A General Principle: {\pi}-Conjugated Confinement Maximizes Band Gap of DUV NLO Materials

TL;DR

This paper introduces a {}-conjugated confinement principle to enhance the band gap and optical anisotropy of deep UV nonlinear optical materials, guiding the design of new compounds with superior properties.

Contribution

It proposes a general design principle based on {}-conjugated confinement and predicts new DUV NLO materials with improved properties.

Findings

{}-conjugated confinement is a shared structural feature in known DUV NLO materials.

Predicted compounds exhibit 3-24 times larger birefringence.

Predicted shortest SHG wavelength is 181 nm, the shortest among phosphates.

Abstract

Current nonlinear optical materials face a conventional limitation on the tradeoff between band gap and birefringence, especially in the deep UV spectral region. To circumvent such a dilemma, we propose a general principle, a {\pi}-conjugated confinement, to partially decouple the inter group {\pi}-conjugated interactions with the separation of a non-{\pi}-conjugated group so as to maximize the band gap in comparison with those of simple {\pi}-conjugated salts, such as borates, carbonates. Meanwhile, to maintain a large optical anisotropy. We uncover that the {\pi}-conjugated confinement is a shared structural feature for all the known DUV NLO materials with favorable properties (45 compounds), and thus, it provides an essential design criterion. Guided by this principle, the carbonophosphate is predicted theoretically for the first time as a promising DUV candidate system, Sr3Y[PO4][CO3]3 and Na3X[PO4][CO3] (X = Ba, Sr, Ca, Mg) exhibit an enhanced birefringence that is 3-24 times larger than that of the simple phosphate, as well as an increased band gap that is 0.2-1.7 eV wider than that of the simple carbonate. Especially, the shortest SHG output of Sr3Y[PO4][CO3]3 is at {\lambda}PM = 181 nm, being the shortest one among phosphates to date.