A chemical cosubstitution strategy was implemented to design potential ultraviolet (UV) and deep-UV nonlinear optical (NLO) materials. Taking the classic β-BaBO as a maternal structure, by simultaneously replacing the Ba and [BO] units with monovalant (K), divalent (alkaline earth metal), trivalent (rare-earth metal, Bi) ions, and the [BO] clusters through two different practical routes, 12 new mixed-metal noncentrosymmetric borates KMRE(BO) (M = Ca, Sr, Ba, K/RE; RE = Y, Lu, Gd) as well as KMBi(BO) (M = Pb, Sr) were successfully designed and synthesized as high-quality single crystals. The selected KCaY(BO), KSrY(BO), and KBaY(BO) compounds were subjected to experimental and theoretical characterizations. They all exhibit suitable second-harmonic generation (SHG) responses, as large as that of commercial KHPO (KDP), and also exhibit short UV cutoff edges. These results confirm the feasibility of this chemical cosubstitution strategy to design NLO materials and that the three selected crystals may have potential application as UV NLO materials.
A series of new rare-earth
borate crystals K7MRE2B15O30 (M = Zn, Cd, Pb; RE = Sc, Y,
Gd, Lu) were synthesized by solid-state reaction method. All of the
title compounds crystallize in the noncentrosymmetric trigonal space
group R32, and their structures consist of the B5O10 groups and the KO8, KO6, MO6, and REO6 polyhedra. Each isolated B5O10 group is connected by the REO6 (Sc3+, Y3+, Gd3+, Lu3+) groups
forming an intricate three-dimensional network, and the K+ and M2+ (Zn2+, Cd2+, Pb2+) cations fill into the void space. Because of the introduction of
different nonlinear optical (NLO)-active structural units (cations
with d10 electronic configuration and stereoactive lone
pairs) into rare-earth metal borates, these compounds exhibit second
harmonic generation (SHG) responses ranging from 1.5 to 2.1 times
that of KH2PO4 (KDP), and are phase-matchable.
Interestingly, this work indicates that the NLO properties can be
artificially adjusted by systematically replacing the bivalent M2+ and trivalent RE3+ cations with NLO-active structural
units, which provides a new way to design new NLO materials. Thermal
analyses, IR spectra, and UV–Vis–NIR diffuse reflectance
spectra were also reported in this work. In addition, the first-principles
calculation was employed for better understanding of the structure–properties
relationships of these compounds. Especially, the origins of SHG responses
were well demonstrated by the SHG-density technique.
Three new complex borate compounds K 7 CaBi 2 B 15 O 30 , K 7 CaLa 2 B 15 O 30 and K 7 BaBi 2 B 15 O 30 have been synthesized by the high-temperature solution method. K 7 CaLa 2 B 15 O 30 and K 7 CaBi 2 B 15 O 30 crystallize in the chiral trigonal space group R32, while K 7 BaBi 2 B 15 O 30 crystallizes in the noncentrosymmetric orthorhombic polar space group Pca2 1. All of the title compounds have similar three-dimensional crystal structures, which are composed of isolated B 5 O 10 groups and LaO 6 or BiO 6 octahedra, and K + , Ca 2+ , and Ba 2+ cations fill into the cavities to keep charge balance. Based on our research, in the system of K 7 M II RE 2 B 15 O 30 (M
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