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Freitas Neto E.S.,University Federal Of Uberlaindia | Da Silva S.W.,University of Brasilia | Morais P.C.,University of Brasilia | Morais P.C.,Huazhong University of Science and Technology | Dantas N.O.,University Federal Of Uberlaindia
Journal of Physical Chemistry C

We report on multiphonon Raman scattering in coupled Cd 1-xMnxS nanoparticles grown within a glass matrix by the melting nucleation approach. Magnetic force microscopy identified two different-sized groups of nanoparticles coupled together. The high-frequency shoulder appearing above the longitudinal optical (LO) phonon mode has evidenced the acoustic-optical phonon coupling in nanoparticles, which depends upon the Mn doping. We found that the multiphonon Raman scattering and the electron-LO phonon coupling can be tuned by thermal annealing. Finally, we found that the magnetic doping induces changes on both the sp-d exchange interaction and the nanoparticles' crystalline quality. We emphasize that our findings may have an impact on possible technological applications that request handling of the optically induced nonlinear features in nanoparticles which are favored by electron-phonon anharmonicities. © 2012 American Chemical Society. Source

Silva A.C.A.,University Federal Of Uberlaindia | Neto E.S.F.,University Federal Of Uberlaindia | Da Silva S.W.,University of Brasilia | Morais P.C.,University of Brasilia | And 2 more authors.
Journal of Physical Chemistry C

In this study we present modifications in a phonon confinement model in order to obtain a better description for the Raman spectra of spherical nanocrystals, namely: bare-core, core-shell, and core-multishell. Our new interpretations allow investigating the influences of the interfacial alloying and strain effects on the vibrational spectra of core-shell nanocrystals. The robustness of the modified phonon confinement model was confirmed by precisely describing the Raman spectra of wurtzite CdSe/CdS core-shell magic-sized quantum dots (CS-MSQDs) synthesized directly in aqueous solution by a new route. The CdSe MSQD sample was used as template to growth CdSe/CdS CS-MSQDs with different shell thickness by setting the synthesis temperature. By using our modified model to fit the Raman spectra of samples, we have obtained the size dimensions of CS-MSQDs (core-diameter and shell-thickness), in excellent agreement with the values obtained by the atomic force microscopy results, confirming that the change in the synthesis temperature is a simple and efficient way to control the CdS-shell thickness during the growth process. Furthermore, we have confirmed the formation of an alloy layer (CdSxSe1-x) at the interface of these CdSe/CdS CS-MSQDs and that the strain effects can be neglected for the wurtzite structure. © 2013 American Chemical Society. Source

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