Shanpeng Wang

Electro-optic properties of BaTeMo2O9 single crystal

The electro-optic (EO) properties of monoclinic BaTeMo2O9 (BTM) single crystals are studied using the interference technique by applying the external electric field. The measured room temperature free EO coefficients at 632.8 nm are 10.2 and 9.0 pm/V for γ12 and γ41, respectively. The EO effect (−12ni3γijE) of BTM is about three times as high as that of KH2PO4 (KDP) crystal, which makes it a very promising candidate for the EO applications.

Continuous-wave and passively Q-switched laser performance of LD-end-pumped 1062 nm Nd:GAGG laser

Continuous-wave (CW) and passively Q-switched operations of LD-end-pumped Nd:Gd(3)Al(x)Ga(5-x)O(12) (Nd:GAGG) laser at 1062 nm were reported. The highest CW output power of 5.7 W was obtained, corresponding to an optical conversion efficiency and slope efficiency of 51.0% and 54.5%, respectively. The CW output efficiency of Nd:GAGG laser is comparable and even better than that of Nd:GGG. The passively Q-switched output was realized for the first time to our knowledge. In addition, a maximum output power of 1.12 W, a maximum pulse repetition rate of 39 kHz and a minimum pulse width of 6 ns were obtained by using Cr(4+):YAG as the saturable absorber.

Temperature dependence of elastic properties and piezoelectric applications of BaTeMo2o9 single crystal [Correspondence]

BaTeMo2O9 (BTM) single crystal, as a lead-free piezoelectric material, belongs to the monoclinic system, space group P21. We report the temperature dependence of the elastic constants by the transmission method over the range -50°C to 150°C. The first-order temperature coefficients of the elastic constant s44 is about 180 × 10-6/°C. Piezoelectric resonators based on BTM crystal using the thickness-stretching vibration and the shear vibration modes were designed and evaluated, which eliminated or minimized the influence of the off-principal axis coefficients. The Qm of one of the resonators is about 600. Our results show that the elastic constants have good temperature stability, and the resonators have already met the requirements for some piezoelectric applications. This study on the BTM crystal has revealed the application for the low-symmetry crystal.

The origin of coloration of CaGdAlO4 crystals and its effect on their physical properties

CaGdAlO4 (CGA) single crystals have been grown in different oxygen concentration atmospheres by the Czochralski method. Crystals grown under an oxygen-containing atmosphere presented an inconsistent brown coloration. The origin of coloration was studied by density functional theory, and the simulated results show the oxygen defects and the absorption matched well with the experimental results. The brown coloration of CGA is due to the interstitial oxygen atoms. The fundamental properties of CGA crystals with different colors, including the crystal density, hardness, thermal and optical properties, were systematically investigated and compared when taking into account the effect of color center inside. The colorless CGA was grown under an inert gas atmosphere and exhibits a wide transparency range of 227–7140 nm. The maximum phonon energy was determined to be as low as 618 cm−1. The colorless CGA host crystal with a disordered structure, good thermal conductivity, low maximum phonon energy and wide transparency is promising for ultrafast ultraviolet and visible laser applications.

Vertical Bridgman growth and optical properties of CdSiP2 crystals

Single crystals of CdSiP2 (CSP) with the dimension of 8 mm in diameter and 40 mm in length were successfully grown using vertical Bridgman method. Optical observations showed the presence of macro-defects including flaws and inclusions in the as-grown crystals. The macro-defects can be restrained through controlling the process of polycrystalline synthesis and growth parameters. For the crystals with improved qualities, the high-resolution X-ray diffraction measurement on the (004)-faced plate indicates that the full-width at half-maximum (FWHM) of the rocking curve is 34′′. The phase-matching curves calculated from refractive indices indicate that, for 1.064 μm pumping, the CSP crystal will produce a noncritically phase-matched output at 6.2 μm through a type-I parametric process, and a noncritically phase-matched output at 5.0 μm through a type-II parametric process. For 1.55 μm and 2.00 μm pumping, the crystal yields continuous tunability from 2 to 6.5 μm through a type-I parametric process. The absorption coefficients for e-polarized light at 1.064 μm, 1.55 μm and 2.0 μm of the as-grown CSP crystal are 0.53 cm−1, 0.39 cm−1, and 0.25 cm−1, respectively.

Flux method growth of bulk MoS2 single crystals and their application as a saturable absorber

Molybdenum disulfide (MoS2) has attracted a great deal of attention because of its outstanding physical, chemical and optoelectronic properties. The method used to prepare large sized MoS2 crystals of very high quality is still an important issue for determining the feasibility of its application. Herein, we propose a novel Sn flux method to grow single crystal MoS2, and bulk MoS2 single crystals with a size of 3 mm × 5 mm were successfully obtained by using a cooling rate of 2–4 °C h−1. The growth mechanism of the MoS2 crystal in Sn flux was investigated in detail using optical microscopy and atomic force microscopy (AFM). The obvious screw dislocation steps that are revealed suggest that the growth of MoS2 is controlled by a screw-dislocation-driven (SDD) spiral growth mechanism. The flux-grown MoS2 crystals were exfoliated to produce high-quality large-scale films using the liquid-phase exfoliation method. Using ultrathin MoS2 films as a saturable absorber, a passively Q-switched laser at a wavelength of 1.06 μm was constructed and operated, with a narrow pulse width of 326 ns.

Modified Bridgman growth and characterization of a novel mid-infrared transparent optical crystal: LiGa3Te5

A large single LiGa3Te5 (LGT) crystal was grown with size up to O16 mm × 50 mm for the first time using a modified vertical Bridgman–Stockbarger method. LGT crystallizes in the non-centrosymmetric system, space group R32, with a = b = 14.343(7) A, c = 17.617 A, Z = 12, and V = 3139 A3. A detailed description of the polyhedral connections in the LGT structure is presented. The X-ray rocking curve, specific heat and thermal conductivity are also investigated. The room-temperature transmission of the as-grown LGT without any coating is above the 40% level from 3.5 to 18 μm. The cut-off edges at short and long wavelength are 0.9 and 25 μm, respectively. Owing to its wide transparency range, LGT is a promising candidate for MIR and far-infrared NLO applications, and even for THz transmission and generation.

Controllable seeded flux growth and optoelectronic properties of bulk o-SiP crystals

Two-dimensional (2D) materials have recently attracted great interest due to their promising optoelectronic applications. Orthorhombic SiP (o-SiP) is a 2D layered crystal and may have a significant impact on optoelectronic technologies. Large-sized bulk o-SiP single crystals have been successfully grown by a seeded flux method. The size and morphology of o-SiP crystals can be controlled by changing the growth conditions. The carrier mobility and band gap of o-SiP were characterized in detail. The photoresponse properties of o-SiP were investigated and a relatively fast response has been demonstrated. The experimental results indicate that o-SiP may be an excellent candidate for applications in electronics and optoelectronics.

Top-seeded solution growth and characterization of a Bi2Mo2.66W0.34O12 single crystal

Single crystals of Bi2Mo2.66W0.34O12 with dimensions up to 70 mm × 55 mm × 45 mm were successfully grown using a top-seeded solution growth (TSSG) method with a MoO3–WO3 mixture as a flux. The material crystallizes in centrosymmetric space group P21/c (no. 14), with unit cell parameters of a = 7.7212(8) A, b = 11.4938(12) A, c = 11.9970(12) A, and β = 115.5070(10)°. The as-grown crystals exhibit {100}, {010}, {011}, {110}, {021}, {012}, {120}, {−111}, {−102}, and {1−1−2} facets, which are in good agreement with the predicted growth morphology based on the Bravais–Friedel and Donnay–Harker (BFDH) method. High-resolution X-ray diffraction (HRXRD) measurement on the (040)-faced plate shows that the full-width at half-maximum (FWHM) of the rocking curve is 54′′, which indicates high crystal quality. Our measurements show that it melts congruently and exhibits a wide transmission range from 475 nm to 5200 nm. It is worth noting that Bi2Mo2.66W0.34O12 has a large birefringence (Δn = 0.24 at 480 nm), indicating that the crystal can be a promising polarizing optical material.

Highly sensitive detection of polarized light using a new group IV–V 2D orthorhombic SiP

Group IV–V 2D semiconductors, such as GeP and GeAs, have attracted increasing attention as a hot research topic due to their high in-plane anisotropic properties. As one among them, orthorhombic SiP (o-SiP) deserves more attention due to its sufficiently high carrier mobility, large band gap, excellent stability and even a direct band gap in the monolayer. In this work, the experimental Raman modes were identified based on DFT calculations and then we demonstrated highly in-plane anisotropy of the phonon vibrations by angle-resolved polarized Raman spectroscopy. In addition, o-SiP based photodetectors were fabricated to investigate the in-plane anisotropic photoresponse. The results indicate that o-SiP is an alternative photodetector with high responsivity and well-reproducible cycles. Furthermore, high anisotropy was revealed with a notably anisotropic on/off switching ratio. Our results show that o-SiP is a new member of the family of group IV–V 2D semiconductors with intriguing optoelectronic properties, and will open new opportunities for promising applications in advanced photonic and optoelectronic devices.