Strain-dependent photoluminescence behavior in three geometries of CdSe/CdS nanocrystals Page: 4 of 21
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The samples were dispersed in a hydrostatic (1:1 v/v pentane:isopentane) or non-hydrostatic
(toluene) pressure medium and loaded into the DAC, with an initial pressure of 0.5-1 GPa.
Toluene freezes at 1.7 GPa and shows high viscosity behavior above ambient pressures,
indicative of a highly anisotropic, non-hydrostatic pressure transmitting medium". The pressure
in the DAC was increased to <6 GPa, and then decreased to ambient pressure. Fluorescence
traces obtained during the experiment (Fig. 2) demonstrate highly contrasting behavior between
hydrostatic and non-hydrostatic pressure conditions, and among particle geometries. The most
obvious trend under hydrostatic pressure is a pressure-induced blue-shift of the PL peak. A
slight asymmetric broadening of the peak at longer wavelengths is observed at higher
pressures. The behavior under non-hydrostatic pressure is markedly different. For dots, the PL
peak splits into a doublet at pressures above 0.7 GPa. For dots and rods, a shallower peak also
typically arises at -650 nm. The PL peak in tetrapods instead slightly red-shifts with increasing
pressure, with the appearance of a small blue shoulder. The fluorescence behavior is reversible,
with no apparent hysteresis, although the PL peaks are somewhat wider at the end of the
experiment. The particles remained intact throughout the experiment as demonstrated by
sample recovery post-compression (Fig. 2 insets); we found that above 6 GPa, recovered
nanoparticles were broken due to the high non-hydrostatic pressure environment within the cell.
We did not observe the abrupt PL intensity decrease or peak broadening associated with a
phase transition to rock salt12; due to the mechanically stiffer CdS shell on the surface, these
particles likely undergo this phase transition at higher pressures 13. The sharp spectral peak
around 700 nm is from fluorescence of the ruby grains used as a pressure gauge within the
To quantitatively evaluate the PL shifts of the particles, we fit the experimental data to a sum of
Gaussian curves (see Methods). PL peak energies as a function of pressure are shown in Fig.
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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/m1/4/?rotate=90: accessed May 27, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.