Strain-dependent photoluminescence behavior in three geometries of CdSe/CdS nanocrystals Page: 7 of 21
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The distinction between tetrapods versus dot and rod particles is that the unique geometry of
tetrapods makes them more physically sensitive to stress-induced effects. Once the medium
has frozen (or become quite viscous) around the tetrapods, further application of anisotropic
stress applies bending moments to each of the tetrapod arms, with each arm's bending moment
dependent on its orientation relative to the principal stress axes. Thus the arms of the tetrapod
act essentially as lever arms, subjecting the zb-CdSe core to large shear stresses so that some
bonds are stretched and others compressed relative to the hydrostatic configuration. The data
suggest that the net result of arm bending is a red-shifting of the energy gap. Consequently,
forces which bend tetrapod arms may be optically detected.
While we considered other mechanisms for previously observed strain- and shape-dependent
optical phenomena to explain our findings, they are ruled out given our experimental design.
First, it has been hypothesized that the blue-PL peak split in CdSe quantum-dot solids arising at
non-hydrostatic pressure conditions is due to an energy transfer mechanism between
particles21. This cannot be the central mechanism in our experiment, since the nanoparticle
sample is dilute. Second, the appearance of the red-peak under non-hydrostatic pressure
conditions is not due to a type I-type II heterostructure transition22, since this peak is also
observed in our bare CdSe dot pressure studies (Supplementary Information, Fig. S2). Finally,
an aspect ratio-induced crossover between the bands formed by the Se 4px 4py and the Se 4pz
orbitals23 does not cause the red-peak observed in the present study; the particle compression
is too slight to increase the aspect ratio. However, under non-hydrostatic conditions the Se 4pz
band may be at higher energy than the 4px and 4py bands for dots and tetrapods due to greater
compression in the z-direction17.
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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/m1/7/: accessed May 20, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.