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

Polarization-resolved magnetophotoluminescence spectroscopy is used to study exciton spin states in 40-80 Angstrom diameter chemically synthesized CdSe quantum dots (QDs) at temperatures T = 1.2-50 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 a factor of similar to0.9 at T = 1.45 K, which is independent of QD diameter and exhibits a surprising increase with increasing temperature.