Spectroscopic study of oscillator strength and radiative decay time of colloidal CdSe quantum dots
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Characterization of samples of cadmium selenide quantum dots (CdSe) QDs dissolved in toluene colloidal solutions at a concentration of 1.4 mg/ml was carried out through UV–Vis absorption and photoluminescence (PL) spectroscopy. The size-dependent absorption and red-shifted PL emission peak wavelengths could be tuned between 510–576 and 545–606 nm respectively. Optical absorption spectral measurements yielded CdSe QDs having diameters about ~ 2.44–3.69 nm with energy gaps 2.32–2.08 eV which are higher than the bulk CdSe (1.74 eV) reminiscent of quantum confinement. This is found to be in good agreement with the semi-empirical pseudopotential model. In addition, the first excitonic absorption transition 1S(e)1S3/2(h) oscillator strength and the corresponding fluorescence radiative decay time of CdSe QDs are assessed using relevant Einstein relations for absorption and emission in a two-level system. The elaborated calculations would anticipate that the transition oscillator scale with the CdSe QD radius as ~ R2.54. Correspondingly, the calculated radiative decay times decrease from 56.4 to 23.2 ns which scale with CdSe QDs radius as ~ R−2.155 in fairly good agreement with experimental values reported in the literature.
KeywordsSpectroscopic analysis Quantum dots Photoluminescence radiative decay time
Authors are deeply grateful to members of the Nanotechnology Lab. at the National Institute of Laser Enhanced Sciences (NILES) and the esteemed staff of the solid-state Lab. at physics department, faculty of science, Cairo University.
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