Resonance Raman Study of Shell Morphology in InP/ZnSe/ZnS Core/Shell/Shell Nanocrystals

Abstract

Resonance Raman spectra and absolute cross sections of InP/ZnSe/ZnS core/shell/shell nanocrystals have been obtained at excitation wavelengths of 501.7, 457.9, and 410 nm. Eight different structures having nearly the same lowest excitonic absorption wavelength but significantly different stoichiometries are compared. The Raman spectra show phonon features attributable to both the InP core and the ZnSe shell. The largest differences among the structures are seen in the ZnSe phonon region by using excitation at 457.9 nm, on the low-energy edge of the absorption features having significant contributions from the ZnSe shell. Here, structures that are nearly stoichiometric (In:P ratio ≈1.0) show a sharp, strongly polarized peak near the bulk ZnSe phonon frequency (∼250 cm −1 ) and a weak lower-frequency shoulder with a higher depolarization ratio. Structures having excess indium show a stronger low-frequency shoulder near 225 cm −1 and lower integrated Raman intensities throughout the ZnSe phonon region. These changes are attributed to the presence of indium atoms in the ZnSe shell. These results support a previous assignment of a slow rise component in the time-resolved photoluminescence spectra of nonstoichiometric structures to transient trapping of holes at indium defects in the shell.

Full-Spectrum InP-Based Quantum Dots with Near-Unity Photoluminescence Quantum Efficiency

“…In agreement with previous studies, − the InP/ZnSe Raman spectrum exhibits two optical phonon bands at around 225–250 cm –1 and 335–360 cm –1 . The band between 225 and 250 cm –1 can be attributed to the longitudinal optical phonon of ZnSe and an interface-related shoulder . The band around 335–360 cm –1 can be assigned to transversal (TO) and longitudinal (LO) optical phonons of InP.…”

“…Selected Raman spectra as recorded on series 1 InP/ZnSe/ZnS QDs, InP core, and InP/ZnS and InP/ZnSe core/shell QDs are depicted in Figure b. In agreement with previous studies, − the InP/ZnSe Raman spectrum exhibits two optical phonon bands at around 225–250 cm –1 and 335–360 cm –1 . The band between 225 and 250 cm –1 can be attributed to the longitudinal optical phonon of ZnSe and an interface-related shoulder .…”

Reversible Interfacial Charge Transfer and Delayed Emission in InP/ZnSe/ZnS Quantum Dots with Hexadecanethiol

“…The experimental methods and materials used in this paper are largely the same as used in previous papers. − The QDs used here are the same as those used in ref . These are very high-quality QDs, having PL linewidths of typically 40 nm (fwhm) and PL quantum yields greater than 90%.…”

“…The bonding at this interface can be elucidated using resonance Raman spectroscopy. As discussed in ref , varying the excitation wavelength permits some selectivity in the excitation of Raman active vibrations in the core, shell, or at the core–shell interface. The low-frequency region (<300 cm –1 ) of the Raman spectra of InP/ZnSe/ZnS QDs is dominated by the ZnSe longitudinal optical (LO) phonons at approximately 248 cm –1 .…”

“…We have previously reported that delayed emission can also be seen in very high-quality InP/ZnSe/ZnS QDs (PL of < 130 meV, fwhm), (QY > 90%), which contain hole traps dispersed throughout the ZnSe shell. In this system, we can summarize the excited-state dynamics as follows. − Following photoexcitation, electron relaxation populates the bottom of the conduction band and hole relaxation populates the valence band as well as a distribution of relatively high-energy hole traps dispersed throughout the ZnSe shell. It is important to note that these are not surface traps and do not result in nonradiative decay of the electron–hole pair.…”