Crystal Growth, Structural And Physical Properties Of Cesium Tellurium Molybdate And Lithium Tellurium Tungstate

Laser has important applications in the field of industry, scientific research, medical care, display and so on, it is one of the indispensable technologies in modern society. Laser is usually produced by a Laser device directly, but sometimes some important laser cannot be generated by this way. They can only be produced by frequency conversion using a nonlinear optical (NLO) crystal. Different laser wavelength needs different NLO crystals because they have different transparent range. The NLO crystals used in UV-VIS-NIR range are already mature, while those for mid-IR region are less developed and they have attracted a lot of attention in the past few years.Recently, noncentrosymmetric building blocks are included to design and synthesize new noncentrosymmetric compounds, and these materials are explored for NLO applications. Two representative examples, both of which are explained based on second-order Jahn-Teller effects, are distorted MO6 octahedra made from d0 transition metal ions such as Mo6+, W6+, V5+, Nb5+ and Ti4+, and asymmetric AOxE polyhedra consisting of I5+, Te4+, Se4+, Pb2+ and so on. Our research group reported the first crystal growth of monoclinic BaTeMo2O9 with centimeter-sized dimensions. The linear and nonlinear optical properties of monoclinic BaTeMo2O9 have been systematically investigated, and results show it is a potential NLO crystal. One of the shortcomings of monoclinic BaTeMo2O9 is its low symmetry, making it difficult to orient and fabricate the crystals. Cs2TeMo3O12 (CTM) is a material having hexagonal P63 space group, and it also exhibits strong second-harmonic generation, In chapter two of this thesis, we carried out systematically study on the nonlinear optical properties of the CTM single crystals. In Chapter three we explored the Li2CO3-TeO2-WO3 system using flux method. For the first time, we identified two completely new compounds:Li2TeW2O9 and o. The structure and physical properties of Li2TeW903o were also investigated.Main contents and results are as follows:(1) The background of this thesis has been summarized in the first chapter, including nonlinear optical effects, nonlinear optical crystals, flux method, etc. More importantly, recent progress on tellurium molybdates as second-order nonlinear optical crystals are summarized.(2) The linear and nonlinear optical properties of CTM single crystals are systematically studied and presented in the second chapter. The transmission spectra show that CTM is transparent in the range of 450-5300 nm. In particular, the transmission can reach up to 80% in the infrared range (1-4μm). Refractive index measurements show that CTM belongs to negative optical uniaxial crystal, and is I-type phase-matchable. The phase-matching angles at different fundamental wavelengths has been calculated. The second-order NLO coefficients (d15=d31=d32=6.8 pm/V, d33=6.5 pm/V) of CTM crystals have been measured. The effective nonlinear optical coefficient is also obtained. When the fundamental wavelength is 1064 nm, the effective NLO coefficient is 4.6 pm/V for frequency doubling process, which is 1.4 times larger than that of KTP and 4.3 times larger than that of LBO under the same conditions. The structure-property relationship is also discussed.(3) Exploration of the ternary phase diagram of Li2CO3-TeO2-WO3 was performed, and two new compounds Li2TeW2O9 and Li2TeW9O30 were identified. By anology to Na2TeW2O9, we synthesized Li2TeW2O9 and obtained its unit cell parameters by fitting the powder X-ray diffraction pattern using the structure of Na2TeW2O9 as a starting model. Our measurements show that Li2TeW2O9 exhibits relative strong second harmonic generation, indicating that it is a potential second-order NLO material. The other material Li2TeW9O30 crystalizes in the centrosymmetric P21/c space group with unit cell parameters a=13.135 A, b=7.322 A, c=30.797 A, β=95.074°, Z=4. Centimeter-sized single crystals of Li2TeW903o have been grown from flux using seeds. Transmission spectra indicate that Li2TeW903o is transparent in the range of 490-4500 nm. DSC-TGA measurements show that it is incongruent melting at 730 ℃, indicating that Li2TeW9O3o can only be grown by flux method. Specific heat measurements show that Li2TeW903o undergoes a second-order phase transition in the range of 250-300 ℃.