K2SrP4O12: a deep-UV transparent cyclophosphate as a nonlinear optical crystal

Abstract

Benefiting from high transmittance of PO₄ tetrahedra in the deep-ultraviolet (deep-UV) region, phosphates have been investigated as deep-UV nonlinear optical (NLO) candidates for years. So far, reported deep-UV NLO phosphates are orthophosphates and polyphosphates while cyclophosphates, important members of the phosphates family, have usually been neglected for use as deep-UV NLO crystals. Here, we first report a novel cyclotetraphosphate K₂SrP₄O₁₂ (KSPO) as a deep-UV transparent NLO crystal. In its structure, the fundamental building groups are ring [P₄O₁₂]⁴⁻ groups. KSPO exhibits a moderate second-harmonic generation (SHG) response that is 0.5 times that of KH₂PO₄ (KDP) and a short deep-ultraviolet absorption edge smaller than 200 nm.