Jie Hua

Dual emissive manganese and copper Co-doped Zn-In-S quantum dots as a single color-converter for high color rendering white-light-emitting diodes.

Novel white light emitting diodes (LEDs) with environmentally friendly dual emissive quantum dots (QDs) as single color-converters are one of the most promising high-quality solid-state lighting sources for meeting the growing global demand for resource sustainability. A facile method was developed for the synthesis of the bright green-red-emitting Mn and Cu codoped Zn-In-S QDs with an absorption bangdgap of 2.56 eV (485 nm), a large Stokes shift of 150 nm, and high emission quantum yield up to 75%, which were suitable for warm white LEDs based on blue GaN chips. The wide photoluminescence (PL) spectra composed of Cu-related green and Mn-related red emissions in the codoped QDs could be controlled by varying the doping concentrations of Mn and Cu ions. The energy transfer processes in Mn and Cu codoped QDs were proposed on the basis of the changes in PL intensity and lifetime measured by means of steady-state and time-resolved PL spectra. By integrating these bicolor QDs with commercial GaN-based blue LEDs, the as-fabricated tricolor white LEDs showed bright natural white light with a color rendering index of 95, luminous efficacy of 73.2 lm/W, and color temperature of 5092 K. These results indicated that (Mn,Cu):Zn-In-S/ZnS QDs could be used as a single color-converting material for the next generation of solid-state lighting.

Temperature-dependent photoluminescence of inorganic perovskite nanocrystal films

Temperature-dependent photoluminescence (PL) properties of inorganic perovskite CsPbBr3 nanocrystal (NC) films were studied by using steady-state and time-resolved PL spectroscopy. The closely packed solid films were obtained by dropping NC solution on silicon substrates. It was found that the PL intensities of the NC films, which are dependent on the size of NCs, slightly decreased with increasing temperature to 300 K, while the PL intensities dropped rapidly with increasing temperature above 300 K and were nearly quenched at 360 K. Further the corresponding average PL lifetimes increased significantly with increasing temperature below about 320 K and then significantly became shorter. The PL quenching mechanisms were demonstrated through heating and cooling experiments. The experimental results indicated inorganic perovskite NCs exhibited a thermal PL quenching in the temperature range of 80–300 K and a thermal degradation at temperatures above 300 K. The linewidths, peak energies, and lifetimes of PL emissions for the NC films as a function of temperature were discussed in detail.

Efficient white light emitting diodes based on Cu-doped ZnInS/ZnS core/shell quantum dots

We report the fabrication of efficient white light-emitting diodes (WLEDs) based on Cu : ZnInS/ZnS core/shell quantum dots (QDs) with super large Stokes shifts. The composition-controllable Cu : ZnInS/ZnS QDs with a tunable emission from deep red to green were prepared by a one-pot noninjection synthetic approach. The high performance Cu : ZnInS QD-WLEDs with the colour rendering index up to 96, luminous efficacy of 70-78 lm W(-1), and colour temperature of 3800-5760 K were successfully fabricated by integration of red and green Cu-doped QDs. Negligible energy transfer between Cu-doped QDs was clearly found by measuring the photoluminescence lifetimes of the QDs, consistent with the small spectral overlap between QD emission and absorption. The experimental results indicated low toxic Cu : ZnInS/ZnS QDs could be suitable for solid state lighting.

Photoluminescence properties of transition metal-doped Zn–In–S/ZnS core/shell quantum dots in solid films

The photoluminescence (PL) properties of transition metal ion (Mn2+ or Cu+) doped Zn–In–S/ZnS core/shell quantum dots (QDs) in solution and solid films were investigated by using steady-state and time-resolved PL spectra. The PL peaks and lifetimes of Mn or Cu doped Zn–In–S/ZnS QD films exhibited almost no variation in contrast to those of the corresponding QD/PMMA blend films, indicating that no energy transfer process occurred in the pure doped QD films, while an obvious energy transfer was found in CdSe/ZnS QD films. Compared with the QDs in solution, the PL lifetimes of pure Mn or Cu doped Zn–In–S/ZnS QD films dropped only 16.2–37.5% which was attributed to the formation of surface traps/defects due to the loss of ligands on the surface of QDs while that of CdSe/ZnS QD films was shortened to the initial value of 50% which mainly came from energy transfer between QDs. Furthermore, the change in PL lifetimes found in Mn or Cu doped QD films could be reduced effectively by increasing the shell thickness of QDs. The experimental results are beneficial to the design of Mn or Cu doped QD-based photoelectronic devices.

Electric-field tuning of magnetic anisotropy in the artificial multiferroic Fe3O4/PMN–PT heterostructure

ABSTRACT Modulation of the magnetic anisotropy by the electric field in epitaxial Fe3O4/PMN–PT multiferroic heterostructure is studied, which shows that the coercive field of Fe3O4 thin films can be decreased from 368 to 113 Oe by applying an electric field in PMN–PT [011] direction. Meanwhile, most shift of ferromagnetic resonance (FMR) field Hr () can reach up to −483 Oe by applying an external electric field. The giant shift of Hr from 251 to 9681 Oe is obtained as the sample rotated from θ = 90° (H // to θ = 0° (H // [100]) when the electric field was applied in Fe3O4/PMN–PT heterostructure. GRAPHICAL ABSTRACT IMPACT STATEMENT A giant shift of ferromagnetic resonance field was obtained by simultaneously applying an external electric field and a rotating sample along axes both parallel and perpendicular to the magnetic field.