Research Projects

Semiconductor nanocrystals (NCs) are single photon or few photon emitters that have already found many applications in bio imaging and display technologies. The spectroscopy of single emitters has been crucial to our understanding of the photophysics of NCs. However, some aspects of their photophysics, such as the interaction between excitons and sub-millisecond stochastic fluctuations in spectra are inaccessible to most current single-emitter spectroscopic techniques. One aim of the proposed work is to use the emerging technology of single photon avalanche diode (SPAD) arrays to build a spectrometer that is capable of recording the wavelength as well as detection time (to ~10 picosecond precision) of each detected photon. Together with a pulsed laser source to generate multiexcitons in single NCs, the spectrometer will be used to study cascaded emission of multiple photons. By identifying multiphoton emission in time and then analysing the wavelength of each photon, the interactions between excitons in multiply excited NCs will be quantified. Since absolute detection time and wavelength are recorded for each photon, temporal correlations of the photon wavelength can be determined at a variety of timescales. A second aim of the proposal is to use such correlations to study fluctuations in photoluminescence spectra, termed spectral diffusion. By studying several NC systems of different material and confinement dimensionality, the influence of the material constituting the NC and its environment on spectral diffusion will be studied. Establishing a clear relationship between spectral diffusion and the environment of an emitter can enable deployment of NCs as sensors of nanoscale environments. The measurements of higher order spectrally resolved photon correlations and spectral diffusion cannot be modelled using simple analytical models. Therefore, models based on Monte Carlo simulation will be developed and used to analyse experimental data.

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