Cs₂Bi₂O(Ge₂O₇) (CBGO): A Larger SHG Effect Induced by Synergistic Polarizations of BiO₅ Polyhedra and GeO₄ Tetrahedra

Abstract

A cesium bismuth germanate, Cs2Bi2O(Ge2O7) (CBGO), was synthesized by a traditional high‐temperature solid‐state reaction. Its structure features a 3D network composed of a 1D chains composed of Bi2O8 dimers that are further bridged by Ge2O7 dimers, forming tunnels of seven member rings (MRs) that are filled by the Cs+ cations. CBGO exhibits extraordinary larger second harmonic generation (SHG) response of about 13.7 times that of KDP (KH2PO4) under 1064 nm laser radiation and 1.1 times that of KTP (KTiOPO4) under 2.05 μm laser radiation, which is the highest among all of the metal germanates reported so far. CBGO possesses a moderate birefringence (0.073 at 1064 nm) and is phase matchable. Furthermore, CBGO melts congruently and exhibits high thermal stability.

Achieving broadband ultraviolet to mid-infrared transparency in germanate-based nonlinear optical crystals Cs3REGe3O9 (RE = Y, Gd)

“…18 In recent years, there has been a notable surge in scientific interest surrounding the pursuit of novel oxide crystals for mid-IR NLO applications. This endeavor involves the incorporation of heavy metal cations that are susceptible to secondorder Jahn-Teller (SOJT) effects, and exemplary crystals include BaTeM 2 O 9 (M = Mo, W), 19 Li 2 MTeO 6 (M = Zr, Ti, Sn), 20,21 LiNbTeO 5 , 22 Cs 2 Bi 2 OGe 2 O 7 , 23 Te 2 V 2 O 9 , 24 and Cs 4 V 8 O 22 . 25 As anticipated, these crystals exhibit an extended IR transmission cutoff edge beyond 5 μm.…”

La3Ga5M0.5Sn0.5O14, (M = Ge, Si): Design and Synthesis of Two Langasite Nonlinear Optical Materials with Large Second Harmonic Generation and Birefringence Induced by Distorted (Sn/M)O6 Octahedra

“…The diffuse reflectance spectra indicate that LGSS and LGGS both have relatively short UV absorption edges of 209 and 212 nm (Figure a,b), which are shorter than those of other langasite crystals, including Pb 3 Mg 3 TeP 2 O 14 (250 nm), Pb 3 TeGa 2 ZnSi 2 O 14 (271 nm), Pb 3 Te­(Zn 2 Ge)­Ge 2 O 14 (299 nm), LGN (285 nm), and LGT (250 nm), and also shorter than those of other materials with large SHG responses (>8 × KDP), such as LN (315 nm), KTP (350 nm), Cs 2 Bi 2 OGe 2 O 7 (357 nm), ZnTeMoO 6 (350 nm), Li 2 Ti­(IO 3 ) 6 (413 nm), and CsPbCO 3 F (300 nm) . It is because the LGMS (M = Ge, Si) structural unit does not include d 0 cations (Ti 4+ , Nb 5+ , Ta 5+ , W 6+ , Mo 6+ , etc.)…”

“…This is consistent with the experimental results: SHG response LGSS (∼10. 4 9 Pb 3 TeGa 2 ZnSi 2 O 14 (271 nm), 65 Pb 3 Te(Zn 2 Ge)Ge 2 O 14 (299 nm), 33 LGN (285 nm), 51 and LGT (250 nm), 51 and also shorter than those of other materials with large SHG responses (>8 × KDP), such as LN (315 nm), 68 KTP (350 nm), 69 Cs 2 Bi 2 OGe 2 O 7 (357 nm), 70 ZnTeMoO 6 (350 nm), 71 Li 2 Ti-(IO 3 ) 6 (413 nm), 72 and CsPbCO 3 F (300 nm). 73 It is because the LGMS (M = Ge, Si) structural unit does not include d 0 cations (Ti 4+ , Nb 5+ , Ta 5+ , W 6+ , Mo 6+ , etc.)…”

Rb8Nb10Ge6O41: a new niobium-germanate crystal featuring unique one-dimensional [Nb7O30]∞ chains and wide mid-IR transparency

“…10 As a result, materials containing both Ge 4+ cations and transition metal cations can exhibit a diverse structural chemistry with adaptable frameworks. 11 Notably, germanate-based materials inherently possess potential for applications in both linear and nonlinear optics, due to their extensive visible and infrared transmittance range, as well as impressive thermal and chemical stability. 12–14 For instance, through the rational integration of customized functional motifs comprising antiparallel [GeO 4 ] tetrahedra and distorted [NbO 6 ] octahedra, the Cs 3 Nb 5 GeO 16 crystal not only demonstrates a wide transparent window but also achieves a breakthrough of experimental birefringence of 0.19 @532 nm among the available germanate oxides, signifying its significant potential for manipulating polarized light.…”