Spin spectroscopy of dark excitons in CdSe quantum dots to 60 T

Abstract

Polarization-resolved magnetophotoluminescence spectroscopy is used to study exciton spin states in 40--80 \AA{} diameter chemically synthesized CdSe quantum dots (QDs) at temperatures $T=1.2--50\mathrm{K}.$ The spin polarization is found not to saturate in magnetic fields to 60 T and time-resolved studies indicate a thermal population of exciton states. A simple model incorporating the angle-dependent Zeeman splitting and bright-dark level mixing in these randomly oriented quantum dots is constructed in quantitative agreement with the data. Fits using this model yield a dark exciton g factor of \ensuremath{\sim}0.9 at $T=1.45\mathrm{K},$ which is independent of QD diameter and exhibits a surprising increase with increasing temperature.