Youxuan Sun

Bulk crystal growth of hybrid perovskite material CH3NH3PbI3

Organic–inorganic hybrid perovskite materials have been receiving considerable attention due to their promising applications in many optoelectronic fields. However, some of the fundamental properties of perovskite materials are still disputed, because most of them are derived from a thin-film state. To comprehend the intrinsic characteristics in a single crystal, herein we report, for the first time, the bulk crystal growth of CH3NH3PbI3. Single crystals of tetragonal CH3NH3PbI3 with dimensions of 10 mm × 10 mm × 8 mm were grown by a temperature-lowering method in HI solution. Studies in to the refinement and orientations of the CH3NH3PbI3 single crystal structure were conducted based on a high quality crystal. The absorption edge of a CH3NH3PbI3 single crystal was located at about 836 nm, indicating that the band gap of CH3NH3PbI3 is approximately 1.48 eV, which is close to the theoretical results and smaller than those derived from polycrystalline and thin-films. CH3NH3PbI3 crystal exhibits a relatively wide absorption (from 250 nm to 800 nm) and a relatively good thermal stability.

MgTeMoO6: A neutral layered material showing strong second-harmonic generation

A noncentrosymmetric (NCS) compound, MgTeMoO6, has been synthesized using the high temperature solution method with TeO2–MoO3 mixture as a flux. MgTeMoO6 crystalizes in the orthorhombic space group P21212 (No. 18) with cell parameters a = 5.03780(10) A, b = 5.26910(10) A, c = 8.8985(2) A, and Z = 2. The compound exhibits a novel neutral layered structure consisting of asymmetric MgO6 octahedra, TeO4 polyhedra and MoO4 tetrahedra. Thermal stability measurements revealed an incongruent melting point of 682.35 °C. The crystal exhibits a very broad transmission range from 360 nm to 5.2 μm. Powder second-harmonic generation (SHG) measurements using 1064 nm radiation indicates that the crystal exhibits a strong SHG efficiency of ∼1.5 × KTiOPO4. Additional SHG measurements indicate the material is type-I phase-matchable. Furthermore, calculations on the local dipole moment indicates that the strong SHG response of MgTeMoO6 is mainly caused by the three types of NLO-active units (TeO4, MoO4 and MgO6).

Bulk crystal growth and characterization of a new polar polymorph of BaTeMo2O9: α-BaTeMo2O9

Bulk single crystals of α-BaTeMo2O9 with dimensions up to 51 × 30 × 20 mm3 were grown successfully by a top-seeded solution growth (TSSG) method using TeO2-MoO3 mixture as a flux. High-resolution X-ray diffraction measurement on the (400)-faced plate indicates that the full-width at half-maximum (FWHM) of the rocking curve is 16.55′′. The as-grown crystal exhibits {010}, {002}, {110}, {111} and {201} facets, which are in good accordance with the predicted growth morphology based upon the Bravais-Friedel and Donnay-Harker (BFDH) method. In addition, thermal properties including thermal expansion, specific heat, thermal diffusivity and thermal conductivity were investigated as a function of temperature. The average linear thermal expansion coefficients along the a-, b-, and c-axis from 30 °C to 500 °C were measured to be αa = 9.10 × 10−6 K−1, αb = 19.58 × 10−6 K−1 and αc = 11.94 × 10−6 K−1, respectively. The specific heat was measured to be 0.433–0.566 J (g K)−1 over the temperature range of 30–540 °C. The thermal conductivity along the a-axis is larger than those along other directions (κa>κb> κc). The transmission spectra and refractive indices were also measured. The α-BaTeMo2O9 crystal exhibits a wide transmission window ranging from 380 nm to 5530 nm. The large birefringence of α-BaTeMo2O9 (Δn = 0.305 for light at 404.7 nm) indicates that it is not only Type I and II phase-matchable, but also a very promising candidate for optical devices.

Theoretical and experimental studies on output characteristics of an intracavity KTA OPO

An acousto-optically Q-switched Nd:YVO(4)/KTiOAsO(4) (KTA) intracavity optical parametric oscillator (OPO) is efficiently realized in singly resonated scheme. With an end-pumping diode power of 25.9 W, output signal (1535 nm) power of 3.77 W and idler power (3467 nm) of 1.18 W are obtained at a pulse repetition rate of 50 kHz. A rate-equation model is set up to simulate the output power and time characteristics of both signal and idler waves. And both the numerical and experimental results show that the idler pulse width is shorter than the signal one in a singly resonant OPO.

Self-frequency-doubled KTiOAsO4 Raman laser emitting at 573 nm

A self-frequency-doubled KTiOAsO4 (KTA) Raman laser is realized in a diode-end-pumped acousto-optically Q-switched intracavity Raman laser configuration. A 30-mm-long x-cut KTA crystal is used as the Raman medium, and its 671 cm(-1) Raman mode is employed to finish the conversion from 1064 nm fundamental laser to 1146 nm Raman laser. Self-frequency doubling of the Raman laser is accomplished in the same KTA crystal, and a 573 nm yellow laser is obtained. With an incident diode power of 10.9 W and a pulse repetition rate of 20.8 kHz, a yellow-laser power of 0.82 W is obtained. The conversion efficiency from diode power to yellow-laser power is 7.5%.

A diode side-pumped KTiOAsO 4 Raman laser

A KTiOAsO(4) Raman laser is realized within a diode side-pumped acousto-optically Q-switched Nd:YAG laser. Efficient nanosecond first-Stokes generations at 1091.4 nm are obtained with three 30-mm-long KTA crystals. Under an incident diode power of 60.9 W and a pulse repetition rate of 4 kHz, a first-Stokes power of 4.55 W is obtained, corresponding to a diode-to-Stokes conversion efficiency of 7.5%. The single pulse energy is up to 1.14 mJ and the peak power is 18.0 kW.

Investigation of the dielectric, elastic, and piezoelectric properties of Cs2TeMo3O12 crystals

The complete sets of dielectric, elastic, and piezoelectric constants of Cs2TeMo3O12 crystals at room temperature were determined by means of the resonant technique and impedance analysis. The piezoelectric strain constants d33 and d15 were on the order of 20.3 and 29.2 pC/N, respectively, with the electromechanical coupling coefficients being k33 = 36.6% and k15 = 14.3%. Moreover, temperature dependence of the electro-elastic coefficients was measured in the range of 0–150 °C, where the elastic constant s44 was found to possess relatively low temperature coefficient (Ts44(1) = 77 × 10−6/ °C), and the variations of d33 and k33 were less than 3.5% and 1.0%, respectively.

Investigation of the second-order nonlinear optical properties of Cs2TeMo3O12 single crystal

The complete set of second-order nonlinear optical (NLO) coefficients of Cs2TeMo3O12 single crystals were obtained using the Maker Fringe techniques. The NLO coefficients d32 and d33 were measured to be on the order of 6.8 and 6.5 pm/V, respectively. Irradiated by 1064 nm laser, the crystal is phase-matchable, and its effective nonlinear coefficient is 4.6 pm/V for type I phase matching at θ = 42.7°. The relationship between the second-order nonlinear properties and the crystal structure is also discussed. Considering its wide transmission range, phase matching, and large effective NLO coefficient, Cs2TeMo3O12 is a good candidate for IR NLO application.

Growth and electric-elastic properties of KTiOAsO4 single crystal

We report the successful growth of high quality potassium titanyl arsenate, KTiOAsO4 (KTA) crystals with size of 34×67×72 mm3 through a K6As4O13 based flux method. The dielectric, piezoelectric, and elastic constants of KTA crystal were determined by the resonance technique and impedance analysis, respectively. The thermal dependence of the elastic constants were also determined by the transmission method over −50–110 °C. The first, second, and third order temperature coefficients of the elastic constants were calculated (T0=25 °C).

Synthesis, crystal growth, and characterization of the orthorhombic BaTeW2O9: a new polymorph of BaTeW2O9

A new polymorph of BaTeW2O9 with space group Pnma was identified during the exploration of the BaO-WO3–TeO2 system. Single-crystal X-ray diffraction measurements show that the material exhibits a 3D tunnel structure consisting of W–O6 octahedra connected with Te–O3 tetrahedra. Bulk single crystals of orthorhombic BaTeW2O9 with dimensions of 24 mm × 22 mm × 15 mm were grown by a top-seeded solution growth (TSSG) method using TeO2 as flux. Theoretical morphology of the crystal was obtained using the Bravais–Friedel and Donnay–Harker methods for comparison. The crystal shows a high transmittance from 360 nm to 5 μm as well as large birefringence (with Δn = 0.247 at 404.7 nm). The Raman spectrum shows that there is a Raman shift with high intensity and narrow peak width at 910.93 cm−1. TGA and DSC analysis indicate that the material melts incongruently at 783 °C. The thermal conductivity of the crystal was measured to be 1.23, 2.61 and 0.95 W m−1 K−1 at 50 °C along the a-, b- and c-axes, respectively.