posted on 2021-06-09, 10:29authored byGaoling Yang, Miri Kazes, Dekel Raanan, Dan Oron
Upconverting semiconductor
quantum dots (QDs) combine the stability
of an inorganic crystalline structure with the spectral tunability
afforded by quantum confinement. Here, we present upconverting type-II/type-I
colloidal double QDs that enable enhancement of the performance of
near-infrared to visible photon upconversion in QDs and broadening
the range of relevant materials used. The resulting ZnTe/CdSe@CdS@CdSe/ZnSe
type-II/type-I double QDs possess a very high photoluminescence quantum
yield, monoexponential decay dynamics, and a narrow line width, approaching
those of state-of-the-art upconverting QDs. We quantitatively characterize
the upconversion cross section by direct comparison with two-photon
absorption when varying the pump frequency across the absorption edge.
Finally, we show that these upconversion QDs maintain their optical
performance in a much more demanding geometry of a dense solid film
and can thus be incorporated in devices as upconversion films. Our
design provides guidance for fabricating highly efficient upconverting
QDs with potential applications such as security coding and bioimaging.