into shape, and cooling naturally to form the precursor glass. The precursor glass was treated by heating at 600 ℃ for 4 h to release internal stresses. Subsequently, the samples were heat treated at 700, 750, 800, 850, 900 ℃ for 6 h to form glass-ceramics (GC) with different degrees of crystallinity. Finally, these GC samples were polished or ground into powder for further characterization.
The phase of the samples was determined by X-ray diffraction analysis, transmission electron microscopy, and scanning electron microscopy. The photoluminescence properties were analyzed by using the excitation spectrum and photoluminescence spectrum of the Hitachi F-7000 fluorescence spectrophotometer with a 150 W Xe lamp as the excitation source. The transmission spectra were determined by using a TU1810 UV/visible spectrophotometer. A miniaturized X-ray tube with Cu-Kα (λ=0.154 05 nm) radiation source was used for X-ray imaging, maintaining a tube voltage and current of 40 kV and 30 mA, respectively, with a Nikon D500 camera for imaging capture. The radiation luminescence spectra of the samples under X-ray irradiation were measured using a fluorescence spectrophotometer (Ocean Optics, QE Pro).
For the precursor glass treated at the temperature ranging from 700 ℃ to 800 ℃, the samples exhibit a transmittance of over 80% in the wavelength range of 400 nm to 800 nm. However, when the heating temperature exceeds 850 ℃, the transmittance of the samples gradually decreases attributing to the increase of the size of ZnGa2O4 nanocrystals precipitated within the glass matrix, resulting in an increase in Rayleigh scattering and the decrease in transparency. Under different doping concentrations of rare earth ion, there is no impurity observed in the XRD diffraction patterns. Additionally, the samples maintain a transmittance of over 80% under different concentrations of Tb3+ doping. Based on the intensity of photoluminescence spectra, the optimal Tb3+ doping concentration is determined to be 1.5%.
The ZnGa2O4∶1.5%Tb3+ glass-ceramics exhibits a high absorption coefficient in the range of 0 to 50 keV, with a radiation luminescence yield of 13 000 photons/MeV, which is superior to that of commercial BGO in both absorption coefficient and radiation luminescence yield. Additionally, it exhibits a linear response relationship with X-ray dose rates and demonstrates long-term stability under X-ray irradiation. Indirect X-ray imaging by using this material could clearly visualize the internal structure of printed circuit boards with an imaging resolution of 16 lp/mm. Furthermore, the ZnGa2O4∶1.5%Tb3+ glass-ceramics could restore its radiation luminescence performance to its initial state via thermal treatment.
ZnGa2O4∶1.5%Tb3+ glass-ceramics exhibits characteristic emissions of Tb3+ under both UV and X-ray irradiation, with a high transmittance of over 80%, which is beneficial for achieving high-resolution X-ray imaging (16 lp/mm). Additionally, under high-energy radiation exposure for a long duration (1 000 h), the RL intensity of ZnGa2O4∶1.5%Tb3+ glass-ceramics only decreases by 20%, and the radiation damage caused by high-dose X-ray can be restored through simple low-temperature thermal treatment, which reduce the cost of scintillators and meet the long-term lifetime. This study demonstrates that ZnGa2O4∶1.5%Tb3+ could provide high-quality, efficient, and precise imaging results, and making it promising for applications in medical imaging and non-destructive testing.
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