Deformation-induced blueshift in emission spectrum of CdTe quantum dot composites

Polymer or glass films impregnated with quantum dots (QDs) have potential applications for mesoscale stress/strain sensing in the interior of materials under mechanical loading. One requirement in the development of such nanocomposite sensor materials is the establishment of calibrated relations between shifts in the emission spectrum of QD systems and the input stress/strain on the composites. Here, we use a multiscale computational framework to quantify the strain-dependent blueshift in the emission spectrum of CdTe QDs uniformly distributed in a matrix material under loading of a range of strain triaxiality. The framework, which combines the finite element method, molecular dynamics simulations and the empirical tight-binding method, captures the QD/matrix interactions, possible deformation-induced phase transformations and strain-dependent band structures of the QDs. Calculations reveal that the response of the QDs is strongly dependent on state of input strain. Under hydrostatic compression, the blueshift increases monotonically with strain. Under compression with lateral/axial strain ratios between 0.0 and 0.5, the blueshift initially increases, reaches a peak at an intermediate strain, and subsequently decreases with strain. This trend reflects a competition between increases in the energy levels associated with the conduction and valence bands of the QDs. The deformation-induced blueshift is also found to be dependent on QD orientations. The averaged blueshift over all orientations for the composite under uniaxial strain condition explains the blueshift variation trend observed in laser-driven shock compression experiments. Based on the simulation result, guidelines for developing QD composites as stress/strain sensing materials are discussed.