Duorong Yuan

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.

Investigation of Ca3TaGa3Si2O14 piezoelectric crystals for high temperature sensors

The dielectric and electromechanical properties of fully ordered Ca3TaGa3Si2O14 (CTGS) crystals were investigated over the temperature range of −60∼700 °C. The highest electromechanical coupling factor, k26 (18.9%) and piezoelectric coefficient, d26 (−11.5 pC/N) were obtained for (YXl)-25° cuts. The temperature dependent behavior of resonance frequency (fr) was investigated in single-rotated thickness shear mode (TSM) (YXl)θ cuts (θ = −35°∼10°). The turnover temperatures of resonance frequency were found to increase from 20 °C to 330 °C, as the rotation angle θ varied from −22.5° to −35°. Bulk acoustic wave (BAW) resonators based on Y(−30°) monolithic disks with a fundamental frequency ∼2.87 MHz were fabricated, where the in air mechanical quality factor Q was found to be on the order of 24000 and 10000 at 20 °C and 700 °C, respectively. The high coupling k26, high mechanical Q, and high electrical resistivity (16 MΩ·cm) at 700 °C, together with the near zero TCF characteristics at elevated temperatures, ...

Investigation of zero temperature compensated cuts in langasite-type piezocrystals for high temperature applications

Langasite-type crystals, including La3Ga5.5Nb0.5O14 (LGN), and La3Ga5.5Ta0.5O14(LGT) with disordered structure, and Ca3TaGa3Si2O14 (CTGS) and Ca3NbGa3Si2O14 (CNGS) with ordered structure, were grown using the Czochralski method. Resistivity was studied as a function of temperature. Temperature coefficients of frequency (TCFs) for different cuts were investigated in the above crystals at elevated temperatures, which were found to be ±11 ppm K−1 and ±6.0 ppm K−1 up to 400 °C for LGN (YXl)1.5° and LGT (YXl) − 20° cuts, respectively, in thickness shear mode, while the TCF was found to be 21 ppm K−1 up to 800 °C for CTGS (YXl) − 20° and CNGS (YXl) − 20°. Furthermore, the dielectric and electromechanical behaviour of the above crystals with low TCF cuts as a function of temperature were studied. It was observed that CTGS and CNGS crystals with an ordered structure possessed temperature independent dielectric and electromechanical behaviour up to 800 °C, making CTGS and CNGS potential candidates for high temperature sensor applications.

Photoluminescence characteristics of ZnS nanocrystallites co-doped with Co2+ and Cu2+

Zinc sulfide (ZnS) nanoparticles co-doped with Cu2+ and Co2+ have been prepared by precipitation from homogeneous solutions of zinc, copper and cobalt salt compounds, with S2− as precipitating anion formed by decomposition of thioacetamide. X-ray diffraction shows that the average crystallite size of doped and undoped ZnS nanometer-scale samples is about 2–3 nm. Novel luminescence characteristics (strong and stable visible-light emission, λem∼515–560 nm) have been observed for the co-doped ZnS nanocrystals at room temperature. The relative fluorescence intensity of the co-doped sample is dramatically higher than that of undoped ZnS nanocrystallites. The emission wavelength of the co-doped samples varies with change in the impurity mole ratio of Cu2+ and Co2+.

Cation distribution in co-doped ZnAl2O4 nanoparticles studied by X-ray photoelectron spectroscopy and 27Al solid-state NMR spectroscopy.

Co(x)Zn(1-x)Al(2)O(4) (x = 0.01-0.6) nanoparticles were synthesized by the citrate sol-gel method and were characterized by X-ray powder diffraction and transmission electron microscopy to identify the crystalline phase and determine the particle size. X-ray photoelectron spectroscopy and (27)Al solid-state NMR spectroscopy were used to study the distribution of the cations in the tetrahedral and octahedral sites in Co(x)Zn(1-x)Al(2)O(4) nanoparticles as a function of particle size and composition. The results show that all of the as-synthesized samples exhibit spinel-type single phase; the crystallite size of the samples is about 20-50 nm and increases with increasing annealing temperature and decreases with Co-enrichment. Zn(2+) ions are located in large proportions in the tetrahedral sites and in small proportions in the octahedral sites in Co(x)Zn(1-x)Al(2)O(4) nanoparticles. The fraction of octahedral Zn(2+) increases with increasing Co concentration and decreases with increasing particle size. Besides the tetrahedral and octahedral coordinations, the presence of the second octahedrally coordinated Al(3+) ions is observed in the nanoparticles. The change of the inversion parameter (2 times the fraction of Al(3+) ions in tetrahedral sites) with Co concentration and particle size is consistent with that of the Zn fraction in octahedral sites. Analysis of the absorption properties indicates that Co(2+) ions are located in the tetrahedral sites as well as in the octahedral sites in the nanoparticles. The inversion degree of Co(2+) decreases with increasing particle size.

Dielectric and electromechanical properties of rare earth calcium oxyborate piezoelectric crystals at high temperatures

The electrical resistivity, dielectric, and electromechanical properties of ReCa₄O(BO₃)₃ (ReCOB; Re = Er, Y, Gd, Sm, Nd, Pr, and La) piezoelectric crystals were investigated as a function of temperature up to 1000°C. Of the studied crystals, ErCOB and YCOB were found to possess extremely high resistivity (p): p >; 3 × 10⁷ ω.cm at 1000°C. The property variation in ReCOB crystals is discussed with respect to their disordered structure. The highest electromechanical coupling factor κ₂₆ and piezoelectric coefficient d₂₆ at 1000°C, were achieved in PrCOB crystals, with values being on the order of 24.7% and 13.1 pC/N, respectively. The high thermal stability of the electromechanical properties, with variation less than 25%, together with the low dielectric loss (<;46%) and high mechanical quality factor (>;1500) at elevated temperatures of 1000°C, make ErCOB, YCOB, and GdCOB crystals promising for ultrahigh temperature electromechanical applications.

Crystal growth and physical properties of UV nonlinear optical crystal zinc cadmium thiocyanate, ZnCd(SCN)4

Abstract Zinc cadmium thiocyanate, ZnCd(SCN) 4 (ZCTC) single crystals of optical quality have been grown from aqueous solution by controlled evaporation at 40 °C. The morphology of the crystal was indexed. Raman spectroscopy, refractive indices, optical transmission and optical damage threshold of the ZCTC crystal were all performed at room temperature. Violet and ultraviolet (UV) light output by frequency doubling of a 808 nm GaAlAs laser diode and a continuous wave Ti:sapphire laser at 760 nm were achieved. The dielectric constants, piezoelectric strain constants, electroptic coefficients, and direct current resistivities have also been measured.

Photoluminescence characteristics of ZnS nanocrystallites co-doped with Cu2+ and Cd2+

Abstract ZnS nanocrystallites co-doped with Cu 2+ and Cd 2+ have been prepared by precipitation from homogeneous solutions of transition metal (Zn 2+ , Cu 2+ and Cd 2+ ) salt compounds, with S 2− as precipitating anion formed by decomposition of thioacetamide (TAA). X-ray diffraction (XRD) patterns of the samples show that the average crystallite size of the doped and undoped ZnS nanocrystallites is ∼2.5±0.4 nm . Novel luminescence phenomena (green emission) have been observed from the co-doped ZnS nanocrystals. The photoluminescence (PL) property of the co-doped samples is significantly different from that of ZnS nanocrystallites doped with Cu 2+ or Cd 2+ .

Investigation of the dielectric and piezoelectric properties of ReCa4O(BO3)3 crystals

Piezoelectric ReCa4O(BO3)3 (ReCOB, Re: rare earth) crystals, including ErCOB, SmCOB, PrCOB and LaCOB, were successfully grown by the Czochralski (Cz) method. The dielectric constants were determined to be , and for ErCOB, , and for SmCOB, , and for PrCOB, , and for LaCOB, respectively. The electromechanical coupling factors k26 and piezoelectric coefficients d26 were found to be 18.5% (7.6 pC N−1), 27.0% (12.7 pC N−1), 31.5% (15.8 pC N−1) and 25.0% (11.8 pC N−1) for ErCOB, SmCOB, PrCOB and LaCOB crystals, respectively. The dielectric and piezoelectric properties as a function of Re3+ ion radius were studied, with maximum values being observed in the PrCOB crystals, due to the similar ion radius of Pr3+ and Ca2+. The relationship between the structure and dielectric/piezoelectric properties of ReCOB crystals was explored, to further optimize the dielectric and piezoelectric properties in ReCOB series crystals.

Crystal growth and characterization of a new organometallic nonlinear-optical crystal material: MnHg(SCN)4(C3H8O2)

A potentially useful second harmonic generation (SHG) organometallic nonlinear-optical crystal: manganese mercury tetrathiocyanate glycol monomethyl ether, MnHg(SCN) 4 (C 3 H 8 O 2 ) (MMTG) has been prepared, and high optical quality single crystals have been successfully grown by the slow temperature-lowering technique. Its structural, physicochemical and optical properties are characterized by elemental analyses, infrared spectroscopy, transmission electron microscopy (TEM), X-ray powder diffraction, thermal analysis, powder SHG measurements and Vis/UV/NIR spectroscopy. The results of characterizations have shown that MMTG possesses good physicochemical stabilities up to 145 °C, exhibits powder SHG efficiencies close to that of urea. The UV transparency cutoff is 375 nm, and the transmission is 33.54% at 404 nm, the sample thickness was 2.76 mm, which is 6% greater than that of MnHg(SCN) 4 (MMTC).