(Color online) Calculated spatial distributions of electron (solid line) and hole (dashed line) wave functions in “inverted” core∕shell NCs with a fixed ZnSe core radius and three different CdSe shell thicknesses 0.45, 1.3, and ) that correspond to three different localization regimes. (a) Thin shell: an electron and a hole reside primarily in the core [type-I (core∕core) regime]. (b) Intermediate shell: the electron is preferentially localized in the shell while the hole still stays primarily in the core [type-II (core∕shell) regime]. (c) Thick shell: both the electron and the hole are localized primarily in the shell [type-I (shell∕shell) regime].
(Color online) Evolution of the PL maximum with time during the growth of the CdSe shell leading to the formation of type-II (solid circle) and type-I (open square) structures, respectively. The ZnSe core radius is ca. . The two dependences shown in the plot are obtained for two different relative amounts of the Cd and Se precursors compared to ZnSe cores. (b) Optical absorption spectra of inverted core-shell NCs with a fixed core radius (ca. ) and three different shell thicknesses that correspond to the three different localization regimes illustrated in Fig. 1: type I (core∕core) (dotted line), type II (core∕shell) (dashed line), and type I (shell∕shell) (solid line).
(Color online) (a) Pump dependence of the absorption bleaching for inverted core∕shell NCs (samples 1–5) measured at after excitation (pump photon energy is ). The solid lines are the fits to Eq. (3) used to derive absorption cross sections. (b) Absorption cross sections at 3.1 eV plotted as a function of emission wavelength for monocomponent CdSe quantum dots (solid squares) and inverted core∕shell NCs (open circles).
(Color online) (a) Extracted Auger recombination dynamics of NC biexciton states, , for three core-shell samples emitting at (solid circles), (open squares), and (solid triangles). Inset: a comparison of the biexciton decay in monocomponent CdSe and heterostructured NCs emitting at 2.35 and , respectively. (b) The dependence of the biexciton Auger life time on the emission wavelength for CdSe NCs (solid squares), CdSe quantum rods (open circles), and inverted core∕shell heterostructures (crosses) (CdSe NCs have radii from , while quantum rod samples have the same radius of and different lengths from ).
(Color online) Amplified spontaneous emission tunable from red to blue using CdSe quantum rods (red emission color), CdSe quantum dots (red through green emission colors), and inverted core∕shell NCs (green through blue emission colors). These spectra are obtained either at room temperature or at (labeled). All samples were excited at using frequency-doubled pulses from an amplified Ti:sapphire laser.
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