P-State Luminescence in CdSe Nanoplatelets: Role of Lateral Confinement and a Longitudinal Optical Phonon Bottleneck.

Alexander W Achtstein,Anatol V Prudnikau,Sebastian Kickhöfel,Andrei Schliwa,Guillaume H V Bertrand,Stefan T Jagsch,Iwan Moreels,Ulrike Woggon,Riccardo Scott,Sotirios Christodoulou,Artsiom Antanovich,Mikhail Artemyev

doi:10.1103/physrevlett.116.116802

Abstract

We evidence excited state emission from p states well below ground state saturation in CdSe nanoplatelets. Size-dependent exciton ground and excited state energies and population dynamics are determined by four independent methods: time-resolved PL, time-integrated PL, rate equation modeling, and Hartree renormalized k·p calculations-all in very good agreement. The ground state-excited state energy spacing strongly increases with the lateral platelet quantization. Depending on its detuning to the LO phonon energy, the PL decay of CdSe platelets is governed by a size tunable LO phonon bottleneck, related to the low exciton-phonon coupling, very large oscillator strength, and energy spacing of both states. This is, for instance, ideal to tune lasing properties. CdSe platelets are perfectly suited to control the exciton-phonon interaction by changing their lateral size while the optical transition energy is determined by their thickness.

Highlights

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
With this letter we report on energies and dynamics of excited state emission from pstates in CdSe nanoplatelets by the means of temperature and time-resolved photoluminescence (PL) and Hartree renormalized k·p modeling
We show in this letter that the ground state-excited state energy difference of CdSe NPLs strongly increases with the lateral platelet quantization and that the already described bi-exponential PL decay of NPLs is connected to the very large dipole moments of the excited state (ES) and ground state (GS) and a phonon bottleneck suppressing inter-relaxation

Summary

Introduction

We show in this letter that the ground state-excited state energy difference of CdSe NPLs strongly increases with the lateral platelet quantization and that the already described bi-exponential PL decay of NPLs is connected to the very large dipole moments of the excited state (ES) and ground state (GS) and a phonon bottleneck suppressing inter-relaxation. The ground state-excited state energy spacing strongly increases with the lateral platelet quantization.

Results

Conclusion