Photoluminescence from quasi-type-II spherical CdSe-CdS core-shell quantum dots

• Spherical CdSe-CdS core-shell quantum dots (QDs) are found to be flexible in the transition between the type-I regime and the type-II regime with different core/shell dimensions. The quasi-type-II feature of the colloidal dots is confirmed with time-resolved photoluminescence (PL) measurements. Two recombination paths of the excitons with significantly different decay rates are observed and analyzed. The spherical CdSe-CdS core-shell QDs are numerically simulated to investigate the carrier separation. A relatively long radiative lifetime and high degree of spatial carrier separation provide good potential to achieve lasing under continuous-wave excitation. Amplified spontaneous emission at room temperature is detected from the QDs embedded in the polymer matrix. It is shown that a larger shell thickness results in a lower pumping threshold, while a smaller shell thickness leads to higher PL efficiency.

Nyckelord

Amplified spontaneous emissions

Carrier separation

Colloidal dots

Continuous waves

Core-shell quantum dots

Core/shell

Decay rate

PL efficiency

Pumping threshold

Radiative lifetime

Room temperature

Shell thickness

Time-resolved photoluminescence

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