Optical Floating Zone Method Growth and Optoelectronic Studies of Zn₂TiO₄ and MgNb₂O₆ Single Crystals

The overwhelming majority of natural materials exist, like the number of natural gemstones as the structural integrity of the large-size single crystal rare form of microcrystalline or polycrystalline. Thus, compared with microcrystalline or polycrystalline material, the history of the development of the application of the crystal material to be much shorter. As little material in the form of a complete single-crystal nature, is not able to meet the various needs of the people, so people began the study of crystal growth. Significance of crystal growth in the development of high-tech, the crystal is an important material basis of the information age, sound, light, heat, electricity, magnetism, force the mutual transformation matrix carrier in the sustainable development of the national economy and national defense construction. has a wide range of important applications. Second, in basic research, many of the basic properties of the substances only from the crystal state to the understanding and application development. Currently Development of new crystalline materials have made significant progress, but there is a great gap between today's technology development needs; crystal variety, quantity, size itself unsatisfactory, crystal growth studies are very important now and in the future and very meaningful work. Optical floating zone method as a melt-crystal growth method. The liquid phase obtained elliptical reflector focusing the infrared light from a halogen lamp or a xenon lamp, and the melt mainly rely on surface tension to maintain the shape, the crystal growth is carried out along the vertical direction. Its crucible and pollution-free and fast growth rate, it is widely used in a variety of crystal growth, especially strong growth response and high melting point oxides and intermetallic compounds crystal. Use floating zone method has been successfully grown very value of research and application of single crystal piezoelectric single crystal BaTiO3-of CaTiO3 laser crystal Nd: GdVO4 12CaO · 7Al2O3 single. A spinel structure zinc titanate (Zn2TiO4) of having excellent dielectric properties, and therefore has a wide application in the microwave dielectric device; It is also a the efficient renewable catalytic adsorbent mainly used for adsorption of oil combustion process generated H2S, As, Se, and other contaminants. ZnNb2O6 and MgNb2O6 are binary niobate compounds with columbite structure. Because of its excellent dielectric properties, optical properties, magnetic properties, etc., has aroused extensive attention from researchers. The microwave dielectric performance of ZnNb2O6 Q × f = 83700 GHz, εr = 25 and τf = -56 ppm / ° C, and the low temperature sintering characteristics and low loss so that it is very promising to achieve low-temperature co-sintering of dielectric material. In addition to the excellent microwave dielectric properties (Q × f = 93.8 thousand GHz, εr = 21.4 and τf = -70 ppm / ° C) and the optical properties of MgNb2O6 can be used to detect defects in LiNbO3 substrate used for manufacturing waveguide . Present work, the FZ-T-10000-H-VI-VP single crystal furnace equipment advantages, research the Zn2TiO4, ZnNb2O6, and MgNb2O6 single crystal growth, further growth of single crystal optical properties, Raman spectroscopy and photoluminescence The light emitting research. The growth of of 1. Zn2Ti04 crystal: optical floating zone method grown for Zn2TiO4 crystals and found that the high speed inside the crystals grown in a large number of air bubbles appear, the crystal inside the bubble is eliminated by reducing the speed, to obtain the best growth conditions as follows: in the air under the conditions, the growth speed of 10 mm / h, and the vertical rod in the opposite direction 5rpm rotation. Growth Zn2TiO4 crystals as a pale yellow, transparent, the crystal diameter of 6mm, length 30mm. Polarizing microscope detection, Zn2TiO4 inside the crystal without low-angle grain boundaries and bubbles and other microscopic defects. The structure of the spinel structure, and the growth direction of the a-axis direction. Polarized Raman studies and temperature-dependent Raman study does not exist within the range of -193 ° C to 544 ° C Zn2TiO4 crystal phase change; through the temperature-dependent Raman spectra of the thermal expansion coefficient of the the Zn2TiO4 crystal Growth Zn2TiO4 crystals. By transmittance, reflectance test and Raman Spectra obtained Zn2TiO4 interband transitions, the band gap of 3.29eV, the phonon energy is involved in the transition 0.09eV; Zn2TiO4 the refractive index of the crystal obtained through theoretical derivation, complex dielectric constant, refractive index dispersion equation and a series of photoelectric constant, discrete Ed to comply with the values ??of the ionic crystals. 2.ZnNb2O6 crystal growth: grown for ZnNb2O6 crystals under conditions of oxygen, the melt region will have a lot of bubbles so that growth can not continue, but the melting region when grown in air bubbles can eliminate. Similarly consider the speed of crystal growth, high speed also lead crystals inside the bubble. Through a series of optimal growth conditions, the successfully grown to a diameter of 4-6mm, length 30mmm crystals inside the blue transparent external as a colorless and transparent. To be larger than the size of the crystals grown by cosolvent after annealing treatment, the internal, from blue to colorless transparent. XRD and Raman results show that the growth of the crystal structure for niobite ZnNb2O6, growth direction of the a-axis direction. Using polarized light microscopy, the crystal does not exist within the bubble and the low-angle grain boundaries and other microscopic defects. Polarized Raman and variable temperature Raman study of crystal growth, polarized Raman line with selection rules; -193 ℃ to 544 ℃ variable temperature Raman display the Raman vibrational modes varies linearly, there is no new peak only the peak position of the superimposed; and by temperature Raman peak thermal expansion coefficient of the calculated ZnNb2O6 crystals. Measuring the transmittance and reflectance of the the ZnNb2O6 crystals obtained bandgap 3.84 eV, to allow the direct transition semiconductor. Through theoretical derivation given refractive index, complex dielectric constant, refractive index dispersion equation series photoelectric constant. Photoluminescence tests showed that a strong blue emission peak at 450 nm, 285 nm excitation, Nb06 octahedral edge shared luminous center, can be attributed to the composite effect of the self-trapped exciton. Discussed the interior of crystals of the oxygen defects on the luminous efficiency and Raman mode FWHM change. 3) MgNb2O6 crystal growth: the use of the optical floating zone method successfully grown crystal of quality MgNb2O6, the growth of crystals to dark brown transparent, diameter 4-6mm, length 80mm color from dark brown to pale after annealing treatment brown. XRD and Raman measurements analysis the columbite MgNb2O6 determine the crystal growth structure, growth along the c-axis direction, cleavage along the (010) direction. Contact with the crystal axis polarized Raman study, get all Raman vibration mode, vibration mode in line with the selection rules. Crystals in the range of -193 ℃ to 544 ℃ MgNb2O6 variable temperature Raman study results showed that all the Raman frequency shift varies linearly with increasing temperature, the full width at half maximum (FWHM) ever-widening. The strongest four Ag vibration mode FWHM changes with temperature there is an inflection point. Through the temperature-dependent Raman obtained MgNb2O6 coefficient of thermal expansion of the crystal. The emission spectra show the MgNb2O6 crystals at 435nm a strong blue band from the edge shared Nb06 octahedron, can be attributed to the compounding effect of the self-trapped exciton. Annealing before FWHM Houla Man vibration mode change and the change in fluorescence intensity is caused because of the crystal's internal oxygen defects much annealing eliminates the oxygen defects. Contrast ZnNb2O6 crystal emission peak (450 nm), the emission energy of MgNb2O6 crystal to be high; both the A bit atom emission peak change should be a definite link with the A-site atom. Through the above study, knowledge and understanding of the floating zone growth of single crystal growth conditions, grasp the growth furnace FZ-T-10000-H-VI-VP floating zone technology, characteristics, etc., for further growth in the future with more practical value The high-quality single crystal has laid a solid foundation. Characterization of single crystal growth can help the understanding of the basic physical properties of these materials, and to provide valuable experimental data for further applications.