Low Threshold Multiexciton Optical Gain in Colloidal CdSe/CdTe Core/Crown Type-II Nanoplatelet Heterostructures.
Colloidal cadmium chalcogenide core/crown type-II nanoplatelet heterostructures, such as CdSe/CdTe, are promising materials for lasing and light-emitting applications. Their rational design and improvement requires the understanding of the nature of single- and multiexciton states. Using pump fluence and wavelength-dependent ultrafast transient absorption spectroscopy, we have identified three spatially and energetically distinct excitons (in the order of increasing energy): interface-localized charge transfer exciton (XCT, with electron in the CdSe core bound to the hole in the CdTe crown), and CdTe crown-localized XCdTeand CdSe core-localized XCdSeexcitons. These exciton levels can be filled sequentially, with each accommodating two excitons (due to electron spin degeneracy) to generate one to six exciton states (with lifetimes of ≫1000, 209, 43.5, 11.8, 5.8, and 4.5 ps, respectively). The spatial separation of these excitons prolongs the lifetime of multiexciton states. Optical gain was observed in tri- (XXCTXCdTe) and four (XXCTXXCdTe) exciton states. Because of the large absorption cross section of nanoplatelets, an optical gain threshold as low as ∼43 μJ/cm2can be achieved at 550 nm excitation for a colloidal solution sample. This low gain threshold and the long triexciton (gain) lifetime suggest potential applications of these 2D type-II heterostructures as low threshold lasing materials.
Department of Chemistry, Emory University , 1515 Dickey Drive, NE, Atlanta, Georgia 30322, United States.
Qiuyang
Q
Li
Department of Chemistry, Emory University , 1515 Dickey Drive, NE, Atlanta, Georgia 30322, United States.
Zihao
Z
Xu
Department of Chemistry, The Vanderbilt Institute of Nanoscale Science and Engineering, Vanderbilt University , Nashville, Tennessee 37235, United States.
James R
JR
McBride
Department of Chemistry, Emory University , 1515 Dickey Drive, NE, Atlanta, Georgia 30322, United States.
Tianquan
0000-0002-8351-3690
T
Lian
Auger recombination; charge transfer exciton; colloidal nanoplatelets; multiple excitons; nanocrystal laser; optical gain threshold; type-II heterostructure