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Manganese-Doped Ag2S-ZnS Heteronanostructures Shuling Shen,† Yejun Zhang,† Yongsheng Liu,‡ Long Peng,† Xueyuan Chen,‡ and Qiangbin Wang*,† †
Division of Nanobiomedicine and i-Lab, Suzhou Institute of Nano-Tech and Nano-Bionics, Chinese Academy of Sciences, Suzhou, 215123 China ‡ Key Laboratory of Optoelectronic Materials Chemistry and Physics, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, Fuzhou, 350002 China S Supporting Information *
ABSTRACT: Doping semiconductor nanocrystals and integrating disparate components together are two effective ways for modulating the optical properties of semiconductor nanocrystals. For the first time, we successfully synthesized Mn-doped Ag2SZnS heteronanostructures (HNSs) by combining these two strategies together. The obtained Mn-doped Ag2S-ZnS HNSs exhibit multicolor emissions of blue, orange, and near-infrared (NIR), in which the blue emission originates from ZnS trap state, the orange emission is induced by the 4T1−6A1 transition in Mn2+ dopant, and the NIR emission is attributed to the band gap emission of Ag2S. Reaction temperature-dependent and Mn2+ dopant concentration-dependent optical properties, as well as the growth kinetics of Ag2S-ZnS HNSs during doping process, were systemically studied to achieve the desirable optical properties and preserve well-defined HNSs simultaneously. We expect that the prepared Mn-doped Ag2S-ZnS HNSs with tunable multicolor emissions will create numerous opportunities for potential applications in bioimaging and optoelectronic devices, and the facile methodology modulating Ag2S-ZnS HNSs with desirable properties will be general and be ready to other complex semiconductor nanostructures. KEYWORDS: manganese dopant, Ag2S, ZnS, heteronanostructures, multicolor emissions
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tunable dual emissions under a single wavelength excitation source at varying intensities.16 Liu and colleagues reported the Mn-doped ZnS quantum rods (QRs) with high quantum yields (QYs) (up to 45%), multiphoton emissions, and tunable dualcolor (blue and orange) by using different excitation wavelengths at room temperature.17 Integrating different functionalities from disparate components into one nanounit is another effective avenue for obtaining multifunctional nanostructures.18−20 We successfully synthesized matchstick-shaped Ag2S-ZnS HNSs with Ag2S QDs as matchstick head and ZnS QRs as matchstick stem, which possess both blue and NIR emissions from the photoluminescence (PL) natures of ZnS QRs and Ag2S QDs, respectively.21 Inspired by the Mn-doped zinc chalcogenide
emiconductor nanocrystals with controllable structure and unique optical and electrical properties have attracted great interest due to their applications in bioimaging, optoelectronics, photocatalysts, photovoltaic devices, etc.1−7 It has been demonstrated that doping semiconductor nanocrystals with paramagnetic transition-metal ions is an effective way for tuning the optical properties of semiconductor nanocrystals.8−12 Among them, Mn-doped semiconductor nanocrystals have been regarded as a promising new class of nanophosphors and stimulated many efforts to investigate the properties and the intrinsic emission mechanism of Mn2+-doped semiconductor nanocrystals. For example, Peng et al. reported color-tunable Mn-doped ZnSe quantum dots (QDs) with low toxicity and high thermal and environmental stability as an alternative of CdSe nanocrystal emitters.13,14 Gamelin demonstrated that the emission color (orange and green) of Zn1−xMnxSe/ZnCdSe core/shell QDs could be tuned by changing the temperature between 210 and 400 K.15 Cao and co-workers reported that Mn-doped CdS/ZnS core/shell nanocrystals exhibited color© XXXX American Chemical Society
Received: May 1, 2012 Revised: May 29, 2012
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dx.doi.org/10.1021/cm301342z | Chem. Mater. XXXX, XXX, XXX−XXX
Chemistry of Materials
Article
room temperature. The NIR fluorescence spectra were collected on an Applied NanoFluorescence spectrometer (U.S.A.) at room temperature, applying the excitation laser source of 658 nm. Inductively coupled plasma atomic emission spectroscopy (ICP-AES) (Optima 7300DV, Perkin-Elmer, U.S.A.) was used to measure the concentrations of Mn, Ag, and Zn elements in Ag2S-ZnS HNSs. The Mn doping level was then calculated by the equation of [Mn]/([Mn] + [Zn] + [Ag]). X-ray photoelectron spectra (XPS) were recorded using a PHI 5000 Versaprobe spectrometer fitted with a monochromated Al Kα X-ray source (hν = 1486.6 eV). The XPS binding energies were calibrated by referring the C1s to 284.6 eV. X-ray diffraction (XRD) patterns of dried powders were recorded in thin film mode using a Bruker D8 Advance X-ray diffractometer (with Cu Kα radiation at 0.15418 nm). Room-temperature X-band electron paramagnetic resonance (EPR) spectra were recorded using a JEOL JES-FA200 EPR spectrometer (300 K, 9064 MHz, X band). The PL lifetimes were obtained on an Edinburgh Instruments FLS920 spectrofluorimeter equipped with both continuous (450 W) and pulsed xenon lamps and a customized UV to mid-infrared steady-state and phosphorescence lifetime spectrometer (FSP920-C, Edinburgh) by using a 300 nm femtosecond laser (240−2600 nm, pulse duration
