NaSr₃Be₃B₃O₉F₄: A Promising Deep‐Ultraviolet Nonlinear Optical Material Resulting from the Cooperative Alignment of the [Be₃B₃O₁₂F]¹⁰⁻ Anionic Group

Abstract

The demand for deep-ultraviolet (deep-UV) coherent light sources (l < 200 nm) has become increasingly urgent because they have important applications in semiconductor photolithography, laser micromachining, modern scientific instruments (super-high-resolution and angle-resolved photoemission spectrometer, for example) and so forth. To date, the most effective method to generate deep-UV coherent light with solid-state lasers is through cascaded frequency conversion, in particular multiharmonics, using deep-UV nonlinear optical (NLO) crystals. Therefore, the discovery of suitable deep-UV NLO crystals is of great importance.In the past decades, the anionic group theory, [1][2][3] which reveals that the overall nonlinearity of a crystal is the geometrical superposition of the microscopic second-order susceptibility tensors of the NLO-active anionic groups, has been very successful in developing borate NLO crystals. Several important NLO crystals have been discovered, including b-BaB 2 O 4 (BBO), [4] LiB 3 O 5 (LBO), [5] CsB 3 O 5 (CBO), [6] CsLiB 6 O 10 (CLBO), [7,8] and YCa 4 O(BO 3 ) 3 (YCOB), [9] which have been widely used in NLO optics. However, they cannot be used to generate deep-UV coherent light (l < 200 nm) by multiharmonic generation owing to some inherent shortcomings. Thus, the search for new NLO materials, particularly for deep-UV applications, has attracted considerable attention. [10][11][12][13][14] A deep-UV NLO material must have a very short absorption edge, and in this respect, beryllium borates are attractive as they are supposed to possess very large energy gap.[15] It is also well known that the incorporation of fluorine can effectively cause the UV absorption edge of a crystal to blue-shift, so our group has made great efforts to search for new deep-UV NLO fluorine beryllium borate crystals. After more than ten years of intensive research in our group, the [20] Unfortunately, the KBBF crystal is very difficult to grow in thickness because of its strong layering tendency, which severely limits the coherent output power. Therefore, there is great demand for new types of fluorine beryllium borates which have deep-UV transmission, moderate birefringence, and relatively large second harmonic generation (SHG) coefficients, and at the same time overcome the crystal-growth problems found in the KBBF crystal.Alkali-metal and alkaline-earth-metal cations are favorable for the transmission of UV light because there are no d-d electron or f-f electron transitions in this spectral region. As shown in numerous explorations, the size and charge of cations have great influence on the macroscopic packing of anions, which in turn determines the overall NLO properties in a crystal. [21,22] Herein, we utilize both alkali-metal and alkaline-earth-metal cations. Different charge/size combinations of mixed cations may have different influences on the packing of anions, so it is more likely to isolate new phases with interesting stoichiometries, structures, and properties. To date, no fluorine beryllium borates with...

Analysis of Deep‐UV Nonlinear Optical Borates: Approaching the End

“…After the discovery of KBBF, over the last two or three decades, quite a few novel NLO borate crystals with the BO 3 group have been synthesized and grown, including the Sr 2 Be 2 B 2 O 7 (SBBO), [ 14 ] MM'Be 2 B 2 O 6 F (M = Na, M' = Ca; M = K, M' = Ca, Sr), [ 15 ] NaSr 3 Be 3 B 3 O 9 F 4 [ 16 ] and its isostructural K 3 B 6 O 10 Cl, [ 17 ] and NaBeB 3 O 6 (NBBO) families. [ 18 ] The fi rst two families, in which the BO 3 groups are arranged in almost the same orientation so they can be considered as variants of KBBF, were developed by molecular engineering design, while in the last two families the arrangements are different.…”

“…[ 15 ] The birefringence of this crystal is predicted to be 0.055 by fi rst-principles calculations, so the shortest SHG phase-matching wavelength is above 200 nm. The arrangements of (BO 3 ) 3− groups in NaSr 3 Be 3 B 3 O 9 F 4 [ 16 ] and KB 6 O 9 Cl crystals [ 17 ] are somewhat out of the planar layout and therefore are classifi ed as a collateral branch of KBBF. They have quite the same geometry in crystal structure in that both belong to the R3m space group and have similar triple six-membered rings as fundamental building clocks, (Be 3 B 3 O 12 F) 10− for the former and (B 6 O 13 ) 8− for the latter.…”

Cs2B4SiO9: A Deep‐Ultraviolet Nonlinear Optical Crystal

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The generation of deep-ultraviolet (UV) coherent light from nonlinear optical (NLO) materials [1][2][3][4] as one of the most promising resource, has become a topic of intensive study because of its important applications in a broad range of fields, such as semiconductor photolithography, laser micromachining, photochemical synthesis, and material processing. They are able to shorten the wavelength of light by a factor of two (or doubling the frequency), based on the process of second-harmonic generation (SHG), which occurs only when a centrosymmetric symmetry operation is absent in a crystal.

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“…However, for a noncentrosymmetric (NCS) crystal to be used as a nonlinear optical material the essential crystal property requirements are that the crystals possess a large NLO response, wide transparent window, suitable birefringence for phase-matching, good mechanical strength, and chemical stability. [4,5] After continuous efforts over several decades, many NCS compounds were obtained by incorporating functional borate structure units, such as B 3 O 6 and B 3 O 7 . b-BaB 2 O 4 (BBO) [6] and LiB 3 O 5 (LBO) [7] are the most advanced NLO materials, which have widely been used as optoelectronic devices.…”

Borate-Based Ultraviolet and Deep-Ultraviolet Nonlinear Optical Crystals

“…By sharing the fluorine ions, three (BeO3F) 5− tetrahedra constituted a (Be3O12F) 19− cluster ( Figure 9, ref [41]). The oxygen atoms of (Be3O12F) 19− cluster are connected by three (BO3) 3− groups, forming (Be3B3O12F) 10− building block.…”