Size Dependence\nof Temperature-Related Optical Properties\nof PbS and PbS/CdS Core/Shell Quantum Dots

Abstract

The\neffect of PbS core size on the temperature-dependent photoluminescence\n(PL) of PbS/CdS quantum dots (QDs) in the temperature range of 100–300\nK was thoroughly investigated and compared with shell-free PbS QDs.\nThe core/shell QDs show significantly smaller PL intensity variation\nwith temperature at a smaller PbS size, while a larger activation\nenergy when the PbS domain size is relatively large, suggesting both\ndifferent density and different distribution of defects/traps in the\nPbS and PbS/CdS QDs. The most remarkable difference consists in the\nPbS size dependence of the energy gap temperature coefficient (d<i>E</i>/d<i>T</i>). The PbS/CdS QDs show unusual non-monotonic\nd<i>E</i>/d<i>T</i> variation, resulting in the\nreversal of the d<i>E</i>/d<i>T</i> difference\nbetween the PbS and PbS/CdS QDs at a larger PbS size. In combination\nwith theoretical calculations, we find that, although lattice dilation\nand carrier-phonon coupling are generally considered as dominant terms,\nthe unique negative contribution to d<i>E</i>/d<i>T</i> from the core/shell interfacial strain becomes most important in\nthe relatively larger-core PbS@CdS QDs.