Investigations on the Synthesis, Crystal Structure, Linear- and Nonlinear-Optical Properties of the Zinc Germanate Rb₂ZnGe₂O₆

Abstract

A quaternary nonlinear-optical (NLO) zinc germanate, Rb2ZnGe2O6 (RZGO), was prepared from its stoichiometric melts, which belongs to the noncentrosymmetric space group C2221 (No. 20) and features a 3D framework formed by GeO4 tetrahedra, ZnO4 tetrahedra, and Rb+ cations filling into the void space. RZGO displays a good phase-matchable second-harmonic-generation (SHG) intensity similar to that of KH2PO4. The UV cutoff edge for RZGO was found to be approximately 0.37 μm with a broad optical band gap of 3.22 eV, indicating a large laser-induced damage threshold. Further characterizations suggested that this compound displays an excellent thermal stability (1014 °C) and melts congruently. Besides, theoretical analysis was also implemented to investigate the electronic structures and effective NLO coefficients as well as the origin of the observed SHG response for RZGO. The present study can enrich the diversity of acentric germanate structures and pave the way for the synthesis of new NLO compounds.

Cs2Bi2OSi2O7: A Promising Bismuth Silicate Nonlinear Optical Crystal with Face-Sharing BiO5 Polyhedra Exhibiting Strengthened Second Harmonic Generation Response and Birefringence

“…As presented in Figure a, the SHG signal of CBSO enhances along with the increasing particle sizes before it reaches the maximum value that implies phase-matching nature, as defined by Kurtz and Perry, and CBSO displays a strong SHG intensity of ∼3.5 × KDP in the particle size range of 180–212 μm (Figure b). Notably, the observed result of CBSO is comparable to that of the universally used practical crystal LBO (3 × KDP). , As deposited in Figure c, CBSO has an impressive UV cut-off edge of 279 nm and gives wide band gaps of 3.6 eV, which may be beneficial for reducing two-photon absorption, according to the previous studies. − The IR spectrum tests demonstrate that CBSO exhibits no obvious absorption in a broad range of 4000–1045 cm –1 (Figure d); thus, CBSO is transparent in a wide region over 3–5 μm based on the two-phonon approximation, which is favorable for mid-IR NLO applications Table S3 lists the absorption bands and assignments of CBSO. , …”

Shedding Light on the Structure and Characterization of K2ZnGe2O6: A Phase-Matchable Nonlinear Optical Crystal

“…There are one unique K, Zn, Ge atoms and four O atoms in the asymmetric unit cell. The title compound exhibits a novel three-dimensional (3D) framework built of corner-sharing [ZnO 4 ] and [GeO 4 ] units, as shown in Figure a, analogous to that of Rb 2 ZnGe 2 O 6 . In the [ZnO 4 ] motif, one Zn atom is connected with four O atoms with lengths of 1.950(5)–1.972(5) Å.…”

“…24 In KZGO, the ratio of the longest/shortest K−O bonds was found to be 1.25, whereas 1.18 for Rb−O bonds in Rb 2 ZnGe 2 O 6 , which indicates that [KO 9 ] may be more distorted than [RbO 9 ]. 2,38 However, according to the anionic group theory, the alkali metal ions have little contribution to the SHG effects of NLO materials. The crystallographic details of KZGO are available in Table S1.…”

“…The discovery and innovation of nonlinear optical (NLO) materials are of current scientific interest due to their optoelectronic applications. So far, most reported NLO crystals are mainly inorganic materials, which have intriguing merits of diversified functions and good physicochemical stability. − Over the past decade, considerable attempts have been made to innovate NLO inorganic materials. It is widely accepted that the acentric structural configuration is a prerequisite for second-order NLO compounds.…”

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

“…The frequency doubling capabilities of 1 and 2 were tested under 1.064 μm irradiation since they adopt NCS space groups. The measurement results indicate that both the 1 and 2 samples cannot achieve phase-matching (PM) behavior (Figure 3a), while they exhibit strong SHG intensities 3.3 and 1.4 times that of KDP with 110−150 μm particle size (Figure 3b), larger than those of some oxides such as Rb 2 ZnGe 2 O 6 (1 × KDP), 41 NaZnSiO 3 (OH) (0.5 × KDP), 43 Li 3 AlSiO 5 (0.8 × KDP), 12 and Li 2 SrSiO 4 (0.3 × KDP). 44 Theoretical Calculations.…”