Cs₂B₄SiO₉: A Deep‐Ultraviolet Nonlinear Optical Crystal

Abstract

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. 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. However, to date, KBe 2 BO 3 F 2 (KBBF) [8,9] is the only material that can generate coherent light wavelengths below 200 nm by direct SHG, which makes KBBF a research hotspot. Unfortunately, the KBBF crystal is very difficult to grow in thickness owing to the growth habit of the layer, which severely limits the coherent light output power. Thus, finding the optimal composition that is facile to synthesize, yields large single crystals, and simultaneously satisfies the NLO requirements has attracted considerable attention. [10,11] The presence of large NLO coefficients in a structure is usually in contradiction with wide band gaps in one compound. For instance, the structural units in the known compounds are second-order Jahn-Teller (SOJT) polar dis- [17] which combine with diverse other functional building units to produce materials with large NLO coefficients, for example, Cd 4 BiO-(BO 3 ) 3 (6 KDP), [18] Pb 2 B 5 O 9 I (13.5 KDP), [19] and Ba 23 Ga 8 Sb 2 S 38 (22 AgGaS 2 ).[20] However, the structural units produce an unwanted effect-the UV absorption edge shifts toward the red region, making them less suitable for the deep-UV applications. It is necessary to create the subtle balance of above-mentioned conflicting factors so as to search for the new deep-UV NLO crystals with excellent comprehensive performances.To circumvent the wide absorption window requirement, basic structural units having excitation energies near the UV region are necessary. Such units are BO 3 , BO 4 , SiO 4 , and PO 4 . [6,7,21] A compound Rb 2 Be 2 Si 2 O 7 [22] was ever expected to be a substitution for KBBF owing to its similar structure characteristics with KBBF and without the layer habit. But, the weak SHG response of Rb 2 Be 2 Si 2 O 7 makes the substitution end in naught. However, the borosilicate may be a potential candidate for a deep-...

Borates—Crystal Structures of Prospective Nonlinear Optical Materials: High Anisotropy of the Thermal Expansion Caused by Anharmonic Atomic Vibrations

“…All boron atoms in this 4B-group are tetrahedrally coordinated because each tetrahedron belongs to two 3B-rings. Recently, this large B 4 O 10 tetrahedron was experimentally found for the first time by Wu et al in a borosilicate, Cs 2 B 4 SiO 9 (# 425583-ICSD), which has NLO properties in the deep-ultraviolet range [70]. In 2016, the 4B-group known as "supertetrahedron" was found in the new indium borate In 19 B 34 O 74 (OH) 11 , synthesized under high-pressure/high-temperature conditions by Huppertz et al [71].…”

“…All triborates of univalent metals except for the two modifications of α-and β-NaB 3 O 5 are also built up from <2∆ > 3B-groups. These are the topologically identical three-dimensional frameworks of [70].…”

Beryllium-free Li4Sr(BO3)2 for deep-ultraviolet nonlinear optical applications

“…Over the past decades, continuous intensive studies [4][5][6][7][8][9][10][11] have resulted in the development of various commercial NLO materials, such as b-BaB 2 O 4 (BBO) 12 , LiB 3 O 5 (ref. 13), AgGaS 2 (ref.…”

Borate-Based Ultraviolet and Deep-Ultraviolet Nonlinear Optical Crystals

“…All these properties indicate that K 3 B 6 O 10 X could be a good candidate for second-and third-harmonic generation for laser at 1064 nm [61,62]. [67] I-4 190 4.6 × KDP -sites are disordered occupied by boron and beryllium atoms in the molar ratio of 1:1. Via sharing the corner oxygen atoms, two (B(1)O4) 5− tetrahedra form an (B2O7) 9− dimmer.…”