Search

Metal halide perovskite nanocrystals (NCs) have attracted great attention in the fields of light-emitting diodes, lasers, X-ray imaging, solar cells and photoelectric detectors due to their excellent optoelectronic properties. Compared with organic-inorganic hybrid perovskite NCs, all inorganic perovskite CsPbX3 (X = Cl, Br, I) NCs have good photoelectric properties and high stability. To further improve the photoluminescence (PL) quantum yields (QYs) and stability of CsPbX3 NCs, researchers reduced the defects as nonradiative recombination centers in NCs by the following strategies: 1) surface treatment with different ligands; 2) control of synthesis conditions with halide rich compounds; 3) doping of metal ions. Among them, metal doping is considered as a universal and effective way to adjust the optoelectronic properties of semiconductors. It is found that the type and the concentration of metal ions have great influence on the electronic band structure and PL performance of NCs after the metal ions have been doped into CsPbX3 NCs. At the same time, compared with II-VI and III-V semiconductors, the unique structure of all inorganic perovskite NCs makes the doping of metal ions easier. Appropriate doping can not only enhance the intrinsic optical properties of the NCs without affecting their crystal structure, but also introduce new electronic energy levels into the NCs and new luminescent properties of doped metal ions. Based on metal ions doping strategy, the PLQYs of doped CsPbX3 NCs have been enhanced to nearly 100%. In this work, we summarize recent advances in metal doping of the four typical kinds of perovskite NCs, including CsPbCl3, CsPbBr3, CsPbI3, and Mn2+ doped CsPbX3, and discuss the physical mechanisms of the improved properties through doping metal ions. It should be pointed out that the doping of some metal ions such as Ni2+ and Cd2+ into the above four kinds of NC systems can effectively passivate NC defects, thus improving the PL QY and stability of NCs. In addition, we put forward some personal perspectives on the future research subjects of interest and directions of metal doping for enhanced PL of CsPbX3 NCs, which needs to be further explored in order to promote extensive application of perovskite NCs to various optoelectronic devices.

Thermal stability of quantum dot( QD) luminescence is considered as an important factor for their applications in luminescent devices because of the Joule heat caused by inevitable current. The temperaturedependent photoluminescence( PL) properties of Mn-doped Zn Se( Mn∶ Zn Se) QDs with different shell thickness in the temperature range from 80 to 500 K were studied by steady-state and time-resolved PL spectra. It was found that the Mn∶ Zn Se QDs with thick shell( 6. 5 monolayers( MLs)) exhibited better PL thermal stability than the thin shell coated ones( 2. 6 MLs). Because almost no PL quenching occurred for thick shell-coated Mn-doped QDs from 80 to 400 K,their PL quantum yield( QY) could keep 60% even at 400 K. Moreover,based on the change in temperature-dependent PL intensities and lifetimes of Mn ∶ Zn Se QDs,the thermal quenching mechanism was proposed. Finally,the stability of Mn∶ Zn Se QDs with different shell thickness are discussed on the basis of heating-cooling cycling examination( 300-500-300 K). For Mn∶ Zn Se QDs with thick shell,the PL was nearly totally recovered after the cycling examination. Thus,Mn∶ Zn Se QDs are promising for applications in luminescent devices,where strong thermal effect is inevitable.

Cu-doped quantum dots( QDs) were used as color converting materials for preparing efficient white light-emitting diodes( LEDs). The Cu-doped QDs synthesized by chemical method showed composition-tunable emission from green to deep red and large Stokes shifts. By using the combination of green light-emitting Zn In S∶ Cu QDs and red emitting Zn Cd S∶ Cu QDs with blue Ga N chips,a high color rendering white LED was fabricated. The resulting three-band RGB QD-white LED exhibits high performance with luminous efficacy of 71 lm / W,color rendering index up to 94,CIE-coordinates of( 0. 352 4,0. 365 1),and color temperature of 4 788 K. Based on the changes in the photoluminescence lifetimes of Cu-doped QDs,it is found that the energy transfer process from green Zn In S∶ Cu QDs to red Zn Cd S∶ Cu QDs can be negligible,because the red QDs had no absorption at green band. These results suggest that Cu-doped QDs are promising for solid state lighting.

The photoluminescence(PL) spectra of ZnCuInS quantum dots(QDs) were measured in the temperature range from 100 to 300 K.The temperature dependences of the PL energy,linewidth,and intensity of the ZnCuInS QDs were investigated in detail.An anomalous increase in band gap of ZnCuInS QDs with temperature was observed.The full width at half maximum of the PL and thermal activation energy Ea of ZnCuInS QDs were 300 and 100 meV,respectively.These results suggested that the PL in the ZnCuInS QDs originated from the recombination of many kinds of defect-related emission centers in the interior and on the surface of the QDs.

The effect of mercaptopropionic acid(MPA) molecules on the charge transfer process from the quantum dots to ZnO nanocrystal films was studied in this paper by the steady-state and time-resolved photoluminescence spectroscopy.The obtained high efficiently photoluminescent CdSe-core CdS/ZnS-multishell quantum dots with few defects are air stable in quantum dot based devices.Three samples were prepared to make the measurements of time-resolved photoluminescence spectra,CdSe quantum dots film,CdSe quantum dots spun cast on ZnO nanocrystal film(CdSe/ZnO),and MPA molecules linked CdSe quantum dots and ZnO nanocrystal film(CdSe/MPA/ZnO).The shortening of photoluminescence life times of CdSe quantum dots deposited on ZnO nanocrystal films with and without MPA molecules indicated the electron transfer process happened in the interface between CdSe quantum dots and ZnO nanocrystals.But the decreased rate of electron transfer from CdSe quantum dots to ZnO nanocrystal films with MPA molecules was found,compared to the electron transfer rate of the CdSe/ZnO sample.Considering the fact that MPA molecules did not improve the charge transfer process from CdSe quantum dots to ZnO nanocrystal films,it was indicated that the MPA molecules was not a good choice in CdSe quantum dot sensitized solar cell.The experimental result suggested that the direct adsorption of CdSe quantum dots on metal oxide nanocrystal films would obtain quantum dot sensitized solar cell with higher power conversion efficiency.

In this paper the microemulsion preparation, the morphology and structural characteristics of toil nanoparticles are reported in detail. The quantum confinement effect upon the strong polarizable nanoparticle are described with interfacial polarization, and their linear and nonlinear optical absorp-tion responses are explained with self trapped exciton model.

This paper reports the theoretical calculation of the ambipolar diffusion coefficient in TDFWM-IL. We have obtained the ambipolar diffuion coefficient Da= 0.3cm2/s for CdS:Cu and compared with measured results for PbS ultrafine particles.

The relaxation time of excited state of FeTTP in CHCl3 has been measured by laser frequency domain technique. The relaxation time of the first excited state is obtained to be 0.82 ps by the numerical fitting for the experimental curve.