Highly Enhanced Exciton Recombination Rate by Strong Electron–Phonon Coupling in Single ZnTe Nanobelt

Abstract

Electron-phonon coupling plays a key role in a variety of elemental excitations and their interactions in semiconductor nanostructures. Here we demonstrate that the relaxation rate of free excitons in a single ZnTe nanobelt (NB) is considerably enhanced via a nonthermalized hot-exciton emission process as a result of an ultrastrong electron-phonon coupling. Using time-resolved photoluminescence (PL) spectroscopy and resonant Raman spectroscopy (RRS), we present a comprehensive study on the identification and the dynamics of free/bound exciton recombination and the electron-phonon interactions in crystalline ZnTe NBs. Up to tenth-order longitudinal optical (LO) phonons are observed in Raman spectroscopy, indicating an ultrastrong electron-phonon coupling strength. Temperature-dependent PL and RRS spectra suggest that electron-phonon coupling is mainly contributed from Light hole (LH) free excitons. With the presence of hot-exciton emission, two time constants (∼80 and ∼18 ps) are found in photoluminescence decay curves, which are much faster than those in many typical semiconductor nanostructures. Finally we prove that under high excitation power amplified spontaneous emission (ASE) originating from the electron-hole plasma occurs, thereby opening another radiative decay channel with an ultrashort lifetime of few picoseconds.

A room temperature low-threshold ultraviolet plasmonic nanolaser

“…The plasmonic cavities exhibit ultrasmall modal volume V m Bl 3 / 10-l 3 /1,000 (l is wavelength) enabling the tailoring of the strong light-matter interaction in a variety of linear (BQ/V m ) and nonlinear (BQ 2 /V m or Q/V m 1/2 ) optical process, where Q is the cavity quality factor. However, due to high intrinsic metal ohmic losses and radiation leakage, particularly in visible and ultraviolet regime, the Q ranges B10-100 which is still much smaller than their dielectric counterpart [20][21][22][23] . As a result, the threshold of optical-pumped visible plasmonic lasing (400-700 nm) is still nearly three orders higher than II-VI/III-VI semiconductor nanostructure photonic lasing.…”

Recent progress and frontiers in the electromagnetic mechanism of surface-enhanced Raman scattering

“…The luminescence at variable excitation energies revealed that the spectrum was mediated by phonons in a hot-luminescence process. They also measured the temperaturedependent spectroscopy and confirmed the hot-luminescence [56].…”

“…This light emission means that the molecular electronic dynamics deviate from those in a free space by a large EM enhancement effect. This deviation indicates the breakdown of conventional molecular electronic dynamics by plasmonic de-excitation, and it has been investigated as the ultra-fast emission of light [42,48,[52][53][54][55][56]. II.…”

“…This decay can elucidate the breakdown of conventional molecular electronic dynamics, as this breakdown arises when the enhanced decay rate exceeds the vibrational decay rate in S 1 [42,[52][53][54][55][56]. When the enhanced decay rate is smaller than the vibrational relaxation rate ∼10 12 s −1 , the SEF spectra can be reproduced as conventional fluorescence spectra modulated by radiative plasmons.…”

“…In the case of the non-radiative decay, the breakdown is indicated by anomalous ratios between the SERS intensity and SEF intensity [52]. In the case of the radiative decay, the breakdown is indicated by strange, blue-shifted SEF spectra [42,[53][54][55][56]. We focus on the breakdown by the radiative plasmon, rather than the non-radiative plasmon, because it is practically important for the development of electrically driven nanoscale light sources, ultrahigh-resolution spectroscopy, and ultrafast dynamic techniques.…”