Sr₂[B₅O₈(OH)]₂ ⋅ [B(OH)₃] ⋅ H₂O: A Strontium Borate That Shows Deep‐Ultraviolet‐Transparent Nonlinear Optical Properties

Abstract

A new noncentrosymmetric strontium borate, P1‐Sr2[B5O8(OH)]2·[B(OH)3]·H2O (1), has been synthesized under the hydrothermal condition. The P1‐Sr2[B5O8(OH)]2·[B(OH)3]·H2O shows a layered B‐O network with 9‐ring windows in the ab plane. Sr2+ cations, H3BO3, and H2O molecules are located in the voids of layers and interlayers, respectively. The P1‐Sr2[B5O8(OH)]2·[B(OH)3]·H2O is the first synthetic phase of veatchite, while the other three polymorphs are found in different natural minerals. This strontium borate is a potential deep‐ultraviolet‐transparent nonlinear‐optical (NLO) crystal whose second‐harmonic‐generation (SHG) intensity is 1.7 times that of KH2PO4 (KDP) and is phase‐matchable. The short wavelength cutoff edge of compound 1 is below 190 nm. Density functional theory (DFT) calculations show that the B–O units are responsible for the nonlinear optical property.

Designing promising ultraviolet (UV) birefringent crystals with different hydrogen-bonded phosphate frameworks

“…Birefringent crystals are key materials used in the production of optical devices, including polarizers, optical isolators, circulators, and phase retarders. 1–7 Inorganic phosphate crystals, known for their short ultraviolet cutoff edges and good crystal growth habits, represent a classic optoelectronic material. 8–13 KDP (KH 2 PO 4 ) and KTP (KTiPO 4 ) are quintessential examples of phosphates, boasting significant application as nonlinear optical (NLO) materials.…”

Galloborates as ultraviolet nonlinear optical crystals: advances and perspectives

“…To date, a large number of alkali and alkaline earth metal borate-based NLO crystals have been found. 21–27 One very recent example is Ba 4 B 14 O 25 , which shows a highly polymeric three-dimensional geometry with a closed-loop anionic framework constructed by the fundamental building blocks (FBBs) [B 14 O 33 ], and it is a deep-UV transparent NLO crystal with strong second harmonic generation (SHG) (3.0 × KH 2 PO 4 , KDP). 28 Generally, a perfect UV or deep-UV NLO crystal should possess certain characteristics including a wide optical transparency window, large NLO coefficient, and moderate birefringence, and it should be easy to grow large single crystals.…”