Review of KBe2BO3F2-like second-order nonlinear optical materials and their structure-performance relationships

Abstract

Nonlinear optical (NLO) materials have attracted widespread attention since they can greatly expand the spectral range of the laser output through second harmonic generation (SHG). Recently, employing advantageous structural templates to design and fabricate NLO materials has promoted their rapid development, compared with the traditional “trial-and-error” methodology. KBe₂BO₃F₂, an outstanding usually can be as a good structure prototype for oriented exploring NLO materials. In the crystal structure of KBe₂BO₃F₂, the π-conjugated planar triangle anionic group [BO₃]³⁻ and tetrahedra [BeO₃F]⁵⁻ can be replaced by other π-conjugated planar groups and tetrahedra/polyhedra to form KBe₂BO₃F₂-like structures, respectively. After the literature survey, the π-conjugated planar groups are [BO₃]³⁻ itself or [BO₂]⁻, [B₂O₅]⁴⁻, [B₃O₆]³⁻, [CO₃]²⁻, [BeO₃]⁴⁻, [BeN₃]⁷⁻, [BS₃]³⁻, [C(NH₂)₃]⁺, while the tetrahedra include [BeO₃F]⁵⁻ itself or [MO₄]ⁿ⁻ (M = B, P, S, Si, Li, Be, Al, Ga, Zn, Cl; n = 1, 2, 3, 4, 5, 6, 7), [SiN₄]⁸⁻, [BO₃T]⁴⁻ (T = F, (OH)), [MO₂F₂]ⁿ⁻ (M = P, Si; n = 1, 2), [MO₃F]ⁿ⁻ (M = Li, S, Y; n = 1, 4, 6), [BeO₃(OH)]⁵⁻, [AlO₃X]⁴⁻ (X = F, Cl), [ZnO₂(OH)₂]⁴⁻, [ZnO₃X]⁵⁻ (X = (OH), F, Cl, Br), and [ZnS₃Br]⁵⁻, as well as polyhedra [C₃O₄H₂]²⁻, [C₃H₆NO₂]⁻, [AlO₃F₂]⁵⁻, [MgO₄F₂]⁸⁻, [A^IIO₆]¹⁰⁻ (A^II = Mg, Ca), [LaO₈]¹³⁻, [LaO₉]¹⁵⁻, [PbO₃X₃]⁷⁻ (X = Cl, Br, I), and [IO₃]⁻. Accordingly, about 107 related compounds were collected: 37 borate-halides, 17 fluorooxoborates, 16 borates, 13 γ-Be₂BO₃F analogues, seven hydroxyborates, four borosulfates, three borophosphates, two guanidiniums, two borosilicates, and one malonate, hydroxycarbonate, carbonate-halide, borate-iodate, sulfate, silicate. According to their relationships between crystal structures and NLO properties: (i) KBe₂BO₃F₂-like materials that can achieve deep-ultraviolet NLO behavior all contain π-conjugated planar groups ([BO₃]³⁻, [CO₃]²⁻, [B₃O₆]³⁻) and fluorooxo-heteroleptic tetrahedra ([BO₃F]⁴⁻, [LiO₃F]⁶⁻, [SiO₂F₂]²⁻, [PO₂F₂]⁻). (ii) The combination of the π-conjugated planar groups with large polarization anisotropy and large first-order hyperpolarizability and great HOMO-LUMO energy gaps tetrahedra to design excellent NLO materials is the flexible and benign strategies. (iii) The emergence of the KBe₂BO₃F₂-like infrared NLO structural template has expanded the study sights of infrared NLO materials. The intention is to help insights into the effective designing of novel NLO materials using KBe₂BO₃F₂ as a structural template.