Borate nonlinear optical crystals occupy a prominent position in nonlinear optical crystal material science and have been studied very thoroughly… Now we will briefly review the research process of BiB3O6 (BIBO) crystal in order to deepen our understanding of this crystal. As early as 1962, Levin, McDaniel and others first discovered the BiB306 compound during the study of the Bi203-B203 binary phase diagram.
In 1982, Liebertz grew the first single crystal. In 1984, Fuchlich et al. determined the BIBO crystal structure. In 1999, Becker et al. first used the top-seeded growth method to grow a BIBO single crystal with an optical grade size of 20 mm × 20 mm × 30 mm from a stoichiometric melt. Subsequently, Hellwig et al. The linear and nonlinear optical properties of BIBO crystal were measured, and it was found that the effective frequency multiplication coefficient (deff) of BIBO crystal was larger than that of KTP, BBO, LBO and LiIO crystals that have been widely used, and it was theoretically derived It was concluded that the laser damage threshold of BIBO crystals is comparable to that of high optical deuterated tetrahydrofuran quality LBO crystals. Since then, BIBO crystal has received great attention internationally. In 2000, xue Donng et al. used the perspective of chemical bonds to study the second-order nonlinear optical behavior of BIBO crystals, and explained the structural origin of the large nonlinear optical effects of BIBO crystals. Since the second half of 1999, the State Key Laboratory of Crystal Materials of Shandong University has conducted more systematic research on the growth of BIBO crystals and their nonlinear optical properties. It has published a series of papers in domestic and foreign scientific journals, and in 2004, Teng Bing et al. Using the [101] orientation seed crystal, a complete BIBO single crystal with a size of 30mm × 30mm × 40mm and a weight of 1209 was successfully grown. In the same year, Wang Zhengping et al. reported for the first time that the noncollinear second-harmonic generation emciency of BIB0 crystal was as high as 49.2%, which attracted international attention. As an excellent nonlinear optical material, BIBO crystal is still in the early research stage. Now we only give a brief review on the research status of BIBO crystal growth, structure and properties.
A review of bismuth triborate (BiB3 06) crystal research and BIBO crystal growth
Crystal growth is a phase change process, which is the result of the interaction of various complex physical phenomena. Affected by the interaction of various factors such as crystal growth thermodynamics and kinetics, and people’s lack of full understanding of the structural details of melts or solutions, it is still difficult to provide a perfect theoretical basis for the actual crystal growth process. The purpose of artificially growing single crystals is to obtain high-quality large-sized crystals, and the quality of crystals is a comprehensive reflection of the interaction of multiple growth parameters. BIBO crystals are grown from stoichiometric melts and have significant growth characteristics.
A review of bismuth triborate (BiB3 06) crystal research and BIBO crystal growth characteristics
BIB0 crystal can be said to be a “difficult to grow” crystal type. Its remarkable growth characteristics are: The viscosity of the BIB0 melt is very high, which limits the mass transport during the crystal growth process and hinders the spontaneous formation of crystal nuclei. BIBO crystals are polar crystals with prominent polar growth habits. The growth rates at both ends of the polar axis are very different. It is difficult for the crystal to develop in a near-balanced form, making it easy to form crystal defects. Crystal raw materials Bi: 0, and B: O. The density (|p) of the two is very different (Bi2O3: p=9.3∥cm3; B203: p=2.469/cm3), which makes it difficult to form a uniform melt and is detrimental to the formation of crystal growth cells.
From the Bi:O, -B:0 in Figure 1, the relationship between the binary phase diagram components and temperature can be seen, BiB, 0. The melting point of solid fluoroboric acid-liquid is 726℃, and the existing composition range is 72.5~77.5n101%B203; the melting point of Bi2880.5 is 715℃, and the existing composition range is 72.5-80.7 mol %B203, the difference between the two is very small, so in BiB, 0. During the crystal growth process, Bi:B tends to appear. O. , miscellaneous crystals, thereby destroying BiB3O6. Normal growth of crystals. Practice has proven that based on the above-mentioned BIBO crystal growth characteristics, accurately designing crystal growth equipment and formulating strict crystal growth process technology, it is possible to grow BIBO single crystals with larger optical grade sizes.
A review of bismuth triborate (BiB3 06) crystal research BIBO crystal growth equipment
Based on the growth characteristics of BIBo crystals and the physical and chemical properties of the melt, people often use the top seeding method to grow BIBO single crystals. The schematic diagram of the designed crystal growth furnace is shown in Figure 2. Both the axial and longitudinal directions in the furnace are required to have uniform temperature gradients. The main heating components of the tubular furnace are wound with high-resistance wires. The temperature distribution of the three temperature zones (1, 2, 3) are controlled individually so that The desired temperature profile is established in the furnace body. Within the entire axial distance of the furnace body, the thermal uniformity ΔD = 2°C. In order to better control the crystal growth process, a crucible (Au, or Pt) balancing device is set up. . In order to avoid concentration gradients at the crystal growth interface, an accelerated seed crystal rotation device was introduced. The seed crystal at the top of the pulling rod is cooled by air to control the local subcooling of the melt. Use high-resolution transfer components to achieve pull rates below 0.75 min/d.
A review of bismuth triborate (BiB3 06) crystal research and Bmo crystal growth process technology
Synthesis of melt according to stoichiometric ratioWeigh high-purity Bi2O3 and B2O3 at a ratio of 1:3. The raw material (Bi2O3, slightly excessive), after being fully ground and uniform, is placed in a crucible (Au or Pt) for preheating. The preheating temperature is about 600°C, and the solid phase reaction is carried out for 24 hours, and then it is melted. The melting temperature is Around 850℃, then cooled to 600℃ at a rate of 3℃/h, and then used the temperature range of 600 to 500℃ for temperature oscillation to achieve solid glass body recrystallization. Use a differential thermal analyzer (DTA) to analyze the obtained glass powder sample to observe the uniformity of the recrystallized glass. Heat the raw material for glass body recrystallization to about 850°C and keep it for 24 hours to obtain uniform and transparent BiB3O6. Melt.
A review of bismuth triborate (BiB3 06) crystal research and the properties of BIBO crystals
As an excellent nonlinear optical crystal material, not only its nonlinear optical properties, but also its physical and chemical properties and corresponding linear optical properties must be considered, and finally its application value can be comprehensively analyzed.
Physical and chemical properties of crystals
The density of BIBO crystal: 5.0339/cm3, the hardness of the crystal: 5~5.5Mohs, the crystal is not sensitive to moisture and is stable in the air. In this way, the crystal will undergo thermal expansion and contraction. This strongly anisotropic thermal expansion will have an adverse effect on crystal growth.
Linear optical properties of crystals
The relationship between the crystal optical axes a, b, c and the crystal physical axes x, y, z: 6//X, (a, Z)=31.6°, (c, X)=47.2° The crystal is an optical biaxial crystal with a light transmission band of 270-2600nm. Refractive index is an extremely important optical parameter. The refractive index (ni) of the crystal was measured with a goniometer spectmmeter system. The results are as follows:
Three main axis refractive index (λ=1079.5nm): nx=1.9166, ny=1.7567, nz=1.7855.
Conclusions on the review of bismuth triborate (BiB3 06) crystal research
Through the above review of BIBO crystal growth, structure number, etc., the following three conclusions can be roughly drawn:
(1) BIBO crystal has stable physical and chemical properties, moderate light transmission band, large effective nonlinear optical coefficient, very high frequency doubling conversion efficiency, and large laser damage threshold. It is promising as a practical crystal for new high-efficiency laser frequency conversion. Material;
(2) BIBO crystals are polar crystals with significant polar growth habits and are difficult to develop in a nearly balanced form. The viscosity of BIBO melt is very high, which is not conducive to mass transport during crystal growth. Bi:O. With B:O. The density of the two is very different, which hinders the formation of BIB0 crystal growth elements. For these reasons, BIBO crystals are a relatively “difficult to grow” crystal type;
(3) Compared with KTP, BBO, LBO and other crystals that have been widely used, BIBO crystals can be said to be still in the early research stage regardless of the depth or breadth of research. Especially in terms of crystal growth, there are indeed some related And interesting research topic. For example: the polar growth form and growth mechanism of BIBO crystals; the basis for crystal coloration (brown) and its formation mechanism; how high-viscosity glass melts gradually transform from short-range ordering to long-range ordering crystals; whether high-viscosity glass can be mixed with Using highly dissociable ionic compounds as fluxes reduces the viscosity, which not only speeds up the crystal growth rate, but also enables the growth of high-quality, larger-sized BIB0 crystals. In order to make BIBO crystals widely used, further and more in-depth research is needed.
