Quantum dots (QDs) are semiconductor nanocrystals that have significant advantages over organic fluorophores, including their extremely narrow Gaussian emission bands and broad absorption bands. Thus, QDs have a wide range of potential applications, such as in quantum computing, photovoltaic cells, biological sensing, and electronics. For these applications, aliasing provides a detrimental effect on signal identification efficiency. This can be avoided through characterization of the QD fluorescence signals. Characterization of the emissivity of CdTe QDs as a function of concentration (1 to 10 mg/ml aqueous) was conducted on 12 commercially available CdTe QDs (emission peaks 550 to 730 nm). The samples were excited by a 50-mW 405-nm laser with emission collected via a free-space CCD spectrometer. All QDs showed a redshift effect as concentration increased. On average, the CdTe QDs exhibited a maximum shift of +35.6 nm at 10 mg/ml and a minimum shift of +27.24 nm at 1 mg/ml, indicating a concentration dependence for shift magnitude. The concentration-dependent redshift function can be used to predict emission response as QD concentration is changed in a complex system.
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 Föster resonance energy transfer (FRET) which causes energy transfer between two light-sensitive molecules.