Unusual Excitation Wavelength Dependency of Quantum Yield in Water Soluble CdTe Quantum Dots

Abstract

Abstract The Quantum yield (QY) of the semiconductor quantum dots (QDs) severely hampered by the inherent fluorescence intermittency. The QY of QDs usually increases with the increase in excitation wavelength. Here, we present an unusual behaviour where QY is found to decrease with increase in excitation wavelength in water soluble CdTe QDs (CQDs). Single particle measurement highlights the increase in permanent single dark particles at longer wavelength that comprehend the overall QY of the QDs in bulk solution. Fluorescence correlation spectroscopy further revealed an increase in number of dark particles at longer wavelength. The presence of H+ ion in the water plays an important role in creating the permanently dark states in the CQDs. This observation was further supported by the cell internalization study of the QDs where much brighter images at shorter wavelength than longer wavelength were observed. A study of the excitation wavelength-dependent QY in QDs may reveal new insights into the applicability of QDs in different device fabrication cases.