Borate has a rich chemical structure. B atoms can adopt two coordination modes, BO3 and BO4, and further polymerize into one-dimensional chains, two-dimensional layers and three-dimensional networks, making borate rich in crystals. structure. Therefore, borate is the preferred system for designing and synthesizing new optical crystal materials. Based on the anion group theory, the BO3 plane unit has a π-conjugated orbit with an asymmetric electron cloud distribution and a large microscopic polarizability. The parallel arrangement of the BO3 plane unit is conducive to achieving good frequency doubling effect and birefringence of the material. Properties, these two parameters directly determine the laser conversion efficiency and frequency doubling application band range of the material.
The research team of new optoelectronic functional materials of Xinjiang Institute of Physics and Chemistry Technology, Chinese Academy of Sciences conducted systematic exploration and research on the design and synthesis of new ultraviolet optical crystal materials. Through a large number of experiments, they synthesized the borate Li6Zn3 (BO3) with novel structural characteristics. 4. The crystal is crystallized in the triclinic system P-1 space group, and the structure contains nearly planarly arranged isolated BO3 groups, giving it a relatively large birefringence (0.065@1064 nm). Coplanarly connected LiO4 tetrahedra are reported for the first time in this structure. The researchers comprehensively and systematically summarized nearly 100 lithium-containing borate compounds, analyzed the Li-O polyhedral characteristics of the crystal structure, and summarized the types of Li-O coordination anionic groups and the coordination modes between the groups. The study found that due to the large repulsion between Li-Li atoms when the LiO4 tetrahedrons are connected coplanarly, the situation of coplanarly connected LiO4 tetrahedrons is very rare. In addition, scientific researchers found through relevant performance tests that Li6Zn3(BO3)4 has two reversible phase transitions in the temperature range of 290℃-360℃ and 650℃-770℃, making it a potential phase change material.
Relevant research results were published as a cover article in Inorganic Chemistry Frontiers.
This research work was funded by the National Natural Science Foundation, the Autonomous Region International Cooperation and other projects.
[Achievements Introduction]
Pan Shilie’s team at the Xinjiang Institute of Physics and Chemistry Technology, Chinese Academy of Sciences made a breakthrough in exploring the next generation of deep ultraviolet NLO crystal materials. Through research on the relationship between material structure and properties, they established a structure database of typical nonlinear optical crystal materials, and analyzed the mutual constraints between the properties of borate crystals “deep ultraviolet transmission-large frequency doubling effect-large birefringence tetrahydrofuran radiation” For this reason, a design strategy was proposed based on the material simulation method to introduce a type of BO4-xFx (x = 1, 2, 3) functional groups into the borate framework; based on this strategy, a series of promising candidates were successfully screened. Fluorine-containing lithium borate deep ultraviolet NLO crystal represented by Li2B6O9F2. Relevant research results were published in “German Applied Chemistry” (Angew. Chem. Int. Ed. 2017, 56, 3916–3919) in the form of a Very Important Paper (VIP) article. After the article was published online, it attracted great attention from the American news weekly Chemical & Engineering News (C&EN) in a short period of time. With the title Nonlinear optical laser material avoids beryllium (“Beryllium-free nonlinear optical crystal material”), the research results were reviewed with Science Concentrates.
On the basis of this work, the researchers learned from the structural characteristics of KBBF crystal and further replaced (BeO3F)5- with (BO3F)4- to successfully design and synthesize a series of AB4O6F family (A = NH4+, K, Rb, Cs) materials. Crystal structure analysis revealed that this series of materials is composed of [B4O6F] anionic groups in a two-dimensional layered structure and cations filling the gaps. Among them, cations play an important role in regulating the symmetry and overall structure of the [B4O6F] anion group. At the same time, theoretical and experimental tests show that this type of material has a very short UV absorption edge (<190 nm, as short as 155 nm), and the powder frequency doubling effect is 0.8 to 3 times that of commercial KDP materials, and it has moderate birefringence. Able to meet deep ultraviolet phase matching (shortest matching wavelength 158nm).
At the same time, compared with KBBF, the structure of the AB4O6F family crystal is more compact, and the interlayer force is significantly enhanced, thereby weakening the layered growth habit; in addition, the raw material does not contain highly toxic beryllium elements, and the frequency doubling effect is stronger than that of KBBF , used in deep ultraviolet laser light sources to achieve higher conversion efficiency. AB4O6F family crystal materials have excellent comprehensive properties and are expected to become the next generation of deep purple sodium carbonate outer NLO crystals. Relevant research results have been published in the top journals “Journal of the American Chemical Society” and “German Applied Chemistry” (J. Am. Chem. Soc., 2017, 139, 10645; Angew. Chem. Int. Ed. 2017, 56, 14119 ; Angew. Chem. Int. Ed. 2018, DOI:10.1002/anie.201712168)
