Mengkai Lü

Interfacial Confined Formation of Mesoporous Spherical TiO2 Nanostructures with Improved Photoelectric Conversion Efficiency

Uniform mesoporous TiO(2) nanospheres were successfully developed via an interfacial confined formation process for application in dye-sensitized solar cells. The mesoporous spherical structures greatly promote the dye-loading capacity, electron transfer, and light scattering, resulting in remarkable enhancement of the cell performance. The designed interfacial platform caused a reaction-limited aggregation of the TiO(2) nanocrystals, resulting in the formation of mesoporous spherical nanostructures with sphere diameter of 216 nm and pore size of 8 nm. The oriented attachment of adjacent TiO(2) nanocrystals facilitated the electron transfer process when the mesoporous TiO(2) nanospheres were used as electrode films. The dye coverage was enhanced remarkably in the mesoporous spherical TiO(2) samples. Owing to the enhanced light-harvesting efficiency, solar conversion efficiency was enhanced about 30% for the dye-sensitized solar cell (DSSC) based on mesoporous spherical TiO(2) in comparison with that made by commercial TiO(2) nanoparticles.

Synthesis of Anatase TiO2 Nanoshuttles by Self-Sacrificing of Titanate Nanowires

Anatase TiO(2) nanoshuttles have been successfully prepared via a hydrothermal method under alkaline conditions by employing titanate nanowires as the self-sacrificing precursors. The experimental results showed that a radical structural rearrangement took place from titanate wires to anatase TiO(2) shuttles during the hydrothermal reaction on the basis of a dissolution-recrystallization process. The surface of titanate nanowires plays a key role in the transformation process by providing both the structural units (e.g., TiO(6) octahedra) to realize anatase transformation and locations for the deposition and rearrangement of the dissolved structural units, while the formation of shuttle morphology is attributed to the minimization of surface energy with thermodynamically stable (101) facets of anatase TiO(2). The shape and phase transformation process were foundto be dependent on the hydrothermal reaction time. Raman and photoluminescence spectra confirmed the crystalline nature of the TiO(2) nanoshuttles.

Growth and properties of UV nonlinear optical crystal ZnCd(SCN)4

Abstract A second-order nonlinear optical coordination crystal, zinc cadmium thiocyanate, ZnCd(SCN) 4 (ZCTC) was grown as a frequency doubler, emitting UV light. A large typical single crystal with dimensions up to 15 × 7 × 7 mm 3 has been obtained by slow solvent-evaporation method for the first time. The infrared (IR) spectroscopy and X-ray powder diffraction (XRPD) of single crystals were performed at room temperature. The specific heat of the crystal has been measured to be 367.9 J/mol.K at 300 K. The thermal expansion coefficients, c- and a-oriented, have been measured to be −1.69 × 10 −5 and 1.95 × 10 −4 K −1 , respectively. The second harmonic generation (SHG) efficiency of ZCTC crystal is 51.6 times as high as that of urea reference, and the measured transmittance spectra from 190 to 3200 nm showed that the UV transparency cutoff occurs at 290 nm and the transmission is 73.22% at 380 nm. UV laser light of wavelength 380 nm has been achieved by the frequency doubling of a 760 nm laser diode at room temperature.

Photoluminescence properties of aeschynite‐type LaNbTiO6:RE3+ (RE = Tb, Dy, Ho) down‐converting phosphors

In this study, a series of LaNbTiO6:RE(3+) (RE = Tb, Dy, Ho) down-converting phosphors were synthesized using a modified sol-gel combustion method, and their photoluminescence (PL) properties were investigated as a function of activator concentration and annealing temperature. The resultant particles were characterized using X-ray diffraction, transmission electron microscopy, scanning electron microscopy, UV/Vis diffuse reflectance spectroscopy and PL spectra. The highly crystalline LaNbTiO6:RE(3+) (RE = Tb, Dy, Ho) phosphors with an average size of 200-300 nm obtained at 1100°C have an orthorhombic aeschynite-type structure and exhibit the highest luminescent intensity in our study range. The emission spectra of LaNbTiO6:RE(3+) (RE = Tb, Dy, Ho) phosphors under excitations at UV/blue sources are mainly composed of characteristic peaks arising from the f-f transitions of RE(3+), including 489 nm ((5) D4 → (7) F6) and 545 nm ((5) D4 → (7) F5) for Tb(3+), 476 and 482 nm ((4) F9/2 → (6) H15/2) and 571 nm ((4) F9/2 → (6) H13/2) for Dy(3+), and 545 nm ((5) F4 + (5) S2 → (5) I8) for Ho(3+), respectively. The luminescent mechanisms were further investigated. It can be expected that these phosphors are of intense interest and potential importance for many optical applications.

Combustion synthesis of novel Li0.9Y(0.9−x−y)Zr0.1O2:Eux3+, Ry3+(R = Ce,Bi) red luminescence nanocrystal and emission-mechanism research

Novel Li(0.9)Y((0.9-x-y))Zr(0.1)O(2):Eu(x)(3+), R(y)(3+) (R = Ce,Bi) red nanocrystal phosphors were synthesized by the sol-combustion process at 800 degrees C. XRD and TEM were used to evaluate the crystallinity and the morphological characterization of the samples. The photoluminescence properties and lifetime of the obtained phosphor nanoparticles were measured using an Edinburgh FLS920 at room temperature. The result showed that the luminescence intensity of Li(0.9)Y((0.9-x-y))Zr(0.1)O(2):Eu(x)(3+) was increased by Bi(3+) and Ce(3+) by 900% and 600%, respectively. The emission mechanism and sensitization mechanism of Bi(3+) and Ce(3+) on Eu(3+) emission intensity were described and explained in detail in this work. The high bright and color-uniform fluorescence images of the doped samples with short luminescence decay times (nanosecond level) confirmed the potential applications of the phosphors in light-emitting diodes and display devices.

Morphology-tunable fibers with Fe3O4 nanocrystals fabricated through assembly

A facile method has been developed to encapsulate Fe(3)O(4) nanocrystals (NCs) in morphology-tunable fibers (belt-like, solid, and tubal) by using a sonochemistry driven synthesis and a subsequent reflux procedure. By adapting the use of tetraethyl orthosilicate, ammonia, Cd(2+), and thiolglycolic acid (TGA) to an ultrasound-driven synthesis, the Fe(3)O(4) NCs were coated with a thin composite shell. Supersonic treatment plays an important role to prevent the agglomeration of the Fe(3)O(4) NCs in an alkaline condition. The composite shell became thicker due to the deposition of SiO(2) monomers, Cd-TGA clusters, Cd(2+), and free TGA molecules during reflux. In addition, these composite shell-coated Fe(3)O(4) NCs were assembled in composite fibers which were created by the growth of Cd-TGA clusters and the deposition of SiO(2) monomers. The Fe(3)O(4) NCs mono-dispersed in fibers revealed superparamagnetic behavior. The magnetic saturation value of tubal fibers is lower than those of belt-like and solid fibers. These fibers with Fe(3)O(4) NCs would be utilizable for further application. The strategy described here should give a useful enlightenment for the design and fabrication of morphology-tunable fibers with functional NCs.

Optical absorption properties of potassium iodate single crystals

Abstract The optical transmissivity of potassium iodate (KIO3) single crystals was measured from ultraviolet to infrared ranges. By using the results in visible range the wavelength dependence of absorption coefficient α and the root of it (α-hν, α1/2-hν) were calculated and the characteristic of absorption edge was discussed. The forbidden energy gap Eg of the crystals, which corresponds to intrinsic absorption related to direct transitions, is 4.13 eV, slightly higher than that in the literature. The absorption edge below 4.13 eV is attributable to indirect transition. The energy gap Eg (3.88 eV) corresponding to indirect transition and the energy Ep (806.7 cm−1) of phonons taking part in indirect transition at room temperature were calculated from α1/2-hν curve, the latter was verified by Raman spectrum of the crystals.

Measurement of Electro-Optic Coefficients of ZnCd(SCN)4 Crystal

In this paper, the electro-optic coefficients of ZnCd(SCN) 4 crystal measured by the interferometric method are reported. The results obtained are: γ 13 = 0.40 × 10 -12 m/V, γ 63 = 0.94 × 10 -12 m/V, γ 41 = 1.3 × 10 -12 m/V, γ 51 = 1.7 × 10 -12 m/V.

Photoluminescence characteristics of Ti2S3 nanoparticles embedded in sol–gel derived silica xerogel

Abstract Ti 2 S 3 nanocrystallites embedded in sol–gel derived silica xerogel have been prepared. Their photoluminescence (PL) characteristics have been evaluated and compared with those of pure silica xerogel. UV–vis absorption spectra, transmission electron micrograph, excitation spectra and PL spectra of the doped and undoped samples have all been investigated. Two emission peaks have been observed from the doped samples, one at 440 nm ( λ ex =380 nm) while the other at 600 nm ( λ ex =550 nm). The latter has been assigned to the Ti 2 S 3 nanocrystallites in the silica xerogel. Therefore, a novel luminescence property can be observed by introducing the semiconductor nanoparticles into the silica xerogel.

Electroelastic properties of THAMP

Abstract A new polar crystal trihydroxylaminomethane phosphate (THAMP) was synthesized from the aqueous solution. Belonging to point group 2, the crystal has independent 13 elastic, 8 piezoelectric and 4 dielectric constants. All these parameters have been determined using 14 properly oriented specimens and 4 vibration modes.