Simultaneous Type-I/Type-II Emission from CdSe/CdS/ZnSe Nano-Heterostructures

Abstract

Core/intermediate/shell (C/I/S) structures with Type-I emission are well-known and are gaining immense importance due to their superior luminescence properties. Here, we report a unique C/I/S structure composed of CdSe/CdS/ZnSe that exhibits both Type-I and Type-II phenomena. The structures have been well characterized using a combination of optical and structural techniques. The photoluminescence (PL) and photoluminescence excitation (PLE) data indicate the formation of a combined Type-I and Type-II structure in one material, results supported by simple theoretical calculations. Single particle fluorescence reveals colocalization of both the emissions. The X-ray diffraction (XRD) and transmission electron microscopy (TEM) results confirm the structure of these particles. The time-resolved fluorescence studies show the possibility of tuning the lifetime of these materials by changing the Type-I/Type-II thickness ratios. It is possible to form these two separate excitons in the same system separated by a CdS intermediate layer that acts both as a barrier and an active member of the Type-II system allowing the generation and recombination of two excitons, in violation of Kasha's rule.

Enhanced Electron Lifetime of CdSe/CdS Quantum Dot (QD) Sensitized Solar Cells Using ZnSe Core–Shell Structure with Efficient Regeneration of Quantum Dots

“…Hence, the reduced electron lifetime of the cell with ZnSe3 should be related with the increased electron recombination with the electrolyte due to a high density of hole at the ZnSe shell layer. Since the charge separation of type II core-shell alignment increases with the increase of shell thickness, [26][27] it is reasonable to believe that the density of hole in the shell material and density of electron in the core and then in TiO 2 film increase with the shell thickness. The high density of hole in the shell can attract more negatively charged species in the liquid electrolyte including both S 2-and S n 2-in the TiO 2 film through static Given that D n is largely unaffected while τ n is significantly enhanced using ZnSe coating, it is expected that the electron diffusion length, L n , which is the square root of product of D n and τ n should follow the same trend with τ n , that is, ZnSe0 < ZnSe1< ZnSe3 < ZnSe2.…”

Large-scale synthesis of single-source, thermally stable, and dual-emissive Mn-doped Zn–Cu–In–S nanocrystals for bright white light-emitting diodes

“…For example, dual emissive CdSe/ ZnS/CdSe NCs have been used to produce white light by combination with blue and ultraviolet LEDs [52]. However, the emission wavelength of these dual emissive NCs can only be tuned in a limited spectral range [51][52][53][54][55][56][57][58][59][60], which also limits the tunability of color temperature for the NCs-based WLEDs. Generally, these most widely used color converters are not only highly sensitive to the temperature, but are also restricted, especially the cadmium/lead-based, particularly in view of recent environmental regulations and potential application in the fabrication of WLEDs.…”

Recent Progress in Quantum Dot Based White Light-Emitting Devices

“…Nizamoglu et al [73] realized WLEDs by depositing dual color (green and red)-emitting CdSe/ZnS/CdSe core/shell/shell QDs on a blue InGaN/GaN LED, with CIE of (0.36, 0.30), LER of 278 lm/W, CCT of 3929 K, and CRI of 75.1. Such QDs suffered from a rather strong self-absorption, which could be minimized by a proper structural QD design as recently demonstrated by Sapra et al [74]. As already mentioned above, doped dual-emitting QDs with little, or even zero, self-absorption offer great potential for WLEDs.…”