Spectroscopy of Colloidal Semiconductor Core/Shell\nNanoplatelets with High Quantum Yield

Abstract

Free\nstanding two-dimensional materials appear as a novel class\nof structures. Recently, the first colloidal two-dimensional heterostructures\nhave been synthesized. These core/shell nanoplatelets are the first\nstep toward colloidal quantum wells. Here, we study in detail the\nspectroscopic properties of this novel generation of colloidal nanoparticles.\nWe show that core/shell CdSe/CdZnS nanoplatelets with 80% quantum\nyield can be obtained. The emission time trace of single core/shell\nnanoplatelets exhibits reduced blinking compared to core nanoplatelets\nwith a two level emission time trace. At cryogenic temperatures, these\nnanoplatelets have a quantum yield close to 100% and a stable emission\ntime trace. A solution of core/shell nanoplatelets has emission spectra\nwith a full width half-maximum close to 20 nm, a value much lower\nthan corresponding spherical or rod-shaped heterostructures. Using\nsingle particle spectroscopy, we show that the broadening of the emission\nspectra upon the shell deposition is not due to dispersity between\nparticles but is related to an intrinsic increased exciton–phonon\ncoupling in the shell. We also demonstrate that optical spectroscopy\nis a relevant tool to investigate the presence of traps induced by\nshell deposition. The spectroscopic properties of the core/shell nanoplatelets\npresented here strongly suggest that this new generation of objects\nwill be an interesting alternative to spherical or rod-shaped nanocrystals.