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Conventional wisdom says that nonpolar structures do not favorably produce strong second-harmonic generation (SHG) responses since the polarization in their microscopic functional groups are counte...

Discovering new functional genes and developing high-performance materials are the goals being pursued by scientists. In this work, we successfully obtained a second-order nonlinear optical (NLO) material via the aqueous solution method, Y[N(CN) 2 ] 4 [NH(C 2 H 5 ) 3 ]∙3H 2 O, which is the first NLO material with anionic group N(CN) 2 - . Remarkably, this material not only is strongly NLO-active at 1064 nm with a response of about 2.8 × KH 2 PO 4 , but also possesses a short UV absorption edge of 250 nm. In-depth first-principles calculations well illustrate that the optical properties are mainly from the strong interaction of N, C and Y atoms. This result indicates that the N(CN) 2 - anion may be a new NLO functional gene. This work enriches the diversity of NLO functional genes and materials.

The stereochemical activity of lone pairs (SCALP) in a cation favors the formation of acentric materials and can enhance the second-harmonic-generation (SHG) response and/or the birefringence. By introducing functional SbIII into sulfates, an anhydrous sulfate of Sb6 O7 (SO4 )2 (1) is explored. Sb3+ cations are in seesaw configurations and in-phase aligned in a 3D asymmetric dense structure. Compound 1 exhibits an enhanced phase-matching SHG response, a moderate birefringence, a wide transparency window, and considerable environmental stabilities, which result in it being a promising UV nonlinear optical (NLO) material. Theoretical studies reveal that the stereoactive lone pairs on Sb3+ cations make the predominant contribution to the SHG effect. This work will attract more interest from scientists for research into SCALP-cation-based NLO materials.

A new noncentrosymmetric iron-iodate-fluoride Ba2[FeF4(IO3)2]IO3 was ingeniously obtained based on the centrosymmetric Ba[FeF4(IO3)] through chemical tailoring. Ba2[FeF4(IO3)2]IO3 exhibits a strong phase-matchable second-harmonic generation effect, a large band gap, and a wide mid-infrared transparent window. The chemical tailoring design based on oxide-fluoride anions affords a feasible approach to design nonlinear optical materials.

This research was financially supported by the National Natural Science Foundation of China (no. 51432006), the Ministry of Education of China for the Changjiang Innovation Research Team (no. IRT14R23), the Ministry of Education and the State Administration of Foreign Experts Affairs for the 111 Project (no. B13025), and the Innovation Program of Shanghai Municipal Education Commission. C.W. thanks the National and Shanghai Postdoctoral Program for Innovative Talents (nos. BX201800216 and 2018192). M.G.H. thanks the Australian Research Council for support (DP170100411).

This article discusses the growth and characterization of (((4-sulfonatophenyl) ammonio)oxy) zirconium (SAOZ) single crystals. Sulphanilic acid incorporated zirconium oxychloride semi-organic single crystals have been synthesized by slow evaporation technique. From the X-ray studies, lattice parameters a = 7.31 Å, b = 7.51 Å, c = 13.92 Å, volume = 765 Å3 have been found and so the crystal has been identified as orthorhombic with non-centrosymmetric space group P212121. The powder XRD examination demonstrated the quality and high crystalline nature of the grown crystal. The presence of functional groups was confirmed by FT-IR technique. The chemical structure of the compound was established by 1H and 13C NMR spectra. The optical transmittance window and the low cutoff wavelength of SAOZ have been identified by UV-Vis-NIR studies. Photoluminescence studies showed a wide blue light emission. TG and DTA examinations were carried out to characterize the thermal behavior of the grown crystal. The mechanical strength of the grown crystal was analyzed by the Vickers microhardness test. The elemental analysis was done by EDAX. The dielectric response of the crystals was analyzed in the frequency range of 50 Hz to 5 MHz at various temperatures and the outcomes were discussed. The SHG efficiency was estimated in correlation with KDP by employing powder Kurtz method.

Searching for coexistence of wide energy gap (Eg > 3.5 eV) and large second-harmonic generation efficiency (dij > 0.6  AgGaS2) for the non-centrosymmetric (NCS) materials in the IR nonlinear optic...

Infrared nonlinear optical (IR-NLO) crystals possess excellent comprehensive performance are highly desirable, yet their acquisition remains enormous challenging. Particularly, inorganic chalcogeni...

The balance between second harmonic generation (SHG) intensity and laser-induced damage threshold (LIDT), together with phase-matchable behavior, is the key point for exploration of novel nonlinear...

Nonlinear optical materials are the vital components of future photonic technologies as they can transfer and process data at the speed of light. However, the necessary prerequisites for a practica...

Infrared nonlinear optical (IR NLO) crystals play a significant role in the development of IR laser technology. But rationally designing a new IR NLO crystal remains a huge challenge because of the unpredictability of inorganic structures. Herein, inspired by phase transformation of the famous BaB2 O4 (BBO) crystal, a temperature-induced centrosymmetric (CS) to noncentrosymmetric (NCS) transformation approach is employed in CS BaGa2 Se4 to uncover a new NCS ternary chalcogenide, β-BaGa2 Se4 which can exhibit the well-balanced NLO properties, including moderate phase-matching SHG response (≈0.6×AgGaS2 ), high LDT (10×AgGaS2 ), and large birefringence (Δn=0.18 in the visible region). Therefore, β-BaGa2 Se4 will be a promising IR NLO crystal. The analysis for the structure-property relationship shows that the excellent NLO properties of β-BaGa2 Se4 mainly originate from edge-sharing GaSe4 tetrahedral chains, which are different from B3 O6 groups in β-BBO and respect a new direction for the design of IR NLO crystals. So, we believe that the current research provides not only a new IR NLO crystal but also some insights for the design of new IR NLO crystals.

A novel noncentrosymmetric (NCS) metal-free formic-borate, (NH4)3[B(OH)3]2(COOH)3, has been discovered, which exhibits an infrequent graphite-like structure. The alliance of two types of π-conjugated planar anions BO33- and COOH- produced an optimized layered structure to maximize the anisotropic polarizability, resulting in an extremely large birefringence (0.156@546 nm), larger than that of the classical commercial UV birefringent material α-BBO (0.122@546 nm). This strategy that structural optimization could enhance birefringence will guide the discovery of large birefringence materials, especially in the UV region.

Introduction of Pb2+ cations in silicate systems generates a new compound, PbSrSiO4, which exhibits excellent properties, including a strong second harmonic generation response (∼5.8 × KDP), a short UV cut-off edge (240 nm) and moderate birefringence (0.053@1064 nm). These results suggest that PbSrSiO4 is a promising UV NLO material.

Semi-organic nonlinear optical material L-methioninium nitrate have been synthesized by the slow evaporation technique at room temperature. The synthesized crystal structure lattice parameters are found to be a = 10.68 (2) Ǻ, b = 5.47 (2) Ǻ, c = 16.725.47 (2) Ǻ; α = γ = 90º, β = 100.7º by single crystal X-ray diffractometer. The grown crystal belongs to a monoclinic structure and non-centrosymmetric space group P21. Optical properties were determined from optical absorption studies to compute the absorption range, band gap, refractive index and electrical susceptibility of L-methioninium nitrate. Dielectric parameters of the sample carried out at different temperature in the frequency range from 100 Hz to 5 MHz. The solid parameters such as plasma energy, Penn gap, Fermi energy and polarizability of L-methioninium nitrate have been determined using dielectric studies. The second harmonic generation efficiency of the grown crystal has been confirmed by Kurtz and Perry technique. These preliminary investigations suggest that the present compound L-methioninium nitrate can serve as a potential material for optoelectronic device fabrication.

Novel mixed-metal thiophosphate CuCd3PS6 has been firstly discovered and fully characterized. Careful experimental and theoretical investigations demonstrate that CuCd3PS6 is a benign infrared nonlinear optical material with a moderate second harmonic generation response of 0.9 × AgGaS2 at 41–74 μm, a large laser damage threshold of 4.1 × AgGaS2, a wide band gap of 2.24 eV and a low melting point of 603 °C. Moreover, first principles calculations indicate that CuCd3PS6's intriguing nonlinear optical performance is activated by its three-in-one tetrahedra-stacking architecture.

Discovering new mid-IR nonlinear optical (NLO) materials with high laser damage thresholds and easy crystal growth is an urgent and challenging task. Through cationic substitution of Si4+ in Li2K4(...

A noncentrosymmetric mixed alkali metal borate–bicarbonate, NaRb3B6O9(OH)3(HCO3), was synthesized and characterized. The compound crystallizes in the monoclinic space group P21 (No. 4) with a = 8.9...

Discovery of new nonlinear optical (NLO) crystals, especially crystals that can produce coherent light in the deep-ultraviolet (DUV) region is essential for the development of diverse fields. Here,...

A new infrared nonlinear optical material with diamond-like structures, Li4HgSn2Se7, was synthesized by the traditional high-temperature solid-state method. It crystallizes in the non-centrosymmetr...

L-cysteine hydrogen fluoride (LCHF) single crystals were grown from aqueous solution. Single crystal X-ray diffraction, FT-IR, UV-Vis-NIR, and TG-DTA were used to test the grown crystals. The specimen dielectric and mechanical behaviors were also studied. Powder X-ray diffraction of the grown crystal was recorded and indexed. The optical properties of the LCHF crystal were determined using UV-Vis spectroscopy. It was found that the optical band gap of LCHF was 4.8 eV. The crystal functional groups were identified using FT-IR. Second harmonic generation (SHG) efficiency of the LCHF was three times higher than that of KDP. The dielectric constant, dielectric loss and AC conductivity were measured at different frequencies and temperatures.

The deficiency of nonlinear-optical (NLO) materials in the IR region inspires strong research interest in this field. Here, Sn2Ga2S5 (1), crystallizing in the orthorhombic Pna21 space group, demonstrates obvious NLO activity, around a maximum of 1.6 times that of AgGaS2 and a strong laser-induced damage threshold of 9.7 times that of AGS. 1 represents the first NLO-active compound in the MII2MIII2Q5 (MII = divalent Ca, Sr, Ba, Pb, Sn, and Eu; MIII = B, Al, Ga, and In; Q = S and Se) family. The NLO performances of 1 are systematically studied experimentally and theoretically.

Fluorooxoborates have inspired investigations of deep-ultraviolet (DUV) nonlinear optical (NLO) materials that can meet the multiple criteria. Herein, five stable structures with the composition of BaB2 O3 F2 (I-V) are discovered using the ab initio evolutionary algorithm. Among them, BaB2 O3 F2 -I has been synthesized experimentally and confirms the reliability of the method. All of the predicted structures possess extremely wide band gaps (8.1-9.0 eV). Moreover, four new structures exhibit giant second harmonic generation (SHG) coefficients (>3×KDP, d36 =0.39 pm V-1 ). A novel type of the [BOF] layer with BO3 :BO3 F ratio of [1:1] is found in BaB2 O3 F2 -II and BaB2 O3 F2 -III. While BaB2 O3 F2 -IV and BaB2 O3 F2 -V are solely composed of the BO3 F group and have colossal SHG coefficients (ca. 4×KDP). It gives the direct evidence that the BO3 F group could generate strong SHG effect. Most importantly, the influences of BO3 :BO3 F ratio and their number density on band gap, birefringence and SHG effects are investigated.

A novel barium silicon phosphide was synthesized and characterized. Ba2Si3P6 crystallizes in the noncentrosymmetric space group Pna21 (No. 33) and exhibits a unique bonding connectivity in the Si–P...

Single crystal of sodium 4-hydroxybenzenesulfonate dihydrate (Na-4-HBS) was grown from an aqueous solution by slow evaporation method. Powder X-ray diffraction study was carried out to identify the lattice parameters of the crystal. FT-IR spectral analysis confirmed the existence of various functional groups in the compound. The optical transmittance, cut-off wavelength and band gap energy were estimated from the UV-Vis studies. Photoluminescence studies revealed the transition mechanism by optical excitation. The variation of dielectric properties and AC conductivity of the grown crystal with frequency was studied at different temperatures. Measurements of mechanical properties of Na-4-HBS were carried out to find the hardness of the material. The laser induced surface damage threshold and relative second harmonic generation nonlinear optical properties of the grown crystal were studied using Q-switched Nd:YAG laser.

In this work, combined experimental and computational studies of an organic nonlinear optical material, phenylurea (PU), are reported. Optical quality single crystal of PU, was successfully grown by the slow evaporation method. The unit cell parameters of the grown PU crystal belong to the monoclinic system and these belong to the non-centrosymmetric (NCS), P21, space group. Morphology of the crystal was indexed and it reveals its 14 distinct faces. Vibrational modes of PU functional groups were assigned successfully using FTIR and Raman spectrum. The grown crystal exhibits low cutoff wavelength at UV region with good optical transparency and blue wavelength emission. The preliminary measurements confirmed that second harmonic generation (SHG) activity (∼7.6 KDP and ∼2.2 urea) with excellent laser induced threshold damage (LDT) having a value of 2.92 GW/cm2 (∼1.95 urea). TG/DTA analysis shows that endothermic nature of grown crystal with thermal stability up to 154 °C. The Vickers micro hardness test confirms soft material behavior of PU crystal and it was further explored by crystal void percentage calculation. Electrical properties such as dielectric and photoconductivity measurements were carried out for grown crystal. Furthermore, density functional theory (DFT) studies such as Mulliken charge distribution, frontier molecular orbitals (FMOs), molecular electrostatic potential (MEP) map and first order hyperpolarizability (β) were determined to probe the structure-property relationship. These results suggest that PU single crystal can be a better alternate for urea in NLO applications.

In this work, we propose the synthesis of a novel bromine chalcone (E)-3-(2-bromophenyl)-1-(2-((phenylsulfonyl)amine))phenyl)prop-2-en-1-one (BRC) that has been crystallized by the slow evaporation...

Van der Waals (vdW) deep-UV (DUV) nonlinear optical (NLO) crystal is an important material system recently developed. Herein, we review its concept and original intention, and then summarized the discovery process of related materials, including the role of A-site cations and the resulting two-/one-dimensional vdW DUV NLO systems. Finally, we evaluate the practical DUV NLO performance and prospected the opportunities and challenges.

Carbon nanoparticles (CNPs) with high porosity and great optical features can be used as a luminescent material. One year later, the same group investigated the NLO properties CNPs and boron-doped CNPs by 532 nm and 1064 nm laser excitations to uncover the underlying physical mechanisms in their NLO response. Hence, a facile approach, laser ablation technique, was employed for carbon nanoparticles (CNPs) synthesis from suspended activated carbon (AC). Morphological properties of the prepared CNPs were studied by transmission electron microscopy (TEM) and scanning electron microscopy (SEM). UV-Vis and fluorescence (FL) spectra were used to optical properties investigation of CNPs. The size distribution of nanoparticles was evaluated using dynamic light scattering (DLS). The nonlinear optical (NLO) coefficients of the synthesized CNPs were determined by the Z-scan method. As a result, strong reverse saturable absorption and self-defocusing effects were observed at the excitation wavelength of 442 nm laser irradiation. These effects were ascribed to the presence of delocalized π-electrons in AC CNPs. To the best of our knowledge, this is the first study investigating the NLO properties of the AC CNPs.

Herein, a promising infrared nonlinear optical (IR NLO) material, Li2ZnGeS4, was successfully synthesized in the typical quaternary diamond-like semiconductor (DLS) system. This material exhibits excellent performances including a wide band gap (3.49 eV), a high laser-damage threshold (LDT, 8 × benchmark AgGaS2), and a good NLO effect (0.7 × AgGaS2) with phase-matching behavior. Furthermore, based on first principles calculations, the theoretical results are in agreement with the experimental results.

Three mixed-metal phosphates, namely, centrosymmetric LiSrP3O9 and LiCsP2O6 as well as noncentrosymmetric K2SrP4O12 have been synthesized by the high temperature solution method. These structures were characterized by single-crystal X-ray diffraction and their P-O units are shown to feature distinct polyanionic configurations from [PO3]∞ chains in LiSrP3O9 to [P4O12]4- rings in LiCsP2O6 and K2SrP4O12. Besides, K2SrP4O12 shows a moderate second harmonic generation response about 0.6 times that of KH2PO4 and can be applied as a potential nonlinear optical material for the ultraviolet spectral region. Thermal behaviour analyses indicate that the compounds LiSrP3O9 and K2SrP4O12 remain stable up to 659 and 698 °C, respectively. In addition, the crystal structures, thermal stabilities and infrared spectra of the title compounds have been examined.

A new nonlinear optical material, Ba11[Al(PO4)4](P2O7)(PO4)3, was rationally synthesized via the hybridization of three types of anionic groups, namely [AlO4]5−, [PO4]3− and [P2O7]4−, via a spontaneous nucleation method. Ba11[Al(PO4)4](P2O7)(PO4)3 was characterized with high thermal stability, deep ultraviolet transparency and moderate second-order optical nonlinearity, which were favourable for practical applications.

This study reports, for the first time, the second-harmonic generation (SHG) property of Pb7F12Cl2 as a promising infrared nonlinear optical (NLO) material. Powder second-harmonic generation (SHG) indicates that the compound exhibits phase-matchable SHG properties, which are 1.6 times stronger than those of KH2PO4 (KDP). The infrared transmission range could reach 20 μm. The UV absorption indicated that the band gap was about 4.5 eV. A preliminary measurement of laser damage threshold (LDT) is about 80 MW cm−2, which is much higher than AgGaS2 (currently commercialized IR NLO material, 5.2 MW cm−2, measured in the same condition), indicating that Pb7F12Cl2 is a potential IR NLO material with high LDT. Theoretical calculations were also performed to elucidate its band structure, electronic configuration and second-order nonlinear coefficients. Particularly, the distinct role of different Pb atoms located in divergent coordinations has also been elaborated using orbital analysis.

Ultrafast photonics based on two-dimensional (2D) materials has been used to investigate light-matter interactions and laser generation, as well as light propagation, modulation, and detection. Here, 2D metal-phosphorus trichalcogenides, which are known for applications in catalysis and electrochemical storage, also exhibit advantageous photonic properties as nanoflakes that are only a few layers thick. By using an open-aperture Z-scan system, few-layer NiPS3 nanoflakes exhibited a large modulation depth of 56% and a low saturable intensity of 16 GW cm-2 at 800 nm. When NiPS3 nanoflakes were used as a saturable absorber at 1066 nm, highly stable mode-locked pulses were generated. Thus, these results revealed the nonlinear optical properties of NiPS3 nanoflakes which have potential photonics applications, such as modulators, switches, and thresholding devices.

Sulfates have been overlooked as nonlinear optical materials in the past few decades. Herein, a new sulfate nonlinear optical material, RbSbSO4Cl2, was prepared via a facile hydrothermal synthetic route. The title compound crystallizes in the polar non-centrosymmetric (NCS) space group P212121 and exhibits an intricate three-dimensional network constructed by interconnecting RbO5Cl4, SbO3Cl2 distorted polyhedra and a SO4 tetrahedron. The powder second-harmonic generation (SHG) measurements display that RbSbSO4Cl2 exhibits a strong SHG response of about 2.7 times that of KH2PO4 (KDP) and is type I phase-matchable. Theoretical calculation analysis confirmed that the large SHG effect originated from the synergistic effect of three coexisting NCS chromophores: Sb3+ with SCALP effect, highly polarizable Rb+ cations and a SO4 distorted tetrahedron.

A novel compound with four mixed anions, Y8O(OH)15(CO3)3Cl, exhibiting an infrequent three-dimensional (3-D) inorganic cationic framework, has been successfully designed and synthesized by introducing π-conjugated planar triangular CO3 groups and chloride anions into a rare earth oxide system, which exhibits good balance among its wide UV transmission range, large second harmonic generation (SHG) coefficient and suitable birefringence to meet the phase-matching condition, indicating that the titled compound is a promising short-wave UV nonlinear optical material.

We discuss low-pressure HVPE growth of ZnSe on GaAs substrates (~350 µm thick) and on OP-GaAs templates (~115 µm thick) that achieved single-crystalline quality ZnSe layers which will be used to develop OP-ZnSe QPM structures for nonlinear frequency conversion devices. Material characterization techniques including SEM, HR-XRD, XTEM, and PL have been used to verify that the ZnSe grown by HVPE has a superior quality to the commercially available ZnSe substrates. Current focus is to obtain thicknesses beyond 500 µm using plain and OP templates for frequency conversion in the MLWIR.

4-N,N-dimethylamino-4′-N′-methyl-stilbazolium tosylate (DAST) is one of the most important organic nonlinear optical (NLO) materials, but its controlled growth remains a challenge. Herein, we describe a novel method to control the growth of DAST on the surfaces of indium tin oxides coated with the patterned photoresists by electric field. Results indicate that zero-dimensional (0D) spherical DAST microcrystals tend to grow along the photoresist lines if an electric field with a low frequency of 500 Hz is applied. Rather differently, one-dimensional (1D) DAST microwires preferentially grow along the gaps of the photoresist lines under the control of an electric field with a high frequency of 1000 Hz. Growth of DAST microcrystals controlled by electric field leads to the increase in the crystallinity, but the chemical structures remain unchanged. Moreover, second harmonic generation signal was measured from the as-grown DAST microcrystals. The results presented in this work are helpful for rationally controlling the growth of 0D or 1D DAST microcrystals, and particularly, the strategy can be further expanded to control the growth of DAST derivatives or other organic NLO materials with similar chemical structures.

The exploration and improvement of excellent mid-infrared nonlinear optical (NLO) materials is still in great demand. The perovskite-type Sr2Nb2O7 is found to be a good predictor of NLO properties due to the similar band gap and NLO coefficients to KTiOPO4 (KTP). In this paper, we systematically investigated the electronic structures, linear and nonlinear properties of pure and V-doped Sr2Nb2O7 based on DFT. It is found that the V-doped Sr2Nb2O7 doubles the NLO coefficient and exhibits higher birefringence, which is moderate and sufficient for phase-matching. The results are helpful to the further development of the mid-infrared NLO crystals with perovskite structure.

A new nonlinear optical material, the first fluoride selenite nitrate PbCdF(SeO3)(NO3), was successfully synthesized by traditional solid state reactions. This compound crystallizes in the polar space group of Pca21, and its structure features a novel 2D layered structure consisting of 1D lead nitrate chains and 2D cadmium selenite layers. PbCdF(SeO3)(NO3) exhibits a phase-matchable SHG efficiency of about 2.6 times that of KDP and a wide band gap of 4.42 eV. Its laser damage threshold was measured to be 135.6 MW/cm2, which is comparative to that of the reported Li7(TeO3)3F with a short ultraviolet cutoff edge. Theoretical calculation confirmed that the synergistic effects of all the four functional units make PbCdF(SeO3)(NO3) a remarkable SHG material.

4-aminopyridinium adipate monohydrate (4APA) was grown by slow evaporation solution growth technique. The functional groups in the grown crystal were identified from FT-IR spectral evaluation. The optical properties together with transmittance of the grown crystal were obtained from UV-Vis spectroscopic study. The mechanical and thermal properties of the grown crystal were studied using Vickers microhardness and TGA/DTA analyses, respectively. Microhardness test revealed that 4-aminopyridinium adipate monohydrate crystal is a soft category material. The density functional method (DFT) was performed using B3LYP with the 6-311G (d,p) basis set. The electronic charge distribution, reactivity of the molecules and the molecular electrostatic potential (MEP) of the grown crystal were analyzed using the B3LYP method. The intermolecular interactions that exist in the crystal structure of the 4APA have also been investigated by Hirshfeld surface analysis. The nonlinear optical properties of the 4APA crystal were confirmed by Kurtz-Perry technique.

Deep-ultraviolet (DUV) nonlinear-optical (NLO) materials generating coherent DUV light by a direct second-harmonic-generation (SHG) process have long been pursued as industrially useful lasers. For several decades, KBe2BO3F2 (KBBF) has been regarded as the best DUV-NLO material; it is characterized by a short DUV phase-matching edge of 161 nm and a large SHG coefficient of 0.47 pm/V. However, it suffers a strong layering tendency, hindering the growth of large crystals for commercial use. Here, we use a computer-aided swarm structure searching technique to design an alternative DUV-NLO material with a new atmospheric-pressure phase Be2BO3F2 with a P62 c space group (γ-BBF) that outperforms the DUV-NLO properties of KBBF. The predicted DUV phase-matching edge and SHG coefficient of γ-BBF are 152 nm and 0.70 pm/V, respectively. The structure of γ-BBF reduces the layering tendency compared with KBBF because of the absence of K atoms in the γ-BBF crystal. Our work paves the way for superior DUV-NLO materials that can be grown as large crystals for commercial applications.

New quaternary sulfide PbGa2GeS6 crystal was synthesized from co-melting high-purity elements The studies of second harmonic generation and the third harmonic generation for new quaternary sulfide PbGa2GeS6 crystal have shown that its nonlinear optical response is higher with respect to other similar compounds. The band structure analysis performed by X-ray spectroscopy methods and first principles DFT band structure calculations indicate that the main contributions of the S 3p states are located at the top of valence band, while those of the Ga 4p states give contribution to the central and upper portions of the valence band of the PbGa2GeS6 compound. The calculations reveal that the band gap Eg = 2.445 eV is indirect and is formed between the valence Γ-point and the conduction X-point of Brillouin zone. The theoretically evaluated band gap energy is close to the experimental value, namely Eg = 2.37 eV at 300 K The present results allow recommending PbGa2GeS6 for nonlinear optical application in the near IR spectral range. At the same time, the crystal possesses a good transparency in the mid-IR spectral range.