Nonlinear optical (NLO) crystals are essential materials for generation of coherent UV light in solid state lasers. KBBF is the only material that can achieve coherent light below 200 nm by direct second harmonic generation (SHG). However, its strong layer habits and the high toxicity of the beryllium oxide powders required for synthesis limit its application. By substituting Be with Zn and connecting adjacent [Zn2BO3O2]∞ layers by B3O6 groups, a new UV nonlinear optical material, Cs3Zn6B9O21, was synthesized. It overcomes the processing limitations of KBBF and exhibits the largest SHG response in the KBBF family.

Polar materials are of great technical interest but challenging to effectively synthesize. That is especially true for iodates, an important class of visible and mid-IR transparent nonlinear optical (NLO) materials. Aiming at developing a new design strategy for polar iodates, we successfully synthesized two sets of polymorphic early transition-metal (ETM) oxide-fluoride iodates, α- and β-Ba[VFO(IO)] and α- and β-Ba[VOF(IO)]IO, based on the distinct structure-directing properties of oxide-fluoride anions. α- and β-Ba[VFO(IO)] contain the trans-[VFO(IO)] polyanion and crystallize in the nonpolar space groups Pbcn and P222. In contrast, α- and β-Ba[VOF(IO)]IO contain the cis-[VOF(IO)] Λ-shaped polyanion and crystallize in the polar space groups Pna2 and P2, respectively. Detailed structural analyses show that the variable polar orientation of trans-[VFO(IO)] polyanions is the main cause of the nonpolar structures in α- and β-Ba[VFO(IO)]. However, the Λ-shaped configuration of cis-[VOF(IO)] polyanions can effectively guarantee the polar structures. Further property measurements show that polar α- and β-Ba[VOF(IO)]IO possess excellent NLO properties, including the large SHG responses (∼9 × KDP), wide visible and mid-IR transparent region (∼0.5-10.5 μm), and high thermal stability (up to 470 °C). Therefore, combining cis-directing oxide-fluoride anions and iodates is a viable strategy for the effective design of polar iodates.

Angle phase-matching in nonlinear optical (NLO) materials is critical for technological applications. The purpose of this manuscript is to describe the concept of phase-matching for the materials synthesis NLO community. Refractive index and birefringence are defined with respect to uniaxial and biaxial crystal systems. The phase-matching angle and wavelength range, Type I and Type II, are explained using real NLO materials, K 3 B 6 O 10 Cl (KBOC) and Ba 3 (ZnB 5 O 10 )PO 4 (BZBP) In addition, we describe how refractive index measurements are performed on single crystals and how the resulting birefringence impacts the phase-matching. Our goal is to provide a description of phase-matching that is relevant for the materials synthesis NLO community.

Access to the elusive deep-ultraviolet by direct second harmonic generation (SHG) enabled by a new beryllium-free zincoborate-phosphate crystal is reported. Ba3(ZnB5O10)PO4, exhibits large SHG responses at 1064 and 532 nm and a short 180 nm absorption edge. Centimeter-size crystals are grown, and quantum mechanical calculations demonstrate the key role played by ZnO4 tetrahedra in the enhanced optical responses.