Prof. YANG Zhihua | Publications & Academic Profile | SinoGreenTech

Research Publications & English Decoded Briefs

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SCIENCE CHINA Materials•2025•DOI: 10.1007/s40843-025-3444-0

Cation-Modulated Aligned Arrangement of [B3O7] Units in an Unprecedented 2∞[B3O5] Layer with Remarkable Birefringence

Birefringence is a critical linear optical parameter governing polarization modulation in birefringent crystals and phase-matching in nonlinear optical (NLO) crystals. Anionic group theory posits that the spatial arrangement of B–O functional motifs in borate frameworks can be tuned via cation modification, enabling the discovery of novel structures and optimized optical properties. Using LiB3O5 as the parent structure, we designed and synthesized two novel borates, Li2Rb2BaB18O30 (LRBBO) and K0.7Rb1.3BaB6O11 (KRBBO), through a dimension-reduction strategy induced by cation substitution. KRBBO features an unprecedented 2∞[B3O5] layered structure and exhibits a significantly enhanced birefringence of Δn = 0.08 at 546 nm, surpassing both the parent compound and other borates containing only [B3O7] groups. This work establishes an effective route for designing short-wavelength borate optical crystals with large birefringence and for enhancing the birefringence of [B3O7]-based NLO crystals to extend deep-ultraviolet phase-matching capabilities. The findings underscore the role of cation modulation in achieving aligned arrangement of anisotropic functional units, offering a viable strategy to overcome the intrinsic limitations of conventional borate NLO materials.

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SCIENCE CHINA Materials•2025•DOI: 10.1007/s40843-025-3474-2

A strategy to achieve giant optical anisotropy via integrating linear pseudohalogen and stereochemical active lone pair cation

The precise control of optical polarization states underpins photonic engineering, yet commercial birefringent crystals such as MgF2, α-BaB2O4, and CaCO3 are restricted to specific wavelength ranges and exhibit insufficient birefringence for ultracompact systems. This study introduces a dual-functional group-driven polarization enhancement strategy integrating linear pseudohalogen units ([SCN] and [NCN]) with stereochemically active lone pair electrons (LPEs) of Sn2+. Four compounds—SnCN2, Sn2OCN2, Sn(SCN)2, and Sn(SCN)F—were synthesized and characterized. They exhibit exceptional birefringence values of 0.44–0.73 at 1064 nm, surpassing commercial benchmarks (α-BBO, YVO4, TiO2) by 1.7- to 6.1-fold. SnCN2 achieves the highest birefringence (0.73) due to maximal [NCN] density (0.048 Å−3) and Sn-polyhedra density (0.024 Å−3). Sn(SCN)2 exhibits 0.64 birefringence, four times that of CaCO3, despite lower active unit density, underscoring the pivotal role of spatial configuration. Electron density analysis reveals extreme anisotropy in [SCN] units of Sn(SCN)2, with LPE density concentrated along the nz axis. In contrast, Sn(SCN)F shows minimal electron density variation due to stereochemical inactivity and omnidirectional polarization contributions. This work establishes a fundamental design paradigm for high birefringence materials by maximizing electron density gradients along distinct optical axes.

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SCIENCE CHINA Materials•2025•DOI: 10.1007/s40843-025-3680-8

Two-dimensional graphene-like BeO sheet: a promising deep-ultraviolet nonlinear optical material with strong and highly tunable second harmonic generation

Two-dimensional (2D) materials with ultrawide band gaps and strong, tunable second-harmonic generation (SHG) coefficients are critical for miniaturized deep-ultraviolet (DUV) nonlinear optical (NLO) devices. Despite extensive experimental synthesis of 2D materials, none have satisfied DUV NLO requirements. Here, an experimentally available graphene-like BeO monolayer composed solely of NLO-active [BeO3] units is identified as an excellent 2D DUV NLO material via first-principles calculations. It exhibits an ultrawide band gap of 6.86 eV and a strong SHG coefficient χ22(2)(2D) = 6.81 Å pm/V. Through stacking, strain, and twist engineering, numerous 2D BeO sheets are predicted, and their flexible structural characteristics enable tunable NLO properties. Remarkably, extremely stress-sensitive out-of-plane χ15(2)(2D) and χ33(2)(2D) (with an exceptional 30% change) and robust in-plane χ22(2)(2D) against large strains are achieved together in AC- and ACE-stacked BeO sheets under in-plane biaxial strain, exhibiting emergent phenomena uniquely not observed in other known 2D NLO materials. These results establish 2D BeO systems as a new option for 2D DUV NLO materials.

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