Raman spectroscopy of very small Cd_1−xCo_xS quantum dots grown by a novel protocol: direct observation of acoustic‐optical phonon coupling

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.

Diluted Magnetic Semiconductors Nanocrystals: Saturation and Modulation

“…The anisotropic characteristic of the eight lines (hf 1 ; hf 2; hf 3 ; hf 4 ; hf 5 ; hf 6; hf 7 ; hf 8 ) of the hyperfine interaction between the electron spin (S = 3/2) and the nuclear spin (I = 7/2) and its similar shapes for all xCo concentrations confirms magnetic doping in distorted tetrahedral sites. The result is compatible with a region where there is a large, inhomogeneous crystal field due to the lack of interface between the host glass matrix and the NCs [42].…”

“…Furthermore, the p-d and spin-orbit interactions in an asymmetric tetrahedral coordination complex [CoS 4 ] 6− provide a higher intensity for 3d-3d transitions [14,15,20,42]. Therefore, the exotic properties of these new materials called diluted magnetic semiconductors (DMS) NCs are linked to the nature of the sp-d exchange interaction that occurs between the charge carriers of the Bi 2 S 3 semiconductor bands around the electrons in the central metal ion orbital (Co 2+ ) with 3d 7 electronic configuration (spin) 3d 7 (S = 3/2) [15,20,36,42]. For Bi 2-x Co x S 3 NCs, the spin allowed transitions 4 A 2 ( 4 F) → 4 T 1 ( 4 F) and 4 A 2 ( 4 F) → 4 T 1 ( 4 P) are obtained with the energy value of the barycenter for a normal distribution of the bands observed in the spectrum absorption in the range of 0.62-1.24 eV and 1.70-2.60 eV.…”

Cd1−xMnxTe ultrasmall quantum dots growth in a silicate glass matrix by the fusion method

“…Thus, the energy of formation of quantum dots (QDs) decrease with increase magnetic impurities increases. [8][9][10][11] Several types of semiconductor QDs have been doped with semimagnetic ions to form nanostructures, such as Cd 1Àx Mn x S, 12 Cd 1Àx Co x S, 13 Cd 1Àx Mn x Se, 14 Pb 1Àx Mn x Se, 15 Pb 1Àx Mn x S, 16,17 Zn 1Àx Mn x O, [18][19][20] and Zn 1Àx Mn x Te. 21 The exchange properties of Mn 2þ incorporated in II-VI, III-V, and IV-VI semiconductors QDs enhance as the quantum confinement effect increases.…”

Controlling Densities of Manganese Ions and Cadmium Vacancies in Cd1–xMnxTe Ultrasmall Quantum Dots in a Glass Matrix: x-Concentration and Thermal Annealing

“…Furthermore, E SDL emission intensification is also related to an increase in the density of shallow level defects caused by the accumulation of dopant ions on and near the surface of the USQDs. 47 More specifically, the broadening and red shift in the PL spectra result from sp−d exchange interactions as manganese concentration increases. 47 E Mn emissions occur between the 4 T 1 → 6 A 1 levels, 48 which are characteristic of the d-orbital of Mn 2+ ions when incorporated substitutionally in II−VI semiconductors.…”