Strain-dependent photoluminescence behavior in three geometries of CdSe/CdS nanocrystals Page: 5 of 21
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3a-c, and the percentage of particles in the red-most peak, calculated from the area under the
fitted peak, shown in Fig. 3d. There are four notable observations from this analysis. First, under
non-hydrostatic pressure for all three particle morphologies, two PL peaks are observed: a blue-
peak, whose energy as a function of pressure matches with that of the peak under hydrostatic
pressure, and a red-peak, which does not exist under hydrostatic pressure conditions. The two
peaks are due to fluorescence from two populations within the cell, rather than two allowed
transitions within individual particles, since the energy difference between the two peaks is
much larger than the thermal energy available. That the blue-peak and hydrostatic peak
energies match so well suggests that the particles emitting at the blue-peak experience a near-
hydrostatic environment within the DAC, while those emitting at the red-peak are affected by the
non-hydrostaticity. Second, under non-hydrostatic pressure for dots, the blue-peak further splits
into at least two peaks, but possibly more, as evidenced by the greater spread in peak position
(Fig. 3a). The hydrostatic pressure peak for dots, with a broader red side, is also fit to two peaks
for comparison. This blue-peak splitting phenomenon is not observed for rods or tetrapods.
Third, for dots and rods under non-hydrostatic pressure, the energy of the red-peak changes
somewhat (-5.6 and 5.2 meV/GPa respectively), while for tetrapods the red-peak emission red-
shifts at nearly two times this rate (-9.9 meV/GPa) (Fig. 3a-c insets). Fourth, tetrapods are
clearly the most affected by the non-hydrostatic pressure, with more than 95% of the population
in this red-peak state (Fig. 3d). This agrees intuitively considering the shape and larger size of
tetrapods compared with dots and rods. This also demonstrates that tetrapods are the most
suitable particle geometry for strain sensing as they are most likely to be strained. Under
hydrostatic pressure, the particles are isotropically compressed, while under non-hydrostatic
pressure, the particles additionally experience a net deviatoric stress which includes uniaxial
and shear stresses. The difference between the two informs the net strain due only to non-
hydrostatic stress. To investigate the optical effects of only non-hydrostatic stress on the
tetrapods, which leads to arm bending, the energy difference between the non-hydrostatic peak
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Choi, Charina L; Koski, Kristie J; Sivasankar, Sanjeevi & Alivisatos, A Paul. Strain-dependent photoluminescence behavior in three geometries of CdSe/CdS nanocrystals, article, May 26, 2009; Berkeley, California. (https://digital.library.unt.edu/ark:/67531/metadc1013869/m1/5/: accessed May 26, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.