Xiufeng Cheng

Luminescence characteristics of ZnS nanoparticles co-doped with Ni2+ and Mn2+

Abstract ZnS nanoparticles doped with Ni2+ and Mn2+ have been prepared by co-precipitation from homogeneous solutions of Zn, Ni and Mn salt compounds, with S2− as precipitating anion formed by decomposition of thioacetamide (TAA). X-ray diffraction analysis shows that the average crystalline particle size of the doped and undoped ZnS nanometer scale samples is about 2–4 nm. A novel luminescent property has been observed in the photoluminescence (PL) spectra of the ZnS nanoparticles co-doped with Ni2+ and Mn2+. The ZnS nanoparticles can be doped with Ni2+ and Mn2+ during synthesis without altering the X-ray diffraction pattern. However, the emission wavelengths (with a color range from blue to green, λem=475–540 nm) and PL intensities of the co-doped samples vary with changing the impurity mole ratios of Ni2+ and Mn2+ in the co-doped samples. When the mole ratios of Ni2+ and Mn2+ in the co-doped sample are 0.3% and 2.0%, respectively, the relative fluorescence intensity of the co-doped samples is about four times of that of un-doped ZnS nanocrystals. The PL properties of the co-doped samples are dramatically different from those of Ni2+- and Mn2+-doped ZnS nanocrystals.

Growth, properties and application as an electrooptic Q-switch of langasite crystal

Abstract La 3 Ga 5 SiO 14 (langasite, LGS) was successfully grown by the Czochralski method. The transparency range, specific heat, thermal expansion, resistivity, dielectric constants, optical damage threshold and electrooptic (EO) coefficients of langasite crystal, have been determined. The transmission spectrum showed that the UV absorption edge of the colorless crystal is about 240xa0nm. The EO coefficients γ 11 and γ 41 are measured by the interferometric method and are 2.3 and 1.8xa0pm/V, respectively. A new EO Q-switch was successfully designed and fabricated by using the LGS crystal. The experimental results show that the new EO Q-switch made of langasite works properly. This is the first time that an EO Q-switch has been successfully operated with LGS as an EO crystal.

Spectroscopic properties of Co2+: ZnAl2O4 nanocrystals in sol–gel derived glass–ceramics

Abstract Transparent glass–ceramics containing zinc–aluminum spinel (ZnAl 2 O 4 ) nanocrystals doped with tetrahedrally coordinated Co 2+ ions were obtained by the sol–gel method for the first time. The gels of composition SiO 2 –Al 2 O 3 –ZnO–CoO were prepared at room temperature and heat-treated at temperature ranging 800–950xa0°C. When the gel samples were heated up to 900xa0°C, ZnAl 2 O 4 nanocrystals were precipitated. Co 2+ ions were located in tetrahedral sites in ZnAl 2 O 4 nanocrystals. X-ray diffraction analysis shows that the crystallite sizes of ZnAl 2 O 4 crystal become large with the heat-treatment temperature and time, and the crystallite diameter is in the range of 10–15xa0nm. The dependence of the absorption and emission spectra of the samples on heat-treatment temperature were presented. The difference in the luminescence between Co 2+ doped glass–ceramic and Co 2+ doped bulk crystal was analysed. The crystal field parameter D q of 423xa0cm −1 and the Racah parameters B of 773xa0cm −1 and C of 3478.5xa0cm −1 were calculated for tetrahedral Co 2+ ions.

Crystal growth, thermal and optical performance of BiB3O6

Abstract Large optical-quality BIBO crystals with sizes of 46×23×10xa0mm 3 and weight of 26.0xa0g have been grown by the top-seeded method. The data of thermal expansion and specific heat have been measured. The transmittance spectra along the different phase matching (PM) directions were measured in the range of 190–3200xa0nm. Their second-harmonic generation (SHG) properties were measured.

Crystal growth and properties of Ca3NbGa3Si2O14 single crystals

Abstract A new ordered langasite structure piezoelectric single crystal Ca 3 NbGa 3 Si 2 O 14 (CNGS) had been grown by the Czochralski method. X-ray powder diffraction experiments showed that the CNGS single crystals had a single phase and had the same structure as the La 3 Ga 5 SiO 14 (LGS) crystal. The differential scanning calorimetric experiment showed that CNGS crystal melted congruently at 1349.9°C. The thermal expansion coefficient perpendicular to Z direction had been measured to be 1.7×10 −6 /K between 293.15 and 403.15xa0K, and along Z -axis was almost unchanged between 283.15 and 433.15xa0K. The specific heat of the crystal had been measured to be 133.189xa0cal/molxa0K at 300.42xa0K. The transmittance spectra from 190 to 3200xa0nm were measured.

Crystal growth, spectral and thermal properties of nonlinear optical crystal: MnHg(SCN)4

Abstract Single crystals of the coordination complex nonlinear optical crystal material, manganese mercury thiocyanate with dimensions of 18×13×12xa0mm 3 , were grown from aqueous solutions by temperature-lowering method. The morphology of the crystals was indexed. The grown crystals were characterized by Raman spectroscopy, X-ray powder diffraction and thermal analysis. The specific heat of the crystal has been measured to be 468.1xa0Jxa0mol −1 K −1 at 330xa0K. The thermal expansion coefficients, a- and c-oriented, have been measured to be −1.06×10 −5 and 1.44×10 −4 xa0K −1 , respectively.

Growth and optical properties of Ho, Yb:YAl3(BO3)4 crystal

Abstract Single crystal of holmium, ytterbium-codoped yttrium aluminum tetraborate Ho,Yb:YAl3(BO3)4(Ho,Yb:YAB) has been grown by the flux method. The crystal structure still belongs to the space group R32. The absorption spectra in the visible and NIR regions have been measured at room temperature; and fluorescence spectrum of Ho,Yb:YAl3(BO3)4 crystal are also measured at room temperature excited by 976xa0nm laser. Not only the strong NIR emission peaks located at 1966xa0nm was observed, but also the visible upconversion luminescence has been found. The most strong upconversion luminescence of the Ho,Yb:YAl3(BO3)4 crystal is 5S5→5I8 transition (570xa0nm), and that of 5F5→5I8 transition (652xa0nm) of Ho3+ ion is 1.3 times smaller relatively. The mechanism of upconversion luminescence was discussed.

Growth and characterization of a novel UV nonlinear optical crystal: [MnHg(SCN)4(H2O)2]·2C4H9NO

Abstract Single crystals of the organometallic nonlinear optical material, diaqua(thiocyanato) manganese(II)mercury(II)]- N , N -dimethylacetamide (MMTWD), were grown from aqueous solutions. The morphology of the crystals was indexed. The grown crystals were characterized by elemental analyses, scanning electron microscopy (SEM), Raman and infrared spectroscopy, X-ray powder diffraction (XRPD), thermal analysis and Vis/UV/NIR spectroscopy. The MMTWD crystal exhibits good physicochemical stability at normal temperature and pressure. Its UV transparency cutoff is 360xa0nm, which is shifted to the violet by 13xa0nm, as compared with MnHg(SCN) 4 (MMTC). The optical transmission is 55.17% at 404xa0nm, which is by 27.81% higher than that of MMTC.

Thermal and laser properties of Yb:YAl3(BO3)4 crystal

Abstract Large optical-quality Yb:YAl3(BO3)4(Yb:YAB) crystals have been grown by the flux method. The thermal properties of Yb:YAB crystal were measured for the first time. The thermal properties of Yb:YAB crystal with different Yb3+ ion concentrations are also reported. The results show that the ytterbium concentration influences the properties of Yb:YAB crystal. The specific heat decreases with the increase of Yb3+ ion concentrations in the experiment range. Apparently, the thermal expansion coefficient increases along the c-direction with the increase of Yb3+ ion concentrations, while it changes slightly along the a-direction. The output laser in 1120–1140xa0nm ranges has been demonstrated pumped by InGaAs laser. The slope efficiency is 3.8%. The self-frequency-doubling output power of 1xa0mW is achieved.

The growth and properties of Ca3TaGa3Si2O14 single crystals

Abstract We have successfully grown a new ordered langasite structure piezoelectric single crystal Ca3TaGa3Si2O14 (CTGS) using the Czochralski (CZ) method. The single crystal structure was investigated by X-ray powder diffraction (XRPD) experiments and showed that the CTGS single crystals had a single phase and had the same structure as the La3Ga5SiO14 (LGS) crystal. The transmittance spectra from 190 to 3200xa0nm were measured and the transmittance of CTGS crystal was about 85% above 350xa0nm. The specific heat of the crystal has been measured to be 0.52xa0J/gxa0K at room temperature. The thermal expansion coefficients perpendicular and parallel to Z direction has been measured to be 5.2×10−6 and 3.7×10−6/K between 298.15 and 450xa0K by a thermomechanical analyzer (TMA).