Narrow Intrinsic Homogeneous Linewidths and Electron-Phonon Coupling of InP Colloidal Quantum Dots

InP quantum dots (QDs) are the material of choice for QD display applications. They have been used as active layers in QD light-emitting diodes (QDLEDs) with high efficiency and color purity. Optimizing the color purity of QDs requires understanding mechanisms of spectral broadening. While ensemble-level broadening can be minimized by synthetic tuning to yield monodisperse QD sizes, single QD linewidths are broadened by elastic/inelastic exciton-phonon scattering and fine-structure splitting. Here, using photon correlation Fourier spectroscopy, we extract average single QD linewidths of 50 meV at 293K for red emitting InP/ZnSe/ZnS QDs, among the narrowest for colloidal QDs. By measuring InP/ZnSe/ZnS single QD emission lineshapes at temperatures between 4K – 293K, and modelling the spectra using a modified independent boson model, we find that acoustic phonon coupling and fine-structure splitting, which contribute similarly to the homogeneous linewidth, are most prominent at low temperature, whereas pure dephasing is the primary broadening mechanism at elevated temperatures, and optical phonon coupling contributes minimally across all temperatures. By measuring CdSe/CdS/ZnS QD emission lineshapes across the same temperature range, we find that optical phonon coupling is a larger contributor to the lineshape at elevated temperatures likely as a result of the more polar nature of CdSe/CdS/ZnS. For the first time, we are able to reconcile narrow low-temperature linewidths and broad room temperature linewidths within a self-consistent model that enables parameterization of linewidth broadening, for different material classes. Our findings reveal that red-emitting InP/ZnSe/ZnS QDs have intrinsically narrower linewidths than typically synthesized CdSe QDs, suggesting that these materials could be used to realize QDLEDs with unprecedented color purity.