Discovery of Deep-UV Nonlinear Optical Material

To address the fundamental scientific conundrum of how to obtain the full performance balance of “large SHG response, deep-UV cut-off edge and suitable birefringence” in the design of deep-UV NLO materials, the fluorinated borate groups were suggested by Pan’s group as the best groups to use when creating deep-UV NLO materials.

Pan’s group recently expanded the “fluorination strategy” to the borophosphate system and synthesized a novel deep-UV NLO crystal (NH₄)₃B₁₁PO₁₉F₃ (ABPF) with intricate anionic units.

ABPF has an exceptional fundamental building block [B₅PO₁₄F], and its anionic outline presents a KBBF-like layer [B₅PO₁₀F]_∞. Strong B-O-P covalent connections are introduced, which reduces the interlayer distance, improves interlayer contact and prevents the layered growth pattern.

ABPF has exceptional optical features with a short cutoff edge (183 nm), a large SHG effect (1.2 × KDP), and an adequate birefringence (0.088 at 1064 nm) for deep-UV phase-matching.

What the anionic groups do, [BO₃], [BO₄], [BO₃F], and [PO₄] on the linear and nonlinear optical features of ABPF are uncovered by analysis of structures and first-principles calculations

The addition of π-conjugated units [BO₃] benefits the significant SHG effect and enough birefringence, allowing ABPF to penetrate through the so-called “200 nm” wall.

Conversely, the addition of non-conjugated units [BO₄], [BO₃F], and [PO₄] with significant HOMO-LUMO gaps aids in the elimination of the [BO₃] units’ dangling bonds, resulting in deep-UV transparency.

As a result, the superior overall efficiency of ABPF is mostly due to its unique KBBF-like structure composed of π-conjugated and non-π-conjugated units. The current study exhibits the advancement of the “fluorination strategy” and the efficacy of employing several anionic groups in the investigation of high-performance deep-UV NLO crystals.

Journal Reference:

Cheng, B., et al. (2022) (NH₄)₃B₁₁PO₁₉F₃: a deep-UV nonlinear optical crystal with unique [B₅PO₁₀F]_∞ layers. National Science Review. doi.org/10.1093/nsr/nwac110.