|关键词||红外 倍频 光学带隙 硫属化合物 含d10构型金属|
Infrared nonlinear optical (IR NLO) materials as frequency-conversion devices in laser have drawn more and more attention because of their wide applications in civil and military regions including laser guidance, long distance laser communication, laser radar and cosmetic laser surgery etc. Commercially applied IR NLO materials, AgGaS2，AgGaSe2 and ZnGeP2 exhibit good properties like large second-harmonic generation (SHG) responses, wide IR transparent range etc., however, their small band gaps lead to their low laser damage thresholds or serious two-photon absorption, which limit their further applications. Therefore, exploring new IR NLO materials with good balance between large band gaps and large SHG response is still an imperative and meaningful work.In this work, investigations were made and the result shows that many promising IR NLO materials contain cations with d10 configuration (like Zn2+, Cd2+), with which they can display large SHG responses besides wide band gaps. Therefore, theoretical study about the mechanism how these cations adjust the properties of materials means really much for designing and synthesizing new IR NLO materials.Guided by the idea above, we successfully synthesized four compounds containing cations with d10 configuration: Na2ZnGe2S6, Na2ZnSn2S6, Na2CdGe2S6 and Na2CdGe2Se6. The main achievements in detail are as follows.1 Na2ZnGe2S6, a new IR NLO material, has been successfully synthesized with solid-state reaction technique in fused silica tubes. Its structures are composed of two 3D tunnel frameworks, one is constructed by polar wave-shaped infinite ∞[GeS3]n chains and isolated [ZnS4] tetrahedra, and the other is constructed by the Na(1)S5 and Na(2)S6 polyhedra. Remarkably, it exhibits not only wide transparent region (0.38-22 μm), large direct band gap (3.25 eV) and chemical stability, but also achieves the balance between large laser damage threshold (LDT) (228 MW/cm2, about 6 × AgGaS2) and large SHG response (30 × KDP). Moreover, single crystals of Na2ZnGe2S6 have been obtained with size up to millimeter level. Calculated SHG density and dipole moment demonstrate that the good SHG response is mainly attributed to the cooperative effects of the [GeS4] and [ZnS4] units; total and partial density of states (TDOS and PDOS) diagrams present that it has a direct band gap and the optical absorption is determined by the [GeS4] and [ZnS4] units. All the properties, especially the balance between large SHG response and high LDT, indicate that it has the potential to be a candidate crystal applied in the IR NLO region, and we will pay more attention to grow large single crystal for evaluating its application in the future.2 A mixed-metal thiostannate, Na2ZnSn2S6 has been synthesized through solid-state reaction. It crystallizes in non-centrosymmetric space group of Fdd2 and in its structure the secondary building block ∞[SnS3]n chains are rarely found among all alkali thiostannates. In addition, Na2ZnSn2S6 exhibits good optical properties, including wide IR transmission region (0.35 – 25 μm), large SHG response (4 × AgGaS2 at 55 – 88 mm crystal size range) and high LDT (2 × AgGaS2), which indicates that Na2ZnSn2S6 can be expected as a promising IR NLO material.3 We report the successful design and synthesis of two metal-mixed chalcogenides containing divalent cations with d10 electronic configuration: Na2CdGe2S6 and Na2CdGe2Se6. Both of them crystallize in the polar Cc space group and exhibits the three-dimensional tunnel structures constructed by the CdQ4 tetrahedra and ∞[GeQ3]n chains with Na+ located in the tunnels. Furthermore, an interesting space group transformation between the monoclinic (Cc) and tetragonal (I4/mcm) systems from Na2CdGe2Se6 to Na2ZnGe2Se6 was discovered, which may arise from the different connection types of their building blocks (more flexible corner-sharing type in Cc while tightly edge-sharing type in I4/mcm). Remarkably, it exhibits not only wide transparent region (0.38-22 μm), large direct band gap (3.25 eV) and chemical stability, but also achieves the balance between large LDT (228 MW/cm2, about 6 × AgGaS2) and large SHG response (30 × KDP). Moreover, single crystals of Na2ZnGe2S6 have been obtained with size up to millimeter level. Calculated SHG density and dipole moment demonstrate that the good SHG response is mainly attributed to the cooperative effects of the [GeS4] and [ZnS4] units; TDOS and PDOS diagrams present that it has a direct band gap and the optical absorption is determined by the [GeS4] and [ZnS4] units. All the properties, especially the balance between large SHG response and high LDT, indicate that it has the potential to be a candidate crystal applied in the IR NLO region, and we will pay more attention to grow large single crystal for evaluating its application in the future.Among all the compounds obtained, Na2ZnGe2S6 and Na2CdGe2S6 exhibit more comprehensive properties, including the balance between large band gap and large SHG response, which make them have the promising opportunity to be candidates as IR NLO materials.
|李广卯. 含d10构型二价金属的新型红外非线性光学晶体材料的研究[D]. 北京. 中国科学院大学,2017.|
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