Laser-excited optical emission response of CdTe quantum dot/polymer nanocomposite under shock compression

Abstract

Laser-driven shock compression experiments and corresponding finite element method simulations are carried out to investigate the blueshift in the optical emission spectra under continuous laser excitation of a dilute composite consisting of 0.15% CdTe quantum dots by weight embedded in polyvinyl alcohol polymer. This material is a potential candidate for use as internal stress sensors. The analyses focus on the time histories of the wavelength blue-shift for shock loading with pressures up to 7.3 GPa. The combined measurements and calculations allow a relation between the wavelength blueshift and pressure for the loading conditions to be extracted. It is found that the blueshift first increases with pressure to a maximum and subsequently decreases with pressure. This trend is different from the monotonic increase of blueshift with pressure observed under conditions of quasistatic hydrostatic compression. Additionally, the blueshift in the shock experiments is much smaller than that in hydrostatic experiments at the same pressure levels. The differences in responses are attributed to the different stress states achieved in the shock and hydrostatic experiments and the time dependence of the mechanical response of the polymer in the composite. The findings offer a potential guide for the design and development of materials for internal stress sensors for shock conditions.

Exploration of CdTe quantum dots as mesoscale pressure sensors via time-resolved shock-compression photoluminescent emission spectroscopy

“…Similar to experimental results we reported previously 13 in both glass and polymer, the maximum blueshift does not increase monotonically with increasing shock pressure. Instead there is a turnover pressure where the blueshift reaches a peak and then starts decreasing at $4 GPa in the polymer and $9 GPa in the glass.…”

“…As mentioned in the previous work 13 and Ref. 12, non-hydrostatic strain states of the QD can result in lower blueshift and non-monotonic dependence on pressure.…”

“…Previous studies have indicated that positively-charged QDs are needed with the PVA matrix, since negatively-charged QDs heavily aggregate in PVA, leading to a complex and abnormal spectroscopic response. As shown in our previous theoretical study, 13 the overall shock-induced blueshift mechanism can be understood based on strain tuning of the QD bandgap using a simplified model of a QD without surface capping groups in a matrix. However, factors such as shock-induced photoluminescent emission intensity change, peak width change, and the possibility of dynamic phase transformations, require more detailed experimental studies.…”

“…[10][11][12] In our recent theoretical study 13 on QDs subjected to shock-compression and associated non-hydrostatic loads, pressure-induced blueshifts were observed to initially increase to a maximum and then decrease. The effect was also confirmed through experimental studies 13 of the photoluminescent emission spectra of shocked $3 nm CdTe QDs in a hydrophilic polymer matrix (poly-vinyl alcohol; PVA).…”

“…[10][11][12] In our recent theoretical study 13 on QDs subjected to shock-compression and associated non-hydrostatic loads, pressure-induced blueshifts were observed to initially increase to a maximum and then decrease. The effect was also confirmed through experimental studies 13 of the photoluminescent emission spectra of shocked $3 nm CdTe QDs in a hydrophilic polymer matrix (poly-vinyl alcohol; PVA). However, the time response of the measured blueshift from the QDs in the PVA matrix was not very fast (of the order of $60 ns), indicating that the highly sluggish mechanics of the surrounding (polymer matrix) medium plays an important role in influencing the optomechanical response of the QDs.…”