1. Homogeneously Alloyed CdSe1-xSx Quantum Dots (0 ≤ x ≤ 1)
Tangi Aubert, Marco Cirillo, Stijn Flamee, Rik Van Deun, Holger Lange,
Christian Thomsen, Zeger Hens
E-MRS Spring Meeting 2013, Strasbourg, France

2. Tuning optical properties of QDs
size
dependent
alloyed
QDs
composition
dependent

3. Alloyed QDs II-VI alloys: Cd(Se,Te), Cd(Se,S), Cd(Te,S), (Cd,Zn)Se, …
core-shell
gradient
homogeneous
Bailey et al., J. Am. Chem. Soc. 2003, 125, 7100; Swafford et al. J. Am. Chem. Soc. 2006, 128, 12299; Gurusinghe et al. J. Phys. Chem. C 2008, 112, 12795; Zheng et al. Adv. Mater. 2007, 19, 1475.

4. Heterogeneous Se-ODE synthesis
Synthesis of CdSe, ZnSe, CuInSe2 and Cu2(Zn,Sn)Se4 QDs TC
ODE
carboxylic acid
CdO
- open air (no flushing)
- T = 260°C
- 5 min reaction
- nearly full yield
- high solid load
heterogeneous
Se-ODE
allow large production
S. Flamee, M. Cirillo, S. Abe, K. De Nolf, R. Gomes, T. Aubert, Z. Hens, submitted.
S. Flamee, R. Dierick, M. Cirillo, D. Van Genechten, T. Aubert, Z. Hens, Dalton Trans doi /c3dt50757b
S. Flamee, Z. Hens, patent n°PCT/EP2012/072428, 2012.

5. Heterogeneous Se-ODE synthesis
Heterogeneous Se-ODE vs. Homogeneous S-ODE OR
heterogeneous
Se-ODE
homogeneous
S-ODE
CdSe
CdS
equivalent reactivities towards Cd
T. Aubert, M. Cirillo, S. Flamee, R. Van Deun, H. Lange, C. Thomsen, Z. Hens, Chem. Mater., /cm401019t

6. CdSe1-xSx synthesis 1-x x AND
Tunable synthesis through entire composition range (0 ≤ x ≤ 1)
1-x x
AND
heterogeneous
Se-ODE
homogeneous
S-ODE
CdSe1-xSx
T. Aubert, M. Cirillo, S. Flamee, R. Van Deun, H. Lange, C. Thomsen, Z. Hens, Chem. Mater., /cm401019t

7. size = 3 nm (myristic acid)
CdSe1-xSx alloyed QDs
Morphology and structure (TEM)
CdSe0.5S0.5
size = 3 nm (myristic acid)
size can still be tuned
with acid length
T. Aubert, M. Cirillo, S. Flamee, R. Van Deun, H. Lange, C. Thomsen, Z. Hens, Chem. Mater., /cm401019t

8. lattice parameter follows Vegard’s law
CdSe1-xSx alloyed QDs
Morphology and structure (XRD)
lattice parameter follows Vegard’s law
T. Aubert, M. Cirillo, S. Flamee, R. Van Deun, H. Lange, C. Thomsen, Z. Hens, Chem. Mater., /cm401019t

9. CdSe1-xSx alloyed QDs Morphology and structure (Raman)
fitted LO bands
LO frequency and FWHM
- LO shifts with composition
- narrow FWHM for x = 0, 0.5 and 1
- large FWHM for uneven compositions
homogeneous alloying

10. CdSe1-xSx alloyed QDs Optical properties absorption emission
T. Aubert, M. Cirillo, S. Flamee, R. Van Deun, H. Lange, C. Thomsen, Z. Hens, Chem. Mater., /cm401019t

11. CdSe1-xSx/CdS core-shell QDs
Synthesis: layer-by-layer (SILAR)
→ PL enhancement decreases with increasing S content in the core
Li et al., J. Am. Chem. Soc. 2003, 125,

12. CdSe1-xSx/CdS core-shell QDs
Confinement energy:
Econf (CdSe1-xSx/CdS) = Eg (CdSe1-xSx/CdS) - Eg,∞ (CdSe1-xSx)
Eg,∞ (CdSe1-xSx) = (1-x)Eg (CdSe) + xEg (CdS) - bx(1-x)
T. Aubert, M. Cirillo, S. Flamee, R. Van Deun, H. Lange, C. Thomsen, Z. Hens, Chem. Mater., /cm401019t

13. just accepted in Chemistry of Materials, DOI: 10.1021/cm401019t
Conclusion
CdSe1-xSx alloyed QDs
- fast, high yield and tunable synthesis
- homogeneous alloying (Raman spectroscopy)
- efficient tuning of the band gap
just accepted in Chemistry of Materials, DOI: /cm401019t

14. Thanks for your attention !
Aknowledgement
Max Kade
Foundation
Thanks for your attention !