Transient photoluminescence and simultaneous amplified spontaneous emission from multiexciton states in<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:mi mathvariant="normal">CdSe</mml:mi></mml:mrow></mml:math>quantum dots

Abstract

We use transient photoluminescence to spectrally resolve the emission from 1, 2, and 3 electron-hole pairs states in $\mathrm{CdSe}$ colloidal quantum dots with radii ranging between 2.3 and $5.2\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$. The power dependence of the triexciton, biexciton and single exciton emission intensities are reported. We incorporate $\mathrm{CdSe}∕\mathrm{ZnS}$ core-shell nanocrystals into a ${\mathrm{TiO}}_{2}$ host matrix and observe simultaneous amplified spontaneous emission from the $1{\mathrm{S}}_{3∕2}\text{\ensuremath{-}}1\mathrm{Se}$ and $1{\mathrm{P}}_{3∕2}\text{\ensuremath{-}}1{\mathrm{P}}_{\mathrm{e}}$ quantum dot transitions. The achievement of amplified spontaneous emission from the $1{\mathrm{P}}_{\mathrm{e}}$ QD state suggests that the $1{\mathrm{P}}_{\mathrm{e}}$ state sixfold degeneracy might be lifted by the $\mathrm{e}\text{\ensuremath{-}}\mathrm{h}$ exchange interaction.