Polarons Explain Luminescence Behavior of Colloidal Quantum Dots at Low Temperature

Meenakshi Khosla,Shilpi Gupta,Sravya Rao

doi:10.1038/s41598-018-26678-w

Meenakshi Khosla, Shilpi Gupta + Show 1 more

Open Access

https://doi.org/10.1038/s41598-018-26678-w

Copy DOI

Abstract

Luminescence properties of colloidal quantum dots have found applications in imaging, displays, light-emitting diodes and lasers, and single photon sources. Despite wide interest, several experimental observations in low-temperature photoluminescence of these quantum dots, such as the short lifetime on the scale of microseconds and a zero-longitudinal optical phonon line in spectrum, both attributed to a dark exciton in literature, remain unexplained by existing models. Here we propose a theoretical model including the effect of solid-state environment on luminescence. The model captures both coherent and incoherent interactions of band-edge exciton with phonon modes. Our model predicts formation of dressed states by coupling of the exciton with a confined acoustic phonon mode, and explains the short lifetime and the presence of the zero-longitudinal optical phonon line in the spectrum. Accounting for the interaction of the exciton with bulk phonon modes, the model also explains the experimentally observed temperature-dependence of the photoluminescence decay dynamics and temperature-dependence of the photoluminescence spectrum.

Highlights

Colloidal quantum dots show size-tunable luminescence spectrum[1,2], have high luminescence efficiency at room temperature[3,4], and can be functionalized for incorporation into a variety of systems[5]
We propose that the photoluminescence spectrum and photoluminescence decay dynamics of colloidal quantum dots at low temperatures can be explained by strong coupling between exciton and a confined acoustic phonon mode, resulting in dressed exciton-phonon states
We model a colloidal quantum dot as a three level system consisting of a ground 0 qd, caednacrekbeexhcaitvoinor116.qTd haendHaambriiltgohnt ieaxncaitcocnou2nqtdinsgtaftoer(tFhieg.in1tae)r, awchtiiocnh is of sufficient for modeling the photoluminesthe quantum dot with a confined acoustic phonon mode, under rotating wave approximation, is HS = ω1σ11 + ω2σ22 + ωphb0†b0 + η0(σ21b0 + σ12b0†)

Summary

Introduction

Colloidal quantum dots show size-tunable luminescence spectrum[1,2], have high luminescence efficiency at room temperature[3,4], and can be functionalized for incorporation into a variety of systems[5] These properties make them useful as biomarkers[6], gain materials for light emitting diodes[7,8] and lasers[9,10], and electroluminescent materials for displays[11]. The third hypothesis states that the shortening of lifetime is caused by the exciton coupling to confined acoustic phonon modes[32,33,40,41,51]; no specific coupling mechanism has been proposed or demonstrated

Methods

Results

Conclusion