Carrier relaxation dynamics of ZnxCd1−xSe/C core/shell nanocrystals with phase separation as studied by time-resolved cathodoluminescence

Abstract

The optical properties and carrier relaxation kinetics of Zn x Cd 1−x Se/ C core/shell nanocrystals with compositional phase separation occurring on a ϳ1-5 nm size scale were examined with time-resolved cathodoluminescence ͑CL͒ spectroscopy and imaging. The CL spectral lineshape was found to depend on the level of excitation, temperature, and the time-window during time-delayed spectroscopy. The kinetics of carrier thermalization and transfer between Cd-rich phase-separated regions and the homogenous ZnCdSe alloy were examined. We show that the rare phenomenon of compositional phase separation in II-VI nanocrystals leads to interesting and potentially useful optical properties.

Direct Correlation of the Morphologies of Metal Carbonates, Oxycarbonates, and Oxides Synthesized by Dry Autoclaving to the Intrinsic Properties of the Metals

“…A simple, straightforward approach of dry autoclaving has been used to synthesize a wide variety of materials such as carbon coated metal oxide, − chalcogenide, carbide, boride, nitride, phosphide nanostructures, ,− and various carbon micro- and nanostructures such as carbon nanotubes and nanowhiskers. − The metal alkoxides are sealed inside a closed reactor, and the reactions occur under autogenic pressure due to decomposition of the alkoxides at elevated temperatures. It has the advantage of reaching higher temperatures and pressures close to ∼3 MPa .…”

Phase-separation in ZnxCd1-xSe/C Core/shell nanocrystals studied with cathodoluminescence spectroscopy

“…These labels correspond to similar CL peaks observed in an analysis of spatially integrated CL spectra for the same ZC3 sample. 13,14 The intensity of the longer wavelength P 2 component decreases relative to that of P 3 as the temperature increases from 60 to 90 K, suggesting that carrier excitation from the phase-separated region to the homogenous regions [x  0.47 (h)] of the nanocrystal occurs over this temperature range. 14 Considerable spatial variations in the spectral lineshape were observed during local CL spectroscopy, and representative spectra showing two and three components are shown in Fig.…”

“…1) is estimated as n ex  I b 2.5  10 12 cm -2 per striation with the e-beam current in units of nA. 14 In Fig. 4, the intensity ratio I p3 /I p2 as a function of I b is shown with black dots, revealing a gradual increase in I p3 /I p2 as phase space and real space filling of carriers occur in the two-dimensional (2D) Cd-rich regions.…”

“…13 CL of these nanocrystals further showed that a composition modulation, x, of ~0.11 is consistent with a broadened emission and set of decomposed peaks in spatially integrated CL spectra. 13,14 In this paper, we further build on the results of phase separation in Zn x Cd 1-x Se nanocrystals by examining the excitation dependence of CL spectra that exhibit multiple components. Excitationdependent effects in 2D Cd-rich regions of the nanocrystals are modeled with a random quantum well (RQW) approximation.…”