Raman spectroscopy of very small Cd1−xCoxS quantum dots grown by a novel protocol: direct observation of acoustic-optical phonon coupling

Authors

  • E. S. Freitas Neto,

    Corresponding author
    • Instituto de Física, Universidade Federal de Uberlândia, CP 593, Laboratório de Novos Materiais Isolantes e Semicondutores (LNMIS), Uberlândia, MG, Brazil
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  • A. C. A. Silva,

    1. Instituto de Física, Universidade Federal de Uberlândia, CP 593, Laboratório de Novos Materiais Isolantes e Semicondutores (LNMIS), Uberlândia, MG, Brazil
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  • S. W. da Silva,

    1. Instituto de Física, Universidade de Brasília, Núcleo de Física Aplicada, 70910-900, Brasília, Brazil
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  • P. C. Morais,

    1. Instituto de Física, Universidade de Brasília, Núcleo de Física Aplicada, 70910-900, Brasília, Brazil
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  • J. A. Gómez,

    1. Departamento de Física, Faculdade de Filosofia, Ciências e Letras de Ribeirão Preto, Universidade de São Paulo, Ribeirão Preto, SP, Brazil
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  • O. Baffa,

    1. Departamento de Física, Faculdade de Filosofia, Ciências e Letras de Ribeirão Preto, Universidade de São Paulo, Ribeirão Preto, SP, Brazil
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  • N. O. Dantas

    Corresponding author
    • Instituto de Física, Universidade Federal de Uberlândia, CP 593, Laboratório de Novos Materiais Isolantes e Semicondutores (LNMIS), Uberlândia, MG, Brazil
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Correspondence to: E. S. Freitas Neto and N. O. Dantas, Laboratório de Novos Materiais Isolantes e Semicondutores (LNMIS), Instituto de Física, Universidade Federal de Uberlândia, CP 593, 38400–902, Uberlândia, MG, Brazil. E-mail: ernestosfn@yahoo.com.br; noelio@ufu.br

Abstract

Glass-embedded Cd1−xCoxS quantum dots (QDs) with mean radius of R ≈ 1.70 nm were successfully synthesized by a novel protocol on the basis of the melting-nucleation synthesis route and herein investigated by several experimental techniques. Incorporation of Co2+ ions into the QD lattice was evidenced by X-ray diffraction and magnetic force microscopy results. Optical absorption features with irregular spacing in the ligand field region confirmed that the majority of the incorporated Co2+ ions are under influence of a low-symmetry crystal field located near to the Cd1−xCoxS QD surface. Electron paramagnetic resonance data confirmed the presence of Co2+ ions in a highly inhomogeneous crystal field environment identified at the interface between the hosting glass matrix (amorphous) and the crystalline QD. The acoustic-optical phonon coupling in the Cd1−xCoxS QDs (x ≠ 0.000) was directly observed by Raman measurements, which have shown a high-frequency shoulder of the longitudinal optical phonon peak. This effect is tuned by the size-dependent sp-d exchange interaction due to the magnetic doping, causing variations in the coupling between electrons and longitudinal optical phonon. Copyright © 2013 John Wiley & Sons, Ltd.

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