Homogeneous Width of Confined Excitons in Quantum Dots at Very Low Temperatures

The temperature-dependent homogeneous width of confined excitons in CuCl, CuBr and CdSe quantum dots was investigated at very low temperatures down to 0.6 K by means of accumulated photon echo. The observed nonlinear temperature dependence of the homogeneous width at low temperatures is explained by the interaction with confined acoustic phonons for CdSe quantum dots or very small excitation in the two-level system for CuCl and CuBr quantum dots. At the lowest temperature, the homogeneous width of confined excitons in CuCl, CuBr and CdSe quantum dots becomes 1-2 μeV, 23-59 μeV and 0.16-0.25 meV, respectively. It depends on the surrounding matrix for CuCl quantum dots and the radius of dots for CuBr and CdSe quantum dots. These results suggest surroundings of quantum dots dominate the low temperature dephasing mechanism, i.e. homogeneous width of the optical spectra, of real quantum dots.

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