Energetics and dynamics of exciton–exciton interactions in compound colloidal semiconductor quantum dots

Abstract

The energetics and dynamics of multiply excited states in single material colloidal quantum dots have already been shown to exhibit universal trends. Here we attempt to identify similar trends in exciton-exciton interactions within compound colloidal quantum dots. For this end, we thoroughly review previously available data and also present experimental data on several newly synthesized systems, focusing on core/shell nanocrystals with a type-II band alignment. A universal condition for the transition from binding to repulsion of the biexciton (type-I-type-II transition) is established in terms of the change in the exciton radiative lifetime. A scaling rule is also presented for the magnitude of exciton-exciton repulsion. In contrast, we do not identify a clear universal scaling of the non-radiative Auger recombination lifetime of the biexciton state. Finally, a perspective on future applications of engineered multiexcitonic states is presented.

Excitation intensity dependence of photoluminescence spectra of SiGe quantum dots grown on prepatterned Si substrates: Evidence for biexcitonic transition

“…Our conclusion is also supported by extensive work on exciton-exciton repulsion in colloidal semiconductor nanocrystals reported in Ref. 23 and 26.…”

“…Extensive work on the exciton-exciton interaction energies has been reported for selfassembled epitaxial III-V compound quantum dots [17][18][19][20][21][22] as well as for chemically synthesized colloidal nanocrystals [23][24][25] for material systems with both type-I and II band alignment. The understanding of the multi-exciton interaction and the exciton relaxation dynamics has been shown to be important for the realization of hot carrier extraction and optical gain.…”

Photoluminescence Intermittency from Single Quantum Dots to Organic Molecules: Emerging Themes

“…Emission from charged 1Xs (trions) is potentially convolved with the 1X decay [69]. Emission from 1X and 2X states can be resolved at low temperature where emission of 2Xisshifted by ~10 meV to lower [62] or higher energy [66] relative to 1X when the exciton-exicton interaction [70] is attractive or repulsive, respectively [71]. Emission from2X can also be identified through intensity dependence of the emission decay and the presence of photon bunching.…”

State-resolved observation in real time of the structural dynamics of multiexcitons in semiconductor nanocrystals

“…[1][2][3] In extension, the nonlinear processes are completely determined by multiexcitons (MX), the simplest of which is the biexciton (XX). 1,2,4 The structure of excitons in nanocrystals has largely been advanced by linear optical spectroscopy, such as absorption and photoluminescence (PL). 2,[5][6][7][8][9] These measurements have demonstrated an excitonic coarse structure to X as revealed in the absorption spectra, and an excitonic fine structure which yields a Stokes shift (δ X ) between the absorbing and emitting bands.…”

“…Hence, an understanding of the factors which govern XX formation will dictate the design of nanocrystals for efficient optical gain. 4,13,16 In the case of MEG, one of the areas of most intense investigation in NCs, one of the main parameters in the theory is the density of biexcitonic states, 15,[17][18][19] Fig. 2(b).…”