The systematic variation of the EPR parameters of manganese in II–VI semiconductors

Koh, A.K.; Miller, David J.

doi:10.1016/0038-1098(86)90449-7

Cited by 18 publications

(12 citation statements)

References 22 publications

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“…This hyperfine coupling constant indicates that the Mn ions are in cubic ZnS lattice sites, and this result confirms that the dopants are indeed located inside the core/shell nanocrystals. [31][32][33] In addition, the Mn-doped nanocrystal sample before pyridine treatment shows a nearly identical EPR spectrum (grey line in Figure 1 D) to that of the sample after pyridine treatment (black line in Figure 1 D). Moreover, ICP measurements show that these two samples have a nearly identical doping level of 0.36 % (Figure 1 E).…”

Section: Resultsmentioning

confidence: 75%

Radial‐Position‐Controlled Doping of CdS/ZnS Core/Shell Nanocrystals: Surface Effects and Position‐Dependent Properties

Yang

Chen

Angerhofer

et al. 2009

Chemistry A European J

108

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Energy transfer in doped semiconductor nanocrystals: Mn-doped CdS/ZnS nanocrystals show interesting photoluminescence and EPR properties that are strongly dependent on the radial position of Mn dopants inside nanocrystals (see graphic). Furthermore, the results suggest a two-step mechanism for the energy transfer inside the doped nanocrystals.This paper reports a study of the surface effects and position-dependent properties of Mn-doped CdS/ZnS core/shell nanocrystals, which were prepared by using a three-step synthesis method. The Mn-doping level of these nanocrystals was determined by a combination of electron paramagnetic resonance spectroscopy and inductively coupled plasma atomic emission spectroscopy. These nanocrystals were further characterized by using transmission electron microscopy and fluorescence spectroscopy. First, we found that injecting a large excess of zinc stearate at the end of nanocrystal synthesis can sufficiently eliminate the surface-trap states from the doped CdS/ZnS core/shell nanocrystals and enhance their photoluminescence (PL) quantum yield (QY). Second, our results demonstrate that the Mn-PL QY is determined by the product of the efficiency of energy transfer from an exciton inside the CdS core to a Mn ion (Phi(ET)) and the efficiency of the emission from the Mn ion (Phi(Mn)). Third, Phi(Mn) strongly depends on the radial position of Mn ions in the doped core/shell nanocrystals. The position-dependent changes of Phi(Mn) nearly perfectly correlate to those of the linewidth of Mn EPR peaks: the higher the Phi(Mn), the narrower the linewidth of the Mn EPR peak. Fourth, the results demonstrate that Phi(ET) depends on the Mn-doping level as well as the inverse sixth power of the distance between a Mn ion and the center of its host nanocrystal. Accordingly, we propose a two-step mechanism for the energy transfer: 1) the energy transfer from an exciton inside the CdS core to a bound exciton around a Mn center, which is the rate-determining step and follows the Förster mechanism, and 2) the energy transfer from the bound exciton to the Mn center, which might follow a mechanism such as dark exciton (triplet exciton) or Auger transfer.

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Section: Resultsmentioning

confidence: 75%

Radial‐Position‐Controlled Doping of CdS/ZnS Core/Shell Nanocrystals: Surface Effects and Position‐Dependent Properties

Yang

Chen

Angerhofer

et al. 2009

Chemistry A European J

108

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“…If Mn would reside in the core of the nanocrystal, then typical A should be in the range of ∼65 × 10 −4 cm −1 . 13,30,31 It is reported in the literature that at such high A value the Mn atom exists as isolated Mn 2+ ions on the surface. 32 have demonstrated that ligand field splitting progressively increases from core-accumulated Mn to the surface-accumulated Mn-doped QD.…”

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confidence: 98%

“…If Mn would reside in the core of the nanocrystal, then typical A should be in the range of ∼65 × 10 −4 cm −1 . 13,30,31 It is reported in the literature that at such high A value the Mn atom exists as isolated Mn 2+ ions on the surface. 32,33 Thus, such high A value can exclude the option for the formation of MnSe 2 (or similar) compound.…”

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confidence: 99%

“…Such high value of A indicates that most of the dopants atoms (Mn) reside near the surface layer of the crystal structure of CdSe QD. If Mn would reside in the core of the nanocrystal, then typical A should be in the range of ∼65 × 10 –4 cm –1 . ,, It is reported in the literature that at such high A value the Mn atom exists as isolated Mn 2+ ions on the surface. , Thus, such high A value can exclude the option for the formation of MnSe 2 (or similar) compound. Santra et al have demonstrated that ligand field splitting progressively increases from core-accumulated Mn to the surface-accumulated Mn-doped QD.…”

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confidence: 99%

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Electron Trap to Electron Storage Center in Specially Aligned Mn-Doped CdSe d-Dot: A Step Forward in the Design of Higher Efficient Quantum-Dot Solar Cell

Debnath

Maity

Maiti

et al. 2014

J. Phys. Chem. Lett.

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Specially aligned surface-accumulated Mn-doped CdSe (MnCdSe) quantum dots (QDs) have been synthesized to study the effect of dopant atom on charge-carrier dynamics in QD materials. EPR studies suggest that the (4)T1 state of Mn(2+) lies above the conduction band of CdSe, and as a result no Mn-luminescence was observed from MnCdSe. Femtosecond transient absorption studies suggest that Mn atom introduces structural defects in surface-doped CdSe, which acts as electron trap center in doped QD for the photoexcited electron. Bromo-pyrogallol red (Br-PGR) were found to form strong charge-trasfer complex with both CdSe and MnCdSe QDs. Charge separation in both the CdSe/Br-PGR and MnCdSe/Br-PGR composites was found to take place in three different pathways by transferring the photoexcited hole of CdSe/MnCdSe QDs to Br-PGR, electron injection from photoexcited Br-PGR to the QDs, and direct electron transfer from the HOMO of Br-PGR to the conduction band of both the QDs. Hole-transfer dynamics are found to be quite similar (∼1.1 to 1.3 ps) for both of the systems and found to be independent of Mn doping. However, charge recombination dynamics was found to be much slower in the MnCdSe/Br-PGR system as compared with that in the CdSe/Br-PGR system, which confirms that the Mn dopant act as the electron storage center. As a consequence, the MnCdSe/Br-PGR system can be used as a better super sensitizer in quantum-dot-sensitized solar cell to increase efficiency further.

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“…EPR analysis (SI Figure 2) suggests the Mn-doped CdTeSe alloy has a large A value (∼95 G), which indicates that Mn atoms are localized on the surface of the alloy NCs. 35,59 Sarma and co-workers 48 demonstrated that in surface-doped NCs, ligand field splitting is much higher as compared to the core doped NCs. Because the 4 T 1 − 6 A 1 splitting is more, the 4 T 1 state of the Mn atom will lie above the conduction band edge of the CdTeSe alloy; as a result, the Mn-d emission was not observed from Mn-doped CdTeSe alloy NCs.…”

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confidence: 99%

Unusually Slow Electron Cooling to Charge-Transfer State in Gradient CdTeSe Alloy Nanocrystals Mediated through Mn Atom

Debnath

Maiti

Ghosh

2016

J. Phys. Chem. Lett.

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We have synthesized Mn-doped CdTeSe gradient alloy nanocrystals (NCs) by a colloidal synthetic method, and charge carrier dynamics have been revealed through ultrafast transient absorption (TA) spectroscopy. Due to the reactivity difference between Te and Se, a CdTe-rich core and CdSe-rich shell have been formed in the CdTeSe alloy with the formation of a gradient type II core-shell structure. Electron paramagnetic resonance studies suggest Mn atoms are located in the surface of the alloy NCs. Steady-state optical absorption and emission studies suggest formation of a charge-transfer (CT) state in which electrons are localized in a CdSe-rich shell and holes are localized in a CdTe-rich core which appears in the red region of the spectra. Electron transfer in the CT state is found to take place in the Marcus inverted region. To understand charge-transfer dynamics in the CdTeSe alloy NCs and to determine the effect of Mn doping on the alloy, ultrafast transient absorption studies have been carried out. In the case of the undoped alloy, formation of the CT state is found to take place through electron relaxation to the conduction band of the CT state with a time of 600 fs and through hole relaxation (from the CdSe-rich state to the CdTe-rich state) to the valence band of the CT state with a time scale of 1 ps. However, electron relaxation in the presence of Mn dopants takes place initially via an electron transfer to the Mn 3d state (d(5)) followed by transfer from the Mn 3d state (d(6)) to the CT state, which has been found to take place with a >700 ps time scale in addition to the hole relaxation time of 2 ps. Charge recombination time of the CT state is found to be extremely slow in the Mn-doped CdTeSe alloy NCs as compared to the undoped one, where the Mn atom acts as an electron storage center.

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The systematic variation of the EPR parameters of manganese in II–VI semiconductors

Cited by 18 publications

References 22 publications

Radial‐Position‐Controlled Doping of CdS/ZnS Core/Shell Nanocrystals: Surface Effects and Position‐Dependent Properties

Radial‐Position‐Controlled Doping of CdS/ZnS Core/Shell Nanocrystals: Surface Effects and Position‐Dependent Properties

Electron Trap to Electron Storage Center in Specially Aligned Mn-Doped CdSe d-Dot: A Step Forward in the Design of Higher Efficient Quantum-Dot Solar Cell

Unusually Slow Electron Cooling to Charge-Transfer State in Gradient CdTeSe Alloy Nanocrystals Mediated through Mn Atom

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