Pressure-induced shift of energy levels and structural phase transition in CdSe/ZnS quantum dots


Pressure-induced shift of energy levels and structural phase transition in CdSe/ZnS quantum dots

Tauch, J.; Braun, J. M.; Keller, J.; Hinz, C.; Haase, J.; Seletskiy, D. V.; Leitenstorfer, A.; Pashkin, A.

Electronic band structure of CdSe/ZnS quantum dots under high pressures is studied using fluorescence spectroscopy. We observe a strong blue shift of about 50 meV/GPa for the emission line at 655 nm. At moderate pressures (below 3 GPa) this shift is linear and it is dominated by increase of the fundamental band gap of CdSe under pressure [1]. In contrast to bulk CdSe where the fluorescence is quenched above 3 GPa as a results of the phase transition into the rock-salt structure, the CdSe/ZnS quantum dots remain structurally stable up to 6.5 GPa. The shift of the fluorescence line below this pressure is strongly nonlinear with tendency to saturation. This behavior can be well described using the Murnaghan equation of state giving the deformation potential value of -3.5 eV.
The remarkably high pressure of the structural phase transition in the studied CdSe/ZnS quantum dots exceeds previously reported values for CdSe nanocrystals [2] and bulk CdSe [1]. Presumably, the wurtzite structure of the quantum dots is stabilized by the ZnS shell. This structural robustness together with the high fluorescence yield and the large pressure coefficient of the wavelength shift make CdSe quantum dots a promising alternative to bulk ruby crystals for precise pressure calibration at moderate pressures.

[1] W. Shan et al., Appl. Phys. Lett. 84, 67 (2004).
[2] S. H. Tolbert and A. P. Alivisatos, J. Chem. Phys. 102, 4642 (1995).

Keywords: quantum dots; high pressure; structural phase transition

  • Poster
    Pressure and Strain Effects in Correlated Electron Materials, 06.-10.10.2014, Dresden, Germany

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