Pb7F12Cl2: a promising infrared nonlinear optical material with high laser damage threshold.

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.

Synthesis, crystal structures and nonlinear optical properties of ß-RbCdI3·H2O and CsCdI3·H2O.

Searching for new IR nonlinear optical (NLO) crystals with a high laser damage threshold (LDT) is still a challenge. In this paper, two new halides, ß-RbCdI3·H2O and CsCdI3·H2O, have been synthesized by a conventional solution reaction. Both of them crystallize in the monoclinic space group Pc (no. 7). In their crystal structures, all the corner-sharing [CdI4] tetrahedra connect with each other to form 1D chains, which further connect with [Rb(H2O)]+/[Cs(H2O)]+ complexes to form three-dimensional (3D) frameworks. All the polar [CdI4]2- groups align in such a way that results in a favorable net polarization. Powder second-harmonic generation (SHG) measurements indicate that ß-RbCdI3·H2O and CsCdI3·H2O show phase-matchable SHG responses of 2.7 and 2.6 times that of KH2PO4 (KDP). The infrared transmission range can reach 21 µm. The UV-vis diffuse reflectance spectra indicate that the band gaps of ß-RbCdI3·H2O and CsCdI3·H2O are about 3.26 and 3.54 eV, respectively. A preliminary measurement indicates that the LDT of their powders is about 90 and 100 MW cm-2, respectively, suggesting that ß-RbCdI3·H2O and CsCdI3·H2O are two new promising IR NLO materials. Their band structure and optical property calculations based on DFT methods are carried out.