Li13YGe4O16: A Mid-infrared Rare-Earth Germanate Nonlinear Optical Crystal Featuring a Broad Transmission Range and an Enlarged Band Gap

Germanate is garnering increasing attention in the field of optoelectronics owing to its competitive optical transparency and robust stability. Herein, a novel lithium-rich rare-earth germanate, Li13YGe4O16, was fabricated for the first time using a high-temperature solution approach. This compound adopts the asymmetric space group Cmc21 (no. 36), characterized by isolated [YO6] and [GeO4] structural motifs with Li+ cations located in the channel. Notably, Li13YGe4O16 presents a short ultraviolet cutoff edge at 240 nm, indicative of an enlarged band gap of 4.96 eV and showcases a wide mid-infrared transmission region exceeding 6.0 μm. Moreover, Li13YGe4O16 features exceptional thermal stability and moderate second harmonic generation (SHG) intensity. Additionally, a theoretical analysis suggests that the distorted [YO6] octahedra. [GeO4] and [LiO4] tetrahedra play a significant role in the optical activities of Li13YGe4O16. These attributes endow Li13YGe4O16 with the potential to serve as a new mid-IR nonlinear optical (NLO) crystal and enrich the structural chemistry of germanates.

Intense d-p Hybridization in Nb3 O15 Tripolymer Induced the Largest Second Harmonic Generation Response and Birefringence in Germanates

We herein report two asymmetric germanate crystals, KNbGe₃ O₉ and K₃ Nb₃ Ge₂ O₁₃ , with different structures and optical properties derived from divergent polymerized forms of GeO₄ and NbO₆ groups. Remarkably, K₃ Nb₃ Ge₂ O₁₃ achieved a rare combination of the strongest second harmonic generation (SHG) response of 17.5×KDP @ 1064 nm and the largest birefringence of 0.196 @ 546 nm in germanates. It features unique [Nb₃ O₁₂ ]_∞ tubular chains constructed by circular Nb₃ O₁₅ tripolymers. Theoretical calculations reveal that the d-p interactions in the Nb₃ O₁₅ group are responsible for outstanding optical properties. This work emphasizes the significance of the polymerizable functional units in obtaining high-performance nonlinear optical (NLO) crystals.

Pb5(GeO4)(Ge2O7) and Pb3.32Ca1.68(GeO4)(Ge2O7): Two Nonlinear Optical Germanates Induced by Diverse PbOx Polyhedra

Oxide nonlinear optical (NLO) crystals have drawn wide interest for their comprehensive physical performances including wide infrared (IR) transparency ranges, large band gaps, and good stability in open air. Here, two isostructural germanate oxides, Pb₅(GeO₄)(Ge₂O₇) (1) and Pb_3.32Ca_1.68(GeO₄)(Ge₂O₇) (2), adopting the noncentrosymmetric (NCS) space group P6̅, were composed via a conventional solid-state reaction. The latter was designed by the partial cation substitution strategy based on parent 1. The whole structures of 1 and 2 are composed of isolated distorted GeO₄ tetrahedra, Ge₂O₇ dimers, and diverse M (M = Pb, Ca, or Pb/Ca)-centered polyhedra. They exhibit second-harmonic generation (SHG) responses around 3.3 and 1.4 times that of KH₂PO₄ (KDP) under 1.064 μm laser radiation, respectively. Theoretical calculation results reveal that the Pb²⁺ cations with stereo-active long pair (SCALP) electrons of 1 favor the large SHG response, while Pb-based polyhedra showing inert SCALP electrons make predominant contributions to the moderate SHG effect of 2.

Centrosymmetric Rb[Te2O4(OH)5] and noncentrosymmetric K2[Te3O8(OH)4]: metal tellurates with corner and edge-sharing (Te4O18)12- anion group

New nonlinear optical (NLO) crystals have become urgent need for extending laser wavelengths. By cation substitution between alkali metal (K+, Rb+), anion group arrangement transition were realized, and centrosymmetric Rb[Te2O4(OH)5]...

Y2(Te4O10)(SO4): a new sulfate tellurite with a unique Te4O10 polyanion and large birefringence

Y₂(Te₄O₁₀)(SO₄), featuring a unique (Te₄O₁₀)⁴⁻ polyanion, exhibits a large birefringence (0.124@1064), wide energy band gap (4.1 eV) and high thermal stability (>700 °C), which make it a potential birefringent material.

Sr(M,Te)2O6 (M = Cr, Mn, Fe, Co, Ni): A Magnetically Dilute Family of Honeycomb Tellurates

We report the synthesis and characterization of five new honeycomb tellurates with the PbSb₂O₆ structure type. These materials, SrM_2/3Te_4/3O₆ (M = Cr, Mn, Fe) and SrM_1/2Te_3/2O₆ (M = Co, Ni), are prepared by conventional solid state synthesis. Rietveld refinements of powder X-ray and neutron diffraction data reveal that these materials crystallize in the P3̅1 m space group, in which M and Te are octahedrally coordinated and randomly distributed over the honeycomb sublattice. In three of these materials (M = Cr, Mn, Fe), the transition metal takes a 3+ oxidation state, and hence, charge neutrality necessitates that the honeycomb sublattice is 66% occupied by nonmagnetic Te. In the remaining two of these materials (M = Co, Ni), the transition metal takes a 2+ oxidation state, requiring that 75% of the honeycomb lattice is occupied by nonmagnetic Te. Thus, the honeycomb sublattice is highly diluted, as only 33% or 25% of the sites are occupied by a magnetic ion. These occupation values fall well-below the percolation threshold for the honeycomb lattice, p _c = 70%. Accordingly, magnetic susceptibility measurements reveal no magnetic order or spin freezing down to 1.8 K.

Pb2Cd(SeO3)2X2 (X = Cl and Br): two halogenated selenites with phase matchable second harmonic generation

The second harmonic generation (SHG) efficiencies of Pb₂Cd(SeO₃)₂X₂ (X = Cl and Br) are higher than that of commercial KDP (KH₂PO₄) and their laser damage thresholds are 30 times more than that of AGS (AgGaS₂).

PbMnTeO6: a chiral quasi 2D magnet with all cations in octahedral coordination and the space group problem of trigonal layered A2+M4+TeO6

Neutron diffraction rejects the prismatic P6̄2m model with Mn/Te disorder and proves the chiral structure with octahedral coordination for all cations.