Date of Award

Spring 1-1-2011

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Physics

First Advisor

Daniel Dessau

Second Advisor

Arthur Nozik

Third Advisor

Charles Rogers

Abstract

This work presents temperature-dependent photoluminescence spectra for nanocrystalline films, cast from PbS and PbSe quantum dots with diameters ranging from 0.6 nm to 9.2 nm (band gaps from 0.52 eV to 1.96 eV). Across all sizes and materials, two emission peaks are observed in the photoluminescence spectra. A low-energy peak dominates at low temperatures, and a high-energy peak dominates at high temperatures. No materials-dependent effects are noted, but the spectral behavior is a strong function of nanocrystal band gap. Intensity trends, the spacing of the two emission peaks, and the shift of peak emission energy with temperature are all affected by band gap changes. Results are suggestive of a scenario in which one emission peak is due to a fixed-energy trap state. The impact of air exposure on spectral behavior is also considered, and likely explains many previous inconsistencies between similar studies. High-temperature emission is strongly quenched by exposure to oxygen, with quenching effects beginning within seconds of exposure. Low-temperature emission is largely unaffected by short-term air exposure. These results are modeled with the introduction of a dark trap state whose concentration grows as air exposure increases.

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