Abstract
Cu-doped ZnSe/ZnS/L-Cys core–shell QDs are prepared by both nucleation doping and growth doping in an aqueous synthesis method. Transport of photogenerated free charge carriers (FCCs) in these Cu-doped QDs is probed via a combination of surface photovoltaic (SPV), photoacoustic (PA), and electric-field-induced SPV techniques, supplemented by the UV–VIS absorption spectrum and Raman spectrum. The results confirm that the two doping mechanisms result in different doping locations and microelectronic structures of the Cu-doped QDs. The distinctive microelectronic structure of the QDs prepared by nucleation doping, as compared with those prepared by growth doping, results in a number of favorable SPV characteristics. For example, the QDs prepared by nucleation doping exhibit a higher SPV response intensity at 600 nm because of a higher concentration of photogenerated FCCs. The ratio of the strongest SPV response and the strongest PA signal of the QDs prepared by nucleation doping is up to 2.41 times greater than those of the QDs prepared by growth doping. This is because the greater numbers of photogenerated FCCs in the QDs prepared by nucleation doping generate the PV effect rather than the PA effect that is caused by a nonradiative de-excitation process. The position of the shoulder peak of the SPV response at a long wavelength of the QDs prepared by nucleation doping is significantly red-shifted compared with that of the QDs prepared by growth doping, leading to a broader SPV response range in the visible region. The QDs prepared by nucleation doping have a more obvious donor feature than those prepared by growth doping.
Highlights
In the past two decades, group II/VI semiconductor nanocrystals have been extensively investigated because of their unique microelectronic structure and optical and photoelectric properties.[1–8] They have had a variety of applications to date in solar cells, light-emitting diodes, photonic crystals, and biomarkers.[9–13] some problems are encountered in their practical use, such as the high toxicity of Cd-containing QDs and the photoluminescence self-quenching of some pure QDs.[14,15] efforts are being made to avoid the use of cadmium in QDs, with particular attention being paid to transition-element-doped noncadmium QDs because of their broad Stokes shift and tunable energy band structure.[14–20] For example, Mn-doped ZnS nanocrystals exhibit higher luminescent efficiency than the undoped nanocrystals owing to emission from the dopant centers.[21]
Cu-doped ZnSe/ZnS/L-Cys core–shell QDs are prepared by both nucleation doping and growth doping in an aqueous synthesis method
Cu-doped ZnSe/ZnS/L-Cys self-assembled core– shell QDs have been prepared via both nucleation doping and growth doping in an aqueous synthesis method
Summary
In the past two decades, group II/VI semiconductor nanocrystals (i.e., quantum dots, QDs) have been extensively investigated because of their unique microelectronic structure and optical and photoelectric properties.[1–8] They have had a variety of applications to date in solar cells, light-emitting diodes, photonic crystals, and biomarkers.[9–13] some problems are encountered in their practical use, such as the high toxicity of Cd-containing QDs and the photoluminescence self-quenching of some pure QDs.[14,15] efforts are being made to avoid the use of cadmium in QDs, with particular attention being paid to transition-element-doped noncadmium QDs because of their broad Stokes shift and tunable energy band structure.[14–20] For example, Mn-doped ZnS nanocrystals exhibit higher luminescent efficiency than the undoped nanocrystals owing to emission from the dopant centers.[21]. Researchers suggested that the formation process of doping QDs can be divided into two cases: nucleation and growth.[26] The former is to mix the precursor of QD reactant and dopant together at the nucleation initial stage. Cu-doped ZnSe/ZnS/L-Cys self-assembled core–shell QDs are prepared by the modified aqueous synthesis method under different experimental conditions, with the aim of studying the effect of various reaction mechanisms and doping sites on the transport of photogenerated FCCs in Cu-doped QDs. The photovoltaic characteristics of Cu-doped QDs are probed via a combination of surface photovoltaic (SPV), photoacoustic (PA), and electric-field-induced surface photovoltage (EFISPV) techniques, supplemented by ultraviolet-visible (UV–VIS) absorption spectrum and laser Raman spectrum
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