Absolute Photoluminescence Quantum Yield Measurement in a Complex Nanoscopic System with Multiple Overlapping States

Using a metal nanocavity, we measure absolute values of the photoluminescence quantum yield in a mixture of different types of chromophores (dye molecules and semiconductor nanocrystals). We show that measurements can be performed in an attoliter volume, both in liquid and solid phases, even if both types of chromophores absorb and emit light in the same spectral range. The method is based on recording photoluminescence decay curves of the chromophore mixture as a function of the cavity length. Changing the distance between the cavity mirrors modifies the local density of states of the electromagnetic field and thus, the radiative transition rate of the enclosed emitters. By extracting individual decay components, corresponding to the different types of the emitters, we determine their quantum yield values separately and simultaneously. The nanocavity-based method opens up new perspectives for studying quantum emitters in complex photophysical systems, for instance, multichromophoric thin films, fluorescent proteins, or dyes incorporated into a lipid bilayer.