Realizing Deep-Ultraviolet Second Harmonic Generation by First-Principles-Guided Materials Exploration in Hydroxyborates.

Aimed to realize deep-ultraviolet (DUV, λ < 200 nm) second harmonic generation (SHG), herein we systematically investigate the scheme for screening DUV nonlinear optical (NLO) material "genes" from traditional borates to hydroxyborates. From our first-principles studies, it is demonstrated that, if hydroxyborate motifs can be aligned by reasonable layered crystallization types, the resulting crystal will exhibit potential DUV NLO capability. Guided by the theoretical analysis and prediction, two targeted hydroxyborates AEB8O15H4 (AE = Sr, Ca) screened from the inorganic crystal structure database are obtained in the experiments. Preliminary measurements including powder absorption spectra and SHG effects are in good agreement with our simulation results, well confirming our prediction that AEB8O15H4 (AE = Sr, Ca) would be promising DUV NLO crystals with large band gaps, strong SHG effects, and sufficient birefringence. This work is the first demonstration that hydroxyborates can realize DUV SHG, which may bring new opportunities for finding DUV NLO materials in the hydroxyborate system.