Dapeng Xu

CaNb₂O₆ single crystals with an orthorhombic columbite structure are grown via an optical floating zone (OFZ) method. The as-grown crystals are colorless and free of low-angle grain boundaries and inclusions. They are transparent (up to 62%) in the visible to the infrared region (400–1000 nm) and have a low absorption coefficient (α = 1.56). The bandgap is determined as a direct transition and E_g = 4.28 eV. The wavelength-dependent refractive index and extinction coefficient of the CaNb₂O₆ crystals are derived from the obtained T and α spectra. Their photoluminescence spectra exhibit a strong and broad emission band centered at 465 nm.

The spinel structure Zn _1.8 Co _0.2 TiO ₄ single crystals with 5 mm diameter and 30 mm length were successfully grown by an optical floating zone method.

The spinel Zn₂TiO₄single crystals were grownviaoptical floating zone technology in an argon atmosphere for the first time. And temperature dependent Raman spectra were presented.

A high‐quality Zn₂TiO₄ crystal was used as a prototype for determination of the optical interband transitions by measuring the absorption spectrum of the crystal along the a‐axes at room temperature in the range of 200–1000 nm. Based on the theory of band‐to‐band transitions, the indirect energy gap and the phonon energy were determined as E_gi = 3.29 eV and E_p = 0.09 eV, respectively. Also, this phonon was just the vibrational mode at 721 cm⁻¹ in the Raman spectra, which participated in the indirect transitions of the Zn₂TiO₄.

Using Y(NO₃)₃·6H₂O and Co(NO₃)₂·6H₂O as the starting materials, the single‐phase YCoO₃has been synthesized by a two‐step process involving a sol–gel technique and a sintering method. The structure, electromagnetic properties, and thermal stability of the synthesized samples were measured by XRD, thermogravimmetry and differential thermal analysis (TG–DTA), TEM, and vibration sample magnetometer (VSM). The experimental results show that the synthesis conditions of the single‐phase YCoO₃are 900–950 °C for 10 h in air. And the synthesis temperature is extended to 900–1000 °C and the sintering time is shortened to 5 h in an oxygen atmosphere. The synthesized powders have orthorhombic structure, with a diameter of ∼30 nm, which is stable in air below 1050 °C and in oxygen atmosphere below 1100 °C. Above those temperatures, YCoO₃decomposes into Y₂O₃and Co₃O₄.

The transmittance and absorption spectra of a high‐quality Zn₂TiO₄ single crystal have been measured along the a‐axes at room‐temperature in the range of 200‐1000 nm. The wavelength dependent refractive index, extinction coefficient, real and imaginary parts of the complex dielectric constant of the Zn₂TiO₄ crystal have been derived from the measured T and α spectra. By fitting the refractive index spectrum, the Sellmeier dispersion equation of the Zn₂TiO₄ crystal has been obtained. The validity of Cauchy‐Sellmeier equation has been evaluated in the energy range of 2.90–3.20 eV representing the Urbach tail. Applying the single‐effective oscillator model, the dispersion energy E_d and the oscillator energy E₀ have been determined as 18.76 and 5.05 eV, respectively. The obtained dispersion energy E_d takes on ionic crystal value.

The Raman spectra of all-trans-lycopene in n-hexane were measured under high pressure, and the results compared with those of β-carotene. The different pressure effects on Raman spectra are analyzed taking into account the different structures of lycopene and β-carotene molecules. It is concluded that: (a) the vibronic coupling between the S₁ and S₀ states of β-carotene is stronger than that of lycopene, (b) the diabatic frequency increment of the ν₁ mode is more susceptible to pressure than that of the ν₂ mode for lycopene, and (c) β-rings rotation can relieve the pressure effect on the C=C bond length in β-carotene. This work provides some insights for elucidating the structural and environmental effects on Raman spectra of carotenoids.

Manganese oxyborate (Mn₂OBO₃) necklace‐like nanofibers have been successfully synthesized by an electrospinning technique. First, poly(vinyl pyrrolidone) PVP/[Mn(CH₃COO)₂ + H₃BO₃] composite fibers (average size of 300 ± 10 nm in diameter) were fabricated by an electrospinning method using a solution that contained PVP and manganese acetate and boric acid. Manganese oxyborate (Mn₂OBO₃) nanofibers were prepared by sintering the above composite fibers in air at 600, 700, and 800 °C, and the calcined nanofibers were characterized by X‐ray diffraction (XRD), Raman, scanning electron microscopy (SEM), and transmission electron microscopy (TEM), respectively. After sintering at 600 °C, monoclinic phase Mn₂OBO₃ nanofibers of 180 ± 20 nm in diameter were successfully obtained. Morphology analysis showed that the surface of the 700 °C‐sintered Mn₂OBO₃ nanofibers (average size of 250 ± 20 nm in diameter) was rough and they had fiberlike structure with packed particles. The 800 °C‐sintered Mn₂OBO₃ fibers have necklace‐like morphology. The crystallite size of the nanoparticles contained in nanofibers increases from 100 to 200 nm with increasing calcination temperature between 700 and 800 °C. The morphology changes of the Mn₂OBO₃ nanofibers can be attributed to the grain growth during the calcinations process. The Raman spectrum of Mn₂OBO₃ was provided and assigned.