Study of emissivity dependence upon concentration in CdTe quantum dots

Due to their unique optical properties, quantum dots (QDs) have received a great deal of interest for their potential applications, such as in quantum computing, photovoltaic cells, and electronics. With such increased usage, the effect that altering QD concentration has on optical properties of the solution should be explored. Characterization of the emissivity of CdTe QDs as a function of concentration was conducted on three commercially available CdTe QDs. All have optimal absorption around 400-500 nm with peak emission wavelengths at 530 nm, 550 nm, and 570 nm, respectively. The QDs were suspended in an aqueous solution at 13 different concentrations ranging from 0.37 mg/ml to 10 mg/ml. The samples were excited at room temperature by a 50 mW diode laser emitting at a central wavelength of 405 nm and the fluorescence of the QDs was measured with a free-space CCD spectrometer. The measured spectra showed a general redshift in peak emission wavelength with increasing concentration. A +6.12 nm per mg/ml shift for the 530 nm QDs was observed when a linear fit with a coefficient of determination (R-squared) of 0.96 was applied. The 550 nm QDs and the 570 nm QDs showed a +8.70 nm per mg/ml shift (R-squared=0.94) and a +10.27 nm per mg/ml shift (R-squared=0.97), respectively. The redshift is attributed to a Foster resonance energy transfer (FRET) which causes energy transfer between two light-sensitive molecules.