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.
© 2012 Optical Society of America
Original Manuscript: October 4, 2012
Revised Manuscript: November 29, 2012
Manuscript Accepted: November 30, 2012
Published: December 21, 2012
Lin Dong, Abhilash Sugunan, Jun Hu, Sicheng Zhou, Shanghua Li, Sergei Popov, Muhammet S. Toprak, Ari T. Friberg, and Mamoun Muhammed, "Photoluminescence from quasi-type-II spherical CdSe-CdS core-shell quantum dots," Appl. Opt. 52, 105-109 (2013)