p-State Luminescence in CdSe Nanoplatelets: The Role of Lateral Confinement and an LO Phonon Bottleneck

TL;DR

This study reveals excited state emission in CdSe nanoplatelets influenced by lateral confinement, showing an LO-phonon bottleneck affecting PL decay, supported by experimental and theoretical methods.

Contribution

It provides new insights into the role of lateral confinement and phonon bottleneck effects in the excited state dynamics of CdSe nanoplatelets.

Findings

Observation of p-state emission at low excitation fluences

Size-dependent energy spacing between states

Identification of an LO-phonon bottleneck affecting PL decay

Abstract

We report excited state emission from p-states at excitation fluences well below ground state saturation in CdSe nanoplatelets. Size dependent exciton ground state-excited state energies and dynamics are determined by three independent methods, time-resolved photoluminescence (PL), time-integrated PL and Hartree renormalized k$\cdot$p calculations -- all in very good agreement. The ground state-excited state energy spacing strongly increases with the lateral platelet quantization. Our results suggest that the PL decay of CdSe platelets is governed by an LO-phonon bottleneck, related to the reported low exciton phonon coupling in CdSe platelets and only observable due to the very large oscillator strength and energy spacing of both states.