Targeting the Next Generation of Deep-Ultraviolet Nonlinear Optical Materials: Expanding from Borates to Borate Fluorides to Fluorooxoborates

Abstract

Coherent light radiation down to the deepultraviolet spectral range (λ < 200 nm) produced by common laser sources is extensively used in diverse fields ranging from ultrahighresolution photolithography to photochemical synthesis to highprecision microprocessing. Actually, it is hard to immediately obtain certain wavelengths, deep-ultraviolet coherent light in particular, from commercial laser sources. However, the direct second harmonic generation process governed in part by nonlinear optical crystals is a feasible and effective approach to generate deep-ultraviolet coherent light, which motivates chemists and materials scientists to find potential deep-ultraviolet nonlinear optical materials that can practically meet the scientific requirements. The research progress required to go from a new singlecrystal structure to final device applications involves many pivotal steps and is highly time-consuming and challenging, and therefore, it is necessary to commence systematic studies aimed at shortening the research cycle and accelerating the rational design of deep-ultraviolet nonlinear optical materials. In this Account, we choose borates as raw materials because they have ever-greater possibilities to form desired noncentrosymmetric structures, wide optical transparency windows, rich structural chemistry, and also large polarizabilities to guarantee the coexistence of large second-order nonlinear optical coefficients and suitable birefringence. Besides, the effects of fluorine atoms on the structural chemistry and optical properties of borates have been summarized and analyzed. On the basis of these favorable influences, three specific rational design strategies, including experimental and theoretical methods, have been proposed in order to shorten the investigational cycle of discovering the new expected compounds with high physicochemical performances required for practical applications. In this way, the progress of searching for candidates for the next generation of deep-ultraviolet nonlinear optical materials was accelerated from borates to borate fluorides to fluorooxoborates with three effective strategies: (1) expansion of the frontier from borates to borate fluorides with the introduction of fluorine to achieve enhanced optical performance; (2) computer-assisted design of new deep-ultraviolet nonlinear optical materials with a newly introduced systematic global structure optimization method; and (3) expansion of the frontier from borate fluorides to fluorooxoborates by proposed functionalized oxyfluoride [BO x F 4−x ] (x+1)− (x = 1, 2, 3) chromophores to balance multiple criteria. The preliminary development of fluorooxoborates exhibiting high performance as a new fertile field to search for deepultraviolet nonlinear optical materials is highly encouraging and inspiring and can guide chemists and materials scientists with new directions and thoughts aimed at finding the next generation of practical deep-ultraviolet nonlinear optical materials.

Quantitative Polarization‐Resolved Second‐Harmonic‐Generation Microscopy of Glycine Microneedles

“…The efficiency of this conversion is governed by the second-order susceptibility tensor χ (2) . While inorganic materials are generally used for NLO applications [1] organic materials have advantageous properties such as large molecular polarizability and the ability to tune their properties by chemical modification to create biocompatible photonic devices. [2] For example, the π-conjugated electronic structure formed by stacked organic zwitterions allows the entire stack length to be perturbed by an external electric field leading to increased NLO activity.…”

CsAlB3O6F: a beryllium-free deep-ultraviolet nonlinear optical material with enhanced thermal stability

“…12,13 Thereaer, numerous uorooxoborates and uorophosphates with an unprecedented crystal structure and high performance as potential DUV NLO materials have been reported. [14][15][16][17] Nevertheless, because these materials are relatively unstable at high temperature in air, one need to develop a suitable crystal growth method under sealed conditions and/or search for a suitable ux (solvent) system at relatively low temperature. 14,16 Alternatively, it is possible to achieve a beryllium-free, higher stability DUV NLO crystal by combining other anionic groups, such as [AlO 4 ], [PO 4 ], [SiO 4 ], and [ZnO 4 ].…”

“…[14][15][16][17] Nevertheless, because these materials are relatively unstable at high temperature in air, one need to develop a suitable crystal growth method under sealed conditions and/or search for a suitable ux (solvent) system at relatively low temperature. 14,16 Alternatively, it is possible to achieve a beryllium-free, higher stability DUV NLO crystal by combining other anionic groups, such as [AlO 4 ], [PO 4 ], [SiO 4 ], and [ZnO 4 ]. [18][19][20][21] Enlightened by the successful synthesis of NLO-active uorooxoborates and uorophosphates, we proposed that aluminum borate uorides with [AlO m F n ] (m + n ¼ 4, 5, 6, AlOF for short) units might be another choice for exploring new NLO materials.…”

Research and Development of Zincoborates: Crystal Growth, Structural Chemistry and Physicochemical Properties

“…Over the past decades, borates have attracted burgeoning attention owning to their excellent properties and wide applications such as non-linear optical (NLO) materials, birefringent materials, electrode materials, etc [1,2,3,4,5,6,7]. The attractive properties of borates mainly depend on their structural diversity, as the boron atoms can be three- or four-coordinated with oxygen atoms to construct the planar triangular [BO 3 ] 3− groups or tetrahedral [BO 4 ] 5− groups, respectively, which could further link together via corner- or edge-sharing to form different types of fundamental building blocks (FBBs) [8,9,10,11]. For example, the FBBs of classical KBe 2 BO 3 F 2 (KBBF) [12,13] and Sr 2 Be 2 B 2 O 7 (SBBO) [14,15] are [BO 3 ] 3− triangles, while the commercial NLO crystals β -BaB 2 O 4 ( β -BBO) [16] and LiB 3 O 5 (LBO) [17] are composed of [B 3 O 6 ] 3− and [B 3 O 7 ] 5− groups, respectively.…”