Effect of Core/Shell Interface on Carrier Dynamics and Optical Gain Properties of Dual-Color Emitting CdSe/CdS Nanocrystals.
Two-color emitting colloidal semiconductor nanocrystals (NCs) are of interest for applications in multimodal imaging, sensing, lighting, and integrated photonics. Dual color emission from core- and shell-related optical transitions has been recently obtained using so-called dot-in-bulk (DiB) CdSe/CdS NCs comprising a quantum-confined CdSe core embedded into an ultrathick (∼7-9 nm) CdS shell. The physical mechanism underlying this behavior is still under debate. While a large shell volume appears to be a necessary condition for dual emission, comparison between various types of thick-shell CdSe/CdS NCs indicates a critical role of the interface "sharpness" and the presence of potential barriers. To elucidate the effect of the interface morphology on the dual emission, we perform side-by-side studies of CdSe/CdS DiB-NCs with nominally identical core and shell dimensions but different structural properties of the core/shell interface arising from the crystal structure of the starting CdSe cores (zincblende vs wurtzite). While both structures exhibit dual emission under comparable pump intensities, NCs with a zincblende core show a faster growth of shell luminescence with excitation fluence and a more readily realized regime of amplified spontaneous emission (ASE) even under "slow" nanosecond excitation. These distinctions can be linked to the structure of the core/shell interface: NCs grown from the zincblende cores contain a ∼3.5 nm thick zincblende CdS interlayer, which separates the core from the wurtzite CdS shell and creates a potential barrier for photoexcited shell holes inhibiting their relaxation into the core. This helps maintain a higher population of shell states and simplifies the realization of dual emission and ASE involving shell-based optical transitions.
Dipartimento di Scienza dei Materiali, Università degli Studi di Milano-Bicocca , Via Cozzi 55, IT-20125 Milano, Italy.
Valerio
V
Pinchetti
Dipartimento di Scienza dei Materiali, Università degli Studi di Milano-Bicocca , Via Cozzi 55, IT-20125 Milano, Italy.
Francesco
F
Meinardi
Dipartimento di Fisica, Politecnico di Milano , Piazza Leonardo da Vinci 32, IT-20133 Milano, Italy.
Andrea
A
Camellini
Dipartimento di Fisica, Politecnico di Milano , Piazza Leonardo da Vinci 32, IT-20133 Milano, Italy.
Gianluca
G
Sirigu
Istituto Italiano di Tecnologia , Via Morego 30, IT-16163 Genova, Italy.
Sotirios
S
Christodoulou
Chemistry Division, Los Alamos National Laboratory , Los Alamos, New Mexico 87545, United States.
Wan Ki
WK
Bae
Istituto Italiano di Tecnologia , Via Morego 30, IT-16163 Genova, Italy.
Francesco
F
De Donato
Istituto Italiano di Tecnologia , Via Morego 30, IT-16163 Genova, Italy.
Liberato
L
Manna
Dipartimento di Energia, Politecnico di Milano , Via Ponzio 34/3, IT-20133 Milano, Italy.|Institute for Photonics and Nanotechnologies IFN-CNR , Piazza Leonardo da Vinci 32, IT-20133 Milano, Italy.
Margherita
M
Zavelani-Rossi
Istituto Italiano di Tecnologia , Via Morego 30, IT-16163 Genova, Italy.
Iwan
I
Moreels
Chemistry Division, Los Alamos National Laboratory , Los Alamos, New Mexico 87545, United States.
Victor I
VI
Klimov
Dipartimento di Scienza dei Materiali, Università degli Studi di Milano-Bicocca , Via Cozzi 55, IT-20125 Milano, Italy.
Sergio
S
Brovelli
amplified spontaneous emission; core/shell heterostructures; dual emission; exciton dynamics; interface structure; nanocrystal quantum dots