Towards Chemical Fingerprinting of Deep-Level Defect Sites in CdS Nanocrystals by Optically Detected Spin Coherence

Abstract

AbstractCarrier trapping in colloidal nanocrystals represents a major energy loss mechanism for excitonic states crucial to devices, yet surprisingly little is known about the chemical nature of these trap centers or the types of interactions that charges experience in them. Here, we use a pulsed microwave optically detected magnetic resonance (pODMR) technique in order to probe the interaction pathways existing between shallow band edge trap states and the deep-level emissive chemical defect states responsible for the broad, low energy emission common to CdS nanocrystals. Due to the longer spin-coherence lifetimes (T 2) of these states, Rabi flopping in the differential luminescence under resonance provides access to information regarding coupling types of shallow-trapped electron-hole pairs, both isolated species and those in proximity to the emissive defect. Corresponding Hahn spin-echo measurements expose an extraordinary long spin coherence time for colloidal nanocrystals (T 2 ≈ 1. 6 μs), which allows observation of local environmental interactions through electron spin-echo envelop modulation (ESEEM). Such an effect provides future opportunities for gaining the detailed chemical and structural information needed in order to eliminate energy loss mechanisms during the synthetic process.KeywordsElectron Spin ResonanceDipolar CouplingTrap StateRabi OscillationElectron Spin Echo Envelope ModulationThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.