Zhang Zeng-ming

Effect of oxygen-deficiency of CuO2 plane on the structure, magnetism, and transport properties

Polycrystalline samples La2 − xSrxCuO4 − δ (0.06 ≤ x ≤ 1.0) and the corresponding vacuum annealed samples were investigated systematically by means of XRD, infrared (IR) spectra, ESR, and resistivity. It is found that the doping of Sr and the oxygen vacancies in CuO2 planes show different effects on the lattice parameters a and c, and the changes of a and c of La2 − xSrxCuO4 − δ samples (x ≥ 0.2) rest with the cooperation of the two factors. The two high frequency IR vibration modes at 500 and 689 cm−1, which are referred to the vibrations of apical oxygen and planar oxygen, are analyzed in detail. The disappearance of the mode at 689 cm−1 is interpreted in terms of the screened effect of charge carriers in CuO2 planes. ESR results indicate that oxygen deficiency of CuO2 layers not only decreases carrier concentration, but also destroys the antiferromagnetic spin correlation or spin fluctuation and results in localized Cu2+ spins. The effect of localized Cu2+ spins (or spin scattering) on the superconductivity and transport properties is discussed in the text.

Thickness dependence of the optical constants of oxidized copper thin films based on ellipsometry and transmittance

Thin oxidized copper films in various thickness values are deposited onto quartz glass substrates by electron beam evaporation. The ellipsometry parameters and transmittance in a wavelength range of 300 nm-1000 nm are collected by a spectroscopic ellipsometer and a spectrophotometer respectively. The effective thickness and optical constants, i.e., refractive index n and extinction coefficient k, are accurately determined by using newly developed ellipsometry combined with transmittance iteration method. It is found that the effective thickness determined by this method is close to the physical thickness and has obvious difference from the mass thickness for very thin film due to variable density of film. Furthermore, the thickness dependence of optical constants of thin oxidized Cu films is analyzed.

Temperature dependence of the photoluminescence of MnS/ZnS core—shell quantum dots

The temperature dependence of the photoluminescence (PL) from MnS/ZnS core—shell quantum dots is investigated in a temperature range of 8 K–300 K. The orange emission from the 4T1 → 6A1 transition of Mn2+ ions and the blue emission related to the trapped surface state are observed in the MnS/ZnS core—shell quantum dots. As the temperature increases, the orange emission is shifted toward a shorter wavelength while the blue emission is shifted towards the longer wavelength. Both the orange and blue emissions reduce their intensities with the increase of temperature but the blue emission is quenched faster. The temperature-dependent luminescence intensities of the two emissions are well explained by the thermal quenching theory.

Temperature Dependence of Luminescence of CdS:Mn/ZnS Core-Shell Quantum Dots

Luminescence intensity of CdS:Mn/ZnS core-shell quantum dots (QDs) can be strongly enhanced in comparison with bulk CdS:Mn and nanoparticles, while the luminescence due to the surface state is greatly suppressed by a capping ZnS shell. We find that with the increasing temperature, the peak position of CdS:Mn/ZnS core-shell QDs blue shifts due to the reduction of phonon coupling. Unlike the bulk CdS:Mn, the luminescence of the core-shell QDs is less sensitive to thermal quenching.

Energy Transfer in Cubic PbF2:Gd Crystals

The emission and excitation spectra of cubic PbF2:Gd were measured. Compared with pure crystals, the emissions from Gd3+ were observed upon cation exciton excitation in lattices, while the emission from intrinsic self-trapped excitons was quenched. It indicates the energy transfer from exciton to the 4f state of Gd3+.