Dongsheng Yuan

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.

Bulk growth, structure, and characterization of the new monoclinic TbCa4O(BO3)3 crystal

Bulk TbCa4O(BO3)3 single crystals with diameter of 25 mm and length of 70 mm were successfully grown by the Czochralski (Cz) method for the first time to the best of our knowledge. The main problems of crystal growth were discussed and solved resulting in a high quality crystal. The crystalline perfection of the as-grown crystal was evaluated with full-width at half-maximum (FWHM) of the rocking curve being 35.05′′, and the optical homogeneity being 7.76 × 10−5. TbCa4O(BO3)3 crystallizes in the monoclinic space group Cm with unit cell parameters of a = 8.0715(7) A, b = 16.0000(15) A, c = 3.5454(3) A, and β = 101.2550(10)°. Several interesting phenomena of atom occupancy and structure distortion were observed and analysed. Furthermore, the hardness, density, absorption and transmission spectra were measured. The TbCOB crystal has a Mohs hardness value of 5.58, and it exhibits a high transparency ranging from 490 nm to 1500 nm.

Bulk crystal growth and characterization of semi-organic nonlinear optical crystal tri-diethylammonium hexachlorobismuthate (TDCB)

Bulk semi-organic nonlinear optical (NLO) single-crystals of tri-diethylammonium hexachlorobismuthate (TDCB) with sizes up to 22 × 21 × 15 mm3 have been grown from concentrated hydrochloric acid by the slow-cooling method. TDCB crystallizes in the trigonal system, the R3c space group, with a = 14.699(4) A and c = 19.102(5) A. Its morphology has been indexed to reveal the major facets of the crystal to be {110} and {012}. Transmittance spectra of TDCB show an optical transmission in the entire visible region with the cutoff wavelength at 365 nm. The powder second harmonic generation (SHG) measured by using the Kurtz and Perry technique indicates that TDCB is a phase-matchable NLO material with a SHG efficiency of 1.8 times that of KH2PO4 (KDP). Its specific heat and thermal expansion were investigated as a function of temperature, and the relationship between the structure and the thermal properties has been discussed. Furthermore, laser-induced damage threshold measurements show a threshold up to 2.32 GW cm−2. All the results demonstrate that the semi-organic crystal TDCB is promising in NLO applications.

Linear and nonlinear optical properties of terbium calcium oxyborate single crystals

The linear and nonlinear optical properties of TbCa4O(BO3)3 (abbreviated as TbCOB) single crystals were investigated for the first time. The refractive indices of TbCOB at several wavelengths were measured by using the minimum deviation method and the parameters of Sellmeiers dispersion equation were determined from the experimental data. The complete set of six second-order nonlinear optical (NLO) coefficients of TbCOB single crystals were obtained using the Maker fringe (FM) technique, with the largest d32 being on the order of 1.65 pm/V. Moreover, the phase-matching (PM) configurations of second-order harmonic generation (SHG) in the principal planes were calculated, and the largest effective NLO coefficient is deff = 0.86 pm/V along (22.56°, 180°) PM direction. The SHG conversion efficiency from 1064 nm to 532 nm of 8 mm long crystal samples without AR coating along this direction was achieved 57.1% at 28.2 mW input power, and it has a small walk-off angle of 13.8 mrad. In addition, the comparison and discussion with GdCOB and YCOB were carried out.

Crystal growth and characterization of Nd 3+ :(La x Gd 1-x ) 3 Ga 5 O 12 laser crystal

A bulk mixed Nd3+:(LaxGd1-x)3Ga5O12 (Nd:LaGGG) laser crystal with dimensions of Ф 26 × 30 mm3 was successfully grown by the Czochralski (Cz) method. The structure and the effective segregation coefficients of Nd3+ and La3+ ions in the as-grown Nd:LaGGG crystal were measured. The thermal properties were also investigated as a function of temperature. In addition, the spectral properties were measured and the Judd-Ofelt (J-O) theory was applied to calculate the spectral parameters. In the 1062 nm CW laser operation, the maximum output power of 8.75 W was achieved. All the properties show that the Nd:LaGGG crystal is a promising laser materials.

Micro-pulling-down furnace modification and single crystal fibers growth

Single crystal fiber (SCF) combines the excellent instinct properties of conventional bulk laser crystals, and the special geometry advantage of active optical fibers. YAG and LuAG are proper host candidates for single crystal fiber laser with high thermal conductivity. Despite a lower thermal conductivity for pure crystal than YAG, LuAG crystal is easier to obtain homogeneous optical quality, and has a thermal conductivity nearly independent from the doping level. Micropulling- down (μ-PD) has relatively small thermal gradient, and here we use μ-PD to carry out high quality SCFs. Through the μ-PD furnace manufactured by ourselves, crystal fibers with different diameters have been grown successfully. We designed and fabricated a method to adjust the thermal distribution, and with the favor of pulling-down rate, the specific diameter can be controlled perfectly. The crystalline quality and homogeneity along the whole fiber were investigated, and LuAG SCF was confirmed to have a fine crystal quality for laser.